‘Crazy beast’ fossil discovery shows the evolutionary weirdness of early mammals

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Researchers have uncovered the fossil of an early mammal named the “crazy beast” that lived 66 million years ago on Madagascar, and it’s unlike any mammal ever known, living or extinct.

This mammal, about the size of an opossum, had a mix of strange characteristics that haven’t been seen together before. It highlights evolutionary strangeness that can arise from evolution when it occurs in isolation on islands like Madagascar, which is home to other species, living and extinct, found nowhere else in the world.

The mammal is the most complete and well preserved skeleton of a gondwanatherian, which is a mammal that lived on the ancient southern supercontinent Gondwana, which is now the continents of the southern hemisphere.

Fossils from the Mesozoic era, between 65 million and 252 million years ago, are sparse from Gondwana, largely including items such as a single skull, bits of jaw bone and teeth.

But this mammal, which looks a bit like a badger in the artist rendering based on the skeleton, is so well preserved that it includes cartilaginous tissue, small bones and the creature’s short tail.

The researchers named it Adalatherium hui, a hybrid name that combines the Malagasy word for “crazy” and the Greek word for “beast.” Hui is a nod to the late Yaoming Hu, a study co-author at Stony Brook University.

They believe this particular creature was a juvenile, weighing around seven pounds. But compared to the other Gondwana mammals living at the time, which were the size of mice, it was quite large. And it lived among dinosaurs and ancient crocodiles before the asteroid impact wiped them all out 66 million years ago at the end of the Cretaceous period.

It was also incredibly weird.

“Knowing what we know about the skeletal anatomy of all living and extinct mammals, it is difficult to imagine that a mammal like Adalatherium could have evolved; it bends and even breaks a lot of rules,” said David Krause, lead study author, senior curator of vertebrate paleontology at the Denver Museum of Nature & Science and professor emeritus at Stony Brook University.

The study published Wednesday in the journal Nature.

The skeleton contains a number of strange features that researchers can’t quite figure out.

For instance, Adalatherium had more holes on its face than any known mammal, Krause said in a press call Tuesday. These holes, called foramina, created pathways for blood vessels and nerves, leading to an incredibly sensitive snout that was covered in whiskers. It also had a large hole at the top of the snout that can’t be compared to any known mammal that ever lived or is currently living.

Its teeth can’t be compared with anything else either. They’re structured in a strange way that can’t be explained. Krause said its back teeth “are from outer space.”

The animal’s backbone contained more vertebrae than any known mammal from the Mesozoic era. And it must have walked in a strange way, because the front half of the animal doesn’t match the back half. And one of its back legs was bowed.

The forearms and shoulders can be compared to cats and dogs, meaning they were placed under the body — very unusual for early mammals who walked more like reptiles, said Simone Hoffmann, study co-author and assistant professor at the New York Institute of Technology’s department of anthropology.

But the hind legs are the opposite pattern, suggesting that the legs spread out and had more sprawling knee joints like reptiles. Two patterns in one animal means that it walked very differently than anything living today, Hoffman said. But they believe it was capable of running, in addition to other ways of moving.

Adalatherium also had strong, long claws on its back legs, suggesting that it dug using its hind legs.

“Adalatherium is the oddest of oddballs,” Hoffmann said. “Trying to figure out how it moved is nearly impossible because, for instance, its front end is telling us a different story than its back end.”


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