Dog-Like Predator's Bones Belong to Oldest Known Mammal Relative

Before the time of the dinosaurs, a naked, warm-blooded egg-layer known as a gorgonopsian sipped water from Pangea's tropical floodplains amid herb-grazing reptiles off what's now Mallorca in the Mediterranean.

Its death 270 million years ago may provide us with a critical glimpse into our own evolution. Paleontologists suspect it might be the oldest gorgonopsian specimen on record – up to 15 million years older than any previously studied – making it the earliest known example of a mammalian relative.

Though the remains are incomplete, the variety of bones surprised the paleontologists who found them. The fossils include fragments of skull, vertebrae, and ribs, as well as a well-preserved femur, providing vital details on the diversification of what would become the first true mammals.

Replica of the left femur of the gorgonopsian from Mallorca. (Anna Solé/Institut Català de Paleontologia Miquel Crusafont/CC BY-ND)

"Gorgonopsians are more closely related to mammals than they are to any other living animals," says Ken Angielczy, a paleomammalogist from the Field Museum of Natural History in the US. "They don't have any modern descendants, and while they're not our direct ancestors, they're related to species that were our direct ancestors."

While gorgonopsians lacked external ears, they had a precursor feature in their jawbone that later developed into our characteristic mammalian ear bones. Their legs are also positioned more under their bodies than the side-splayed reptilian legs of our older, non-mammalian ancestors.

"If you saw this animal walking down the street, it would look a little bit like a medium-sized dog, maybe about the size of a husky, but it wouldn't be quite right," explains Angielczy. "It didn't have any fur, and it wouldn't have had dog-like ears."

Gorgonopsia's family tree. (Matamales-Andreu et al, Nature Communications, 2024)

Just like mammals today, this this 1 meter (3 foot) long gorgonopsian had jaw-muscle attachment holes on the sides of their skull.

These fossils paint a detailed picture of what's also the earliest known saber-toothed animal. This tooth arrangement suggests gorgonopsians were the superpredators of their time, likely devouring the herbivorous, ancient lizard-like creature, Tramuntanasaurus tiai, whose bones were found at the same fossil site.

Ancient 270-million-year-old reptile, Tramuntanasaurus tiai, found in the same region. (ICP)

"The saber teeth are a common feature in large predators of ecosystems, and what we have found was likely one in the environment in which it lived," says ICP paleontologist Àngel Galobart. "We know that this is a carnivorous animal, a characteristic shared by all gorgonopsians worldwide."

The team suspects the mass extinction event that occurred 273 million years ago, Olson's Extinction, may have provided the ecological space for gorgonopsian and other mammalian ancestors to grow into and flourish, planting the seeds for our later evolution once the dinosaurs had their turn.

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That this discovery was unexpectedly found in what was a tropical region suggests there may be more clues on the origins of mammals in these regions too.

"Before the time of dinosaurs, there was an age of ancient mammal relatives. Most of those ancient mammal relatives looked really different from what we think of mammals looking like today," says Angielczyk.

"But they were really diverse and played lots of different ecological roles. The discovery of this new fossil is another piece of the puzzle for how mammals evolved."

This research was published in Nature Communications.