250 million years ago, it was covered in forests and rivers, and the temperature was rarely dipped below freezing. It was also home to a variety of wildlife, including early relatives of the dinosaurs. Scientists have just discovered the newest member of that family-an iguana-sized reptile whose name means "Antarctic king."
"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 bit like a lizard, but evolutionarily, it's one of the first members of that big group. It tells us how the dinosaurs and their closest relatives evolved and spread."
The fossil skeleton is incomplete, but paleontologists still have a good feel for the animal, named Antarctanax shackletoni (the former means "Antarctic king", the latter is a nod to polar explorer Ernest Shackleton). Based on its similarities with other fossil animals, Peecook and his coauthors (Roger Smith of the University of Witwatersrand and the Iziko South African Museum and Christian Sidor of the Burke Museum and the University of Washington) surmise that Antarctanax was a carnivore that hunted bugs, early mammal relatives, and amphibians.
The most interesting thing about Antarctanax, though, is where it lived, and when. "The more we find out about the prehistoric Antarctica, the weirder it is," says Peecook, who is also affiliated with the Burke Museum. "We thought Antarctic animals would be similar to those that were living in southern Africa, since those landmasses were joined back then. But we find that Antarctic's wildlife is surprisingly unique."
About two million years before Antarctanax lived-the blink of an eye in geological time-Earth underwent its largest-ever mass extinction. Climate change, caused by volcanic eruptions, killed 90% of all animal life. The years immediately after that extinction event were evolutionary free-for-all-with a slate wiped clean by mass extinction, new groups of animals vied to fill the gaps. The archosaurs, including dinosaurs, were one of 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. "
The fact that scientists have found Antarctanax helps bolster the idea that Antarctica was a place of rapid evolution and diversification after mass extinction. "The more different types of animals we find, the more we learn about the pattern of archosaurs taking over after mass extinction," notes Peecook.
"Antarctica is one of those places on Earth, like the bottom of the sea, where we are still in the very early stages of exploration," says Peecook. "Antarctanax is our little part of discovering the history of Antarctica. "
Variation in the recovery of tetrapods
Brandon R. Peecook et al, A novel archosauromorph from Antarctica and an updated review of high-latitude vertebrate assemblage in the wake of end-Permian mass extinction, Journal of Vertebrate Paleontology (2019). DOI: 10.1080 / 02724634.2018.1536664