(CNN) – Researchers have discovered the fossil of a primitive mammal called the “crazy beast” that lived 66 million years ago with giant dinosaurs and crocodiles in Madagascar and is different from any known, living or extinct mammal.
This posum-sized mammal had a mixture of strange features that had never been seen before. It highlights the evolutionary strangeness that can occur when evolution takes place in isolation on islands such as Madagascar, which is home to other species, living and extinct, that are not found anywhere else in the world.
An initial study describing the discovery of the “crazy beast” published in April in the journal Nature. This post was followed by a special issue of the Society of Vertebral Paleontology’s memoir series, which was released on Friday.
The mammal is the most complete and best-preserved skeleton of a Gondwanaterian, which is a mammal that lived on the southern supercontinent Gondwana, which are now the continents of the southern hemisphere.
Fossils from the Mesozoic era, between 65 and 252 million years ago, are rare in Gondwana and mostly include elements such as a single skull, jaw pieces and teeth.
But this mammal, which looks a bit like a badger in the artist’s skeletal rendering, is so well preserved that it includes cartilaginous tissue, small bones, and the creature’s short tail.
This is the well-preserved skeleton of Adalatherium hui, a Gondwanatherian mammal that lived in Madagascar 66 million years ago.
Researchers have called it Adalatherium hui, a hybrid name that combines the Malagasy word for “crazy” and the Greek word for “beast.” Hui is a nod to the late Yaoming Hu, co-author of the study at Stony Brook University.
They believe that this particular creature was young, weighing about 3.5 kilograms. But compared to the other mammals in Gondwana that lived at the time, which were the size of a mouse, it was quite large. And it lived among ancient dinosaurs and crocodiles before the asteroid’s impact destroyed them all 66 million years ago, at the end of the Cretaceous.
An incredibly strange animal
“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 many rules, ”said David Krause, lead author of the study and chief curator of vertebrate paleontology at the Denver Museum of Nature and Science and professor emeritus at Stony Brook University, in an April press release.
The skeleton contains a series of strange features that researchers cannot decipher.
For example, the Adalatherium had more holes in the front than any known mammal, Krause said. These orifices, called the foramen, created pathways for the blood vessels and nerves, leading to an incredibly sensitive snout, which was covered with a mustache. It also had a large hole in the top of its snout that cannot be compared to any known mammal that has lived or is currently living.
Even teeth cannot be compared to anything else. They are structured in a strange way that cannot be explained. Krause said the back teeth “come from outer space.”
The animal’s spine contained more vertebrae than any known mammal from the Mesozoic era. And you must have walked in a strange way, because the front half of the animal does not match the back half. And one of his hind legs was gone.
Forearms and shoulders can be compared to cats and dogs, which means they were placed under the body, something very unusual for early mammals that went more than reptiles, said Simone Hoffmann, co-author of the study and assistant professor at the Institute of Technology in New York Department of Anthropology.
But the hind legs have the opposite pattern, suggesting that the legs are outstretched and have more knee joints, such as reptiles. Two patterns on an animal mean it went very differently from anything it has experienced today, Hoffman said. But they think he was able to run, as well as other ways to move.
Adalatherium also had long, strong claws on its hind legs, suggesting that it dug using its hind legs.
“Adalatherium is the weirdest of the weird,” Hoffmann said. “Trying to find out how it moved is almost impossible, because, for example, the front tells a different story than the back.”
Strange island animals and where to find them
Krause and his colleagues researched fossils belonging to unusual animals that had lived in ancient Madagascar for 25 years. This fossil was found in 1999 at the site of a sedimentary basin in northwestern Madagascar. But it has been investigated recently.
Multiple expeditions to that basin revealed dinosaur bones and other vertebrates well preserved and buried by the old stream of debris in the basin. But they had to collect thousands of specimens just to find a handful of mammal fossils, Krause said.
In 2010, they found the skull of a Gondwanatherian. Prior to this, his discoveries were largely limited to teeth and jaw fragments.
Fossils of a Gondwanaterian were first found in Argentina, followed by discoveries in Africa, India, the Antarctic Peninsula and Madagascar. At first, researchers thought they were related to the lazy, the ants, and the armadillo. But they stand alone, unrelated to anything alive today, “now it is known that they were part of a great evolutionary experiment, doing their thing, an experiment that failed and disappeared. [la época del] Eocene, about 45 million years ago, “said Krause.
If the “crazy beast” can be linked to anything, it is multituberculate, a group of extinct rodent-type mammals that lived on the northern continents, according to researchers.
Researchers attribute it to the evolution of an island’s isolated environment. And Madagascar has been an island for a long time. It separated from the Indian subcontinent 88 million years ago and has been alone ever since.
This allowed Madagascar’s animals and dinosaurs, such as Adalatherium, “enough time to develop its many ridiculous features,” Krause said.
Krause’s team found other bizarre fossils in Madagascar, including a giant armored raptor named Beelzebufo, a short-nosed herbivorous crocodile named Simosuchus, and a deer-toothed dinosaur named Masiakasaurus.
“Madagascar is a rather strange place,” Krause said. Plants and animals are not known anywhere else in the world. The evolution on the islands leads to this in a certain sense. ‘
When animals move to isolated areas, such as islands, they face greater competition from both predators and food sources. This makes them grow in species that do not resemble the animals of the continent, including unusual shapes and sizes.
Researchers call it the “island rule”: small animals grow in size, a form of gigantism, while large mammals decrease in size.
Adalatherium probably disappeared along with the rest of the strange animals of Madagascar 66 million years ago, before the island’s population began again with native species, such as lemurs. But the discovery throws out information about the fascinating mammals that came before the ones we know today. And only more research and discoveries will fill the remaining gaps.
“Adalatherium is just one piece, but an important piece in a big puzzle about the early evolution of mammals in the southern hemisphere,” Krause remarked. “Unfortunately, most of the pieces are still missing.”