Left: Artist’s rendering of Gaiasia jennyae. Credit: Gabriel Lio. Right: Skeleton, including the skull and backbone, of Gaiasia jennyae. Credit: C. Marsicano.
The New York Times has a story about a new stem tetrapod. Gaiasia jennyae lived 280 million years ago, which is about 40 million years before the evolution of the dinosaurs. It lived in what is now Namibia in southern Africa. Its discovery has profound implications about when and where early tetrapods moved onto land from the sea. The description of the animal was published in the journal Nature. Jason Pardo a NSF postdoctoral fellow at the Field Museum was a co-lead author.
Roughly 400 million years ago, colosteids and other early tetrapods evolved from fish amid equatorial jungles. Paleontologists’ understanding of the Paleozoic Era comes almost exclusively from the study of deposits found in North America and Europe, said Jason Pardo, a paleontologist at the Field Museum in Chicago and an author on the paper.
So when archaic tetrapods disappeared from those jungles 307 million years ago, researchers assumed they went extinct everywhere.
But Gaiasia turned up in rocks 20 million years later than expected, Dr. Marsicano said, early in the Permian Period. And while previously known members of the creatures’ family had skulls that could fit in a person’s hand, Dr. Marsicano said, Gaiasia’s skull reached two feet long or more, making it the largest animal of its kind ever found.
“Gaiasia jennyae was considerably larger than a person, and it probably hung out near the bottom of swamps and lakes. It's got a big, flat, toilet seat-shaped head, which allows it to open its mouth and suck in prey. It has these huge fangs, the whole front of the mouth is just giant teeth,” says Jason Pardo, an NSF postdoctoral fellow at the Field Museum in Chicago and the co-lead author of the Nature study. “It’s a big predator, but potentially also a relatively slow ambush predator.”
The fossil is named for the Gai-as Formation in Namibia where it was found, and for Jenny Clack, a paleontologist who specialized in the evolution of early tetrapods-- the four-limbed vertebrates that evolved from lobe-finned fishes and gave rise to amphibians, reptiles, birds, and mammals.
Pardo’s co-lead author, Claudia Marsicano of the University of Buenos Aires and her colleagues found the fossil. “When we found this enormous specimen just lying on the outcrop as a giant concretion, it was really shocking. I knew just from seeing it that it was something completely different. We were all very excited,” said Marsicano. “After examining the skull, the structure of the front of the skull caught my attention. It was the only clearly visible part at that time, and it showed very unusually interlocking large fangs, creating a unique bite for early tetrapods.”
Current hypotheses of early tetrapod evolution posit close ecological and biogeographic ties to the extensive coal-producing wetlands of the Carboniferous palaeoequator with rapid replacement of archaic tetrapod groups by relatives of modern amniotes and lissamphibians in the late Carboniferous (about 307 million years ago). These hypotheses draw on a tetrapod fossil record that is almost entirely restricted to palaeoequatorial Pangea (Laurussia)1,2. Here we describe a new giant stem tetrapod, Gaiasia jennyae, from high-palaeolatitude (about 55° S) early Permian-aged (about 280 million years ago) deposits in Namibia that challenges this scenario. Gaiasia is represented by several large, semi-articulated skeletons characterized by a weakly ossified skull with a loosely articulated palate dominated by a broad diamond-shaped parasphenoid, a posteriorly projecting occiput, and enlarged, interlocking dentary and coronoid fangs. Phylogenetic analysis resolves Gaiasia within the tetrapod stem group as the sister taxon of the Carboniferous Colosteidae from Euramerica. Gaiasia is larger than all previously described digited stem tetrapods and provides evidence that continental tetrapods were well established in the cold-temperate latitudes of Gondwana during the final phases of the Carboniferous–Permian deglaciation. This points to a more global distribution of continental tetrapods during the Carboniferous–Permian transition and indicates that previous hypotheses of global tetrapod faunal turnover and dispersal at this time2,3 must be reconsidered.
