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