One more piece of the terrestrial puzzle. Analysis of a 130-million-year-old fossilized skull has revealed that the ancient supercontinent Pangea may have broken apart more slowly than scientists previously thought. The fossil, found in eastern Utah (USA), exposed an entirely new group of reptile-like mammals that existed in North America. The newly discovered species has been named Cifelliodon wahkarmoosuch in honor of the famous paleontologist Richard Cifelli and the local Ute tribe’s word for “yellow cat.”
“Based on the unlikely discovery of this nearly complete fossil skull, we now recognize a new cosmopolitan group of primitive mammalian relatives,” Adam Huttenlocker of the University of Southern California told the journal Nature that publishes the study.
Using high-resolution CT scanners, the researchers estimated that the creature weighed up to 1.1 kg and would be the size of a small hare ; a giant among his contemporaries at the time.
While its large olfactory bulbs indicate that it had a strong sense of smell, its eye sockets were quite small, suggesting that it had poor vision and poor color perception. This means that the animal was probably nocturnal and relied on its scent for food.
“The Cifelliodon skull is an extremely rare find in a vast fossil-bearing region of the western interior, where more than 150 species of mammals and precursors of reptile-like mammals are represented primarily by isolated teeth and jaws,” says James Kirkland, co-author. from work.
As if the discovery wasn’t remarkable enough, the fossil has significantly changed our understanding of mammalian evolution . “For a long time, we thought that the earliest Cretaceous mammals (145 to 66 million years ago) were anatomically similar and not ecologically diverse,” Huttenlocker said.
This finding reinforces that, even before the rise of modern mammals, ancestral relatives of mammals explored specialized niches: insectivores, herbivores, carnivores, swimmers, and gliders.
The discovery also changes the time frame in which the ancestors of extinct mammals, called haramíyids, dispersed across continents.
Most of the haramyid fossils discovered so far come from the Triassic and Jurassic in Europe, Greenland, and Asia. But this find represents the first large skull in the Lower Cretaceous (145 to 101 million years ago) in North America, which shows that the haramíyids must have existed globally during the Jurassic-Cretaceous transition.
According to the continental drift hypothesis, Pangea began to separate about 225-200 million years ago. Now , the new study suggests that the division of Pangea took about 15 million years longer than previously thought.
Researchers have placed Cifelliodon in the Hahnodontidae subgroup, which until then was only made up of Cretaceous species from North Africa. We continue to complete the puzzle.
Reference: Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana, Nature (2018). DOI: 10.1038 / s41586-018-0126-y, www.nature.com/articles/s41586-018-0126-y
Image credit: Keck School of Medicine of USC / Jorge A. Gonzalez
