New dinosaur relative was ‘king’ of Antarctica

An illustration of the Antarctanax. (Credit: Adrienne Stroup/Field Museum)

Researchers have discovered a new species related to dinosaurs, an iguana-sized reptile whose genus name, Antarctanax, means “Antarctic king.”

Antarctica wasn’t always a frozen wasteland. About 250 million years ago, it was covered in forests and rivers, and the temperature rarely dipped below freezing. It was also home to diverse wildlife, including early relatives of the dinosaurs.

“This new animal was an archosaur, an early relative of crocodiles and dinosaurs,” says Brandon Peecook, a Field Museum researcher and lead author of a paper in the Journal of Vertebrate Paleontology describing the new species.

“On its own, it just looks a little like a lizard, but evolutionarily, it’s one of the first members of that big group. It tells us how dinosaurs and their closest relatives evolved and spread.”

Illustration of three archosaur inhabitants
Illustration “The midnight sun over Early Triassic Antarctica” by Adrienne Stroup. Along the banks of a river, three archosaur inhabitants of the dense Voltzia conifer forest cross paths: Antarctanax shackletoni sneaks up on an early titanopetran insect, Prolacerta lazes on a log, and an enigmatic large archosaur pursues two unsuspecting dicynodonts, Lystrosaurus maccaigi. (Credit: Adrienne Stroup/Field Museum)

Strange creatures, strange land

Senior author Christian Sidor, professor of biology at the University of Washington and curator of vertebrate paleontology at the university’s Burke Museum of Natural History & Culture, collected the fossil during a 2010-2011 expedition to Antarctica. It consists of portions of the backbone, limbs, and skull. The specimen is now part of the permanent collections at the Burke Museum and is one of more than 300 vertebrate fossils from Antarctica in its collection, collected over the course of four expeditions and resulting in one of the largest Antarctic vertebrate fossil collections in the country.

During the museum’s most recent Antarctic expedition in 2017-2018, Sidor led his team back to Graphite Peak, the site where he’d found Antarctanax, which was where scientists discovered the  first vertebrate fossils in Antarctica in 1967.

Although the new specimen is an incomplete skeleton, paleontologists still have a good feel for the animal, named Antarctanax shackletoni—the latter part a nod to polar explorer Ernest Shackleton. Based on its similarities to other fossil animals, the researchers surmise that Antarctanax was a carnivore that hunted bugs, amphibians, and relatives of early mammals.

Antarctanax bones
Part of the fossil type specimen of Antarctanax shackletoni, showing well-preserved vertebrae and a humerus. (Credit: Brandon Peecook/Field Museum)

The most interesting thing about Antarctanax, the authors say, is where and when it lived.

“The more we find out about prehistoric Antarctica, the weirder it is,” says Peecook, who was a doctoral student in the biology department at the time the fossil was collected and is now also a research associate at the Burke Museum.

“We thought that Antarctic animals would be similar to the ones that were living in southern Africa, since those landmasses were joined back then. But we’re finding that Antarctica’s wildlife is surprisingly unique.”

After catastrophe

About two million years before Antarctanax lived—the blink of an eye in geologic time—Earth underwent its largest mass extinction. Climate change, caused by volcanic eruptions, killed 90 percent of animal life. The years immediately after that extinction event were an evolutionary free-for-all. With the mass extinction wiping the slate clean, new groups of animals vied to fill the gaps. The archosaurs, including dinosaurs, were among the groups that experienced enormous growth.

“Before the mass extinction, archosaurs were only found around the equator, but after it, they were everywhere,” says Peecook. “And Antarctica had a combination of these brand-new animals and stragglers of animals that were already extinct in most places—what paleontologists call ‘dead clades walking.’ You’ve got tomorrow’s animals and yesterday’s animals, cohabiting in a cool place,” he adds.

During their 2017-2018 Antarctic expedition, Sidor and his team returned to Graphite Peak, where scientists originally found Antarctanax and where, in 1967, they found the first vertebrate fossils on the continent. (Credit: Christian Sidor/U. Washington)

“Fossil exploration in Antarctica is really difficult, given all of the logistics involved. But since so little work has been done the potential for making important new discoveries is high—and that’s what Antarctanax represents,” says Sidor. “The same rocks that yielded Antarctanax also yield some of the earliest mammal relatives from after the mass extinction.”

The fact that scientists have found Antarctanax helps bolster the idea that Antarctica was a place of rapid evolution and diversification after the mass extinction.

“The more different kinds of animals we find, the more we learn about the pattern of archosaurs taking over after the mass extinction,” says Peecook. “Antarctica is one of those places on Earth, like the bottom of the sea, where we’re still in the very early stages of exploration. Antarctanax is our little part of discovering the history of Antarctica.”

Roger Smith of the University of the Witwatersrand in Johannesburg and the Iziko South African Museum is the paper’s coauthor.

Source: University of Washington