The register fossil of mammals of the Mesozoic (from -252 to -66 million years) coming from Gondwana, the supercontinent that occupied the southern hemisphere, is much less supplied than that of Laurasia, the supercontinent north of the equator. Gondwanatherians are one of the mammal groups in the southern hemisphere but they have been known until now only by a few rare fossils including teeth, parts of mandibles and a single skull, discovered in 2014 at Madagascar. The island Red delivers today a much more complete fossil which reveals all the new peculiarities of these funnyanimals.
A big badger weighing three kilos
The new remains were discovered by an international team led by David Krause of the Denver Museum of Nature and Science. They consist of a very complete skeleton including a part of the skull, a large number of vertebrae of the trunk and tail which is short and wide and large bones of the legs. Small bones and cartilage tissue were also kept on the matrix carrying the bones. The study of the fossil led specialists to identify a new species of gondwanathériens baptized Adalatherium hui, a combination of Greek and Malagasy meaning “crazy beast”. The animal discovered undoubtedly corresponds to a subadult specimen which would have had the appearance of a large badger weighing in the three kilos, which makes it the largest known mammal of the Mesozoic in Gondwana. It lived 66 million years ago and at the time most of the other known mammals did not exceed the size of a large mouse.
The Adalatherium fossil hui in its stone matrix. Credit: Marylou Stewart
If the external appearance of the animal, apart from its large size probably due to its island existence, is not surprising, its anatomy has challenged the researchers. ” Knowing the skeletons of living and extinct mammals, it’s hard to imagine how it may well have evolved. He breaks many rules “, David Krause said in a press release. Thus its snout has characteristics which had not been observed for 100 million years in the line leading to modern mammals. His face is also surprising with foramens (holes in the bone allowing passage to the nerves and vessels) in very large numbers including a huge one just above the snout which has no equivalent in other known mammals, alive or extinct. Just like her teeth, which are like no other.
Funny locomotion
Adalatherium’s quirks don’t stop there, they are the subject of a study published in the journal Nature. It is also noted that the “mad beast” had a backbone with more vertebrae than any mammal in the Mesozoic and that one of its bones in its foreleg was strangely curved. Understanding how it moved is still a challenge: ” its front legs tell us a story different from its rear end“Says Simone Hoffmann of the New York Institute of Technology. A priori, Adalatherium could dig, he was surely able to run and he could also have opted for other forms of locomotion to discover.
To better understand the place of this animal in the ecosystem of Madagascar, 66 million years ago and while he lived surrounded by dinosaurs and particularly massive crocodilians, it will be necessary to continue the excavations on the island Red as well as in all the deposits containing fossils of Gondwana.
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Izland BipBip & sciencesetavenir.fr
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