Meet the crazy beast that lived among the dinosaurs

A strange, 66-million-year-old mammal described in new research offers new insights into the evolutionary history of mammals on the Gondwana supercontinent.

Called Adalatherium, which translated from Malagasy and Greek means “crazy beast”, it is described on the basis of an almost complete and preserved refined skeleton, the most complete for any mammal discovered so far in the southern hemisphere before the extinction of dinosaurs. .

Research now published in the Journal of Vertebrate Paleontology over 20 years shows that Adalatherium was a “giant” compared to mammals, most often the size of a mouse or mouse, that lived during concerned. Cretaceous.

Their “strange” features include more trunk vertebrae than most other mammals, muscular hind limbs that have been placed in a more extended position (similar to modern crocodiles), along with fast, muscular front legs that have been hidden under body (as seen in most mammals today), the front teeth, like those of a rabbit, and the back teeth, completely different from any other known mammal, alive or extinct, and a strange space in the bones at the top of the snout .

A team of 14 international researchers led by Dr. David Krause (Denver Museum of Nature and Science) and Dr. Simone Hoffmann (New York Institute of Technology) published the full description and analysis of this one-size-fits-all mammal. opossum that lived among massive dinosaurs and crocodiles near the end of the Cretaceous period (145-66 million years ago) in Madagascar. The initial announcement of the discovery was made in the journal Nature earlier this year.

Adalatherium, from Madagascar, belongs to an extinct group of mammals known as gondwanatherians, which were first discovered in the 1980s and, until recently, were represented by only a few isolated teeth and jaw fragments. But even those few remains have already indicated that Gondwanatians were very different from other contemporary mammals. So many mysteries had surrounded the Gondwanatherians that it was unclear how they fit into the mammal family tree.

Now, the team of researchers reveals the first skeleton of this mysterious group that once crossed much of South America, Africa, Madagascar, the Indian subcontinent and even Antarctica.

The integrity and excellent preservation of the Adalatherium skeleton open new windows on how the Gondwanatherians were and how they lived, but the strange features still hampered the team.

“Knowing what we know about the skeletal anatomy of all living and extinct mammals, it is hard to imagine that a mammal like Adalatherium could have evolved; he questions and even breaks a lot of rules, ”Krause explains.

Although the realistic reconstruction of Adalatherium is superficially similar to a common badger, its “normality” is only superficial. Beneath the surface, its skeleton is nothing more than extravagant.

As Hoffmann says, “Adalatherium is just weird. Trying to find out how it moved, for example, was a challenge, because its interface tells us a completely different story from the one on the back ”.

While the muscular hind legs and large claws on the hind legs may indicate that Adalatherium was a strong burrower (like badgers), its front legs were less muscular and more similar to those of live mammals that can run fast. .

Adalatherium limbs also indicate that its position was a hybrid between those of living mammals and older relatives. The forelimbs were hidden under the body (as seen in most mammals today), but the hind limbs were wider (as in crocodiles and lizards).

Adalatherium teeth, reconstructed by high-resolution computed tomography and extensive digital modeling, are indicative of herbivore, but otherwise more than bizarre.

Adalatherium not only had constantly growing front teeth, similar to those of a rabbit or a rodent, but its back teeth are completely different from those of any other known, living or extinct mammal. If these teeth had been found, the mystery of what this animal is would probably not have been solved! In addition to the apparent chaos, there is a hole in the top of the snout for which there is simply no parallel.

About the size of a Virginia opossum, the 3.1-kilogram Adalatherium was very large for its time. Although not particularly large by current standards, it was a giant compared to beetle and mouse mammals that lived in the Cretaceous.

The geological history of Gondwana provides clues as to why Adalatherium is so strange.

Adalatherium was found in rocks dating to the end of the Cretaceous, about 66 million years ago. At that time, Madagascar had already been an island separated from Africa for over 150 million years and from the Indian subcontinent for over 20 million years. “The islands are the strange thing,” says Krause, “and therefore there was enough time for Adalatherium to develop its many extraordinarily special features in isolation.”