The ‘crazy beast’ that lived among the dinosaurs

New research published in the Journal of Vertebrate Paleontology describes a bizarre 66 million year old mammal that offers profound new insights into the evolutionary history of mammals of the southern supercontinent Gondwana – now recognized as Africa, South America, Australia, Antarctica, the Indian subcontinent and the Arabian Peninsula.

Called AdalatheriumTranslated from Malagasy and Greek, the word “crazy animal” is described using an almost complete, exquisitely preserved skeleton, the most complete for any mammal discovered in the southern hemisphere before the dinosaurs died out.

Research carried out over 20 years shows this Adalatherium was a “giant” compared to the mostly pointed or mouse-sized mammals that lived during the Cretaceous Period.

Some of the “bizarre” features include more trunk vertebrae than most other mammals, muscular hind legs that were in a more expansive position (similar to modern crocodiles), and muscular sprinting forelegs hidden beneath the body (such as the most mammals seen today)), front teeth like a rabbit and back teeth completely different from any other known mammal, living or extinct, and a strange gap in the bone on top of the snout.

A team of 14 international researchers led by Dr. David Krause (Denver Museum of Nature & Science) and Dr. Simone Hoffmann (New York Institute of Technology) published the comprehensive description and analysis of this opossum-sized mammal that lived between dinosaurs and massive crocodiles near the end of the Cretaceous Period (145-66 million years ago) in Madagascar.

The 234-page monographic treatment, which consists of seven separate chapters, is part of the Society of Vertebrate Paleontology’s (SVP) prestigious Memoir Series, a special annual publication that discusses the most important vertebrate fossils in more detail. The first announcement of the discovery was made earlier this year in the journal Nature.

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

Now the research team is presenting the first skeleton for this mysterious group that once roamed much of South America, Africa, Madagascar, the Indian subcontinent and even Antarctica.

The completeness and excellent preservation of the skeleton of Adalatherium opens new windows of what Gondwanatherians looked like and how they lived, but the bizarre features still puzzled the team.

“When you know what we know about the skeletal anatomy of all living and extinct mammals, it’s hard to imagine a mammal would like it Adalatherium could have developed; it bends and even breaks many rules, ”explains Krause.

Although the lifelike reconstruction of Adalatherium is superficially similar to an ordinary badger, its “normality” is only skin deep. Under the surface, his skeleton is downright unusual.

Hoffmann puts it this way: “Adalatherium is just strange. Trying to figure out how it moved, for example, was challenging because its front end tells us a very different story than its back end. “

While its muscular hind legs and large claws on its hind feet may indicate this Adalatherium was a mighty digger (like badger), its front legs were less muscular and more like those of living mammals that can run fast.

The limbs of Adalatherium also indicate that his posture was a mix of that of living mammals and older relatives. Its forelegs were hidden under the body (as seen in most mammals today), but its rear legs were wider (as in crocodiles and lizards).

This is not where the strangeness ends.

The teeth of Adalatheriumreconstructed using high-resolution micro-computed tomography and extensive digital modeling indicate herbivores, but are otherwise more than bizarre.

Not only Adalatherium have rabbit- or rodent-like, ever-growing front teeth, but the rear teeth are completely different from any other known mammal, alive or extinct. If only those teeth had been found, the mystery of what that animal was likely would not have been solved! In addition to the apparent chaos, there is a hole in the top of the muzzle for which there is simply no parallel.

About the size of a Virginia opossum, the 3.1 kg Adalatherium was very big for his day. Although it is not particularly large by today’s standards, it was a giant compared to the mostly pointed and mouse-sized mammals that lived in the Cretaceous period.

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

Adalatherium was found in rocks dated approximately 66 million years ago towards the end of the Cretaceous Period. At that time, Madagascar had been an island separated from Africa and the Indian subcontinent from the Indian subcontinent for over 150 million years. “Islands are the stuff of madness,” says Krause, “and there was enough time for that Adalatherium to develop its many extraordinarily special characteristics in isolation. “

Adalatherium is an important piece of a very large puzzle about early mammalian development in the southern hemisphere, in which most of the other pieces are still missing, ”adds Hoffmann.

Especially the discovery of Adalatherium highlights how much more remains to be learned from new discoveries of early mammals in Madagascar and other parts of the southern hemisphere.

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