Long before the era of dinosaurs and millions of years prior to the emergence of the first mammals, a group of distant relatives of mammals, known as gorgonopsians, ruled the land as the dominant carnivores. These creatures, characterized by their elongated, serrated canine teeth, had been absent from the fossil record for the earliest members of their lineage. However, a recent discovery has unveiled the oldest saber-toothed animal ever identified, bridging a significant gap in our understanding of gorgonopsian history. While the majority of known gorgonopsian remains are less than 270 million years old, this new find is estimated to be astonishingly between 280 million and 270 million years old.

This newly identified gorgonopsian is a crucial addition to the early branches of the therapsid family tree. The Therapsida order encompasses not only gorgonopsians but also the forebears of today's mammals and other extinct nonmammalian groups. This discovery is a significant piece of the puzzle that may offer insights into the earliest ancestors of mammals, according to experts. Gorgonopsians became extinct around 252 million years ago, taking their lineage with them. All members of this group possessed dagger-like canine teeth, and their sizes varied greatly, with some species being as small as domestic cats and others as large as polar bears.

The fossils of this newly described gorgonopsian include its characteristic knife-like canines, portions of the jaw, some vertebrae, ribs, tailbones, and toe bones, as well as most of the bones from a hind limb, as detailed by researchers in the journal Nature Communications. The incomplete but estimated 7-inch (18 centimeter) long blunt-snouted skull suggests an animal that stood as tall as a medium-sized dog and weighed approximately 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 quadrupedal and having a long tail, the gorgonopsian bore little resemblance to dogs, as it lacked fur and visible ears, similar to reptiles.

It is important to note that while gorgonopsians share some physical traits with lizards, they are not to be confused with "lizard-dogs." Angielczyk clarifies, "Lizards are a type of reptile, whereas nonmammalian therapsids like gorgonopsians belong to a distinct evolutionary lineage, one that also includes mammals." Although mammals and reptiles share a common ancestor dating back about 320 million years, they have since diverged into separate evolutionary lines.

Gorgonopsians share a notable trait with their mammalian relatives: their teeth come in various shapes and sizes, each serving a different function in their feeding system, a feature common in modern mammals. Unlike mammals, which typically have one set of teeth replacements, gorgonopsians, like crocodiles, continuously had new teeth emerging throughout their lives.

The bones of this ancient gorgonopsian were unearthed in Mallorca, a Spanish Mediterranean island, during expeditions conducted in 2019 and 2021, as reported by senior study author Josep Fortuny, head of the computational biomechanics and evolution of life history research group at the Miquel Crusafont Catalan Institute of Paleontology in Spain. Fortuny highlighted the specimen's age as the most intriguing aspect, stating, "It is almost certainly the oldest known gorgonopsian and the oldest known therapsid to date."

There has been a significant temporal gap in the therapsid fossil record, with scientists previously calculating that therapsid fossils should appear in rocks around 300 million years old. However, until now, they have only been found in rocks dating back to about 270 million years ago. This new specimen, dating back at least to that time and likely even older, helps to bridge this gap and clarifies the evolutionary timeline of therapsids.

Refining the evolutionary history of therapsids during the early Permian Period (299 million to 252 million years ago) is crucial for tracing the ancestry of mammals, according to Roger Benson, Macaulay Curator of Dinosaur Paleobiology at the American Museum of Natural History in New York City. Benson, who was not part of the research, noted, "Everything from the early Permian on the mammal lineage is outside of the Therapsida group, and our knowledge of therapsids comes from the middle Permian and later periods. However, paleontologists have long suspected the existence of therapsids before the middle Permian; we just hadn't found their fossils yet. This fossil is the most promising candidate for an early Permian therapsid discovered so far."

The discovery's location is also of particular interest. Gorgonopsid fossils were previously only known from arid, high-latitude sites in South Africa and Russia. During the Permian, Mallorca was situated in the equatorial region of the supercontinent Pangea, which existed from 335 million to 200 million years ago. This area would have experienced alternating wet and dry seasons.

Benson suggests that the find raises the possibility that important events in mammal ancestry may have occurred in the tropics, in environments that have been underrepresented in the fossil record. "One of the intriguing implications of this fossil is the potential that significant events in mammal ancestry took place at lower latitudes," he said. "This discovery in Mallorca indicates that the earliest therapsid fossils may still be waiting to be found in locations where paleontologists have not previously searched," Angielczyk added. "The large temporal gap in the therapsid fossil record might correspond to a need for more geographic sampling, and the discovery in Mallorca supports the idea that we may not be looking in the right places to find the first therapsids."