Before dinosaurs walked the Earth and tens of millions of years before the first mammals appeared, distant mammal relatives with long, serrated canine teeth were the dominant carnivores on land. Called gorgonopsians, the earliest animals in this lineage have long been missing from the fossil record. But the discovery of a newly identified gorgonopsian — the oldest sabre-toothed animal ever found — is filling a longstanding blank space in the group’s history.
These slender predators are known mostly from bones that are less than 270 million years old, but the recent fossil find is thought to be an unprecedented 280 million to 270 million years old.
The newfound gorgonopsian adds to one of the earliest branches of the therapsid family tree — the Therapsida order includes not only gorgonopsians but also the ancestors of modern mammals and other nonmammalian groups that are now extinct.
The finding is a notable puzzle piece that could help shed light on the earliest forebears of mammals, experts said.
What is a gorgonopsian? It’s not a ‘lizard-dog’
Gorgonopsians vanished around 252 million years ago, and their lineage died with them. All gorgonopsians had daggerlike canine teeth, and species ranged widely in size. Some were as small as cats, while others were as big as polar bears.
Fossils of the newly described gorgonopsian included its knifelike canines; parts of its jaw; some vertebrae, ribs, tailbones and toe bones; and most of the bones from a hind limb, researchers reported Tuesday in the journal Nature Communications.
The specimen’s blunt-snouted skull was incomplete but is estimated to measure about 7 inches (18 centimeters) long, and the animal would have been as tall as a medium-size dog and weighed roughly 66 to 88 pounds (30 to 40 kilograms), according to study coauthor Ken Angielczyk, MacArthur Curator of Paleomammalogy at Chicago’s Field Museum of Natural History.
Other than being four-legged and having a long tail, the gorgonopsian wouldn’t have looked very doglike, Angielczyk said. Similar to reptiles, gorgonopsians didn’t have fur or visible ears, he said. But although the animal physically resembled lizards in some ways, please don’t call it a “lizard-dog,” he told CNN.
“Lizards are a kind of reptile, and nonmammalian therapsids like gorgonopsians are part of a completely different evolutionary lineage, part of the lineage that includes mammals,” Angielczyk said. “While mammals and reptiles share a common ancestor that lived about 320 million years ago, they are separate lines of descent.”
Gorgonopsians do share some traits with their mammal cousins. One of those is having teeth of different shapes and sizes, “with those teeth providing different roles in the feeding system,” Angielczyk said. “That’s something that’s very common in mammals today.”
Unlike mammals, gorgonopsians seemingly replaced their teeth — including their long canines — repeatedly throughout their lifetime. “Mammals today, for the most part, just have one replacement cycle of teeth,” Angielczyk said. “Whereas gorgonopsians and other therapsids generally were more like a crocodile today, where they have teeth that are erupting continuously.”
Oldest of its kind
Paleontologists discovered bones of the newfound gorgonopsian in Mallorca, a Mediterranean island that’s part of Spain, during expeditions in 2019 and 2021, said senior study author Josep Fortuny, leader of the computational biomechanics and evolution of life history research group at the Miquel Crusafont Catalan Institute of Paleontology in Spain.
“The most interesting thing about the specific specimen that we describe is its age. It is pretty certainly the oldest known gorgonopsian” as well as the oldest known therapsid to date, Fortuny told CNN in an email.
“There is a big time gap in the fossil record of therapsids, between when they are predicted to have evolved based on our knowledge of relationships of synapsids (a larger vertebrate group that includes therapsids) and when they actually show up in the fossil record,” Fortuny said.
Scientists have previously calculated that therapsid fossils should start showing up in rocks that are about 300 million years old, “and we don’t actually see them, up until now, until about 270 million years ago,” Angielczyk said. The new specimen, which dates back at least to that point in time and is likely even older, aligns with that gap, helping researchers to clarify when therapsids evolved.
The search for early therapsids
Fine-tuning the evolution of therapsids during the early part of the Permian Period (299 million to 252 million years ago) is particularly important for tracing the ancestry of mammals, said Roger Benson, Macaulay Curator of Dinosaur Paleobiology at the American Museum of Natural History in New York City.
“Everything from the early Permian on the mammal line is outside of this group Therapsida, and all our knowledge of therapsids comes from the middle Permian and later,” said Benson, who was not involved in the research. “But paleontologists have long suspected there were therapsids before the middle Permian — we just didn’t find their fossils yet. This fossil is the most promising candidate for an early Permian therapsid so far.”
The location of the find was also unusual. Gorgonopsid fossils were previously known only from arid, high-latitude sites in South Africa and Russia, the study authors reported. During the Permian, Mallorca was smack in the middle of the supercontinent Pangea, which existed from 335 million to 200 million years ago. In this equatorial zone, what’s now Mallorca would have experienced very wet and very dry seasons.
“One of the things people have wondered is if maybe important events in mammal ancestry took place in the tropics, and we’ve been missing fossils of these types of animals at the right age to know about that,” Benson said.
“That’s one of the intriguing implications of this fossil, is the potential that important events in mammal ancestry occurred at lower latitudes in environments that we haven’t sampled so much in the fossil record.”
Finding the oldest documented gorgonopsian in Mallorca hints that the earliest therapsid fossils are yet to be discovered in places where paleontologists previously didn’t look for them, Angielczyk said.
“It’s long been thought that the big temporal gap in the therapsid fossil record might correspond to more geographic sampling,” he said. “The fact that Mallorca is a new place for finding therapsids helps to support that idea that we’re not necessarily looking in the right places to find the first therapsids.”
Editor's note: Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American and How It Works magazine.
