Ediacara: Strange Creatures and a Lost World | S1 B4 | Lost Worlds

[00:00:00]When the ice retreated, bare rock was left behind. Surfaces [music] that had remained under ice for millions of years were exposed for the first time. Floods flowed. Minerals were carried away and mixed into the oceans. Sea levels rose.

[00:00:16]Coastlines changed. The concentration of carbon dioxide in the atmosphere was still high. Volcanoes had kept producing it for millions of years. [music] And this accumulation was now rapidly heating the planet through the greenhouse effect. The Earth was tired, but it was not exhausted. Organisms that had survived [music] in the depths of the oceans, around hydrothermal vents, and in the dark waters of sub ice lakes were now encountering a much broader world. Again, these organisms were not ordinary. They had passed through the civ of 57 million years of freezing. The genetic legacy [music] they carried was the most resilient, most adaptable, and most diverse biological toolkit the planet had produced up to that point.

[00:01:03]The ocean was open. It was rich in minerals, and oxygen was slowly increasing. The stage was being set once again, this time for something much larger, much stranger, and much shorter lived.

[00:01:22]Oxygen changes everything. Before the snowball, atmospheric oxygen levels were low and unstable. During the frozen period, photosynthesis had largely stopped and oxygen production had decreased. But once the glacias melted, cyanobacteria rapidly spread across the newly opened ocean surfaces.

[00:01:44]Photosynthesis picked up speed again.

[00:01:47]Oxygen began mixing into the atmosphere.

[00:01:50]This rise was not linear. There were fluctuations and setbacks. But the overall trend was onedirectional upward.

[00:01:59]The importance of oxygen is not just about respiration. Aerobic metabolism, which uses oxygen for energy production, generates far more ATP than oxygen free pathways. More energy means larger cells, more complex structures, and more active forms of life. For billions of years, life had been forced to stay small because energy [music] was scarce.

[00:02:25]Oxygen loosened this constraint, and this loosening removed the greatest obstacle standing in the way of evolutionary experimentation. The ocean now had the capacity to host something much larger. The story gets interesting here. But a quick reminder, if you're enjoying these videos, you can support us by liking and subscribing. Now, let's continue.

[00:02:53]If you could have looked at the ocean about 635 million years ago, the surface would have looked calm. There were waves, there were currents, and sunlight penetrated a few hundred m into the water. But this calm was misleading. On the ocean floor, especially in shallow coastal regions in muddy bottoms and rocky surfaces, an invisible transformation was taking place.

[00:03:19]Microorganisms still dominated. Bacteria and archa existed in trillions of copies in every drop of water on every square millimeter of the ocean floor.

[00:03:31]Stumatalytes continued [music] growing along the coasts. This world looked familiar. It had been like this for billions of years. But underneath something was changing. Ukarotic cells were now far more widespread. Some groups were staying together. After cells [music] divided, instead of separating from one another, they remained attached and formed small colonies. [music] These colonies did not yet count as an organism, but they were the first steps of a process that would redefine what an organism even is.

[00:04:14]For billions of years, the largest living things on Earth were too small to be seen with the naked eye. This was the result not of an evolutionary barrier, but of an energy constraint. Sustaining a large body requires energy, and energy depends on oxygen. As long as oxygen was insufficient, body size had to remain small.

[00:04:36]After the snowball, this constraint loosened and life did not let the opportunity slip by. The first macroscopic organisms reached a size visible to the naked eye. The shift from the millime scale to the centime scale may seem small, but for a microscopic world billions of years in the making, this was a revolution. For the first time, a living thing that could be visually tracked existed on the ocean floor, on muddy surfaces, or on rocky ground. The trace of this transition in the fossil record is faint and disputed.

[00:05:13]Softbodied organisms do not leave hard traces. They decompose and disappear unless conditions are perfect. But a few special fossil sites in Australia, China, and Russia preserve traces of this transition. And these traces were doorways opening onto an entirely different world.

[00:05:36]The Ediakara Hills stretched through the Flender's ranges in South Australia. In 1946, mining engineer Regginald Sprig noticed strange fossils in old mine workings in this region. Circular shapes, disc-like impressions, leaflike imprints. At first, they resembled jellyfish fossils. But on closer examination, it became clear that this interpretation fell short. These fossils dated to approximately 635 to 541 million years ago. They were the remains of organisms of a size and complexity never before seen in Earth's history.

[00:06:18]And the strangest part was this. Most of these organisms did not fit neatly into any group of living things today. The Idiacrine period and its biota enter the scientific agenda with this [music] discovery. In the following decades, similar fossils were found in Namibia, Russia, Canada, and many other corners of the world. All of them pointed to the same period. The organisms of this period were neither vertebrate nor invertebrate, neither plant nor animal.

[00:06:50]They were entities that did not fit neatly into any category today, forming a biological experiment all their own.

[00:07:05]Modern biology places living things into familiar categories. [music] Animals, plants, fungi, bacteria. These categories work in today's world because today's living things are the product of billions of years of shared evolutionary heritage. But the idi organisms did not fit these categories. Some were radially symmetric structures that look the same from every direction. Some formed three-dimensional layered structures, an internal organization with no equivalent in any organism today. Some had neither a mouth nor a digestive system. How they fed is still debated. Adolf Silkaker named these organisms vendobian and proposed that they represented a completely extinct independent form of life. According to this view, the Edidiain organisms were not the ancestors of any animal group alive today. They were a severed branch of the evolutionary tree. The debate continues, but the debate itself shows just how extraordinary these organisms were.

[00:08:14][music] These beings, which filled the ocean floor for millions of years, were a biological experiment with no reference point today.

[00:08:28]Dickinsonia was first [music] described in 1947.

[00:08:32]Since that day, scientists have debated [music] what exactly it was. oval, flat, and segmented. Some individuals reached 1.4 [music] m. One of the largest known organisms of the Ediakarine period. Viewed from the surface, it looks like a leaf impression or a jellyfish remnant. But the details are far stranger. Fossil trails show that Dickinsonia moved. Two separate impressions were found from the same individual, one slightly larger than the other and positioned side by side. This meant growth and displacement, an organism that moved and grew. In 2018, Russian researchers detected preserved organic molecules in Dickinsonia fossils. Cholesterol derivatives. These molecules are specific to animal cells.

[00:09:24]Plants or bacteria do not produce them.

[00:09:27]This finding made Dickinsonia one of the oldest animal candidates found to date.

[00:09:33]But how did it feed? It had no mouth. It had no digestive system. Perhaps it absorbed organic matter directly through its body surface, much like some marine worms today. Familiar yet at the same time completely alien.

[00:09:56]There were organisms that filled the ocean floor like a forest. But the trees of this forest were fundamentally different. Charioiscus consisted of a stalk and a leaflike structure. It anchored itself to the ocean floor with its stalk and filtered organic particles out of the ocean water with its branch-like arms. Some individuals exceeded 50 cm. They lived in crowded communities on fossilized surfaces. The [music] imprints of dozens of individuals lying side by side can still be seen today. These communities formed the first great multisellular ecosystems in history. Different species live together on the same ground, drawing on different layers of water at different heights. Ecological layering, a logic similar to the structure that today's forests form with trees of different [music] sizes. England's Charwood forest gave its name to these fossils. In 1957, 15-year-old Roger Mason discovered Charnea [music] Masoni on a rock surface in this region. This finding proved that Edidi fossils were not unique to Australia and carried the research onto a global scale. This forestlike ecosystem was silent. There was no movement, no predator prey relationship, only filtering, growing and spreading.

[00:11:27]Kimberella was different. Unlike most other edi organisms, Kimberella's body was symmetric and elongated in one direction. its front and back could be distinguished. This two-sided symmetry, that is bilateral symmetry, is the defining feature of the group that encompasses the vast majority of animals today. Fossils found in Russia's White Sea region preserved this organism in extraordinary detail. An oval flattened body, a hard shell-like structure at the back, and soft tissue at the front.

[00:12:02]Scratch-like marks were found around some fossils. These marks suggest that Kimberella fed by scraping the microbial mat on the ocean floor. Scraping. This behavior mattered. Scraping means active feeding. Active feeding means a mouth-like structure. And a mouth together with a digestive system is a herald of the basic anatomy of an animal. Many researchers consider Kimberella to be a distant ancestor of modern mollisks, that is snails and octopuses. It is not certain, but the fossil evidence warrants taking this relationship seriously.

[00:12:49]The range morphs were among the strangest inhabitants of the Edidiaan period. Their structure was fractal.

[00:12:56]Large branches split into smaller branches, and smaller branches split into even smaller ones, and this pattern repeated at every scale. They anchored their roots to the ocean floor, extended their branches into the water, and waited there. They did not move. But what did they eat? The answer to this question is still debated. They had no mouths. To get enough light for photosynthesis, they would have needed to live in shallow waters rather than in the depths. But fossils [music] have also been found in deep water environments. Some researchers suggest that they absorbed organic [music] molecules directly from the ocean water, osmotrophic feeding. This strategy worked. The rangomorphs were among the earliest and most widespread organisms of the Idiacaran period. In some regions, they covered almost the entire ocean floor. The fractal structure was not random. It maximized surface area.

[00:13:54]Far more absorption surface within the same volume. Evolution would later rediscover this same solution in lungs, [music] in intestines, and in roots. The rangeorphs had applied this principle [music] 600 million years earlier.

[00:14:20]The ocean floor had been motionless for billions of years. Microorganisms did not change [music] position.

[00:14:28]Strumatalytes grew but did not move.

[00:14:31]Colonies of rangers and choiscus anchored [music] to a single spot and stayed there. In this sense, the seafloor was not a dead surface. It was alive but silent. Then something changed. Some idi organisms began to move. Traces of this change are preserved on fossilized ocean floor surfaces. Long straight lines and trail patterns. Organisms were moving in a specific direction toward a specific purpose. This movement was not random.

[00:15:03]Moving in a particular direction.

[00:15:05]Overcoming an obstacle or changing direction requires coordinated muscle activity. Coordinated muscle activity requires a nervous system and a nervous system is one of the most critical steps in animal evolution. The onset of movement changed the world. A predator prey relationship is not possible in a motionless ecosystem. [music] But once an organism is moving, going somewhere, targeting something, evolutionary dynamics change fundamentally.

[00:15:43]Fossils carry two kinds of information.

[00:15:46]The first is anatomical, the shape, size, and structure of the body. The second is behavioral, the trails, channels, and imprints that show what the organism was doing. The second category is called trace fossils. And some of the most valuable documents of the Ediakaran period fall into this category. Trails left on the muddy surface of the ocean floor turned to stone over millions of years. Straight lines, winding channels, points where the organism stopped and changed direction. Some of these trails belonged [music] to a single organism. The size and depth were consistent. Others showed more complex patterns, spiral movements, reversals, trails where the organism lingered in one spot for a long time.

[00:16:34]These patterns reveal the evolution of behavior. Paths followed for feeding purposes look different. Irregular movements that scan a wide area. Trails of relocation, on the other hand, are more linear. Organisms moved in different ways for different purposes.

[00:16:52]To move is to make a decision. To make a decision is to have an information processing system. These trails carry not only clues about where an organism was, but also some of the oldest clues about what it was thinking.

[00:17:13]The ocean floor of the Ediaran period presented a complex picture. Organisms of different sizes [music] with different feeding strategies living at different depths coexisted together.

[00:17:27]This coexistence was not random. Each species had settled into a specific ecological niche. While large chiodiscus colonies [music] filtered the upper layers with their branches extending into the water, smaller organisms on the ground made use of different resources.

[00:17:45]This layering formed the first complex versions of the food web. The flow of energy was onedirectional. Sunlight reached photosynthetic organisms and the organic matter they produced reached the filter [music] feeders. Organisms like Dickinsonia absorbing the microbial mat formed the last link of this flow. Each link was connected to the next. This interdependence also created fragility.

[00:18:11]A change in one component could affect the entire system but at the same time it also provided stability. When there is more than one energy pathway, it becomes harder for the system to [music] collapse from a single point. The first ecosystems were not as complex as today's, but they operated on the same basic logic.

[00:18:36]Size is not free. Sustaining a large body requires energy. More cells, more tissue, and more coordination each carry their own energy cost. And this cost [music] can only be met through aerobic metabolism, that is with oxygen. During the Idiacarine period, atmospheric oxygen levels had reached perhaps only a few% of today's level. This looks low compared to today. But compared to a billions of years long oxygen-free past, it was a revolution. This rise [music] pushed the limits of body size upward.

[00:19:12]Organisms could now be not only larger but also more complex. Developing different cell types with different functions and building systems to feed and coordinate these [music] cells. All of this required energy and energy was now available. The giant individuals of the idi are proof that this threshold had been crossed. Dinenia exceeding 1 m.

[00:19:36]Chario discus reaching 50 cm. These were sizes that had been impossible billions of years earlier. Oxygen was a precondition not just for respiration but for complexity itself.

[00:19:56]Was there a predator in the ediaran world? This question matters more than it appears. A predator prey relationship fundamentally changes ecosystems. Prey organisms evolve to flee, hide, or protect themselves. Predators evolve to catch. This mutual pressure accelerates evolutionary change. For most of the Idiacan period, this pressure did not exist or was extremely weak. Fossil evidence shows no clear signs of active [music] predation, such as bite marks, dismemberment, or trail patterns indicating escape behavior. Organisms were moving but do not appear to have been fleeing. Feeding traces [music] exist, but hunting traces do not. This absence is meaningful. Ecologically, this world called the Idiacaran Garden was a genuinely peaceful place.

[00:20:49]Organisms may have been competing for food sources, but active [music] predation was not a defining feature of this period. The arrival of predators coincides with the end of the Ediaran period. And this arrival is thought to have changed everything. One of the critical dynamics that opened the door to the Cambrian.

[00:21:19]Evolution does not work like an engineer. An engineer designs first, calculates and then builds. Evolution on the other hand tries repeatedly, eliminates the failures and continues with what remains. This process looks inefficient. But over millions of years and trillions of individual trials, an extremely powerful creativity emerges.

[00:21:44][music] The Ediaran period was one of the freest periods of this creativity.

[00:21:48]There was no predator prey pressure or it was extremely weak. Most ecological niches were filled, but enormous gaps also existed. In this environment, evolution tried out entirely different body plans. Radial symmetry, fractal structures, bilateral form, layered internal organization.

[00:22:11]Each was a different answer to a different environmental problem. Most of these experiments were not carried forward into later periods. The fractal structure of the rangomorphs does not appear in the Cambrian. Some ediaran body plans disappeared without leaving any trace at all. But some of these experiments survived and these survivors became the raw material for the explosive diversity of the Cambrian.

[00:22:42]Some organisms vanish without leaving any trace. The fossil record does not document every organism. Softbodied creatures often decompose and disappear.

[00:22:52]The Ediakarine period was lucky in this respect. Thanks to extraordinary preservation conditions, some ocean floors preserved organisms almost like photographs. But even this preservation had its limits. And much of the Edi biota was erased from the record at the Cambrian boundary. This extinction was not a mass destruction event. There was no asteroid, no sudden volcanic crisis.

[00:23:19]It was slow, insidious, and inevitable.

[00:23:22]Newly evolved animal groups began to invade the ocean floor. Organisms that dug into the ground overturned the surface of the ocean floor. The microbial mat disappeared. The ground that had been [music] essential for Charodiscus and the ranger no longer existed. This process is called the Cambrian substrate revolution. The digging up of the ocean floor, the disruption of the surface and new ecosystem dynamics removed the physical foundation of the ediaran world. The end of a world is not always loud.

[00:24:04]The ocean floor was changing. The first signs were faint but readable. New kinds of traces appeared in the sedimentary layers. Vertical channels, tunnels descending into the depths, complex networks etched into the ground. These were different from the surface traces of [music] edi organisms. Traces of movements that had depth that worked the soil. These movements changed the chemistry of the ocean floor. The sediments beneath the surface were airrated for the first time. Oxygen seeped deeper. The rate of organic matter decomposition changed. Nutrient cycles were reorganized. At the same time, the chemistry of seawater was also transforming. Calcium concentration was rising. The exact cause of this rise is debated, but its result is clear. Some organisms began converting calcium carbonate into biological structures that is producing hard skeletons. A hard skeleton changes everything. It provides protection. It makes fossil preservation easier and it fundamentally transforms ecological dynamics. Swallowing a hard-shelled organism is far more difficult. The soft and quiet world of the idiaran was gradually hardening.

[00:25:33]About 560 million years ago, two worlds lived side by side in the oceans. Idi organisms still existed. Johniscus [music] colonies continue to grow in shallow waters. There are Dickinsonia fossils dated to this period. The old world had not disappeared. But right alongside it, something new was present.

[00:25:56]The first bilateran animals, that is, organisms with two-sided [music] symmetry and active movement, were becoming increasingly widespread. Small wormlike creatures were carving paths through the ocean floor. Some were developing hard structures. Some were actively digging into the ground to feed. These two worlds coexisted for a while. Fossil sites show both ediaran forms and early animal traces in the same [music] layers. Competition was not direct. Ecological niches did not yet fully overlap. But the balance was fragile. With every passing million years, new animals occupied a little more space, used a little more resources, and [music] transformed the ocean floor a little more. The Idi clock was ticking down. 541 million years ago.

[00:26:55]The geological record draws a sharp line. Below this line are idiocaran fossils. Above it there are none. The transition looks sudden. But on a geological time scale, even sudden can last millions of years. A slow disappearance, not erosion, but a biological reorganization.

[00:27:18]The rangeomorphs were gone. The chaodiscus were gone. No group was found that carried [music] on to Kinsonia's lineage. The vast majority of these organisms did not make it into the Cambrian. They remained only as fossils, but silent end is not quite the right description. Some forms from the Edidiaan period left a trace.

[00:27:41]Kimberella's bilateral symmetry and scraping behavior may be [music] connected to later Mollisk ancestors.

[00:27:47]Some early sponges and jellyfish-like forms survived [music] this transition.

[00:27:52]And most importantly, the ediaran period was not wasted. The foundation of multisellular life was laid there.

[00:28:01]Division of cellular labor, tissue organization, and coordinated movement were tried there for the first time. The Cambrian was built on this foundation.

[00:28:18]About 541 million years ago, the fossil record suddenly changed. The soft traces of earlier periods were replaced by hard shells, complex trails, and entirely different body plans. Trilobytes appeared. Creatures with jointed legs, eyes, and a hard exoskeleton resembling no idiar organism at all. Brachopods, the first ectoizans, and the ancestors of early mollisks all entered the record almost simultaneously.

[00:28:52]The Cambrian explosion within about 20 to 25 million years. The groups that formed the basis of almost all animal filer alive today appeared in the fossil record. By evolutionary standards, this happened in an instant. The idi was the herald of this explosion. Over the span from 635 to 541 million years ago, multisellular life was tried out, tested, and selected. Which body plans worked? Which strategies were sustainable? And which ecological dynamics accelerated evolution? All of this was learned during this period. The Cambrian explosion will be with you in the next video. If you've watched this far, you [music] probably love the prehistoric world as much as we do. You can show us that by subscribing to the channel and liking the video. See you in the next video.