Tuesday , March 9 2021

Rare Fossil of the Triassic Reptile Discovered in Antarctica

Artist's Representation of Antarctanax Shackleton (left). On the other side of the chain, a great archossaur pursues a pair of unsuspecting dicinodonts.
Editorial Photo: Adrienne Stroup, Field Museum Contact us via email or phone Email us |

The fossilized remains of an ancient reptile, dating to about 250 million years ago, were discovered in the most unlikely places: Antarctica. The discovery shows how wildlife has recovered after the worst mass extinction in planetary history and how Antarctica has housed a different ecosystem than any other.

It goes without saying that paleontological work in Antarctica is very different than elsewhere. Unlike Alberta or Montana, for example, which have abundant rocky outcrops, Antarctica is covered by a huge layer of ice, obscuring much of its paleontological history. And it's not as if Antarctica did not have stories to tell – that's what happens. It was only recently, in the last 30 to 35 million years, that the continent froze. Before that, it was home to a warm climate, lush forests, rushed rivers and a remarkable abundance of life.

To find fossilized traces of this forgotten life, whether in Antarctica or elsewhere, scientists must find rocks. Antarctica offers only two possibilities: islands along its coast and the Central Transantarctic Mountains – a mountain spine that cuts a strip in the middle of the continent. The tops of these mountains run through the glaciers, creating a rocky archipelago – and a place for paleontologists to prospect. It is here in the Fremouw Formation of the Transantarctic Mountains that Brandon Peecook, a paleontologist at the Field Museum of Natural History and lead author of the new study, discovered the rare Triassic reptile.

"Standing on the mountain, it was hard to imagine how Antarctica really should be alien at that time," Peecook told Gizmodo. "Looking around, I did not see any trace of macroscopic life for miles in all directions."

Prospecting of Brandon Peecook in Antarctica.
Image: Roger Smith

In fact, Antarctica can be desolate and inhospitable today, but it has not always been so. Hundreds of millions of years ago, the Fremouw Formation was home to a vibrant forest full of life, from winged insects to four-legged reptilian herbivores. The discovery of a previously unknown iguana-sized reptile, nicknamed Antarctanax Shackletoni, our knowledge of the continent's former ecological glory is now increasing.

Antarctanax means "King of Antarctica" and Shackletoni is a hat tip for British polar explorer Ernest Shackleton. A. Shackletoni It was an archosaur, sharing a common ancestor with dinosaurs and crocodiles and living during the Early Triassic Period, about 250 million years ago. Now it is one of the first lizards to appear in the fossil record. Details of this discovery were published today in the Journal of Vertebrate Paleontology.

The partial fossil consists of an excellently preserved vertebra (including neck and back), a partial skull, two legs, a few ribs and an arm bone. It was discovered during an expedition to the Fremouw Formation during the 2010-2011 Antarctic summer. Analysis of these fossilized bones (particularly of the skull) and the fossils found alongside suggests that he was a giant carnivore, chewing insects, amphibians and early proto-mammals. Roger Smith of the University of Witwatersrand in South Africa and Christian Sidor of the University of Washington in Seattle helped Peecook with the analysis.

One side of the fossil, showing vertebrae and arm bone.
Editorial Photo: Brandon Peecook, Field Museum Contact us via email or phone Email us |

The beginning of the Triassic is of great interest to paleontologists because it came in the wake of one of the worst episodes in Earth's history – mass extinction at the end of the Permian, a time when extreme and prolonged volcanism eliminated almost 90% of the life of the our planet. This has resulted in a broad ecological restart, setting the stage for survivors to take control. Among these survivors were the archosaurs, who made the most of it.

"One pattern we see repeatedly with mass disturbances like mass extinction at the end of the Permian is that some of the animals that managed to survive quickly filled the gaps," Peecook told Gizmodo. "The archosaurs are a great example – a group of animals that managed to do just about everything. This clade was totally ballistic.

Opposite side of the fossil showing several vertebrae, ribs and right foot.
Editorial Photo: Brandon Peecook, Field Museum Contact us via email or phone Email us |

In fact, archosaurs, including dinosaurs, were among the biggest beneficiaries of this recovery period, experiencing tremendous growth and diversity. Prior to mass extinction, these creatures were limited to equatorial regions, but then were "everywhere," according to Peecook – including, as we now know, Antarctica. The continent was home to A. Shackletoni about 10 million years before the appearance of true dinosaurs. As an aside, Antarctica hosted dinosaurs, but not until the Jurassic Period.

This discovery is also shedding light on animals distinct from Antarctica. As Antarctica and South Africa were physically connected at the time, paleontologists worked under the assumption that the two regions had much in common in terms of local wildlife. And because fossils are plentiful in South Africa, paleontologists used this record to make inferences about the kind of life that probably existed in Antarctica. But as Peecook has explained, this is becoming a mistake; Antarctica hosted an ecology unlike any other.

"We know very well the fossil record of South Africa, but in Antarctica we have discovered only 200 species," he said. "But we do not find these species anywhere else." The paleontologists only went to Antarctica a few times, but every time they go, they find new species and surprise new occurrences – it's really exciting. is now incorrect. "The Antarctic registry has many unique things going on."

That Antarctica presented a unique set of species is not surprising. As today, the continent was at a high altitude, presenting long days in the summer and long nights in the winter. Animals and plants had to adapt to survive, thus adopting new physical characteristics and survival strategies.

The mind is amazed at the thought of all the unknown and out of reach fossils trapped under the Antarctic ice. As Peecook said, he maintains the paleontological record of what was once a truly alien environment.

[Journal of Vertebrate Paleontology]

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