About 280 million years ago, a large predator glided through the cold waters. A supercontinent in the Southern Hemisphere. The eight-foot-long hunter had tiny limbs, an eel-like body, and a flat head full of protruding fangs. And according to conventional thinking about vertebrate evolution, it shouldn't have existed.
“It was so chronological, so geographically, and so big,” said Claudia Marsicano, a paleontologist at the University of Buenos Aires and author of a paper describing the animal in the journal Nature on Wednesday. “There were a lot of factors that made it unique.”
The giant salamander-like creature, which Dr. Marsicano and her colleagues named Gaiasia jennyae, could only be a relic of a family thought to have gone extinct millions of years ago. Their discovery could suggest that further research is needed into the emergence of tetrapods, vertebrates with four limbs and feet instead of fins.
The discovery “isn't enough to force us to rethink most of what we think about late Paleozoic tetrapod evolution, but it's a nudge in that direction,” says Spencer Lucas, a paleontologist at the New Mexico Museum of Natural History and Science who was not involved in the study.
Dr. Marsicano and her colleagues discovered the Gaiasia fossils during a series of expeditions in the harsh desert of the Huab Basin in northwestern Namibia, South Africa, in 2014 and 2015. They recovered the remains of four animals, including a pair of skulls and a nearly complete skeleton.
The team pieced together the specimen and says Gaiasia belonged to a family of large-headed swamp-dwelling vertebrates called Colostes, which split off from other land animals long before the ancestors of more modern lineages such as amphibians, reptiles, and mammals evolved.
About 400 million years ago, colostoid and other early tetrapods evolved from fish in equatorial jungles.Paleontologists’ understanding of the Paleozoic Era comes almost entirely from studying sediments found in North America and Europe, said Jason Pardo, a paleontologist at Chicago’s Field Museum and an author of the paper.
So when the ancient tetrapods disappeared from the jungles 370 million years ago, researchers assumed they would have gone extinct everywhere.
But according to Dr. Marsicano, Gaiasia was discovered 20 million years later than expected, in rocks from the Early Permian Period. And while previously known members of this creature’s family had skulls that could fit in a person’s hand, Dr. Marsicano said Gaiasia’s skull was more than two feet long, making it the largest of its kind ever discovered.
The environment in which Gaiasia lived was particularly interesting. During the early Permian, present-day Namibia lay along the southern supercontinent of Gondwana, a landscape of glacial walls and cold, temperate forests like those found in Canada or Norway.
Finding Gaiasia in that landscape would be like finding a crocodile happily living in a lake in Manitoba, Dr. Pardo said. “But this animal could certainly survive in that environment and grow quite large.”
Competition with large fish (and later, larger relatives of modern amphibians) in the jungles around the equator may have kept the early tetrapods small, the team concluded. But the animals may have had better luck in the cool waterways in the shadow of the Gondwana glaciers, even as the equatorial rainforests fragmented into arid ecosystems filled with fin-finned predators like Dimetrodon.
Dr. Marsicano said Gaiasia and its habitat add an interesting wrinkle to the story of tetrapod evolution. Researchers tend to assume that most tetrapods evolved in the tropics and stayed there, with more specialized groups spreading to cooler climates around 280 million years ago. In contrast, the presence of Gaiasia suggests that their ancestors reached higher latitudes before that time.
Early tetrapods were “better adapted to different types of environments from the start,” Dr. Marsicano said.
The global story of tetrapod evolution is based largely on data from fossils found in North America and Europe, but the Gaiasia discovery highlights the importance of studying sites in South America and Africa that have historically been neglected in paleontology, Dr. Pardo said.
“Getting these animals from the Southern Hemisphere is really important for understanding the story of our lineage,” Dr. Pardo said. “Especially the question of whether it’s just a local story or something that’s happening on a global scale.”