Ancient sabre-tooth sheds light on the evolution of hypercarnivores

A recent study published in the journal PeerJ has described the fossils of a sabre-toothed mammal (Diegoaelurus vanvalkenburghae) that lived during the early Eocene, approximately 40 million years ago. The specimen included a lower jaw and well-preserved teeth, thus offering crucial information about the evolution of the first hypercarnivores, or animals that have a predominantly meat-based diet.

“Today the ability to eat an all-meat diet, also called hypercarnivory, isn’t uncommon. 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,” said study lead author Dr. Ashley Poust, a postdoctoral researcher at the San Diego Natural History Museum (The Nat). “One big advance was to evolve specialized teeth for slicing flesh – which is something we see in this newly described specimen.”

The specimen was discovered in the Santiago Formation, a region in the San Diego County in Southern California containing 42-million-old rocks with a large number of fossils including early tapirs, strange sheep-like, herbivorous oreodonts, and tiny rhinos.

D. vanvalkenburghae is part of a mysterious group of animals called Machaeroidines that are now completely extinct and are not closely related to today’s living predators. 

“We know so little about Machaeroidines, so every new discovery greatly expands our picture of them,” said study co-author Dr. Shawn Zack, a postdoctoral fellow in Anatomy at the University of Arizona College of Medicine. “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.”

This ancient hypercarnivore was about the size of a bobcat, but had a downturned bony chin protecting its sabre teeth. 

“Nothing like this had existed in mammals before. 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,” explained Dr. Poust.

According to the scientists, this mammal and its relatives were an evolutionary experiment, a first stab at a hypercarnivorous lifestyle. It is one of the most recent machaeroidine predators and precedes other cat-like animals such as the nimravids or sabre-tooth false-cats. The richness of prey species co-existing with it in the San Diego County 40 million years ago most probably allowed it to live the life of a specialized hunter before most other mammals. 

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By Andrei Ionescu, Earth.com Staff Writer