A ‘crazy beast’ from the time of dinosaurs belongs to an obscure mammal group

A bizarre fossil provides a better look at a little-known group called gondwanatherians

gondwanatherian

Paleontologists finally have identified an odd fossil found in 1999 as a new species of gondwanatherian — an enigmatic group of mammals that lived in the Southern Hemisphere during the age of dinosaurs.

Andrey Atuchin

The ancient mammal Adalatherium hui is so weird that it eluded classification for over a decade.

A roughly 70-million-year-old skeleton of the species, uncovered in Madagascar in 1999, was clearly a mammal. But it boasted several distinctly un-mammalian features, such as a large hole on top of its snout. Also, although the animal’s forelimbs were aligned with its spine, like a typical mammal, its back legs were splayed out to the sides like a reptile.

“It is so strange, compared to any other mammal, living or extinct,” says paleontologist David Krause, of the Denver Museum of Nature & Science, “it was just crazy.” Hence the name Adalatherium hui, from a Malagasy word meaning “crazy” and the Greek word for “beast.”

Now, the crazy beast finally has been identified as a gondwanatherian — an obscure group of mammals that roamed the Southern Hemisphere during the age of dinosaurs, Krause and colleagues report online April 29 in Nature. The key to the animal’s identity was in comparing the skeleton to an intact skull from a different gondwanatherian species, discovered in 2014 also in Madagascar. The arrangement of bones in the snout of the skull matched that of Adalatherium hui, establishing the animals as relatives.

Adalatherium hui fossil
Judging by this fossilized skeleton of Adalatherium hui, “we think it was probably a digging animal, much like a badger,” says paleontologist David Krause of the Denver Museum of Nature & Science. Badgers spread their hind legs and use their front legs to shoot dirt between them. The splayed hind legs of Adalatherium hui might be good for that. What’s more, Krause says, “badgers have these tiny little stubby tails so it doesn’t get in the way of the dirt flying backward, and Adalatherium hui also has a short, stubby tail.”Marylou Stewart

Placing Adalatherium hui among the gondwanatherians gives new insight into how this enigmatic group of animals fit into the mammal family tree. Up to 2014, the only other known traces of gondwanatherians were a handful of teeth and jaws. Given the historically sparse fossil record for gondwanatherians, “we knew very little about their anatomy,” and therefore how they were related to other ancient animals, Krause says.

But the features of Adalatherium hui’s nearly complete skeleton reveal that it was closely related to a group of mammals called multituberculates, which lived in the Northern Hemisphere during the age of the dinosaurs (SN: 12/14/96). “It’s almost like we have a southern counterpart to the multituberculates” in the gondwanatherians, he says.

Try saying that 10 times fast.

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