Australia's Lake Callabonna Has a Secret No One Can Explain

[00:00:00]Inside a glass cabinet at the South Australian Museum in Adelaide, there is something that should not be possible.

[00:00:08]The preserved stomach contents of an animal that died more than 50,000 years ago.

[00:00:15]Undigested leaves, twigs.

[00:00:18]The final meal of a creature the size of a hippopotamus sealed inside dried mud on a salt lake bed in the South Australian Outback for longer than modern humans have existed in Europe.

[00:00:33]The animal was a Diprotodon.

[00:00:36]The lake was Callabonna.

[00:00:39]And the question of why 360 of them died there in one place over an unknown span of time has never been fully answered.

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[00:01:02]Lake Callabonna sits in the far northeast of South Australia.

[00:01:07]A dry salt lake more than 70 km long.

[00:01:11]Part of a horseshoe chain of dead lakes curving around the northern Flinders Ranges.

[00:01:17]It receives almost no rainfall.

[00:01:21]The surface is cracked white salt for most of the year.

[00:01:26]Nothing about it looks like a place where extraordinary things happened.

[00:01:32]But in 1892 an Aboriginal stockman named Jackie Nolan was working a nearby sheep station when he found bones embedded in the cracked lake surface.

[00:01:47]Bones larger than anything alive on the continent today.

[00:01:51]When word reached the South Australian Museum, geologist Henry Hurst arrived in 1893 and began pulling back the lid on what the museum's own director, Edward Stirling, would describe the following year as a veritable necropolis of gigantic extinct marsupials and birds which have apparently died where they lie, literally in hundreds.

[00:02:21]A joint Flinders University and Australian Age of Dinosaurs completed in 2024 has now formally documented 646 megafaunal skeletons at the site across 12 [music] separate species.

[00:02:40]Lake Callabonna is the largest graveyard of prehistoric giants ever found in Australia.

[00:02:47]And before I tell you what killed them, I need to tell you what was actually walking here because nothing in modern Australia prepares you for it.

[00:02:58]The Diprotodon was the largest marsupial that has ever lived.

[00:03:04]Standing over 1 and 1/2 m at the shoulder and weighing close to 3 tons, it was built like a hippopotamus but was distantly related to the wombat.

[00:03:16]Its skull was enormous, its legs columnar, and it walked with a slow, heavy gait that researchers have compared from the fossil trackways preserved at Callabonna more to a bear than to any living Australian animal.

[00:03:36]Those trackways are one of the most remarkable things the site has produced.

[00:03:43]Actual footprints preserved in the old lake mud, recording the exact movement patterns of animals that have been extinct for tens of thousands of years.

[00:03:54]>> [music] >> Some of the trackways show individuals moving at a struggling pace.

[00:04:01]Their stride shortened, their weight distributed unevenly.

[00:04:06]These animals were in trouble before they stopped moving.

[00:04:12]Alongside the Diprotodon lay the remains of Genyornis newtoni, the last of the mihirungs, an ancient lineage of giant flightless [music] birds that had been evolving in Australia for tens of millions of years.

[00:04:30]Genyornis stood 1 and 1/2 m tall and weighed 240 kg. It could not fly. It did not need to.

[00:04:40]Massive gizzard pebbles, stones swallowed to help grind up tough plant material, were found mixed throughout the bird remains at Callabonna.

[00:04:51]In one area of the lake bed, no larger than a small living room, researchers found >> [music] >> three almost complete Genyornis skeletons lying together.

[00:05:04]Three individuals of an enormous flightless bird in the same spot, preserved exactly where they fell.

[00:05:14]And then there is Thylacoleo carnifex, the marsupial lion, an apex predator whose remains have also been recovered from Callabonna, sitting in the same graveyard as its prey.

[00:05:31]Researchers believe Thylacoleo had one of the most powerful bites of any mammal of its size that has ever existed, combined with retractable claws and a body built for ambush rather than pursuit.

[00:05:47]At Callabonna, the marsupial lion was watching the giants die.

[00:05:54]Whatever was pulling these animals to this lake, it was creating an opportunity for the predator that followed them.

[00:06:02]Here is where it gets genuinely difficult to explain.

[00:06:06]The leading theory for what killed the animals at Callabonna is straightforward on the surface.

[00:06:13]Paleontologist Richard Tedford proposed that family groups became trapped in the soft mud while crossing the drying lake bed in search of the last remaining water, sinking under their own enormous weight until they could no longer move.

[00:06:32]Many specimens support this directly.

[00:06:36]They were found with well-preserved lower bodies, but crushed, distorted skulls, consistent with animals that died slowly, sinking upright before their heads eventually dropped forward into the mud.

[00:06:52]But the numbers do not work as cleanly as the theory suggests.

[00:06:57]Diprotodon was not a herd animal in the way the concentration at Callabonna implies.

[00:07:04]Marsupials generally do not form large social groups.

[00:07:10]If each Diprotodon at Callabonna represents a separate family group, making the same fatal decision, then the site represents dozens of independent events, not one catastrophic afternoon.

[00:07:25]Different families at different times, all drawn to the same drying lake, all making the same fatal miscalculation.

[00:07:36]Why this lake specifically?

[00:07:39]Why not the dozens of other lakes >> [music] >> in the same horseshoe chain that were undergoing the same drying process at the same time.

[00:07:50]Nobody has produced a fully accepted answer.

[00:07:54]And then there is the timeline problem, which makes everything more complicated.

[00:08:00]Radiocarbon analysis suggests some individual Diprotodon at Callabonna may have still been alive as recently as 20,000 years ago.

[00:08:13]Diprotodon is generally believed to have gone extinct elsewhere on the continent around 46,000 years ago.

[00:08:24]If those recent dates are accurate, Callabonna was still functioning as a megafauna trap long after the species had disappeared everywhere else.

[00:08:35]An isolated population surviving in this specific corner of South Australia for 26,000 years after their kind had vanished from the rest of the continent until the lake finally finished them.

[00:08:50]That is an extraordinary claim, and it has not been settled.

[00:08:56]There is one piece of evidence connected to the animals buried at Callabonna that changes the entire framing of what happened here.

[00:09:05]In 2016, a paper published in Nature Communications analyzed burnt fragments of Genyornis eggshell found at more than 200 sites across Australia.

[00:09:20]The burn patterns were diagnostic.

[00:09:23]The eggshells had been heated at temperatures and in conditions consistent with being discarded into or around human cooking fires.

[00:09:34]The fragments dated to between 53,900 and 43,400 years ago, likely before 47,000 years ago.

[00:09:46]The conclusion was direct.

[00:09:49]Humans were harvesting Genyornis eggs and cooking them.

[00:09:54]And the systematic removal of eggs from nests across the continent was contributing to the extinction of a 240 kg flightless bird that could not replace its reproductive losses fast enough.

[00:10:10]This is the strongest direct evidence in the scientific record for human interaction with Australian megafauna.

[00:10:19]Not a butchered bone, not a spear point, but burnt eggshell at 200 sites.

[00:10:26]An indirect kill through nest raiding rather than hunting that removed the next generation before it could survive.

[00:10:35]However, a paper published in October 2025 by researchers from UNSW Sydney challenges the eggshell evidence directly.

[00:10:48]Arguing that the fragments attributed to Genyornis cannot be conclusively distinguished from the eggshell of smaller birds.

[00:10:59]The debate is active and unresolved.

[00:11:02]Whether the first Australians drove Genyornis to extinction, were present when it died from climate alone, or played some more complicated role >> [music] >> in a process driven primarily by drought is still being argued in peer-reviewed journals right now.

[00:11:22]The lake sits in Adnyamathanha country.

[00:11:26]The Adnyamathanha people are the traditional custodians of the northern Flinders Ranges and the surrounding region.

[00:11:34]And their oral tradition is one of the oldest continuously maintained knowledge systems on Earth.

[00:11:42]A Diprotodon bone fragment recovered from Warratyi rock shelter in the Flinders Ranges, only a short distance from Lake Callabonna, has been proposed as evidence that Aboriginal people at that shelter were collecting bones from the surface of the lake.

[00:12:03]If the Adnyamathanha were present at Callabonna while Diprotodon were still dying there, their oral tradition may carry a memory of these animals that science has not yet fully explored.

[00:12:21]The connection between Adnyamathanha story and the specific animals whose bones are eroding from the surface of the lake on their country represents a collaboration that has not yet been attempted at the depth it deserves.

[00:12:39]The Flinders University and Australian Age of Dinosaurs expedition of 2024 produced a Genyornis skeleton that now stands on display at Government House in Adelaide.

[00:12:53]It is the most complete specimen recovered in recent years.

[00:12:58]It stands in a cabinet in a building in a city separated from the lake where it died by a 4-hour drive through increasingly empty country.

[00:13:09]What sits beneath Lake Callabonna's cracked white surface today is only partially understood after more than a century of intermittent excavation.

[00:13:20]The museum's own 2202 assessment noted the site receives only minimal active management under its current legal protections, despite being the first fossil reserve declared in Australia.

[00:13:37]646 skeletons have been formally documented.

[00:13:42]The site's total extent has never been fully surveyed.

[00:13:47]The animals that died at the edges of the lake, in sections that have not been excavated, remain exactly where they fell.

[00:13:56]Some of them may be better preserved than anything recovered so far.

[00:14:02]The stomach contents sitting in a glass cabinet in Adelaide are 50,000 years old.

[00:14:09]The leaves inside them came from trees that no longer grow in this region, in a climate that no longer exists here.

[00:14:18]The lake that killed the animals that ate those leaves has been dry for longer than anyone can say with precision.

[00:14:27]And the question of whether the giants died here from drought alone, from human pressure, or from some combination of the two that produced the most concentrated megafauna graveyard on the continent, is still being argued by researchers who visit the same cracked salt flat that Jackie Nolan walked across in 1892 and found something enormous embedded in the ground.