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Before cats ruled and dogs drooled, the hyaenodonts were the top carnivores prowling around. They came in all shapes and sizes, from bear-sized on down, at least until they were supplanted by the carnivorans we know and love today. How this shift happened is still a bit of a mystery, and a new fossil from Tanzania comes to us from right at the cusp of this big change.
There isn't much of the hyaenodont just yet. It's part of an upper jaw with a piece of tooth still embedded in it. But the 25 million year old fossil is distinctive enough that paleontologists Matthew Borths and Nancy Stevens have identified it as something new - a bobcat-sized hyaenodont they've named Pakakali.
Based on the fossil, as well as details from other hyaenodonts, Borths and Stevens hypothesize Pakakali ate small vertebrates and invertebrates. This made the little hunter different from other hyaenodonts of its time, some of which had teeth and jaws specialized for shearing meat and crushing bone. Yet the dog-, cat-, and hyena-like carnivorans of those days were similar to Pakakali in size and dental anatomy, meaning that they might have been competitors in the small generalist niche.
The overall picture, Borths and Stevens write, is that hyaenodonts accommodated their rivals by becoming more specialized and evolving into a different array of body sizes. And as hyaenodonts became more specialized, they became more vulnerable to sweeping environmental changes - they had unintentionally evolved themselves into a corner in response to carnivorans, with ecological disturbances to climate, forest makeup, and other shifts pulling the rug out from under them.
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Fossil Facts
Name: Pakakali rukwaensis
Meaning: Pakakali means "fierce cat" in Swahili, and rukwaensis is a nod to the Rukwa Rift Basin where the fossils were found.
Age: Oligocene, about 25.2 million years ago.
Where in the world?: Rukwa Rift Basin, Tanzania.
What sort of organism?: An extinct form of mammal called a hyaenodont.
How much of the organism’s is known?: Part of the upper jaw with a tooth.
References:
Borths, M., Stevens, N. 2017. The first hyaenodont from the late Oligocene Nsungwe Formation of Tanzania: Paleoecological insights into the Paleogene-Neogene carnivore transition. PLOS ONE. doi: 10.1371/journal.pone.0185301
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