Nimravus sp.
Family: Nimravidae

Time
This family of extinct cat-like mammals lived during Oligocene to Miocene time, between 33 to 8 million years ago. The genus Nimravus became extinct about 20 million years ago.

Place
Europe, Asia and North America

In Our Region
EastLake in Chula Vista, California.

Eusmilus sp. cast skull Cat-like mammal John Day Formation, Oregon

Description
Nimravids have many cat-like similarities, but paleontologists do not classify them as true cats. Differences in important features of the ear region set them apart from modern cats (which are first seen in the fossil record only after about 30 million years ago.) With their short faced skull, nimravids displayed a somewhat heavy-set body on relatively short legs, with long necks and enlarged and sharpened claws. Most of them had short tails.

However, nimravids' most conspicuous feature was their saber-like teeth. These long, curved, enlarged upper canines are good examples of the process of convergent evolution. Several other carnivores evolved similar teeth, including some true cats and even a marsupial sabertoothed Thylacosmilus from Argentina.

The superficial similarities of these saber teeth might seem to imply a close evolutionary relationship between all these animals. Instead, the teeth have evolved in different lineages in response to the environmental challenges of an exclusively meat-eating diet.

An Inside Look Only a few fossils of Nimravus sp. have been discovered in the Oligocene sandstones at Eastlake. Whether this means that the species was uncommon is unknown. Other possible explanations are that Nimravus spent much of its time in habitats less likely to preserve its remains, or perhaps this predator was only a seasonal visitor to the area. Nimravus sp., lower jaws Cat-like mammal SDNHM specimen no. 31242

Ecology
Robustly built nimravids hunted medium to large prey animals. Opinions vary about their use of the fearsome saber teeth. Did they deliver a single, fatal wound to the soft underbelly of the prey, and wait for the animal to bleed to death? Or did they subdue the prey first with powerful front limbs and inflict a precise killing bite to the throat, crushing the windpipe and severing blood vessels? Both methods seem plausible.

The nimravids, unlike the early dogs, had limbs not adapted for sustained running, but would have been capable of short bursts of speed with their powerful back extensor muscles and relatively short legs.

Fossils of Nimravus sp. found at EastLake occur as part of a diverse mammalian fauna that is dominated by herbivores. Especially common are fossils of the small oreodont, Sespia californica. Nimravus sp. may have been one of the principle predators of Sespia.

Suggested Reading
Agusti, Jordi and Mauricio Anton. 2002. Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe. NY: Columbia University Press.

Turner, Alan and Mauricio Anton. 1997. The Big Cats and their Fossil Relatives. NY: Columbia University Press.

Text: Lynett Gillette
Illustration: William Stout
Fossil photographs: Jim Melli