In the eons before dinosaurs roamed the Earth, and tens of millions of years prior to the emergence of the first mammals, the land was ruled by distant relatives of mammals, known as gorgonopsians. These formidable carnivores, characterized by their long, serrated canine teeth, were the apex predators of their time.

However, the earliest members of this lineage had long eluded the fossil record—until now. The discovery of a newly identified gorgonopsian, the oldest saber-toothed animal ever found, is bridging a significant gap in our understanding of this group's history.

These slender hunters are primarily known from bones that are less than 270 million years old, but the recent fossil find is believed 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, which includes not only gorgonopsians but also the ancestors of modern mammals and other nonmammalian groups that are now extinct. This finding is a crucial puzzle piece that could help shed light on the earliest forebears of mammals, according to experts.

Gorgonopsians vanished around 252 million years ago, and their lineage died with them. All gorgonopsians possessed dagger-like canine teeth, and species ranged widely in size, from cat-sized creatures to those as large as polar bears. The newly described gorgonopsian's fossils included its knife-like canines, parts of its jaw, some vertebrae, ribs, tailbones, and toe bones, as well as most of the bones from a hind limb, as reported in the journal Nature Communications.

The specimen’s blunt-snouted skull was incomplete but is estimated to measure about 7 inches (18 centimeters) long. 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.

Despite being four-legged and having a long tail, the gorgonopsian wouldn't have resembled a dog in many aspects, Angielczyk noted. Like reptiles, gorgonopsians lacked fur or visible ears. However, while the animal physically resembled lizards in some ways, it is important not to confuse it with a “lizard-dog,” as they belong to a completely different evolutionary lineage, part of the lineage that includes mammals.

Gorgonopsians share some traits with their mammal cousins, such as having teeth of different shapes and sizes, providing different roles in the feeding system—a feature 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."

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. "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 in an email.

The new specimen, which dates back at least to that point in time and is likely even older, aligns with the gap in the therapsid fossil record, helping researchers to clarify when therapsids evolved. 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.

"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 Roger Benson, Macaulay Curator of Dinosaur Paleobiology at the American Museum of Natural History in New York City.

The location of the find was also unusual, as gorgonopsid fossils were previously known only from arid, high-latitude sites in South Africa and Russia. During the Permian, Mallorca was 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. "It’s long been thought that the big temporal gap in the therapsid fossil record might correspond to more geographic sampling," Angielczyk 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." This discovery not only expands our knowledge of the gorgonopsians but also offers a tantalizing glimpse into the early chapters of mammalian evolution.