Filikomys primaevus, a new genus and late Cretaceous multi-stranded mammals, have been identified from multiple skull and skeleton collections found at a dinosaur nesting site in Montana. , USA. The well-preserved fossils show that Filikomys primaevus Engaging in multi-generational behavior, nesting and burrowing, represents the first example of social behavior in Mesozoic mammals.
Multi-stranded species are mostly small, omnivorous or herbivorous mammals that lived 166 to 35 million years ago, from the Middle Jurassic to Late Eocene.
Most multifibre species are often restored as loose teeth; The skull and jaw are preserved very rarely, except in Mongolia.
They are known from North America and Europe – which was a single continent until the early Eocene – in the Upper Triassic to the Lower Oligocene, and from north Asia in the Upper Cretaceous and Paleocene.
“Multituberculata are one of the oldest groups of mammals, and they have been extinct for 35 million years, but during the Late Cretaceous period they still interact in groups similar to what you would be,” said lead author. will be found in ground squirrels today. Luke Weaver, a graduate student in the Department of Biology at the University of Washington.
Filikomys primaevus roamed the Earth during the Cretaceous period, about 75.5 million years ago.
The skulls and fossil skeletons of at least 22 individuals have been recovered from a famous dinosaur nesting site called Egg Mountain in western Montana.
They usually gather together in groups of two to five people, with at least 13 individuals found within 30 m2 areas in the same rock layer.
Based on the degree of preservation of the fossils, the type of rock in which they are preserved, and Filikomys primaevusWeaver and his colleagues hypothesize that the animals live in caves and nest together.
Furthermore, the ancient animals were a mix of many adults and young people, suggesting that these were real social groups, not just parents raising their children.
“Since humans are social animals, we tend to think that sociability is somehow unique to us, or at least to their evolutionary close relatives. But now we can see that social behavior has gone further in the mammal family tree, ”says Weaver.
Previously, paleontologists believed that social behavior in mammals appeared for the first time after the mass extinction that killed the dinosaurs, and mostly in the Placentalia – a group of animals with The breast to which man belongs, all carry the fetus in the mother’s womb until late development.
But Filikomys primaevus shows that mammals interacted during the Age of Dinosaurs, and in a completely different and older group of mammals – the multifibular species.
“These fossils are game changers,” said senior author Dr. Gregory Wilson Mantilla, research fellow at the Department of Biology at the University of Washington and the Burke Museum of Natural & Cultural History.
“As paleontologists working to reconstruct the biology of mammals during this time, we are often trapped in individual teeth and possibly a jaw rolling into the river. But here we have many of the almost complete skulls and skeletons preserved in the exact same place where the animals lived. “
“Now, we can reliably look at how mammals actually interacted with dinosaurs and other animals that lived at this time.”
The discovery Filikomys primaevus reported in an article in the journal Natural Ecology & Evolution.
LN Weaver et al. Mammals’ original social behavior is revealed by many species from a dinosaur nesting site. Nat Ecol Evol, published online November 2, 2020; DOI: 10.1038 / s41559-020-01325-8