When we think of apex predators, we usually think of large, fearsome beasts that can strike fear into the hearts of their prey with a single roar. So it might come as a surprise that one of the creatures that shot up to the top of the food chain following the dinosaurs' demise was no bigger than a skunk. Named after the jackal-faced Egyptian god of mummification Anubis, the rise and fall of Masrasector nananubis, whose 34-million-year-old fossilized remains were recently identified in Egypt, was also part of an epic evolutionary tale of climate change and continental drift.

Masrasector was part of a group of ancient mammals known as hyaenodonts (so named for their hyena-like teeth and not for any outward resemblance to the animal), which roamed much of the world from around 60 to 10 million years ago. That said, the hyaenodonts varied greatly in size; they were not all small like the Masrasector, with some being as large as rhinos. As a group, they were an evolutionary side branch unto themselves, preceding dogs, cats and other modern mammals, and ultimately dying out despite dominating the landscape for a good part of the Cenozoic era, also known as the Age of Mammals.

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While paleontologists have known about hyaenodonts for a while, what makes the discovery of the Masrasector significant is that the fossils comprise largely complete skulls, jaws, and parts of the skeleton, making them one of the most complete known African hyaenodonts from the Paleogene Period found to date. Previously, researchers only had isolated bone and teeth fragments to work on, making the hyaenodonts something of an enigma.

So, what can researchers deduce from these newly discovered fossils of the Masrasector? For a start, even though it had the kind of meat-slicing blades (incidentally, Masrasector means "the Egyptian Slicer") found in modern carnivores, it also had larger grinding surfaces on its teeth that allowed it to supplement its diet with other types of food, like fruits and nuts.

This in turn situates it within a sub-group of African hyaenodonts with omnivorous habits known as Teratodontinae, (which means "monstrous teeth"). The diversity in their diet was probably one of the reasons they were able to become one of the longest lived group of carnivores in Africa before going extinct some 15 million years ago, says study author and paleontologist Matthew Borths from Ohio University in an interview with Nature Middle East.

Secondly, given its skunk-like size and build – it was probably no heavier than 1.2 kg (2.5 lb) – the researchers believe that the creature was likely a fast moving animal that preyed on smaller mammals on the ground, based on comparisons of its limb bones with other carnivorous mammals.

While this doesn't sound like the kind of stuff that gets one's adrenaline flowing, what is significant about the Masrasector is its place in the grander scheme of things – the Age of Mammals was an evolutionary period marked by continental drift, climate change and the demise of species unable to adapt to these changes.

Back when they were still at the top of the food chain, Africa was an isolated continent, much like modern-day Australia. The L41 quarry in Egypt's Fayum Depression, the place where their fossils were found, may be a desert now, but back then it was a marshy mangrove forest. However, all this began to change when the African and Eurasian continents collided around 18 million years ago. One of the long-lasting effects of this was that it created a rift valley between north eastern Africa and western Arabia, cutting off the Mediterranean, which used to be closer to Cairo, from the Indian Ocean and kickstarting a chain of ecological changes in the process.

Not only did the Masrasector's habitat become warmer, but open grasslands also began replacing the shrinking forests. In addition, the collision of the two continents allowed true carnivorans, the group that includes today's dogs, cats and hyenas, to cross over into Africa, gradually edging them out as the continent's top predators.

That said, while these fossils might be the oldest and most complete ever discovered, there's still much that remains to be discovered as the fossils of other members of this group are "still really fragmentary", says Borths. On the bright side, the abundance of information on the Masrasector can now be used "as a cornerstone of character development" for exploring the evolution and diversity of other hyaenodonts.

"Hyaenodonts were the top predators in Africa after the extinction of the dinosaurs," he says. "This new species is associated with a dozen specimens, including skulls and arm bones, which means we can explore what it ate, how it moved, and consider why these carnivorous mammals died off as the relatives of dogs, cats, and hyenas moved into Africa."

The study was published in PLOS ONE.

Sources: PLOS via EurekAlert