What a mouthful – new sabre-tooth predator named

Palaeontologists have described a new species of sabre-toothed mammal (Diegoaelurus vanvalkenburghae) from a sabre-toothed jaw-bone fossil originally unearthed in 1988. Dating to the Eocene Epoch, it was alive 42 million years ago – preceding modern cats by millions of years.

This new discovery, published in PeerJ, gives us insight into the behaviour and evolution of some of the first mammals to have an exclusively meat-based diet. The specimen includes a lower jaw and well-preserved teeth and is the earliest known cat-like predator in North America.

“Today the ability to eat an all-meat diet, also called hypercarnivory, isn’t uncommon,” says co-author Dr Ashley Poust, researcher from the San Diego Natural History Museum (The Nat) in the U.S. “Tigers do it, polar bears can do it. If you have a house cat, you may even have a hypercarnivore at home.

“But 42 million years ago, mammals were only just figuring out how to survive on meat alone. One big advance was to evolve specialized teeth for slicing flesh—which is something we see in this newly described specimen.”

The fossil comes from a location first discovered in the 1980s by a 12-year-old boy in San Diego County, southern California, USA. Since then, “Jeff’s Discovery Site” has become an important fossil bed within a larger group of rocks called the Santiago Formation. The sabre-toothed jawbone fossil, which you is available for interest and study online as an interactive 3D model, has been in The Nat’s collection since 1988 but was only recently described.

Fossil in collection 3
The Diegoaelurus jawbone fossil has been in The Nat’s collection since 1988. It was recovered from a construction site in Oceanside by the museum’s PaleoServices team. When this carnivorous animal was alive 42 million years ago, San Diego was covered in rainforests populated by many small, unusual rodents, marsupials, primates and hooved mammals. Credit: San Diego Natural History Museum

D. vanvalkenburghae would have been a powerful and relatively new kind of hunter about the size of a modern-day bobcat, with a downturned bony chin to protect its long upper sabre-teeth.

“Nothing like this had existed in mammals before,” says Poust. “A few mammal ancestors had long fangs, but Diegoaelurus and its few relatives represent the first cat-like approach to an all-meat diet, with sabre-teeth in front and slicing scissor teeth – called carnassials – in the back.

“It’s a potent combination that several animal groups have independently evolved in the millions of years since.”

D. vanvalkenburghae is part of a mysterious group of now extinct animals called Machaeroidines – the oldest known saber-toothed mammalian carnivore – which are poorly understood due to their very limited fossil record. They are part of the family Felidae (true cats), and although they are not the ancestors of modern-day cats they do share a common ancestor.

Another example of a slightly more famous Machaeroidine is Smilodon (sabre-toothed tiger) that evolved roughly 40 million years after D. vanvalkenburghae went extinct.

Sabre-toothed mammal. Dr ashley poust holds the jaw fossil in front of a smilodon skull.
Dr Ashley Poust, a post-doctoral researcher at The Nat, has just described what is now the earliest known cat-like predator in North America, west of the Rocky Mountains. The fossil in his hand belonged to Diegoaelurus, a bobcat-sized carnivore that lived around 42 million years ago. Diegoaelurus was much smaller than the commonly known Smilodon, or sabre-tooth cat, seen in the background. Smilodon evolved roughly 40 million years after Diegoaelurus went extinct, but both animals were saber-toothed, hyper-carnivorous predators, meaning their diets consisted almost entirely of meat. Diegoaelurus and its few relatives, from Wyoming and China, were the first predators to evolve sabre-teeth, though several other unrelated animals developed this adaptation much later in time. Credit: San Diego Natural History Museum

“We know so little about Machaeroidines, so every new discovery greatly expands our picture of them,” says co-author Dr Shawn Zack, of the University of Arizona College of Medicine, USA. “This relatively complete, well-preserved Diegoaelurus fossil is especially useful because the teeth let us infer the diet and start to understand how Machaeroidines are related to each other.”

Because there are only a handful of machaeroidine fossil specimens – unearthed in the U.S. and China – scientists previously weren’t even sure if there were multiple species living within the same time period.

“This fossil finding shows that machaeroidines were more diverse than we thought,” says Zack. “We already knew there was a large form, Apataelurus, which lived in eastern Utah. Now we have this smaller form, and it lived at approximately the same time.

“It raises the possibility that there may more out there to find.”

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