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Three views of Megalictis: restoration, skull reconstruction, and original skull. Art by Adam Hartstone-Rose.

Paleo Profile: The Giant, Bone-Crushing Weasel

Some beasts catch you by surprise. I’m not talking about ambush predators – though such a statement would hold true – but rather prehistoric mammals whose very existence comes as something of a shock. The latest to make me go “What the hell?” is an enormous weasel that used to prowl western North America.

Paleontologist William Diller Matthew named carnivore Megalictis ferox way back in 1907. The mammal’s teeth and osteology clearly showed it to be a cousin of martens and stoats, yet their dimensions “indicate an animal which may best be described as a gigantic wolverene [sic], equaling a jaguar or a black bear in size.” And given that cats were meek little things at the time Megalictis lived, paleontologists thought that this weasel had evolved to take on a lion-like lifestyle during North America’s long Cat Gap.

But now paleontologist Alberto Valenciano and colleagues have discovered that Megalictis was no feline wannabe. Through a new analysis of previously-undescribed skull material, the researchers not only refine the evolutionary relationships of America’s giant weasels, but they also make the case that the teeth and jaws of Megalictis were more like those of hyenas and some deep-jawed dogs than to cats. In other words, this huge weasel was a bone-crusher.

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Additional Megalictis skull material. From Valenciano et al., 2016.

Fossil Facts

Name: Megalictis ferox

Meaning: The entire name translates roughly to “fierce giant wolverine.”

Age: Between 22.7 and 18.5 million years ago.

Where in the world?: South Dakota, Nebraska, and Wyoming.

What sort of critter?: A mustelid, or a member of the group that includes weasels and their relatives.

Size: Estimated as being about the size of a jaguar.

How much of the creature’s body is known?: The new study focused on skull material from several individuals, including a nearly-complete cranium and almost-perfect lower jaws.


Matthew, W. 1907. A lower Miocene fauna from South Dakota. Bulletin of the American Museum of Natural History. 23 (9): 169-219

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