A giant, toothy, salamander-like swimmer from ancient Namibia sheds light on evolution in the cool south, long before the dinosaurs.
Described in Nature by Claudia Marsicano of the University of Buenos Aires, Jason Pardo of the Field Museum in Chicago, and a team of colleagues, the new animal is an unusually large ‘stem-tetrapod’.
Marsicano and colleagues have named it Gaiasia jennyae, honouring the Namibian Gai-As Formation – the rock unit that yielded the fossil – as well as Professor Jenny Clack of Cambridge University, a pioneer in stem-tetrapod studies who died in 2020.
When alive, Gaiasia would have looked vaguely like a cross between a big salamander and a moray eel. It was huge for animals of its sort, probably approached four metres in length, and was entirely aquatic.
Its body was long and flexible, and it likely had a deep tail fin like that of a gigantic newt. Its limbs are unknown, but the team suspect that these were tiny, and possibly absent altogether. Its head was broad and flat, with a squared-off snout.
Big, tusk-like fangs lined the edges of its jaws. “After examining the skull, the structure of the front caught my attention. It was the only clearly visible part at that time, and it showed interlocking large fangs, creating a unique bite for early tetrapods”, Marsicano recalled after first seeing the fossil in the field. These fangs were used to subdue prey animals – crustaceans, fishes and smaller tetrapods – after they were engulfed.
There are no indications that Gaiasia was built for pursuit or sustained swimming, so it was probably an ambush predator that lunged from cover or the lakebed. Rapid opening of its jaws would have created suction that pulled prey into the mouth.
Gaiasia is not an archaic member of any group alive today but is instead outside the group that includes all living tetrapods, the animal group that includes amphibians, reptiles, birds and mammals. In currently preferred terminology, a group of organisms that includes both living and fossil species has a ‘crown’ – the part of the family tree where all the branches include living species – and a ‘stem’, this being the part outside the crown, where all branches are extinct. Gaiasia is outside the tetrapod crown, hence its placement as a ‘stem-tetrapod’.
The real surprise about Gaiasia is when and where it lived. Stem-tetrapods of its sort were mostly animals of the first half of the Carboniferous, the so-called ‘coal age’ that lasted from 359 to 299 million years ago. Gaiasia is from the early part of the Permian, the geological age that followed the Carboniferous, and it proves that animals of its sort persisted for about 40 million years longer than previously thought.
The majority of stem-tetrapods come from places that were close to the equator when they were alive. When Gaiasia was alive, Namibia was cool, even seasonally cold. Experts had previously thought that stem-tetrapods were absent from such places during the early part of the Permian, but this was clearly not so.
Were giant stem-tetrapods widespread across high, southern latitudes during the Permian? “Anything is possible”, Pardo said via email, “but we should expect more surprises like Gaiasia”.
Main image credit: Roger M.H. Smith
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