Caption: A group of subadult and adult individuals of Filikomys primaevus huddled together in their burrow while a family of duck-billed dinosaurs roams on the surface.   Artist credit: Misaki Ouchida

We mammals may have been cuddling for over 75 million years

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Peer-reviewed: This work was reviewed and scrutinised by relevant independent experts.

Mammals may have been snuggling up way earlier than we thought, say international researchers who found a 75.5 million-year-old burrow containing fossils of rodent-like mammals cuddled-up together. Previously, scientists believed that mammals had led mostly solitary lives until after the dinosaurs died out around 66 million years ago. The team found multiple individuals of different generations all buried together, which they adorably named Filikomys primaevus after a Greek word for 'friendly' or 'neighbourly'.

Journal/conference: Nature Ecology & Evolution

Link to research (DOI): 10.1038/s41559-020-01325-8

Organisation/s: University of Washington, USA

Funder: Financial support was from the National Science Foundation grant nos 0847777 (D.J.V.) and 1325674 (D.J.V. and G.P.W.M.), a National Science Foundation Graduate Research Fellowship (L.N.W.), the Doris O. and Samuel P. Welles Research Fund (L.N.W.), the University of Washington Department of Biology (L.N.W. and G.P.W.M.) and the Burke Museum (L.N.W. and G.P.W.M.).

Media release

From: Springer Nature

Fossil specimens of rodent-like multituberculate mammals, dated to 75.5 million years ago, including skeletons of multiple individuals burrowed together, suggest that mammals may have been social since the Mesozoic era. These findings are reported in a paper published this week in Nature Ecology & Evolution.

Although a large number of placental mammals are social today, the relative absence of sociality in egg-laying and marsupial mammals has led researchers to believe that the ancestors of mammals led solitary lives until after dinosaurs became extinct approximately 66 million years ago.

Lucas Weaver and colleagues describe deposits of small mammal bones found in Montana, United States, from multiple individuals of different generations buried together, dating to the late Cretaceous. The skeletons represent a new genus of rodent-sized multituberculate mammal the authors named Filikomys primaevus. The genus name comes from the Greek filik√≥s, meaning friendly or neighbourly, because of the behaviour the authors interpreted from the fossils. F. primaevus had powerful legs well-adapted for digging, which allowed them to burrow together in multigenerational groups of up to five individuals. Based on the behaviour of living burrowing social mammals like rabbits, the authors suggest that the fossil individuals were related.

The authors conclude that the fossils provide evidence of social mammal behaviour more than 75 million years ago.

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