Simbakubwa kutokaafrika had three rows of meat-shearing teeth and was larger than a polar bear.Credit: Mauricio Anton

Lions have long held the unofficial title ‘king of the beasts’, but a newfound carnivore from ancient Africa might have proved a worthy challenger for the throne.

The enormous predator, named Simbakubwa kutokaafrika — “big lion from Africa” in Swahili — is described1 on 18 April in the Journal of Vertebrate Paleontology. It roamed what is now Kenya around 22 million years ago and was probably larger than a polar bear.

But don’t let its name fool you: Simbakubwa was not a cat, but one of a group of animals called hyaenodonts that includes some of the biggest predatory mammals ever to walk on Earth. Hyaenodonts were the top carnivores before hyaenas, cats, dogs and bears staged their global takeover.

The Simbakubwa fossil described in the study was unearthed sometime between 1978 and 1981. But its true identity escaped researchers until 2013, when palaeontologist Matt Borths was poking through the fossil-mammal collection at the Nairobi National Museum in Kenya. Borths, who was visiting from the Duke Lemur Center in Durham, North Carolina, spotted the jaw of a huge prehistoric carnivore. The bone was so big that it had to be archived on special shelving.

“I was shocked when I first pulled open the drawer,” Borths says. He recognized the jaw as that of a hyaenodont, but it was much larger and more complete than most examples he’d seen before, and in better condition. “The specimens are so beautifully preserved,” Borths says, down to the shearing edges of the carnivore’s teeth.

He joined forces with Nancy Stevens, a palaeontologist at Ohio University in Athens who he knew had studied fossils from the same site where Simbakubwa was found. The two worked together to study the giant carnivore.

Heather Ahrens, a palaeontologist at High Point University in North Carolina, agrees that “numerous characteristics differentiate Simbakubwa” from previously known giant hyaenodonts, adding another species to the list of these large, extinct carnivores.

Fearsome find

Simbakubwa and other giant hyaenodonts, such as Megistotherium, were a very different form of carnivore from their modern brethren. Whereas modern carnivores have a single row of back teeth that are arranged to chew meat, hyaenodonts had three sets of meat-slicing teeth. “All those extra blades gave them a relatively long jaw that made their heads look a little too big for their bodies,” Borths says. “I imagine them looking a bit like the wargs from Lord of the Rings.”

The ancient carnivore Simbakubwa kutokaafrika is shown here next to a person for size comparison.Credit: Mauricio Anton

This dental arsenal aided giant hyaenodonts’ expansion from Africa into Eurasia. The giant beasts became top predators in their habitats — but that can be a precarious position.

The hyaenodonts’ eventual demise wasn’t prompted by any anatomical fault, Borths says. Rather, the carnivores could have succumbed to dramatic climate change. Giant hyaenodonts likely preyed on large herbivores such as early elephants, hippopotamus relatives called anthracotheres, and giant hyraxes. When increasingly sharp swings between wet and dry seasons spurred the spread of grasslands about 10 million years ago, hyaenodonts' preferred prey might have become scarce or disappeared altogether.

Carnivore clues

Nevertheless, Ahrens says that palaeontologists shouldn’t pity hyaenodonts. “I think this study highlights the importance of recognizing our modern bias in assessing the success of extinct clades,” or lineages, she says.

Giant hyaenodonts, in particular, persisted for 15 million years, part of a larger and even longer-lived family that stretches back more than 56 million years. Simbakubwa might have looked like a monster from a J. R. R. Tolkien novel, but it belonged to one of the most successful carnivore dynasties of all time.

The fossil find is valuable in another way, too — as a reminder, Borth says, of the discoveries lurking in museums’ specimen troves. Last month, for example, a different team of researchers described a new species2 of North American mastodon from fossils that had sat unrecognized in the collections of the Western Science Center in Hemet, California for nearly two decades.

“There are tons, probably literally, of new species lurking in museum collections,” says Borths.