The earliest known prehistoric saber-toothed predator, living west of the Rocky Mountains millions of years ago, has been described for the first time.
Dubbed Diegoaelurus vanvalkenburghae, the cat-like predator was hyper-carnivorous, subsisting entirely on meat. Like the larger and better known saber-tooth cat, called Smilodon, it had saber-like teeth in its jaws, as did unrelated species much later on.
“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 researcher Ashley Poust of the San Diego Natural History Museum.
“One big advance was to evolve specialized teeth for slicing flesh, which is something we see in this newly described specimen.”
Poust is a co-author of a study on D. vanvalkenburghae, published online in the journal Peer J Zoological Science.
“Nothing like this had existed in mammals before,” said 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.”
A fossilized mandible, or lower jaw, of Diegoaelurus is part of a collection of fossils held at the San Diego institution. The fossil jaw also features teeth that give evidence on the evolution of mammals that prefer a diet based on meat.
The mammal lived during the Eocene Period, about 42 million years ago. Diegoaelurus and its relatives ranged from Wyoming in the United States to China. In life, the D. vanvalkenburghae was about the size of a modern bobcat and had a drooping, bony chin to protect its saber teeth. On the San Diego Natural History Museum’s website, visitors can view the fossil in 3D.
By contrast, Smilodon lived during the much later Pleistocene period, which featured various advances and retreats of glaciation and lasted from about 2.5 million to 12,000 years ago. During the Pleistocene period, other megafauna such as the mammoth, horses, giant ground sloth, giant buffalo, cave bear and giant armadillo-like glyptodonts thrived in the Americas.
Diegoaelurus is categorized under the Machaeroidines: a mysterious and now-extinct group of early mammals that are not closely related to modern carnivores. “We know so little about Machaeroidines, so every new discovery greatly expands our picture of them,” said lead author Shawn Zack of the University of Arizona.
Zack added that the fossil he and his colleagues had examined was especially useful because from the teeth, researchers can infer the creature’s diet and understand how Machaeroidines are related to each other.
D. vanvalkenburghae may have been the first to engage in hypercarnivory, which is a trait shared by modern cats. And Machaeroidines as a whole are known only by the very few specimens found in China and North America.
Zack concluded that Machaeroidines were more diverse than previously thought. He said that while a large form of Machaeroidines, the Apataelurus, was already known, the smaller Diegoaelurus was contemporaneous and raises the possibility that there were others like it.
Other saber-toothed animals may have also roamed the Earth at the same time. Poust said that Diegoaelurus may have crossed paths with the nimravids, or saber-tooth false-cats, which were the next cat-like creatures to enter North America more or less contemporaneously.
“Did these groups ever meet or even compete for space and prey?” Poust said. “We don’t know yet, but San Diego is proving to be a surprisingly important place for carnivore evolution.”
The Diegoaelurus fossil was found hidden in the 42-million-year-old rocks of a larger group called the Santiago Formation in San Diego County, California. The fossilized remains of an entire ecosystem have been found, giving evidence that the area was much wetter and warmer at the time. In addition, due to tectonic plate movements, San Diego was further south than it is today.
“The Santiago Formation fossils show us a forested, wet California where tiny rhinos, early tapirs and strange sheep-like, herbivorous oreodonts grazed under trees while unusual primates and marsupials clung to the canopy above. This richness of prey species would have been a smorgasbord for Diegoaelurus, allowing it to live the life of a specialized hunter before most other mammals,” said Poust.
Edited by Siân Speakman and Kristen Butler