Burrowing is a widespread animal behavior involving digging underground for shelter, foraging, and protection, with animals evolving specialized adaptations like shovel-like forelimbs, compact fusiform bodies, and reinforced bones. Fossil burrows, dating back to the Cambrian period (~540 million years ago), provide evidence of ancient burrowing behavior, with the Cambrian substrate revolution marking a shift from surface-level to deep tunneling ecosystems. Scientists identify fossil burrow makers through morphological features, associated remains, and comparative analysis with modern burrows, revealing that burrowing has evolved independently across multiple animal groups including mammals, reptiles, and invertebrates.
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Episode 243 - BurrowersAdded:
You're listening to the Common Descent podcast.
>> Hello, David.
>> Hello, Will.
>> And hello, listeners. Welcome to episode 243 of the Comma Descent podcast. This episode we will be discussing burrowing or burers the act and adaptations for digging and living underground. This will be a very interesting topic but like many behavioral topics it's going to be vast cuz a lot of animals like to go beneath the surface. Yeah, we'll get to talk about some of our favorites and some of the standout examples, but this is going to be one of those where it will be incumbent upon you, dear listener, to go to the Discord and let all of your fellow listeners know the your favorite examples that we missed >> that we slighted by snubbing from the episode. [laughter] >> Rest assured that if there is an animal that is relevant that we didn't mention, it is because we hate them. Yes, absolutely. Like this is the official stance. Yeah, that that is that is how you can tell >> 100%. [laughter] During this discussion, we'll be going over what is burrowing and its benefits.
What are some of the general typical adaptations we you often see in digging animals? And then of course the fossil record of burrows which is vast and the more difficult task of how do you identify who burrowed the burrow that you have found. We'll be discussing this because it was requested quite a few times as all our episodes are requests these days. We got requests for this topic from Nina, Kylie, Aaron, Kai, Tobias, Sam and Sierra, Big Boss Man, Azola Event, Helpless Droid, and Cayman Sorus. Thank you everybody for your requests. We're taking requests for episode topics constantly. You can submit them to these days to the topic request forum on our website, link in the episode description.
>> Absolutely. Before we get into the discussion and before we get to the news, some quick announcements. As always, we have a Patreon. Our Patreon funds the podcast top to bottom. So, the lovely support of all of our patrons is what allows us to be here with you today. And if you join us on Patreon, you can get extra goodies, extra bonus content, episodes for different series, live events, behind the scenes looks, all sorts of stuff like that. And at certain levels you can get your name shouted out here on the podcast. So we would like to welcome Max Dan in D3 Kool-Aid Dan, different Dan Sassy Soraod and Calamari King. Welcome everybody.
Thank you so much for your extraordinary support. Listeners, if you would like to support the podcast through Patreon, you can find that link in the episode description as well. Uh we got bonus news up there. We do live streams. And because we just wrapped up this year's silver screen science series, there's also the corresponding series, More Thoughts. So, currently there's even more goodies on Patreon than an average time during the year.
>> Yes, indeed. And speaking of, go listen to our most recent silver screen science. It's all wrapped up now, including the live stream, which is up on YouTube. We did classic dinosaur movies, so you can go join us as we watch a whole bunch of very, very old films. Uh, some of the earliest depictions of dinosaurs on screen. And speaking of recent things, Leave It to Us is back. Leave it to Us is back for season two. This is our spin-off podcast all about plants, hosted by Nora and Ally to talk about the intersections between plants and our own lives. They get into all sorts of cool detailed conversations, the kind of which get snubbed here on Common Descent because, as we've established, we hate them and so we don't talk about them. Leave it to us is all about that stuff. The first episode of season 2 will already be out by the time this episode releases. It is a whole episode about berries. Tons of fun listening to Nora and Ally geek out about those berries. And just like we do here on Common Descent, the Leave it to us Patreon also includes bonus content, bonus before we leave episodes and other access to things like this year voting for what books will be read in Reading Between the Pines, which is the Leave it to Us plant themed book club. There's a whole lot of cool stuff happening with the launch of Leave it to Us season 2, so go check it out if you haven't already. Very exciting. And for our final bit of news, some upcoming news.
We are very quickly approaching June, which is Croc Month.
>> It sure is. We're going to celebrate Crocs. We're going to do bonus stuff.
We're going to probably have a live stream like we usually do.
>> Yeah, it'll be good. There'll be the Croc channel open up on Discord so you can get all of your Crocy discussions out during this month only. So during next month only will it be open.
>> Yeah. The croc and snake tier will be up on Patreon where we will collect support from patrons that will then fuel donations to reptile conservation organizations. All the details will be coming in as the month of June draws near.
>> Yes. But for now we'll wrap up our announcements and move on to the first section which is the news. Every episode, we like to gather some recent research and science news so that we can all stay up to date on what's going on in the world of paleontology and earth science and whatnot. David, what is your news?
>> My first news today is about human evolution, specifically recent human evolution, and even more specifically, the ways that our evolution has been [snorts] shaped by diseases. H this is research published in the journal science advances by Margarita Kawuchcci at all and we will link in the blog post to a press release on scitec daily from the max plank institute of geoanthropology when we talk about the evolutionary history the deep history of our own species we're talking a lot about adaptations and habitats and foods and whatnot but one of the big focuses of these kinds of studies is also distribution Where were early humans living? Where were they more populous?
Where were they less populous? Because that past organization of our species has major implications for gene flow and our technology and habits and all of these things. Classically, if you ask the question, what was responsible for how humans were distributed in space?
The answers would be things like the climate, food availability, physical barriers, right? Mountains and rivers and stuff. But it has also been suggested that a major shaper of human organization may have been diseases.
This is harder to study. We can study paleocclimate. We can study where food, you know, where different plants and animals were living. diseases are harder to get access to in the archaeological or paleontological record. But this study took a swing at it, specifically looking at the potential impacts of malaria on early human organization.
>> Our species started off in Africa and has been in Africa ever since. Malaria is a majorly influential disease still to this day that afflicts many many communities. Africa in particular sees lots of modern-day cases of malaria.
Malaria is most famously spread by mosquitoes. And there has been tons of research into modern epidemiology which is you know how how and where and when and how quickly and how effectively malaria is popping up and spreading. In this study they took an epidemiological approach to the past. So they looked at modern mosquito distribution models where they're found what populations they have based on climate and conditions. paleoclimate models, our understanding of climate through subsaharan Africa in the past and epidemiological models to understand how these factors affect the spread of the disease and basically came up with malaria transmission potential maps for the past. Cool. They did this for various time periods between about 74,000 and 5,000 years ago. So a big chunk of the time that homo sapiens has lived down in Africa. And then they came up with human niche models based on archaeological evidence of where humans were living at different times and what resources they were using. Where were humans being the most successful and the most populous? And then they compared the two to see if there was any particular pattern. And what they found is that based on their data, the regions with the highest risk of malaria, the highest transmission potential were also the areas that the human model showed humans avoided the most. Oh, >> and on the flip side, the regions where humans seemed to have been the most populous and the most successful were also the regions that the malaria model suggested the lowest risk of transmission.
>> All right, >> this is the kind of result that is makes a lot of sense, right? If there's a place with more disease, you're not going to be there. But if these models are, you know, an accurate representation of how our species has moved around over time, it suggests that it's not just that early humans avoided places with all the mosquitoes. The presence of malaria might have been a major determiner in where people were or were not living over time. that whether or not this was a place that malaria thrived might have been just as important as how much precipitation there was or which plants were growing there. And this is really interesting because diseases are a mostly invisible part of our history. We can find fossil plants and we can find climate data, but it's hard to find disease data from the ancient record. So, this is a first step towards understanding the effect. It's kind of like a I'm thinking of like a black hole. How we detect the presence of a black hole by the way things around it react to it.
>> Yeah. Yeah.
>> The past organization of humans may have been shaped by factors like diseases that we can't see.
>> Makes a ton of sense. And this is a cool way to track it because yeah, unless it leaves scars, you know, on the bones and whatnot, diseases, you know, are are just mostly traceless. So, this is a cool way to get around that problem and very intriguing find. Like you said, it makes sense that we are not wanting to live where malaria is going to kill us.
It is notable how distinct an effect it seemed to be having. Mhm. They also noted that they start to see in their models overlap between the high-risisk malaria zones and human ranges starting around 15,000 years ago more recently >> which they point out does line up with genetic estimates for the origin of cickle cell mutations >> in certain regions. Now cickle cell is a condition that is extremely widespread particularly in African populations and it is also a dangerous condition that that can cause a lot of health problems but it is also thought to be a defense against malaria.
>> Yeah.
>> Because the change to red blood cells that is caused by cickle cell m gives makes it harder for malaria to infect the cells.
>> Yes.
>> And this is a relationship that has been known for quite a while. So their data also seems to suggest that human range expansion may have indeed been made possible because of the advent of this competing disorder.
>> Yeah. Well, and and it brings up the question of were dense populations of humans forming where malaria wasn't common because that's where it was preferential or because that's where it was able to happen, >> right? Could you not have had a dense human population in a malari area before you had some sort of response to it because it was it's just such an effective disease like >> right and and they they make the point in the paper that it's not just that people would avoid those areas. It's that you just can't be as successful in the same way that Yeah. Like what we talk about, you know, where alligators live here in the US.
>> At a certain point, you get far enough north that it stops being a matter of preference and is just a matter of only so many of this species can possibly be sustained in these conditions.
>> Yeah. that now the winters are harsh enough, they kill enough of you each winter that your population just can't boom here. It will always be maintained at a smaller size. You know, it's like if you decide to go start a town on the top of a mountain, it's like cool, that town can only get so big because resources, land, usability is not as good there.
>> But the limiting factor in this case may have been malaria is killing your people off. you can't form a huge society here because malaria says no. Uh which also really drives home just how intense malaria is.
>> Yeah, it's a big malaria is a big deal.
The authors do point out that this not only is this interesting data and an interesting insight, it's also a template that we could potentially now use to do the same sort of thing with other diseases. Yes, >> if we can get similar evidence, we can look at the history of the impact of disease on early human populations, which is a very cool method for understanding how we've shifted over time and to understand the foundations of where our modern species emerged.
>> Cool. Well, my first news has really nothing to do with any of that because it's about the oldest octopus fossil and how it isn't that.
>> It's actually the youngest octopus fossil.
>> It's it's not even what it claims to be.
[laughter] This is research by Thomas Clemens at all in proceedings of the Royal Society B and the article is by Jack Guy in Seaman Science. This research is on a fossil species known as Pulcepia Maison insisas which dates to the late Carboniferous of the Maison Creek formation. So around 3001 to 306 million years old and had been previously ident softly identified or suggested to be our oldest octopus fossil. All right.
>> It is a single specimen, but it has enough information to date it and compare it to molecular clock dating so as to line up for being the oldest octopus fossil, which made it very interesting for a couple reasons. One, oldest member, but by a lot, the next oldest octopus specimen we have is like 90 million years old.
>> So, which is a third the age.
>> Yeah. So really pushed it back a lot further than we, you know, would typically expect, but that was the case.
There have been those who question this identification for a couple of reasons.
Certain features of the specimen didn't quite match what you would expect for an old octopus. And this, you know, this would be an octoberian, so the group that includes octopuses. But some of the things didn't quite fit that group. the length and shape of the arms seemed a little off potentially. So, this study was reassessing the fossil to try to get a better idea. And they used a whole bunch of more recent and high techch ways to analyze the fossil, things that weren't available when it was initially identified. They said they used geocchemistry work to try to identify tissues, scanning electron microscope, and evidently kept coming up blank on any extra information. the fossils being very stubborn to reveal anything new until they used synretton microax-ray fluoresence elemental mapping.
>> Sure. This is this is the kind of thing we've talked about before where you're analyzing basically the composition of the material that is preserved there and you get these beautiful images where like different elements are highlighted in different colors.
>> And this one particularly is a very powerful form of X-ray. It evidently is our currently most powerful way to X-ray something. So, this is getting a scan in that the other things could not and it was finally able to reveal some new anatomical features that had not been able to be seen that were within the matrix of the stone. The big one that is focused on is the radula was able to be identified.
>> All right. The tongueish thing.
>> Exactly. And that confirms it as a mllisk. So mllisks, your shelled invertebrates have radulas. Many of them snails and sephopods have these toothy like toothcoed tonglike appendages. So it is indeed a mllisk, but its radula does not seem to be an octopus radula.
It has at least 11 teeth per row. So you know those toothy sections of the tongue, which does not match octopus anatomy, which typically have seven or nine. and instead means indicates that this is more likely a nautilloid. So cousins of the nautiluses >> and probably why it was misidentified is it seems that it is extremely decomposed that before it was buried they estimate that it was likely decomposing for weeks and degraded quite a bit and then got fossilized.
>> Interesting. That does make a bunch of sense because otherwise speaking as a person who does not know a whole lot about sephopods, [laughter] I feel like you have a hard time confusing an octopus with a nautilloid.
Yep. Yep. Yep. Yep. So this means it does not seem like octopus had a surprisingly ancient origin and that instead it was the expectedly more ancient shelled cousins the nautaloids and is also a cool demonstration of some more recent techniques on stubborn fossils. So another example of how we can reassess old specimens in ways that might really change how we interpret them. Yeah, it's also a helpful reminder of the importance of considering taffonomy, which is the processes that affect the way something ends up preserved as a fossil. In this case, a reminder that things can heavily decompose before becoming a fossil. And when you're getting fossils of softbodied tissue, softbodied animals and their soft tissues, that can be really impactful.
>> Yeah. Because like if you have a skeleton then it doesn't really matter how much you de decompose as long as the skeleton remains intact.
>> But you're all soft body here. So any decomposition really changes what we can get.
>> Yeah. Fascinating.
>> Well, my second news really has nothing to do with that, but it is about fossil footprints trackways that give us some potential insights into the lives of terasaurs.
Oo, nice. This is research published in scientific reports by Jung Yun Jung at all and we will post a link in the blog post to an article on Science Alert by Michael Irving. Terasaurs are the famous flying reptiles of the Mesazoic era, your pteranodons and pterodactyls and kettle katiluses and so on. Despite the fact that they were very much flying animals, we do have a whole bunch of terasaur trackways, footprints of them walking around on the ground. But we don't have a ton of evidence of what exactly they were doing on the ground.
For example, there have been lots of different hypotheses about the hunting strategies of different terasaurs, right? Some terasaurs, particularly the late Cretaceous Ashdarid terasaurs, have been hypothesized as hunting [snorts] on the ground, right? Not just like landing to roost and stuff, but actually stalking things like you might imagine a stork or a heron or, you know, something that hunts along on the ground. So questions of what they were doing remain elusive. This study publishes a fascinating new ignoaxon, a new species of trace fossil that is a terasaur trackway. The new taxon is ginguis proeris which comes from the gingu formation of South Korea. This is around the middle of the cretaceous about 106 million years old. The gingu formation and its surrounding region in South Korea are famous for fossil footprints.
We've these have come up basically anytime we've talked about fossil trackways in a broad sense on the podcast. We've brought up the Gingu Formation and this region. There's tons of dinosaur tracks, there's lizards, there's crocs, there are loads of terasaur footprints. So, finding another terasaur trackway in this area, not surprising. In this case, the new trackway is a total of seven prints, four hand prints and three footprints.
Because terasaurs were quadripeds on the ground, they walked on their hands and feet. This terasaur doesn't I didn't find in the paper a description of its size, like the overall estimated size, but it doesn't seem like it was terribly big. The handprints are about 20 centimeters long and the feet are about 11 centimeters long. So like we're in like the half a foot range for each of the feet. The there's artwork there's paleo art in the paper that just depicts the terasaur being relatively small.
Mhm.
>> But the anatomy of the prince and the shape of the hands and feet suggest that this is an a dark terasaur. This is the group later on in the Cretaceous that have been proposed as walking around on the ground hunting for food. So finding tracks of one walking around on the ground. Not terribly surprising. It's also a new type of terasaur trackway.
Got its own name. And they did an estimate of its walking speed based on the spacing of the footprints and came up with a walking speed estimate of about 1.8 miles per hour.
>> Okay, >> which is not at all very fast by our standards, but compared to other terasaur trackways, it is above average.
Yeah, I was say it's not super slow either, >> especially for animals that you have to imagine were not terribly efficient on land, right? These these weren't racing on land. And this was a relatively small one. So, this does seem to be h having been moved at above average speed compared to other terasaur trackways.
>> Neat. Now, listeners can't see this, but Will and I are on video, and I've been watching Willing for me to explain why this is an exciting find the whole time.
[laughter] >> The terasaur trackway was not alone.
>> Nearby and partially overlapping these terasaur footprints are a series of smaller footprints that create another trackway. These are tiny little hand and foot prints about a centimeter each.
Like the the the feet and hands are like 1 to 2 centimeters. Some kind of small quadriped with a tail trace that it was dragging its tail around. The researchers were not able to definitively identify what kind of little critter this is, but they said most likely it looks like probably a salamander.
>> Okay, makes sense.
>> Some little amphibian, something like a salamander. Could be a lizard, could be a small crocodil form, but something salamandery shaped. In total, there are about 50 footprints of this little critter in one continuous trackway.
About 50 be they they say in the p they're like about this many because some of them are like overlapping or obscured with each other. So, it's hard to count. The most interesting thing that this smaller trackway does is it changes direction at a certain point in its path.
>> Yeah.
>> The first section of these of this trackway, the first, you know, several pairs of hand and footprints are angled sort of toward where the terasaur prints end up having been deposited. And then as they come in line with the terasaur trackway, the track the little or trackway turns 25° to the left >> and the rest of the trackway is in the same line as the terasaur footprints >> partially overlapping. And before the change in direction, the tracks are closely spaced with a distinct tail trace. But after the change in direction, the tracks are more widely spaced with faint tail traces, which lines up with what you might expect to see with a creature that suddenly increased its speed.
>> Yep. [laughter] I believe the the technical term for that change in trackway pattern is going from DA DA TO >> YES. And that seems to be what has happened here is that this [laughter] little critter was walking along and then now obviously the footprints are just what's left behind. So all we can see is the tracks and the footprints.
But the positioning and orientation of all these tracks is very consistent with a little critter that was walking around and then started getting chased by a terasaur that was also chasing it on foot. Now, notoriously with footprints, it is very difficult to tell if indeed two different track makers actually interacted with each other. Right? This could easily be a coincidence. This could easily be that there, you know, there was something scary in the way and they were both the these tracks could have been formed at different times.
Yeah.
>> But the authors of the paper do point out there is always that possibility.
But there are a number of reasons to suspect that these two actually might have interacted. For one, the trackways themselves are of very similar preservation, which suggests that the sediment they were left in hadn't changed very much in between the the steps. They even point out that the depth of the footprints changes in the same way as the tracks go on. So like the sediment was shallower over here and then deeper over here, which again suggests that they were walking over a very similar ground. And they also point out that there are no other obvious traces in the in this slab of sediment.
So nothing else walked across this in between these two. It it seems like this patch of sediment was ripe for footprints for a relatively limited amount of time.
>> Yes. during which both of these creatures walked across it.
>> Yeah.
>> All of which does is support for the idea that they walked across it at a similar, you know, not very far away from each other in terms of time. Also, they are moving in exactly the same direction.
>> Yep.
>> Like if if you were chasing a small thing, this is what your footprints would look like. And not only do we see that increase in speed in the little one, but as I mentioned earlier, this terasaur seems to have been moving fairly swiftly for a terasaur of its type and size.
>> Yeah.
>> All of which does seem to be fairly convincing support for the idea that what we have caught here is a snippet of a terasaur hunting on foot. Yeah. Now, and I think that this was this was either in the article or in the paper.
They said something to the effect of how this interaction ended. We don't know because that is beyond the slab of sediment that preserved the footprints.
So what happened after this is hard to say, but this is potentially some very rare direct evidence of Cretaceous Ashdark terasaurs as terrestrial hunters stalking and catching food on foot.
>> Yeah, that's so cool. That is so supremely cool. If if you go to the link uh we'll put the again we'll put the link in the in the the blog post the full you can see sometimes footprints are really like yes >> you look at the picture of the footprints and you're like all right scientists I'll take your word for it you you seem to know what you're talking about this this one it's pretty evident what they're interpreting here it's really cool there's even a section and I don't think they discuss it in this way in the paper but the the little the smaller trackway is angled and then it changes, but there's a middle section of this trackway where the tracks aren't preserved very well at all.
>> Mhm. which I don't think they said this in the paper, but to me seems consistent with either little critter got snapped at >> and it disturbed the trackway or that cartoon moment of when an animal tries to start running real fast and just kind of like slips over itself for a bit.
[laughter] >> Yeah. Scrambled. That there might have been a a little bit of a scrambling or tussle here. Yes. And then they took off. [laughter] >> Yeah. Well, and this is such a great example of can we confirm this was hunting behavior? You know, we can't say that 100% because yeah, there's a lot of things that can't be for sure confirmed because even if it was a short period, if they happened even an hour apart from each other, then they can't have been chasing each other. They may they may never have met in their lives.
>> Exactly. Like even 10 or 15 minutes could be enough to make it not feasible to call this hunting unless you're suggesting that they was following the scent trail. And I don't know that that's uh something we would expect from Terasaur.
>> The little one had a spider sense and it was like, well, 15 minutes from now a big predator is going to walk by here and I'm going to run away.
So, we can't confirm, we can't say definitively, but it is this one of those kinds of scenarios that comes up in paleontology very often of I can't give you a better explanation right now with the info we have as for why these footprints line up the way they do.
Maybe we're missing some bit of info that if we find it, it will go, "Oh, oh, clearly this is what it is." But without that and if that doesn't exist, everything points to one answer it seems and that answer makes a lot of sense. So it should be considered at least it's a very cool result. And then also a as always is the case with something like this, the Ginger Formation has tons of terasaur tracks.
>> So it makes me say great, go find more.
>> Yes, >> this is awesome. go find another one.
Cuz if we can find a handful of these, that would be both inform informatively extraordinary, but also would really solidify that, yeah, this wasn't just a one-time thing. We've got multiple cases of this. For now, this is a one-off uncertain but pretty convincing case of what seems to be a really cool interaction between two ancient creatures 106 million years ago. And personally, uh, I'm hoping that the terasaur got it.
>> Yes. No, I I hope there is somewhere out there stomach contents [laughter] that is whatever this little critter was.
Yes. That's my I my fanfiction of how this little story ended is that the terasaur got a meal.
>> Yes, [laughter] absolutely. Cuz it would work so hard.
>> It was booking it. It was It was running real hard.
>> It was moving above averageely fast.
[laughter] >> It was going almost 2 miles an hour to catch that thing.
>> Earned it. Well, my next news is does deal with predation, but mostly deals with my first news because it is this time actually about octopus.
>> Oh, since we took away the oldest octopus, this is about some of the oldest octopus and a very cool aspect of some of them were big. This is research by Shin Ikagami at all in science and the article is by Hannah Develin in the Guardian. This research was looking at a bunch of fossilized beaks from ancient octopus. These date to the Cretaceous somewhere between 72 million and 100 million years old, which if you remember is when we were saying the confirmed next oldest fossils of octopus are. So these are some of the oldest octopuses that would have been around. These are from a group known as nimotus. And these are thinned octopus. So serata octopuses, things similar to, you know, like Dumbo octopus and stuff like that where >> Okay.
>> octopus very octopus shaped but has fins on the head kind of like a squid.
>> Yes. These had previously been assigned to vampire squids, which is I don't know if they're in this same group, but they are closely related to uh they're more closely to octopus than squid.
>> And they've got those big fins.
>> Yes. And they're just squid shaped, but not actually.
>> Mhm. This study was re-examining some large fossil beaks from this deposit, from this group, 15 beaks, and were able to ID them to this fin octopus group instead of vampire squid. And that's all super fun. They also uncovered 12 new beaks from the the material via digital imaging. All good stuff. That's not what any of the news has been about >> because they were chasing a small creature. [laughter] They changed direction.
>> They were not chasing a small creature though cuz at least one species is huge.
>> How huge is it?
>> At least giant squid sized.
>> Whoa. [laughter] >> Like at least one species. Naimo Toothus Hagardi had a big old beak. And once again, we're studying beaks because the soft body typically does not fossilize with these animals, but these beaks do give us a lot of info based off of body size estimates compared to modern sephopods. And the beak size is larger than modern giant squid. And when we look at the size of the jaw to the body length that we would expect in modern fined octopuses, the estimates are between 7 m long, which is a little bit shorter than the sizes we know giant squids can get to, which is about like 10 m long.
>> Mhm.
>> Up to 19 m long.
>> That's 19 m is like a humpback whale.
>> Yep. [laughter] So, probably somewhere between those two, but at the lower end, it's just a little bit smaller than the giant squids of today. And then anything up from there is as big or bigger than the giant squid.
>> That's wild. Yeah.
>> Either that or these were octopuses with just proportionately ridiculous beaks.
>> Oh, just just chibi.
>> Yes.
>> Finned octopus with giant eyes, big old mouth. Just a terror bird octopus.
[laughter] Just adorable.
If this size estimate is accurate, it could make them the largest invertebrate on record that we have ever known. Uh, currently giant and colossal squids are the holders of that record. So, if they are indeed bigger than that, that would shift the record to this new species.
And it is notable because it would also mean that this would make them one of the larger predators in Cretaceous oceans.
>> Oh, true.
>> Cuz the top spots have often been held by marine reptiles. These are sizes that are reaching the upper sizes of those marine reptile predators. So, this might have meant that they were also top predators. And this is supported by some features noted on the beat. When we look at the largest individuals of the beak, they show extensive wear patterns, wear and damage on the beak from use.
Octopuses use their beaks when they hunt by grabbing prey and then dismembering it with these very sharp parrot-like beaks. In the smaller, likely more juvenile specimens, the beaks are sharp.
In the larger ones, they have worn down, become more blunted, rounded, and even chipped in spots. This suggests that during their life they were eating tough food, crushing into shells or bone that wore the beaks down, which could include bony fish, shelled prey, but also marine reptiles in tough prey that are bigbodied bony prey animals.
>> Yeah, >> that they were eating tough animals, it seems. And their beaks appear to be more worn on one side than the other, which may indicate some form of handedness.
>> Yeah.
>> That they may have preferred a left or right to their feeding, which we do see in modern sephopods that many of them will have a preference to left or right-handed, you know, armedness, [laughter] >> which could mean that they had a similar neurology to modern seephopods. and thinned in octopuses that we have today, which could mean that they might have a similar sort of intelligence, whether they were as problem solving, but that they may have had a similar brain setup if they were showing similar behaviors.
>> That's so cool. And and and this is one of those findings that I'm not I would not be surprised at all to learn that there were giant squidsized sephalopods back during the Mesazoic because there are giant squidsized sephalopods today, right? They exist today. Makes all the sense in the world that we could have had others. Also, there were giant sephalopods in the Paleozone. We had orthocone that were like similar length that were also like 10 meters long. Mhm.
>> The fact that we have evidence of it is very, very cool. The idea that now we can picture how did these giant octopus like things fit into their ecosystem? An ecosystem of ichthyosaurs and plesiosaurs and stuff. But also my big question that comes to mind is where were these animals living? Because today our giant sephalopods, giant squid and colossal squid are deep sea animals.
>> They live down in the deep sea, which not all seeopods live in the deep sea.
There are tons of shallow sea sephalopods, tons of octopus. When you see you see documentary footage of octopuses, and the reason you can see them is because they're in the photoic zone where there's lots of light and they're around reefs and stuff.
>> Exactly. But also being a giant sephalopod living in the deep sea does make a ton of sense because you're avoiding competition with most of the other ocean giants who have to breathe air. Whales and big sharks and stuff. So it would also make sense that these giant octopuses were also living in the deep sea to avoid competition with big marine reptiles and fish. But we only have two examples today.
>> Yeah.
>> Which isn't enough to suggest that it would be impossible for giant sephalopods to exist in shallow seas alongside these other big predators of the oceans.
>> Yeah. The only two examples we have, we also know very very little about.
>> Like we have not observed much living behavior. We have not observed mating or reproducing. There's a ton that is just still fully a mystery about these our modern giant sephopods. So yeah, are they weird or is this the norm that we could expect for others?
>> Yeah, I would imagine that these beaks weren't found in terribly deep sea sediments.
>> They didn't mention it anywhere in the articles.
>> Yeah, we tend not to get a a lot of fossils from deeper sea settings.
>> Mhm. Oh man. Now I'm I'm picturing a like early Cretaceous reef >> where there with just arms. [snorts] >> Yes. Right.
>> Like there's just like a picture much the way that if you ever get the ch if you ever go to a aquarium. This happens to me. Uh I like noticing this with snakes. One of the really interesting things about snakes is that a snake can be on both sides of its enclosure at the same time because it's because it's this long thing. And just like a picture of a reef ecosystem and there are multiple arms that you can see like wrapping around stuff, but there's only one octopus in the picture. [laughter] >> Yep. The fan art and paleo art for this creature that has been coming out is it's been so delightful.
>> A that's so cool. [laughter] And with that, we can wrap up our news and move on to the main discussion. And if I were a creature living during the Cretaceous in the oceans with these giant sephopods going around, I sure would want to be out of sight. And a great way to do that is to dig a burrow.
So, let's talk about what counts as a burrow and what are some of the tools animals use to dig them.
>> We can dig it.
Something I came to realize while taking the notes for this episode was that I think burrowing is a vastly more widespread and common behavior and feature than many people might realize.
Agreed.
>> There's a lot going on under the ground.
>> Well, we've talked before about how on a planet covered with water, you can't help but have a lot of swimmers.
>> Yep.
>> Well, the the planet's also covered with dirt.
>> Yeah. [laughter] >> So, you can't help but have a lot of diggers.
>> And it's so much easier to go down than up. Like, evolving flights way more difficult. [laughter] >> Yeah, that is true. The planet is also covered in air, but that's that that's a much harder achievement.
>> Gravity's working with you. If you want to burrow, [laughter] if you want to go down, gravity's on your side. Burrowing and burrows is the act and behavior of an animal digging a hole for shelter, for foraging, for escape. Sometimes just because they're moving around, they will leave behind a burrow because they're moving through the dirt. So a burrow is just a very very general term of a hole in the ground created by an animal.
>> Mhm.
>> That's that's basically it. Typically, it's going to be in the ground. You can get burrows and boring holes in other structures, wood and stone and stuff, and we can talk more about that. Animals that engage in this behavior are often called fossoral, which means to dig.
Diggers. Typically, this is going to refer to an animal that digs for part of its life and for part of its behavior, but is not purely underground.
>> Oh, sure.
>> Like posural is going to be something, you know, like dogs will dig holes down and wolves will dig dens, but they don't stay underground. They come back up to go look for food. You will sometimes see for animals that are almost always underground, they'll be called subterranean instead of fossor.
>> Sure. Right. This is the difference between like a bear and an earthworm.
>> Yeah.
>> Yeah. An earth, you might never see an earthworm cuz that's they just live down there.
>> Yes. If the earthworm had its way, it would never have to come above the the soil level. Now, this is not super common. I only found this a couple of times, but I did find it distinguished very often that fossoral means not always underground. Usually foraging or at least frequenting the surface and enough, you know, sometimes. Well, in discussing borrowing animals or fossoral animals has a similar feature to when we discuss swimmers where there is most things can swim and most animals can dig in the dirt, but typically when we're talking about borrowers, we're talking about animals that have specializations.
You are you have evolved into a form that makes you extra good at doing this thing that otherwise Yeah. basically anything can do at least a little bit.
>> Absolutely. And you'll also get degrees in how an animal interacts with a burrow. You know, typically when we think of a burrowing animal, we think of something like a mole that digs a burrow, lives in the burrow that it built with its own two terrifyingly shovel-like hands.
>> Mhm.
>> But there are kind of three categories.
That would be a primary excavator. They dug the burrow they are in.
>> A primary excavator is a perfect description for a mole. Describing it like it's a piece of construction equipment. Absolutely. It's so good.
You'll also get some groups that fall under secondary modifiers. They did not dig the burrow they're in, but they have adjusted it for their own needs. And then, and I love this one, simple occupants.
>> Yep. [laughter] >> They're not doing anything to the burrow. They just live here.
>> You're just squatting. You're just in This is a lot of snakes do this like gopher snakes. Part of the reason they're called gopher snakes is because they hang out in burrows, but they don't dig burrows. They find burrows and then they hang out in there.
>> Absolutely. A lot of your smaller burrow dwelling animals often fall into this category that are not big enough or powerful enough or just don't have the body to be able to move dirt easily.
Burrowing owls, famously underground livers, do not dig their own burrows.
They find someone's and move in when it's empty.
>> Yes, >> there are tons of pretty obvious benefits to having a burrow and to making a burrow. Protection is the most clearcut both from predators and from the environment, you know, from the elements, from heat, from extreme temperatures.
>> A lot of hibernators while hibernating are doing it in a burrow to remain safe.
>> Absolutely. You'll also see specializations with like the opening to the burrow being facing into or away from the direction of the sun or away from cold wind and stuff to try to better utilize and better avoid whatever it is you're trying to avoid. It's also notable that it's a great way to survive forest fires, which feels topical.
Burrows also can gain access to new foods if you are a underground forager.
Most digging animals aren't also eating underground but are using that as a home and then coming up and getting food. But you do get animals like moles, like mole rats that are foraging under the ground as well. And even if you aren't eating underground food, underground's a great place to store food.
>> Yeah. So having a burrow as a place to bury food, hide food, keep it for the winter, super useful. Another very common use of burrows both for permanent burrows and as a specific use is to raise young.
>> Yes. Dens, burrow, or even things like ants. That's where ants are keeping their babies.
>> Like half a big reason that that nest is so useful is because it protects the young. But you get things like bears that dig a nesting den. And the purpose is so that they can give birth in this protected secluded area. Burrowing animals also are super important because they act as ecosystem engineers. They're turning up the earth. They're changing the ecosystem. They're creating environments. A burrow is a new kind of environment that other animals can move into. Especially when you get into places like marine settings that's stirring up and allowing the water to reach into places that it wouldn't be able to. So, they are very important to how they shape the landscape. And this is called biotourbation. Turbation is overturning of soil. Bio meaning it's done by an animal. As we mentioned upfront, burrowing is extremely common.
It's found across just about every group of life you can think of. And it's found globally. Like there's really not a place on the planet that you can go to and be like, "No one's burrowing here."
Because >> Yeah. If if there's earth to move, someone's moving it.
>> Absolutely. Of course. easier to dig in.
Sediments are probably going to be more common. You know, materials, sand, soil, snow, all of those are very common to burrow through. But there's all sorts of examples of things burrowing into unique materials. Lots of wood boring animals, insects, and so forth. There are urchins and clams that can burrow into rock and bore into stone. One paper I saw made the point that Skies mites burrow into their host.
[laughter] >> So they're burrowing into skin.
>> I don't like that.
>> Yeah, but boy, it it that's what it is.
That's how they make those networks.
>> I don't appreciate being a substrate.
>> Nope. Mm- I try to avoid it.
You also get cool specializations for like a lot of marine burers burrowing in sand will use mucus to consolidate the walls of the burrow.
>> Yeah.
>> And keep it together. When it comes to on land though, burrows are more common in some areas than others. And one of the like key indicators is open environments are very very prone to burrowing because you're exposed. And if you can find if you can make shelter, that's huge. In the forest, there's tons of places that you could find shelter naturally. In a field, not so much. So burrowing becomes a very common trait among open environment, aid environment as well, animals. The list of animals that burrow is almost all of them. [laughter] Like >> get in the comments, let us know your favorites.
>> Absolutely. They are common in every group of life. There are some where you see it more commonly. You know, there's not as many burrowing birds as there are mammals. Mammals are often looked at as kind of the stars of burrowing. They're very a lot of very specialized burrowing mammals. Other animals are also extremely well known for this, just not as famous among the general public.
Vermapform animals, wormshaped animals, are by far the the masters of burrowing.
That's like the borrower.
>> Yes.
>> That like that is the it is the most efficient. If you want to be a burrower and you don't want to put in a lot of effort, you just you shaped like a worm and you just push your face into the dirt.
>> It you want to make a tube in the ground, what better shape to be than a tube yourself. And so yeah, worm shaped now true worms, but also all your other wormhaped and wormlike creatures, marine creatures and so forth. There are so many polyets and acorn worms and all sorts of ones making all different kinds of burrows.
You do see similar patterns in that snake like serpentapform morphoypes are very common to evolve in burrowing reptiles and in amphibians, snakes, legless lizards, serenians. All of those are commonly if if not burers often underbrush and moving through substrate.
That long slim body is very good for that. With your legged animals, you tend to see kind of an opposite direction in the body shape. Instead of getting long, they get very compact and fus form like a little torpedo. Often having shorter, more robust limbs for both not getting in the way, but also moving dirt because many animals, especially among mammals, the limbs are the main digging tools.
Yeah, this is the different, you know, a lot of burrowing lizards, you know, like a lot of skinks. We talked about this in episode 221. A a lot of burrowing lizards are digging with their face, >> which is why they can afford to be limbless or have very reduced limbs.
They have a shovel-shaped face that they're wedging into the dirt. Mammals tend to dig with their hands.
>> That's where the shovel is. And so they've got these big scrapy spade hands.
>> Absolutely. And very often you will see mammal digging broken down into three main groups. So fourlim digging is the most common form of mammal digging and the three types of digging which we have mentioned before cuz it's come up with other digging animals is hook and pull, scratch digging and hummeral rotation.
Hook and pull is your anteaters. Big hooked claws usually downwardfacing hands, palm facing toward the ground.
Very powerful at flexing that hand in those claws. Often good at digging. Not always associated with burrow making.
>> Yeah, this is this is more like a using a rake or a hoe.
>> Yeah, like a pickaxe >> or a pig. Yeah, pickaxe is a great example of it. You're piercing the ground and pulling some dirt out of the way.
>> Exactly. Scratch digging is by far the one you're thinking of when you think of something. A dog digging is scratch digging. that you've got powerful front limbs, good at moving dirt, often robust limbs. All of these have robust forlims.
Scratch jiggers will typically have either sharpened claws for breaking up dirt or flat claws for moving dirt. So, think like armadillos and arvarks and stuff like that.
>> And digging like a dog does. This is a very common burrow making method of digging for mammals. And probably I would the most common.
>> Yeah. Well, because this this is how we would dig if we had to dig a hole is Yeah. You're just kind of grabbing hold of dirt. I guess we're kind of doing a little bit of both because we can also grab dirt and pull it with our with our grabby hands.
>> Yes, indeed. And then cumeral rotation is the weird sounding one for the weird looking animals. This is moles.
>> This is moles. Moles. We're all the the the sad thing is that in this episode about burers broadly, we're only going to get to spend so much time talking about moles. Moles are so cool. And so I love moles so much. They really It re like comparing moles to other digging mammals really is like comparing freshwater turtles with sea turtles.
>> Yes. Yep. It's just not. You've just gone the whole you've gone 100% into you are a digging mammal capital D.
>> Yeah, they are intense. And to start off on that, the humal rotation refers to the fact that mole's arms are turned sideways facing out from the face. So each palm facing the left palm facing to the left, right palm facing to the right. And they dig with this sideways scooping. And that's the humorris rotated, the humoral rotation.
>> Yeah. They're digging outward rather than under the body like you would imagine a dog doing.
>> Yes. And this body plan, the moleike ball plan as you'll see it's called sometimes has shown up multiple times.
So, typical mole shape, little cylindrical compact body, big big flat hands, extremely specialized forearms.
The mole armbbones look insane, very reduced eyes, very increased tactile sense, and sometimes smell. This has been found convergently to have evolved in mammals likely about 13 times.
[laughter] you know a we talk a lot about what is the like standard form of different group where like lizard is kind of the standard reptile form and like a little you know a sparrow or something is sort of like standard bird. Well standard mammal is like a rat.
>> So you're already halfway to mole just being a typical mammal.
>> You're on the right path. Yeah. There's a whole bunch of these going from true moles, you know, the group that is named moles in their totality. The African golden mole is another route. The Australian marup marsupial moles is another group.
>> Mhm. This selective pressure for this body shape is so powerful that there is even the mole cricket which also has shovel-like hands that it digs in the same pattern and a little compact fus body.
>> You don't even need bones to be a mole.
>> Nope. Mole is if you're not a worm, mole is the way to move through the ground.
>> It if you have arms, this is the way to do it.
>> Aim toward mole. Another [laughter] tidbit I learned that just really tips them even farther into how awesome they are. Many, many subterranean mammals have specialized bone, not as in the shape of the bones, but the makeup of the bones. They have a special type of bone called compacted coarse cancellous bone, which is a dense strengthening element to the bone. When a study looked at true moles, they found that the degree of compacted coarse cancellous bone they had largely exceeds that of all other digging mammals and exceeds adaptive optimums.
[laughter] They're overengineered. They've got more of this bone that [laughter] they than they should need to have.
>> Well, cuz every now and then you're going to come across a pebble. you gotta be able to push that pebble out of the way. [laughter] >> And so they have extreme bones for this.
And they noted that it looks like evolutionarily this came about before the mole shape. And so that adjustments to the makeup of bones seems to preede the shape of the bones for digging. And we see a similar pattern in aquatic animals that their bone density changes before they get flippers. So they're literally swimming [snorts] through the earth. They are taking a similar evolutionary path to sea sea mammals.
>> And just to listen, send in your request now for a moles episode. We'll do a moles episode. But there are a bunch of moles that dig and swim.
>> Yeah, there are.
>> There's at least one spe I think the starnose mole might be the one I'm thinking of >> that digs burrows that open into the water.
>> Yep. So they just go straight from digging to swimming, >> straight from underground to underwater.
>> Smell underwater by blowing and reatching bubbles cuz they're just the coolest.
>> They're just they're so good, man. Oh, they're so good. Anyway, moving on to other animals for now. [laughter] There are other ways mammals dig. As you mentioned, reptiles very commonly dig with the face because that's what you got. Reptiles are not as much into the robust limbs as mammals are. And many of your digging reptiles are going to be snakes and lizards that have reduced their legs. So, they just push their face into the dirt and make typically quite simple burrows because they don't have a good method of moving the earth, just pushing it aside.
>> Yeah, >> you do get face digging with mammals.
There are things like wild boar which use their snout to dig and shovel up earth. But also rodents are famously tooth diggers. They use their teeth.
>> Right.
>> Yeah.
>> We talked about this in the tusks episode. [laughter] >> Yeah, we did.
>> Episode 107.
>> Mole rats are the most famous for this.
They are extremely specialized group of rodents and it seems like currently there are two groups. The African mulrats and the naked mulats are separate now though they used to be together. So I had to sort that out because a bunch of my papers were before that split. [laughter] >> So I I kept getting confused. They have these extremely large insizer teeth. You know rodents have that specialized ever growing insizers. These stick out of the mouth with the lips being able to seal behind the teeth so they're not swallowing dirt as they use their teeth like chisels. This is called chisel tooth digging. Some of them still will use their forlims to dig, but most don't. Uh it was noted only one genus is really known to be primarily a scratch digger and it digs through sands through sand dunes. So you get a variety of digging styles. There's also a whole bunch of digging insects that also will have shovel-shaped limbs and faces and are doing kind of a very similar of pushing aside the earth with these spatulashaped body parts. And as is often the case with these kind of behavioral episodes, the amount of cool digging adaptations are far too many for us to cover. So send in your request for your favorite subterranean fossoral animal group that you want us to talk about. These many different kinds of digging styles and digging animals also make a huge variety of burrow types and shapes of underground shelter. There is not like a set list of categories that burrows take because it is a very flexible, you know, you can have one just slowly morph like you could do a nice spectrum of burrows in many directions as you just start with a tube and then expand part of it and now you've got a chamber and then you add another tube and you've So you can just continuously sli move your sliders from one burrow to another. But for some examples, burrows can go from very very simple, a just a tube in the ground, a couple cm long for very small organisms is a burrow, all the way up to very complex. You know, rabbit warren are often pointed at as a good example of these intricate interconnected chambers and burrows and passageways with multiple entrances and many organisms all sharing this one structure. Yeah. I think of uh prairie dogs where you get where Yeah. It's just like this is one burrow network just across this whole field.
>> Yeah. And you will have a colony, you know, they they call this a colony of prairie dogs and they Yeah. They can cover huge amounts of area. Among the animals most famous for making extreme burrows are rodents. They have some of the top ones. Prairie dogs fall into this. Groundhogs fall into this. I saw one metric that said a groundhog can construct a burrow that occupies a full cubic meter and displaces about 300 kg or 666 pounds of dirt. That's a lot of earth for a very small animal to move. A prairie dogs or groundhogs are not big animals. They're big rodents, but they're not big animals. Evidently, and I didn't know this, the great gerbil is known to live in huge extensive burrows and are some of the most like known and impressive. Some of these can be seen by satellite, [laughter] >> man. Well, and it's such an interesting, you know, when we're talking about burrowing animals, obviously there are some animals that dig that don't act they they burrow, but they don't make a burrow. Yes, exactly.
>> Like an earthworm moving through the dirt, it it often is like swimming where you're not leaving a hole in the water behind you. It just goes right back to where it was.
>> Yeah. It's going to either collapse or fill in as you pass through it.
>> Yeah. The idea of digging an underground hole by itself is very impressive.
You've dug out a hole that stays that way. digging meters upon meters of tunnels and intricate and not they're not just digging these tunnels in two dimensions. It's not like a labyrinth where yeah, there's a top down view and everything is a left or right turn.
They're up, they're down, they're crisscrossing. Particularly, I get this if I'm in Manhattan and I'm standing in the subway station just going, "Man, this whole island is just crisscrossed by multiple layers of underground tunnels. That's a lot of effort. That's that what an undertaking that is to have accomplished that by a society of people with technology and tools over many many years. The thought of gerbles doing their own version of this [laughter] and just excavating out huge chambers and tunnels and colonies underground is really really impressive. These are some of the most massive animalmade structures.
>> Yeah, absolutely. Like this is huge amounts of energy and investment and often generational, you know, for these colonial living animals. It's not one family makes this entire, you know, a rabbit family doesn't just make the whole war in generation upon generation expands and maintains it.
>> Yeah. My grandpappy crossed that river into this land and dug the first hole right here. [laughter] >> Just standing at some particularly gnarled route. I remember >> just just rocking back and forth on a piece of driftwood. [laughter] I remember when my great grandappy pointed and he said, "Someday, son, you're going to build a burrow all the way out there.
Now get underground. There's a hawk coming." [laughter] You also can just get impressively big burrows that aren't very complex, but are just big. Wombats are evidently known for making very large burrows, some of which are big enough to be mapped via drone.
>> Like you can fly a drone into it. Yeah, that's what it that's what it seems.
>> That's wild. Don't wombats also block the tunnel with their butts?
>> Yeah, with their butt. And they'll crush your skull if you try to sneak in past it.
>> Don't mess with wombats cuz they throw it back and they mean it. [laughter] >> The torque of doom.
>> Yes, artists. I want a gift [laughter] on my desk by Monday. Probably the largest naturally built burrows are bears. Bears will be dig burrows.
Grizzly bears, polar bears will dig their own shelters. And these are very likely largest burrowing animal cuz like earth moved, a lot of those other rodents probably have them beat. But for like single chamber, single animal, yeah, these are probably the largest.
Another neat thing about burrows is like even though a lot of them are are pretty simple just chambers underground, you still can do a lot of identification, you know, so size of the burrow, size of the opening, how far it goes underground, what angle they dig down underground, what elevation you tend to find them at, what structures, you know, are they on a hill, are they on a flat surface? There's a whole bunch of guides for like identifying burrows and like is the burrow roughly 30 centimeters wide with a triangular opening? That's probably a coyote burrow and stuff like that. So even if they're not super like interestingly different, there are particulars and you can get quite specific. And of course, we get other burrows than just mammals. Mammals are going to come up a whole bunch, but there are other burers. Two that stood out to me to mention just that people might not realize are examples of burers. Crayfish, prodads, crawfish.
>> Oh yeah.
>> Very commonly burers. There's many species that burrow. And they do something interesting where they are a freshwater. You know, these are like little lobsters. They're freshwater decapods found in North and South America and some in Australia. And many of them dig that live in drier areas.
Still, they live near water, but they don't dig under the water. They'll actually dig near the water and dig down to the water table.
>> Oh, interesting.
>> It's like I saw a video the other day of a person who saw a hole in their backyard and they're like, "What's this?" And they looked in and a crawfish had dug down in their backyard and was sitting in the up high water table of their backyard.
>> Oh, cool.
>> And they end up forming these little turrets of mud around the opening. So you can end up with this little mound around their hole that raises it up farther. And I've seen pictures of some that are like probably six inches or so.
Like pretty tall.
>> Wow. Yeah. You know, we talk about Yeah.
Obviously, when we think about burers from our perspective, and we're talking about up here on the land, we're thinking about mammals and moles and, you know, all these things. But the most density of burrowing activity is happening on the sea floor where you've just got because there are clams that burrow and there's tons of worms that burrow. There's all sorts of there's a whole ecosystems in the sediment at the bottom of the ocean. And some of them, you know, we were we've talked about animals that use their burrows as like a den or a home or for storage. Some animals just build a burrow and that's just where they are. That's just where they exist. The whole time we've been talking, I've been thinking about the sand striker worms.
>> Yes.
>> Who they make a little burrow. They just sit in it and then when fish come by, they grab the fish and pull it down. And that and they just that they just live in a tube in the dirt and if undisturbed, they will spend their entire life there.
>> Yeah, absolutely. You get things like garden eels which live in colonies and only come out to spawn and then quickly go back into their burrows. And their burrows are a fun example because theirs are squiggly because it's in the pattern that they dug in. But that squiggle also allows them to easily move up and down because they have a pattern to move their body against.
>> So they can just slide in and out surprisingly gracefully and smoothly.
like there's no they're not having to redig. They're just whoop elevatoring up and down their burrow, >> which is something that you see a you were talking about, you know, identifying aspects of different burrows. A lot of animals dig burrows that are beneficial for what they're using it for, >> but also are easy for them to get in and out of.
>> Yes. And so, you know, like the complex burrows you see in rodents and stuff, one of the benefits of a complex burrow is that intruders are liable to get lost in there or not make their way directly to where all the babies are, things like that. So, you get these like, "This burrow was built for me to navigate, and [laughter] if someone else tries to get in here and has trouble moving through the squiggles, good. They don't belong here.
Get out." You may be a fox, but I know where the bathroom is. [laughter] >> Well, and then the speaking of the bathroom, a lot I find I think it's fascinating the way that animals will tidy their burrows.
>> Yeah.
>> Like they will upkeep. Most famously, the example that always comes to mind is ants, right? Ants are extremely good in many cases about if there's an intruder or just like or like an infected ant that gets some sort of disease, they carry it out of the burrow and then they go back down cuz Yeah. No, that's not what we want in here. This is our home.
We want to keep it nice and tidy.
>> Yeah. And that's something I saw noted in some like the identification guides.
What you find in the burrow is also an identifier. Like some animals will bring in plant material to line the burrow.
Some you won't find scat in. Others you will find scat in.
>> Because some some animals burrow. They have like a latrine chamber.
>> Yes. Exactly.
>> This chamber is where all the poop goes.
This chamber is where all the babies go.
Don't put the poop there. Put the poop in the latrine chamber.
>> Don't get those confused.
>> Others go outside to poop. It's like, yeah. Yo, if you have to poop, don't do it in the house. Go outside. So, like there's a whole bunch of ways like if you find an empty burrow to sleuth out who made this den, which is a topic we will speak more on after the break cuz now we're going to start talking about fossil burrows. Both how do we identify them, but also how do we figure out who made an ancient burrow? Stay tuned.
as one might expect for underground structures, burrows fossilize all the time.
>> Yep.
>> We get tons of trace fossils that are the remains of ancient burrows.
>> Well, because a burrow is ma technically a burrow is made of sediment. Yes.
>> The burrow is just the cavity, but it it's made of sediment, and sediment preserves real well throughout history.
That's what all that's what the layers are made of.
>> Absolutely. And it's very easy for them to get preserved because if you leave a hole in the ground, eventually it will typically get filled in with sediment, mud, you either via rain or wind, it will get filled up. And that's great.
That actually helps the fossilization process because now if the sediment that was the burrow preserves, then we've got it. If it doesn't, we have another selection of sediment that has infilled it that might fossilize and might turn to stone. So, we can get an infill. Some of the earliest fossils I remember finding on my own, you know, going out on trips with classes and stuff are you would get like here's a chunk of shale and there's this cylinder of sandstone running through the shale. It's like, yeah, that cylinder was a burrow, got filled in with sand, and then the surrounding sediment petrified into shale, and the infilling sediment petrified into sandstone. So now you have a sandstone cast of a burrow that was, you know, some worm burrow from back in the seafloor. So, finding fossil burrows, not that difficult, not that uncommon, pretty easy to identify in most cases. Identifying who made it supremely more difficult.
>> Most animals don't have the good courtesy to sign their burrows.
>> No, they they really And that's why any of you artists out there, I'm sure you learned in class, always sign your work.
>> Got to sign it. There's a there's a lot of there's a lot of slop burrows going around.
>> [laughter] >> Right. Right.
So, trying to figure out what animal made a burrow is a much more daunting challenge. This is for a number of reasons. Most animals that make a burrow are not found in the burrow. It does happen. We do get remains of animals in the burrows, which is a great indicator.
not a guarantee that's the animal who dug the burrow because we've already talked about a number of examples like birds and snakes that often live in burrows that they did not make. But that this is a fairly rare occurrence like there's we have a number of examples but it's you're not likely most fossil burrows do not have an animal in it. You they don't have a skeleton in it. The conditions that are good for preserving the shape of a burrow are often not the same as the conditions that are good for fossilizing the remains of an animal.
So, typically you're going to get one or the other and not both or neither. And even looking at the burrow can be challenging because a very simple burrow, like a tube down into the soil, that could be for an animal that is sitting into the sand and sticking its head out to filter feed, or sticking its head down into the sand to deposit feed and eat sediment. And those two burrows will look almost exactly the same because it's just a tube in the ground for a worm-shaped thing to sit in. But what direction they're going, what they're doing with the burrow, how they're using it, and what animal it was could be very different. So similar shaped burrows could be from very different organisms for very different purposes. So it's often not easy to just look at it and go, obviously there are definitely cases where we can do some identification, but it's not all it's often not straightforward. Some examples of ways that and techniques that have been used to identify ancient burrows.
Some of the obvious ones are just compare it to ones today. Yeah. Yep.
>> Look at the burrow. Look at it. Look at how it is and look at other burrows and how they is and find the ones that match.
>> Does it look like a clam burrow? Well, great.
>> Exactly. I found one paper that had a really great breakdown of crawfish burrows and had the essential criteria used to attribute burrows to a crayfish.
>> Incredible. It's got all the It's got all It checks all the crayfish boxes.
>> It's awesome. It's like things like length, the depth of penetration into the sediment regularly circular cross-section so that it is consistently a circle. presence of midway enlargement chamber. So partway down a bulge >> for for turning around maybe.
>> Yeah. Yeah. Exactly. Or just stretching out, you know, getting some elbow, some claw room and preservation of a burrow chimney, the little turret above the burrow. So if you have a animal that makes very iconic burrows, you might be able to use those telltale signs. And those features of the burrow are often going to be related to how the burrow is being excavated, how it's being used, and the physical attributes of the digger.
>> Yes.
>> And so that's going to which is why that shape of burrow can end up being very specific to the type of animal that dug it. A different differently shaped animal, even if they're using a burrow for the same reason, is not going to have a burrow with the same features.
>> Exactly. A really cool example of that were some burrows found from the triacic of Greenland that had a vertical to slightly angled burrow that then enlarged at the end to a chamber and that was about it. tube down to chamber, smooth side surfaces with no scratch marks. And the identification that the researchers came to based off of a whole bunch of criteria which are laid out beautifully is that this was a lungfish burrow. So lungfish, many of them burrow for aation burrows, which is their version of hibernation. They go down during dry periods and stay underground where they will stay damp and moist and not dry out. They do this in a really cool way because this is one of those animals where But how does a fish dig a burrow, >> right?
>> By eating the mud, they take mouthfuls of mud and then push it out through the gill openings.
>> Oh, yeah. That's a thing fish can do.
>> Yep. And then they wiggle their body to move that mud backwards and push it behind them. And they just chomp waka waka their way down into the earth. As they get to the bottom, they turn back and start to create that chamber at the end by doubling back and forming a U shape with their body. And they pass back through the channel they came out of to go get air and stuff. And they found evidence for basically all of this within this fossil burrow. The smooth sides suggest an animal without claws and not using limbs to dig. So that fits the lungfish. The size of the burrow is too big to suspect an invertebrate built it. So that was also a key factor. The simple shape fits the simple burrows we expect from lungfish. The tunnel is about one lung fish wide, which we would expect because they don't do any turning around in the tunnel. They're only moving either in or out. And the chamber is roughly twice the width of the tunnel, which is what you would expect for a U bend lungfish sitting in the in the chamber. There's also even a U-shaped mark in some of the chambers where the fish might have been resting.
and in at least one of them a single like mark on the wall or on the the the roof of the chamber. I think it was that seems like it might have been the fin of the lungfish >> scraping dorsal fin scraping along the top. That's very cool.
>> So using these multiple layers of identification and ruling out who it isn't likely to be it. Did we find a lungfish in it? No. But boy, it screams lungfish.
>> So if it is something else, there's something very lungfish like in the Triacic that was making very similar burrows. Similar things have been done with armadillo burrows, taking casts of modern armadillo burrows, filling them with polyurethane foam and then looking at the shape, the markings, how do the claw markings fall out, and then using that to identify not only fossil armadillo burrows, but like what kind of burrow was this? a dinning burrow? Was it a foraging burrow? Does it suggest what kind of armadillo behavior might you might have had? And then of course there are examples where if you have mystery burrows and you finally find one with an animal inside that seems to match being the digger, now you can ID all the ones that you have without an animal inside. There was an example of a trace fossil that had kind of a a dumbbell shape, two chambers connected by a passageway and then each chamber had a tube up to the surface.
>> By fungites was the name of this trace fossil and it was a mystery who made it.
Lots of people suspected worms and you know polyet or something like that for a long time and then finally a deonian specimen from Brazil was found with a polyat inside. And now we had the perpetrator and it sure does seem to match with not only the worm being the right size to make this burrow but also being similar to other similar worm burrows that we have examples of. So sometimes you just have to wait for the the case to crack open you a break in the case and be able to identify your collection. As we mentioned, fossil burrows are extremely common and very old.
>> Animals have been burrowing for about as long as we've had animals. The earliest burrows show up right at the Ediaran Cambrian boundary. That is if you had asked me to guess [laughter] that is that is exactly what I would have guessed.
>> Yep. Like there I found one paper that put it really well that the first few billion years of life the ocean floor was very boring and simple.
>> There was it was all surface level microbial mats things like that. the idi start getting some largebodied organisms, some moving around. A little bit more action on the seafloor going on. Some slight tunneling and burrowing, but nothing intense, nothing very deep.
So, nothing hugely notable. At the idi Cambrian boundary, we start seeing some of some notable infilled tubes. And then, >> so this is going to be around 540 million years ago. This is one of the defining features of the shift into the Cambrian period.
>> Exactly. The Cambrian explosion that burst in diversity of life. One of the identifying trends and types of fossil are burrow makers.
>> Tunneling starts to become much more common. This is the Cambrian substrate revolution where the seafloor the the the the nature of seafloor ecosystems changes because now so much life is living underneath the surface.
>> I also saw it called the agronomic revolution. The shift from surface level grazing to deep tunneling.
>> Yep.
>> This was a dramatic shift. Like the Cameron explosion is famous for a whole bunch of life showed up all at once and diversity went crazy. But what also happened is we went from the ediactin which was a fairly 2D environment >> on the seafloor to a 3D environment of now things burrowing down into the substrate.
>> Yeah. And also swimming up.
>> Absolutely.
>> They were moving in both directions. So, our we went from flatworld to Mario 64.
[laughter] And this had a bunch of side effects.
Not only was this a new behavior like we mentioned with burers being ecosystem engineers and bioturbation. This introduced new environments. It introduced seawater and oxygen to deeper substrates which increased microbial activity in the sediment. It brought nutrients out of the sediment because beforehand if you died and you made it into the dirt, you mostly just stayed there >> and all of your good nutrients was just locked away in the substrate. Now all of those nutrients, all of those biological bits were being brought back out into the ecosystem. Some have suspected that this tunneling may have been one of the causes that fueled the Cambrian explosion. That this revolution led to at least partially maybe the explosion itself instead of being a result of the explosion. There are a whole bunch of notable and famous trace fossil burrows from the Cambrian. Tpticness is one of the most well-known and is used to define the [clears throat] base of the Cambrian. So this is an a dating fossil that we use to date the lower levels of the Cambrian period. It's not a very dramatic burrow, not very deep. So it probably wasn't one of the like big deal ecosystem engineers, but it is really notable for identifying the start of this trend. You get more complex trace fossils, scolithos, >> scolithos. This is the one that I think of first. This is because when I was teaching as a grad student, we had in the geo collection this really nice Skolithos example that's just this Cambrian sandstone with these beautiful vertical stripes running down it.
>> Yes, absolutely. Yeah, they are a cylindrical tube. They do vary. There's some that branch, some that are funnel shaped, some that have a bulb on the end. So, they're getting a little fancier. They are super common, found around the world and these pieces of rock with just a whole bunch of burrows in them, often called pipe rock.
>> Mhm.
>> And are one of the oldest valid ignoaxin. They have been known since 1840.
>> That's so cool. My favorite the thing that I the way that it was explained to me and I don't know a ton about Skolithos but the way that the geology professor there explained it to me and the way that I would present it to kids.
I'd show the that I look these lines.
This is the burrow. Some ancient worm burrow that dug straight down into the thing. And you can see it because the sandstone is like pink beige color.
>> But the burrows are filled in with this darker sediment. And often the sediment is green. It's got this sort of greenish color which as I understand it is uh because of worm poop.
>> Makes sense.
>> That is contribut. Not I don't think the whole burrow is just filled with worm poop, but the sediment has taken on that color. I believe because of what the worm has been leaving behind in the burrow.
>> Yeah, cuz they're adding their own chemical mixture to the burrow that's going to affect the fossilization >> so that you know it's theirs.
>> Yes. [laughter] The idea of them filling it up though is very funny of them just slowly pushing themselves out of their own burrow. [laughter] Gross. I also found one more recent. It doesn't sound like this one has a ignoaxin name yet.
>> That is a more complex and more intricate burrow. Early Cambrian Swedish sediment and it consists of four rows of burrows. Each row consisting of like 31 individual burrow holes and likely there were more in the prefossilized burrow.
These shafts go down and curve a little bit inward, likely merging at the base, though doesn't sound like that's been preserved in any of the specimens. And it is by far, it sounds like, the largest burrow system known from the Cambrian in both size and complexity.
So, this is a very fancy Cambrian burrow compared to what we typically get.
>> Interesting.
>> And we don't have any direct comparable examples. So, we don't have any analoges that fit this fully. What they think it most likely represents is a burrow maker living in a tidal zone. And as the tide moves the sediment over the burrow, the creature is reburing and making a line of holes as the sediment shifts with the tides. Huh. to adjust its position and maintain its spot and your maybe its depth in the water to adjust with the sediment adjust with the tides as they move.
>> It would be fascinating to see if there were also like ripple marks.
>> Yeah. And does the burrow the direction of the burrow is it perpendicular to the ripple marks? The direction of where the water was moving.
>> Oh, cool.
>> Isn't that one neat?
>> That's very cool.
>> All of these burrows, we don't know who made them. Probably some wormshaped thing. Maybe a poll, >> an acorn worm. A lot of them get attributed to priapolids or penis worms.
>> Mhm.
>> So something wormshaped, something like that. who we might never be able to identify it specifically because all of these organisms can make the same shaped kind of holes because they're all very similar shaped animals.
>> Yep.
>> As we go through the fossil record, we have many, many fossils of burrows and many animals that have been identified as likely burrowing animals. This is another category where we cannot go into all of them. There are so many. So, you'll have to make requests. There are thoracids, protomamals that have been identified with burrowing like traits.
>> Thraxodon is one that comes up very often as having very burrowing shape and has been found in dens. There's one example where was one was found in a den with a salamander on top of its body that they seem to have been sharing the den when they both got buried alive.
>> Oh, they were roommates. They were roommates [laughter] or a salamander like amphibian. I should specify >> some teenisp bond >> broomsteggga.
>> That is something that you'll see a lot in modern burrows is sometimes obviously sometimes a creature gets in there that you don't want in there. But sometimes you'll just have multiple species hanging out in the burrow and they're just both making use of it and it's no big deal.
>> Yep. Like the one of my favorite examples is uh tarantulas. Many of them make burrows and there's fun examples of many of them being found with a toad in the burrow with them. And it's thought that there might be a symbiotic relationship with a toad keeping pests away from the tarantula's nest.
>> Oh, interesting.
>> Feeding on insect intruders too small for the tarantula to hunt, but might be damaging to their eggs or whatnot. When we're looking at fossil burrowing animals, there are tons of mammals, lots of rodents, lots of the typical perpetrators.
>> There are some groups that are notably lacking in burers. Dinosaurs, it seems, are equally as unwilling to go into the ocean as they are to go underground.
>> Yeah. Not a lot of subterranean dinosaurs. This is a trend that continues today.
>> Yes. Not a lot of our living dinosaurs are subterranean and the ones that are aren't typically are not digging their own burrows.
>> Nope. And as one study made a point that we do have evidence of digging dinosaurs, which we'll get to, but that when we try to like learn about them, they're modern examples of birds and crocodilians. The two remaining arosaurs are both bad examples cuz the birds we have that burrow aren't usually digging themselves. And most crocodilians do some amount of digging. And some, like alligators, both Chinese and American, actually dig quite extensive dens, both gator holes and into riverbank walls, and will dig tunnels, but they're using a very different body plan. And they are using like all four of their limbs. And none of them are specialized for digging. They're just big, powerful animals that can kind of force their way into the mud and make a hole. So, it's actually quite difficult to analyze dinosaurs for digging traits. And very often studies that do it compare them to mammals because that is a little bit more comparable in body shape, if not exact anatomy, to look for these features. There are dinosaurs that we have evidence of doing some amount of digging. There's nesting dinosaurs, you know, Truidon and Titanosaurs that have made earn nests and so obviously must be able to do some amount of dirt moving to make these nests.
>> Yeah, they're they're making ground nests the same the way that some birds do today where you Yeah. You've dug out a bowl in the dirt to lay the eggs inside.
>> There are others like Monikas we talked about in the anteing episode.
>> Yep. episode 229 >> that seems like it likely was able to dig kind of like anteaters into mounds but likely not digging burrows. So far, basically the only fully confirmed burrowing dinosaur is Orictodrome.
There are other suspects, but this is really the only one that there's robust data for. This is a Cretaceous dinosaur known from here in the US mostly in Idaho and Montana. It is actually the state fossil of Idaho.
>> Oh, that's cool.
>> Right. There are a couple of formations, you know, fossil formations in these two states that are unique for the majority of their dinosaur specimens being dinosaurs from this group, the ordroines, which are basil ornithysian dinosaurs. So, mostly smallalish two-legged herbivores.
>> Mhm. and lacking almost any other group of dinosaurs. So they are dominated by these kinds of dinosaurs. This group which includes our artodromeas and has basically no one else which suggests an unusual bosalization situation that something must be going on for us to be getting one type of dinosaur and almost no one else because it can't be that only these dinosaurs lived here and no one else did, right? So something must be fossilizing them preferentially.
>> Yeah. What what is it that makes these particular dinosaurs so prone to fossilizing?
>> Indeed. And many of them surprisingly are found in really good condition.
Often partial or almost complete specimens.
>> Not just fossilizing, fossilizing well.
>> Yes. This led to the idea that maybe they're already underground when they're fossilized. And that's why >> it came pre-bureried.
>> Pre-buried, self- buried. And that lines up nicely with them being burrow makers.
And in fact, eventually a burrow was found with skeletal remains of an adult and two juveniles preserved in the burrow. This makes them the first dinosaur with trace and body evidence of burrowing or at least burrow dwelling.
And to give you an idea, these aren't huge burrows. These are, you know, large medium dogsized dinosaurs. So, you know, moderate, but still our first major evidence and a lot of other features of the dinosaur line up with them being the burrow maker. They're the right size.
The size of the burrow and the size of the adult fit for an animal this size would make a tunnel this size. You know, the body size fits the burrow size. A number of physical features do lean toward being digging at least prone if not super super specialized. Features of the snout, the shoulders, and the pelvis all have attributes that seem to be consistent with digging behavior. And the most likely way they were digging based off of all this is with their forlims. So digging with their little hands because they still had long back limbs for running around. So, they were probably digging these burrows and then coming out and running around the surface and then darting back into the burrow like a rabbit. Well, the association with the adult and the young also gives credence that this was a chamber they were using for rental care and maybe rearing. Maybe even this was made to help them take care of young.
There are other dinosaurs that have been described as potential burers. Most of them related to Ortoroius. Yeah, I believe Orodomeius is another one that has been suggested that this seems to have been a lineage of potentially borrowing adapted dinosaurs.
>> Yeah, the orodromeines which are in a family called the thesalosaurids which includes thesalosaurines and orodroines. A lot of these have those short and front limbs, those long back limbs and have very similar features. I think there are maybe a couple other species that have been identified to potentially have been preserved in a burrow, but most have not. But they all share very similar features. Some of them being very similar to Artoroius.
Coranosaurus, Sepharosaurus are all examples that have been identified as potentially burers. There's a new species, Fona Herzag, that also has similar features and has been identified as potentially one of the earliest members of the thesalosaurines and also seems to have digging adaptations. So, it seems like this group is a at least digging capable group and go back to the beginnings of the group having those features.
>> Yeah. And it's it's interesting because it get like you said these aren't like mold dinosaurs but the comparison with rabbits or perhaps armadillos where you're or actually I was thinking earlier of like uh tortoises like gopher tortoises >> who you dig a burrow it's pretty simple you go down in there but you're not spending all your time down there because you have to come out and you know go get food and such that these there might have you you might have had a habitat with a bunch of dinosaur dens.
>> Yes.
>> Dotted around it, which is very, very cool.
>> So, it's interesting. Before this discovery, it was kind of just considered that among non-avian dinosaurs, burrowing just wasn't a thing.
>> It was not a habit that they seemed to be doing. We finally found one and some others, but they all seem to be fairly closely related. And so far, still, that's it. There is one nanosaurus that we don't know who it's related to, but it sounds like it is also basil ornithopod shaped. So if it is outside this group, it's not far outside. It's not like a raptor or something.
>> Yeah.
>> It is still that same type of dinosaur.
>> So borrowing in dinosaurs might have only evolved one time.
>> Yeah.
>> And it was this one group, which is really ju just put it on the list. the list of stuff that dinosaurs never did for some reason.
>> Listen, I'm already a dinosaur. What more do you want from me? [laughter] >> I did it. I achieved peak animal.
>> Some other fun and interesting fossil examples and evolutionary notes on burrowing. Burrowing has been connected to turtle evolution and specifically may be why turtles started to develop a shell. Yeah, we talked about this, I believe, back in episode 60, that this is one of those early hypotheses of maybe that's maybe this is linked to why turtles are shaped the way they are.
>> Because when you look at the evolution of the turtle shell, at least in the lineage that led to our modern turtles, the shell started on the underside, the plron started and it began with the widening and broadening of the rib cage.
So, the first baby steps to Shell was getting a big, broad, robust, stiff rib cage, which by itself doesn't make any sense because it's not protective. It's not a shell. That's not an external shell. That's just big bones inside and it limits your mobility and your breathing because you now can't flex your chest. So, on the surface, it seems like all around a bad idea to do to just >> stiffen up your rib cage. But maybe they weren't on the surface.
>> Yes, this stiff chest, this robust chest may have been a platform for them to dig from to strengthen the body and stiffen things up to be able to burrow with. The main chunk of evidence from this is is Eunotasaurus Africanis which is at least to our current knowledge one of the oldest stem turtles early turtles that we have from the Karu basin in South Africa and it has a partial developed shell. The rib cage has started to take on those features. But it also has a whole bunch of fossoral features and many of them in line with gopher tortoises. Both have spadeshaped skulls and powerful necks which they use to brace against the tunnel while they dig.
Powerful shoulders and forlims for digging. And when we look at some of them preserve their sclerotic rings which are the eyebones and this allows us to get an idea of eye size and pupil size which can give us light sensitivity. And they seem to have low light sensitivity, but comparatively larger eyes, which means probably they were still coming out onto the surface like gopher tortoises.
>> Interesting.
>> So everything about them seems to be a digging animal. And they have these expanded ribs. So this might be why turtles started to strengthen and rigid rigidify their internal skeleton which then might have led to the next steps of well we might as well turn this into a shield and make this protective. We've also talked a bunch of times on the podcast about how burrowing has been suggested as potentially also the reason for the shape of snakes that the ancestral snakes might have been burers became the shape of burrowing lizards and then became snakes as we know them.
And similar to snake and similar to snakes where the other side of the hypothesis is maybe they were swimming because that's another good shape.
Another good place to be that shape with turtles the musculature that's good for digging are very very similar to the musc muscles that are good for swimming.
So, this may have been why it's been so common throughout their evolution and their fossil history to transition to aquatic life because if you're already good at digging and moving through the earth, you'll be good at moving through the water as well. And then the last two examples I had are the most dramatic because they are fossil mysteries that persisted for a chunk of time as people were trying to figure out what these burrows were. One you've probably heard of are known as the devil's corkcrews.
>> Some of the most famous fossils. The These are really iconic.
>> Absolutely. These and they have a really dramatic story which is part of why they they get remembered so well. These are structures known from places like Nebraska in the bad lands that as the stone and you know the softer stones wear away from wind and weather there are these spiral structures that started to erode out of the stones and there are these giant corkcrews some of them like seven feet tall. Yeah, they look it's like someone wanted to build a spiral staircase down into the earth.
>> It it is this spiraling burrow shape.
It's really distinct.
>> Yeah. Yeah. They spiral down and then at the bottom they bend back up and a straight portion comes off that sometimes can be like 15 feet long.
>> So it's this weird spiraled check mark.
And >> when people first discovered them, they confused folks because they are very weird. Now these are coming out of rocks that date back to the measine. So 20 to 23 million years old and they were first discovered by a paleontologist known as named Irwin Barber. He found them in 1892. named them Damon Eelix, which is devil screw.
>> And he first identified them as not burrows, which is where the drama starts. First idea that got thrown out were giant freshwater sponges because he believed that this area used to be a lake.
>> Sure.
>> And then settled on these are fossil plants, root systems of ancient plants.
>> All right. That is that does feel closer.
>> Yep.
>> To burrow. And part of the reason was because plant material was found in these structures.
>> So he thought it was plant growth. Very quickly, people disagreed and started to correctly identify what they were. A year later, Cope came out and said, "These look like rodent burrows." And an Austrian paleontologist, Theodore Fuches, who is an authority on trace fossils, said the same thing independently. These are probably just measine rodent burrows, something like a pocket gopher.
>> Part of the reason this story became so historically wellknown is that evidently Barber did not take that criticism.
Well, >> uh, this was one of those late 1800s old guys arguing about fossils disputes.
>> Yep. There are there were multiple quotes in the article I read of Barber responding to other scientists criticisms and basically saying, "Well, if that was the case, here's here's why it's ridiculous what you've suggested."
>> Mhm. One of them, because he believed it was a lake deposit, said, "Dr. Fuches's gopher is left to burrow and build its nest of dry hay in one to 200 fathoms of measine water." And was very, very adamant. Apparently, it seems Barber took this argument to his grave of denying that these were burrows and insisting that they were plants. It doesn't I didn't It doesn't sound like he ever saw reason >> that he was stood by it and multiple times would come back against people arguing for something other than plants.
Not only is your legacy now being wrong about a thing, but your legacy is being wrong about a thing that cope was right about.
>> Yeah.
>> And that's just the worst. That's just the worst position to be in.
>> And it gets so much worse as well because as we continue to find more evidence about these structures, the amount of evidence we have for what they are and who made them is like embarrassingly clear.
>> [laughter] >> not as mysterious as it was first made to seem.
>> Like it's it's so blatant. Later on, as future research was done, another paleontologist, Olaf Peterson, discovered specimens, skeletons in many of the burrows that belong to Paleocaster, the ancient beaver.
>> Not like we finally found a worm in one of the burrows, >> but a bunch of the burrows have bones in them. The the wording used by the article was they often contained skeletons of an ancient beaver.
>> Clearly a beaver who hung out in plant roots.
>> Yeah. Yep. Who was deep diving in the lake bed >> deep >> uh to eat sponges.
>> These were slightly larger than today's prairie dogs. A terrestrial beaver. So, you know, beavers did not always build dams and swim around. Even though uh Barbara would like us to think this one was swimming around.
Inside the surface of these structures, there are claw marks and grooves. And many of the grooves match the shape and size of the insizers of Paleocaster, suggesting that it was likely digging with its teeth and claws as well. Since then, others also pretty uniformly refuted that this was a lake bed, meaning didn't seem to ever hold that it was, but that that idea went away and in time, yeah, the conclusion was pretty obvious. These are ancient rodent burrows from my beavers known as Paleocaster. Even Barber's former student and successor turned to the rodent side. So it it's just it's this very dramatic story that's just so embarrassing for one person over and over and over again.
>> Must be Cork screwing in his grave.
[laughter] >> He's got like an Eddie Brock. Those beavers ruined me. [laughter] These burrows have a whole bunch of cool features to them. They've been found in clusters, so likely they were forming colonies like prairie dogs, which is very neat. There also have been other animals found in the burrows. A cousin of modern weasels has been found, likely hunting for prey down the burrow. And the plant material that was so contentious has an interesting story to it. So these burrows were in a very dry area, but the burrow itself would have been much more humid, which we'll talk about in more detail in just a moment.
But this would have attracted plant roots which would have grown into the walls of the burrow. They noted that probably so much so that they would have needed to be trimmed back by the beavers to maintain access to the burrow. But the rocks of the Harrison Formation where these are found have a lot of ash from volcanic eruptions nearby. As rainwater washes all of this saturated silica into the ground, it gets soaked up by the plant roots and gradually the root lined walls of the burrows mineralized from all this silica to form a silicated root system that preserve the burrows. So, the plants were part of reason they preserved so well and so often. Yeah, this is also a fun note that we'll breeze through real quick that spiral burrows are not only known from Paleoccaster. There's a ton of spiral burrow diggers. This is an extremely common feature and it potentially has a whole bunch of really interesting benefits. We have examples going back to the Cambrian and a bunch of modern animals that do this. Pocket gophers, monitor lizards, scorpions are all known to make spiral helical burrows. Interesting. Some of the reasons you might want to make your burrow spin is that it may have benefits both after you've made the burrow and while making the burrow. This might actually be a helpful shape for constructing the burrow. Obvious benefits. Once again, anti- predator.
This is a complicated shape. Like you were mentioning with rabbit warren. A complicated shape is just going to be a more effective detriment to a predator following you down it. And if the curve of your burrow is more than how flexible your predator is, I can't bend my body as much as your burrow bends. I may not be able to enter. Period.
>> Mhm. It also is going to be better at maintaining a microclimate because you're adding layers to the barrier between you and the outside by spiraling back on yourself.
>> Yeah. You're effectively lengthening the burrow without having to go down deeper.
So the the distance that air or humidity or whatever is going to travel from the surface down to the chamber where you're hanging out is longer.
>> It also may increase drainage for flooding situations because you've added surface area to the burrow for water to be able to drain out of the upkicked tunnel at the end. Also may be for flooding situations to add an air pocket when you're down at the bottom.
>> Yeah. Kind of like a beaver dams. Yes.
where you enter underwater, but then there's a little there's a air pocket inside.
>> For marine helical burrows, it may help with deposit feeding, which is digging down to eat organic matter out of the sediment. This is increasing the amount of sediment you're going to encounter without having to dig farther down. Mhm.
>> And some deposit feeders will kind of farm microbes on the surface of their burrows. And this also will increase the surface area that you're exposing to new micro growth to be able to feed on. It also may have benefits for while building the burrow. If you built a deep tunnel and had to go at a steep angle, you're going to get dirt falling on you as you dig. If you're at a less steep angle as you spiral, the spiral catches the falling dirt, so it never fills back in on top of you and it acts as a storage system as you dig. I would imagine it's also easier to traverse cuz it's not as steep. It's like that video you'll see of that pit that's I I think it's like in China or somewhere where the walls are too steep for you to climb out, so you have to run in a spiral to get yourself out of it.
>> Yes. Exactly. And that's one of the big advantages like you mentioned, you can go deeper at a shallower angle. So you don't have if I want to go seven feet down, but I want to do it at a gradual incline. If I do a straight tunnel, I'm going to end up being like 30 feet out from where I started because I'm just going to have to keep going down and down away, which is the other benefit.
It keeps you in one spot, which is good for a I may have chosen this spot for a very specific reason. I liked the location. I don't want to move out of the location I chose. And anti-crowding.
We can now have a bunch of deeper burrows without running into each other if we're digging next to each other.
>> Yeah. Well, and also you don't know what you're going to run into if you go, you know, you might only have so much space to work with, but also if you're going horizontal, like you're eventually you might hit a river or you might hit just I've played Minecraft. Sometimes you start digging in a direction and suddenly you're underwater and >> suddenly it gets very warm and [laughter] you lose all your items. And that's like not only is the anti-crowding good for a colony situation like Paleocaster, but for scorpions who don't want to encounter each other because they're cannibalistic. Yeah, let's keep our burrows in our own backyard.
>> Yes, there also could be biomechanical advantage because you can brace against one side and dig one direction and it may make it a more efficient mechanism of digging instead of digging straight ahead. So, this is probably my favorite kind of burrowed because you've got a dramatic story and then a really interesting set of potential adaptations and burers. They're all over the place.
>> And also, the burrows look so cool.
They're so awesome because they're huge.
They're these giant structures. We'll we'll for sure hopefully find some pictures for the blog post, but also I think I want to say Eons did an episode about these and I'm sure they have a whole bunch of cool pictures and more details about uh some of the features of it. So these are super famous. You can find information about these. These are these are really uh exciting fossils.
>> Yeah. And then to wrap up our burrow discussion, and speaking of big impressive burrows and our most recent burrow mystery that made big news are paleo burrows, which is what they're called, paleo burrows.
>> Sure. which not as not quite as dramatic as devil's corkers, but you know, >> and definitely feels it's like when a movie comes out that's just like hawk and it's like well but that's like that's just a word and I'm sure there have been other movies. This is one of those paleo burrows is what we've been talking about for the last half of the episode.
>> I had a teacher in middle school who used to complain about soap being labeled antibacterial soap.
>> Yep.
>> Because he was like it's soap.
>> It's soap. That come that goes without saying.
>> That's what it's it's what it's gonna do. These are giant underground tunnels found in South America and they were only discovered a little over 15 years ago. They were initially discovered in 2009 and I think described in 2011 when a farmer with his truck had the truck sink into the ground and noted there was a giant cavern under his farm that actually extended under his house as well. Contacted people to investigate it. [laughter] This is how this is how a Tremors movie starts, >> right?
>> Yeah. I was dig I was building my tractor and I fell into a giant burrow.
Oh, the burrow goes under my house.
>> Yeah. And the burrow is indeed grabboid sized. The tunnel was nearly 2 m high and wide and about 15 m long.
That's graid size.
>> Yep. The only difference is there were notable deep claw marks embedded in the walls.
>> Not better for our [laughter] horror movie scenario. That's Oh, and look, these giant tunnels have enormous claw marks in the walls. I better I better call someone to help. Oh, I don't have signal. [laughter] >> Yeah, I've seen this kind of >> someone get me. Kevin Bacon [laughter] for a a while both before this initial discovery cuz this was not the first time people had found these for indigenous people had noted them but this was the first time it had come under scientific scrutiny. The initial idea was that these were built by ancient humans and were, you know, constructed, the claw marks were interpreted as pickaxe marks.
>> Sure.
>> And that these were dwellings or ritual sites of some sort. Part of this was because many of them contain rock art.
Many of them have art from people often carved into the rocks, which means we can't date them, but >> Mhm.
>> we have paleo art. We can't date them because they're not like paint, like paint or ochre or something. We can date that material. If it's just carved into the rock, there's nothing to date.
>> Yeah. The carving the the rock it's carved into is just going to be how old that rock is. We can't tell because once again, they didn't sign their work and they didn't date it using the Gregorian calendar. So, we can't we can't do anything with that.
>> Come on, guys. [laughter] Now it is the consensus is and conclusion is that these were built by giant sloths or giant armadillos roughly about 10,000 years ago. Yep. Xenarthans.
Well, because this is, you know, a armadillos and anteaters are both borrowers today or at least diggers [clears throat] today. And this is South America.
>> Yep. This is late cenazoic South America and this is who lived down there were massive creatures with giant claws.
>> And that has been like if you look up paleo burrows it just out outright will say yeah giant burrows made by giant ground sloths that is not really a thing that people are hedging their bets on.
There are still quite a number of unanswered questions.
>> Why they were building them we're not positive. They definitely could just be using them as dens. Why they made such massive burrows is unclear. Some of these are insane. Some examples range from burrows that are 40 m long that lead to 10 m wide and 4 m tall chambers, 100 m long tunnels, which was this one was the first one found in the Amazon rainforest, and at least one that was 340 m long.
>> That's just a cave. Yeah. And these things are insanely massive. They're not dug into soil. These are dug into soft rock. So, not like granite, but this is stone that these are dug into, which also indicates that this would have been multi-generational task. probably dug over centuries if not thousands of years, >> which also suggests that maybe these were social and family groups of these Xenarthans digging them.
>> Yeah, my great grandpappy sloth started digging this rock right here on the banks of the ancient Amazon. And we're going to keep going. Someday you'll dig your section.
>> I'm tired of this, Grandpa. [laughter] That's too darn bad. [laughter] [gasps] It also their distribution doesn't make a lot of sense. Brazil is the hot spot. In the last 15 years, more than 1,500 recorded paleo burrows have been found.
The rest are all in South America. None in North America.
>> Sure.
>> Even though the ground slots made it into North America, >> not the right ones, apparently.
>> Yeah. So we don't know exactly why this was happening. We don't know exactly how they were being used. The one potential explanation I saw was that the timing does seem does sync up with from the igosine to the pisosine. The globe was getting a little bit colder and consistently cooler and drier which could be a reason to make underground dens where the temperature will be more stable. you know, temperatures in caves don't fluctuate like outside temperatures. And that during this time, it syncs up with the Gabby, the Great American Biotic Interchange, where North American animals and South American animals are finally able to cross over and share notes with each other. And if the sloths didn't like what the North American animals were bringing to the table, there may have been extra incentive to make these burrows to protect themselves from the new onslaught of predators and competition.
>> Ah, >> we do note that in the early pyiosene, the burrows are smaller to mediumsized and as we move into the late pleaene, we get the larger burrows. So, we do see them get bigger over time, which I don't know how much of that is an indication of like bigger sloths making them or them continuing to excavate and or getting more complex in like how many sloths are digging them.
>> Yeah. Interesting.
>> Yeah. Fascinating mystery. Listen, someday in a hundred years someone will have been extremely wrong about it and we can make fun of them.
>> Yes. Yep. [laughter] Paleocaster. Again, >> the fact that there just it's just a big one. It's just a big paleocaster.
[laughter] >> The the fact that there's rock art in some of them. The fact that there's just some people found it like a cave.
>> Yeah. This is great.
>> Just walked in there and they were like, "Man, I listen. I was foraging over here. I found this big tunnel. It goes under the house."
>> Yep. Yep. There's uh uh the article is like a person who went there and interviewed and visited some and is like do was describing their experiences and they said like the inside was damp, it was cool and the walls were very smooth and they described and I don't know if this is like the official but it is a neat idea that they're smooth because of the hundreds of years of sloths passing through and rubbing up against and polishing that these were used tunnels.
It was not raw. It was worn smooth by use, which is very cool.
>> I do I seem to remember I don't remember what I was working on that I was reading this, but that there are some burrows that you can identify. One of the identifying features of them is the smooth entrance to the burrow.
>> Yep. Yep. Yep.
>> Where like the the floor just outside where whatever was going in and out is constantly dragging its body across the ground.
>> Yeah. It's Yeah. stuff like that's so fun of all the little notes. One of my favorites that that reminded me of was for grizzly bear dens. They noted that they're often on a slope and in the downs slope is all of the debris that there'll just be this pile of all the stuff they've excavated and moved and shoved around and so you just get this waterfall of earth outside a grizzly bear den. [clears throat] And with that we can wrap up our burrow discussion.
This was a ton of fun and there's, as we've said many times, as we always say, so many examples that I had to skip over and not include and not go into detail on. So, please, please, please comment, go on to Discord, send us a message of what animal did we not mention and how have we failed you in not mentioning it.
[laughter] And send us requests for the ones you would like to hear us talk about in future episodes. Before we wrap up the episode, we have one last task, which is to answer our patron question. Every episode, we like to answer one of the questions submitted to us by one of our patrons, which you can do if you sign up at certain levels. What's our question for this ep This episode, our question comes from Brett, and it is mildly burrow related. Brett asks, "Ats, termites, and humans all famously engage in farming domesticated food sources.
Are there any other organisms that farm things?
>> Great question and yes, there's a number of examples.
>> Ants and termites are famous for being fungus farmers. They are many, many species that culture gardens of fungus that for many of them is their only food supply. That's all they eat.
>> Yeah. And it's not just that they like set up shop near where fungus grows.
They collect the fungus. They bring it into their chamber. They bring it food to grow upon. They carry around disinfectant to spread other fungi or bacteria that attack pests and weeds that grow up in there.
They are curating these fungus cultures.
>> Yeah. And for like I believe most of the ant species that do this, the fungus they cultivate are only found in those ant nests. They are >> Yes.
>> fully domesticated. no wild strains of those fungus. This isn't true for all fungus farming insects, but for many ants, that's the only place you'll find that fungus. There are also fungus farming beetles.
>> Yes, ambrosia beetles are a type of weevil that also make dens and have galleries of fungus.
>> We did we talked about this a bunch more in episode 202.
>> Yep. Yep. Absolutely. Ants also are known to farm aphids. Mhm.
>> to maintain herds of aphids which suck the sap out of trees and then produce honeydew which is a sugary liquid that is their poop and the ants gobble it up and they will like train the aphid to only produce that when they're tippy tapped with their antenna. They'll move the aphids to better grazing grounds, protect them from predators. Evidently, some of them will even keep a mixed herd of aphids to have different species. And some have even been known to clip the wings of their aphids to keep them from leaving the plant.
[laughter] >> That's wild.
>> Yep.
>> Oh man.
>> The other examples I found, I found an article that was seven animals that farm and >> fantastic. [laughter] Excellent.
>> Here's some of the notable ones. The [clears throat] long thin dam damsel fish are known to keep gardens of algae.
>> They'll find it an algae patch and the algae they prefer is not very robust. It would be overg grazed very easily. So the only way it persists is with them guarding it. And they also have a symbiot they also have a symbiotic relationship with mid shrimp, a specific species that has been described often as domesticated by the fish because they protect the shrimp in the gardens of algae and the shrimp help to fertilize the algae and make it grow better.
>> Yeah. We in in the fungus episode, we also talked about a re I think it was a recent study that found possible fungus growing by marine snails.
>> Yep. Yep. Yep.
>> That are carving into seaggrass and making space for fungus to grow that they then eat.
>> Yes. And there's even been evidence that they might be defecating into those wounds on the plant to encourage the fungal growth. So >> yeah, >> it does seem that they are, if not maintaining a garden, propagating the fungus so that they can then feed on it.
And then the last example I found were yeti crabs, which are deep sea crabs.
And they've got these bristly arms with these like hairike coverings to their exoskeleton. And they live near methane seeps, which is, you know, like deep sea vents, but these are not going to be hot like the hydrothermal vents, but they are pumping chemicals out of the seafloor. And this promotes chemosynthetic bacteria that eats the methane and grows from it. And the hair on their arms allow or the bristles on their arms allows hair of fungus of of bacteria to grow and then they clean it off their arms with comb like mouth parts. So they are their own field and they grow their crop on their body. So yeah, a handful of other well and also identifying farming is really tough because like the example with the snails, we know that they're carving into these plants and then fungus grows in there and they eat the fungus and we know that they poop on where the fungus is, but we're not sure if they're pooping just where the fungus is or if it's just that like well they live on the plant and so poop gets in there.
>> Yeah. Do they poop there more frequently like seemingly targetedly or is it just it happens to get in there a lot because that's where they just were when they need to poop?
>> Yep. So there is a whole spectrum from farming to things that are kind of farming or maybe farming or like farming. So who's to say? Also I don't know if we have any information about use of domesticated things in other human species. Yeah, I don't know >> our like proper agriculture kicks off.
By the time proper agriculture kicks off, we're the only species left. But it's totally possible that there are ancient relationships between earlier homo sapiens and plants or other animals or Neanderls.
>> Yeah.
>> And Denise. So there very well might have been other hominins or even other apes that have had some domesticated like relationships.
>> It's a very cool question. Thank you very much Brett for submitting it. And with that we can wrap up the episode. If you are itching to learn more and get more details about this topic, check out the blog. There'll be images, there will be links, and as we already said, let us know what else you would like to hear about fossoral and digging animals.
Other episodes that you might enjoy if you like this episode about burrowing, uh, caves, episode 112. Trace fossils was episode 118. Mhm. We've talked about some of the groups like armadillos.
>> Armadillos episode 153 and ante eating we brought up in this episode uh 229 actually. Also ants was episode 149 and they do a lot of burrowing.
>> Uh let us know this would be also in the discord. Let us know if there's any others that we didn't think of. Make a list in the recent episode >> of what other episodes would go well with this one. Pair nicely with Burrows.
Don't forget to go listen to Silver Screen Science. It's all wrapped up now.
>> That's Old School Dinosaurs, uh, this year's series. Four episodes old school dinosaur movies. Go check them out.
Also, more thoughts on Patreon if you want to hear us talk even more about those movies >> and the live streams saved up on YouTube, so you can watch that there if you missed it. Also, if you liked this episode, uh the most recent episode of Bricks with Basque was Will made a Lego graoid, which is very cool.
>> Been very subterranean-minded lately, evidently. [laughter] >> Dig, dig.
>> Next month is Croc Month, so stay tuned for information about what we're going to be doing for Croc and Snake Month this summer.
>> More awesome things that like to dig.
Just all underground. It's all >> very thing is subterranean.
>> We are we are very underground, you know, edgy podcast. This is what I thought that this is what I think that means. Thank you everyone who requested this topic. Thank you to all of our new patrons. Extra special thanks to our top tier patrons, Danielle the Buglover, Jeff Ellington, and Sarah May. I got nothing particular to say. They were into poralial animals before it was cool.
>> Like I am my brain is so like underground animals. I want to like go look up purple worms from D and D and just finally watch the Dune movies. I haven't watched the new Dune movies.
>> Go watch Beetlejuice.
>> Yeah. Just like I'm >> I was waiting and didn't find the opportunity during this episode to make some sort of joke about donkeys.
>> Mhm.
>> Like when you brought up fossil burrows.
>> Yep. But no, the the the you know the moment didn't come. Oh well. [laughter] >> Helical burrows.
That's a horrifying sight that now is in my brain of a helical burrow [laughter] just just braaying in 360 degrees.
[laughter] Good night everybody.
>> We release episodes every Fortnite.
There will be another one in a Fortnite and we'll see you then. [laughter] Bye.
Thanks for listening to the Common Descend podcast. You can follow us on Facebook, Twitter, YouTube, and check our WordPress blog for pictures and links after each episode. Huge thanks to our patrons whose support helps keep this podcast running and who get access to bonus goodies on Patreon. The song you're hearing is called On the Origin of Species by Protodome, which we found at ocreix.org.
Thanks again for listening. We hope you'll join us next time.
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