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The 'Gondwana beasts', Also known asgondwanaterios, They were mammals that inhabited what was the supercontinentGondwana, located in the southern hemisphere, more than 66 million years ago.
Until now, everything that was known about these enigmatic animals, what they lived with dinosaurs and giant crocodiles, was based on the few fossils of teeth, jaws, and a single skull.
A new study, published in the journalNature, now presents the finding of the most complete skeleton of a gondwanatery, in this case of a new species that they have calledAdalatherium hui, which in Greek and Malagasy means "crazy beast" and whose remains were found in 1999.
The fossils allow for the first time "to get a vision of what the gondwanaterians were like, lived and what other mammals were related to," he says. David W. Krause, a researcher in the Department of Earth Sciences at the Denver Museum of Nature and Science in the US.
He is the main author of the work and in 2014 he already described the skull of one of these mammals, calledVintana sertichi.
This mammal, which is much larger than those of the Mesozoic –Which in general were no bigger than a mouse–, adds one of the missing pieces to thepuzzle on mammal evolution on the southern continents between 251 and 66 million years ago.
“We know very little about the evolution of the first mammals in the southern hemisphere. The complete skeleton has allowed us to determine that the closest relatives of the gondwanaterians were a well-known group from the northern hemisphere, themultituberculated (an extinct order of mammals similar to today's rodents that lived between 201 and 23 million years ago), ”says Krause.
A strange primitive badger
The strange animal, with a short and wide tail, was 52 cm long and weighed about three kilos, but it could surely be larger since the specimen found was not yet adult.
Although it looked like acurrent badger, that apparently normal anatomy was justsuperficial. His bones reveal that he had characteristicsprimitive on the snout that had not been appreciated in 100 million years in the lineage that has led to modern mammals.
"The skull is strange because it has ahole between its nasal bones and these was unknown in other mammals. It had more holes in the muzzle, which indicates a rich innervation and a sensitive muzzle, with probably many whiskers ”, details Krause, who also highlights the nasal cavities and the inner ear.
The bony composition of its snout is also unusual for the presence of septa in the maxillary sinuses, and behind its head its skeleton featured more trunk vertebrae than any Mesozoic mammal. “Based on the postcranial skeleton, we believe thatAdalatherium it was probably a digger, and it possibly made burrows ", emphasizes the expert.
TheirteethFurthermore, they were strange: their molars were radically different from those of any other mammal, existing or extinct. As the incisors were very large, scientists believe they were used for gnawing and the back teeth for cutting vegetation. "In other words, it was probably a herbivore," says the paleontologist.
Isolated in Madagascar
The first remains of gondwanaterians were first found in Argentina in the 1980s, but since then they have also been located in Africa, India, the Antarctic Peninsula and Madagascar.
These mammals were initially thought to be related to modern sloths, anteaters, and armadillos, but "it is now known that they were part of a great evolutionary experiment, which failed in the Eocene, about 45 million years ago," he says. Krause.
Thebig size of the new species, compared to others from the same period, may be the result of its evolution in isolation in Madagascar. According to the authors, there is several evidences that evolution on the islands is related to body size.
This one in particular, which separated from Africa 100 million years ago and was isolated about 88 million years ago in the Indian Ocean when it was detached from the Indian subcontinent, allowed the evolution ofAdalatherium hui for more than 20 million years in isolation. "Long enough to develop its strange characteristics," says the researcher.
In addition to this species, Madagascar is home to animals and plants found nowhere else on the planet, including giant cockroaches, giraffe weevils, and tomato frogs, among others. Just a few thousand years ago, Madagascar's fauna also included elephant birds weighing about 600 kilos and gorilla-sized lemurs and pygmy hippos, the authors note.
David W. Krause et al. "Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity” Nature April 29, 2020.