Adalatherium fossils. Credit: Simone Hoffmann and Kathrine Pan
The bizarre features of this mammal make scientists puzzled about how it might have evolved; “He bends and even breaks a lot of rules.”
Adalatherium is an important piece in a very large puzzle about the early evolution of mammals in the southern hemisphere, one in which most of the other pieces are still missing.
New research published today in Journal of Vertebrate Paleontology describes a bizarre, 66-million-year-old mammal that provides new insight into the evolutionary history of mammals in the southern supercontinent of Gondwana – recognized today as Africa, South America, Australia, Antarctica, the Indian subcontinent and the Arabian Peninsula.
Appointed Adalatherium, which, translated from Malagasy and Greek, means “crazy beast”, is described on the basis of an almost complete skeleton, kept refined, most complete for any mammal still discovered in the southern hemisphere before the extinction of the dinosaurs.
Research over 20 years demonstrates this Adalatherium was a “giant” compared to mouse-type mammals or mice that lived during cretaceous period.
Reconstruction similar to the Adalatherium hui life of the Late Cretaceous of Madagascar. Credit: © Denver Museum of Nature & Science / Andrey Atuchin
Its “bizarre” 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), coupled with sprinting front legs, which have been hidden under the body. as seen in most mammals today)), the front teeth like a rabbit and the back teeth completely different from those of any other known mammal, alive or extinct, and a strange space in the bones at the tip 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 a comprehensive description and analysis of this opossum-sized mammal that lived among dinosaurs and massive crocodiles near the end of the Cretaceous period (145¬-66 million years ago) on Madagascar.
The 234-page monographic treatment, consisting of seven separate chapters, is part of the prestigious series of memoirs Society of Vertebrate Paleontology (SVP), a special annual publication that provides a more in-depth treatment of the most significant vertebrate fossils. 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 small remnants have already indicated that Gondwanaterians were very different from other contemporary mammals. So many mysteries had surrounded the Gondwanaterians that it was unclear how they fit into the mammal’s family tree.
Now the research team presents the first skeleton for this mysterious group that once roamed much of South America, Africa, Madagascar, the Indian subcontinent and even Antarctica.
Excellent skeleton integrity and preservation Adalatherium opens new windows on what gondwanatherians looked like and how they lived, but the bizarre features still have perplexing the team.
“Knowing what we know about the skeletal anatomy of all living and extinct mammals, it’s hard to imagine that a mammal like Adalatherium could have evolved; he bends and even breaks a lot of rules, ”Krause explains.
Although the life-like reconstruction of Adalatherium it is superficially similar to a running badger, its “normality” is only profound. Beneath the surface, its skeleton is nothing but extraordinary.
As Hoffmann says, “Adalatherium it’s just weird. Trying to find out how he moved, for example, was a challenge, because our front end tells us a completely different story from his back end.
While his muscular legs and large claws on his hind legs may indicate this Adalatherium it was a powerful excavator (like badgers), its front legs were less sturdy and more like living mammals that can run fast.
Members of Adalatherium it also indicates 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).
This was not the stops of the weirdness.
Teeth of Adalatherium, reconstructed using high-resolution micro-computed tomography and extensive digital modeling, are indicative of herbivore, but are otherwise beyond bizarre.
Not only Adalatherium they have front, growing, rabbit-shaped or rodent-shaped teeth, but the back teeth are completely different from those of any other known, living or extinct mammal. If these very teeth had been found, the mystery of what this animal was would probably not have been solved! To the apparent chaos is added a hole in the top of the muzzle for which there is simply no parallel.
About the size of a 3.1 kg Virginia opossum Adalatherium it was very big for his day. Although not particularly large by current standards, it was a giant compared to the larger lizard and mouse mammals that lived in the Cretaceous.
The geological history of Gondwana provides clues as to why Adalatherium it’s so weird.
Adalatherium was found in rocks dated near the end of the Cretaceous, about 66 million years ago. At this time, Madagascar has already been an island separated from Africa for over 150 million years and from the Indian subcontinent for over 20 million years. “Islands are the weird thing,” says Krause, “and so there was enough time for Adalatherium to develop its many extraordinary special features in isolation. “
“Adalatherium it is an important piece in a very large puzzle about the early evolution of mammals in the southern hemisphere, one in which most of the other pieces are still missing, ”adds Hoffmann.
More than anything, the discovery Adalatherium emphasizes how much remains to be learned from the new discoveries of early mammals in Madagascar and other parts of the southern hemisphere.
Reference: “Introduction to Adalatherium hui (Gondwanatheria, Mammalia) from the Late Cretaceous of Madagascar ”by David W. Krause, Joseph R. Groenke, Simone Hoffmann, Raymond R. Rogers and Lydia J. Rahantarisoa, 18 December 2020, Journal of Vertebrate Paleontology.
DOI: 10.1080 / 02724634.2020.1805455