American scientists published an article in the Journal of Systematic Palaeontology describing three new species of ancient mammals that appeared immediately after the mass extinction of dinosaurs.
Researchers at the University of Colorado Museum of Natural History at Boulder examined the teeth and bones of the lower jaw of 29 ancient ungulates, or condilators, from the Early Paleocene sediments of the Great Divide Basin in Wyoming.
Using phylogenetic methods, the authors determined the anatomical differences between the species, and also established how these species are related to each other and to other Paleocene condilarra in North America. As a result, scientists identified three previously unknown species of ancient mammals among the samples, which were named Miniconus jeanninae, Conacodon hettingeri and Beornus honeyi.
All of them belong to the family of periptychids - extinct placentals. The largest of these, Beornus honeyi, named after the hobbit Beorn, the character in John Tolkien's The Hobbit, or There and Back, was about the size of a modern domestic cat - significantly larger than the earliest mammals to coexist with dinosaurs at the end of the Cretaceous. According to the researchers, this indicates that after the extinction of the dinosaurs, mammals began to evolve rapidly.
"When dinosaurs became extinct, access to food and other environmental resources allowed mammals to rapidly evolve, diversify anatomy and increase body size," lead author Madelaine Atteberry of the Department of Geological Sciences at the University of Colorado said in a press release. "They clearly seized the opportunity, as we can see from the diversity of new mammalian species that emerged in a relatively short period of time after the mass extinction."
The new species differ from other condylators in the structure of their teeth - they have characteristic "blown" premolars and unusual vertical enamel ridges. The researchers believe that the animals were omnivorous, so they developed teeth that allowed them to effectively grind both plant and animal food, but the authors do not exclude that the basis of the diet was still plants.
The results of the study support the existing view that the extinction of non-avian dinosaurs 66 million years ago gave rise to the development of new species and was the beginning of the era of mammals.
"Previous research suggested that mammalian diversity in western North America was relatively low in the first few hundred thousand years after the extinction of the dinosaurs, but the discovery of three new species in the Great Divide Basin suggests rapid diversification," says Atteberry.
The authors note that the periptychid condylarra that they studied make up only a small percentage of the more than 420 mammalian fossils found in the Great Divide Basin, and suggest that descriptions of several more new early Paleocene mammalian species will appear in the near future.