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Filikomys family
The earliest evidence of social behavior in mammals.

In 2019 Summer, I got a contact from Luke Weaver, a graduate student at the time getting his PhD with Dr. Greg Wilson at the University of Washington. Their group was getting ready to submit a publication and I was asked to craft a reconstruction of the animal they were writing about.

The paper was about a new, exceptionally preserved skeletons (75.5 million years old!) from Egg Mountain in Montana, a famous dinosaur nesting locality. This animal was named as Filikomys primaevus, a genus of multituberculate and considered to be terrestrial, scratch-digging mammals (analogous to modern day chipmunks.) The set of fossils showed that there were multiple individuals (both adults and juveniles) preserved right next to each other, which represents the earliest evidence of mammalian social behavior.

My first sketch of Filikomys family. I first misunderstood that they were like a meerkat.

This image needed to be modified because the study showed that F. primaevus were rarely above ground and were usually within a shelter.


Photographs (left) and annotated line drawings (right, my work) of the fossils.

(Weaver, L.N., Varricchio, D.J., Sargis, E.J. et al. Nat Ecol Evol 5, 32–37 (2021))

 The study also found that F.primaevus had a functional morphology of burrowing/digging behavior by examining its shoulders, elbows and paws. Furthermore, F.primaevus was capable of powerful hip extension and knee flexion and had a habitually flexed knee, and thus was adapted for living in tight, confined spaces, such as burrows.

A reconstruction plate of F.primaevus. A lot of iterations were made, especially regarding the angles of its joints. A referred extant animal is a chipmunk, but a body proportion is quite different.

A reconstructed scene of 5 individuals mingling together. Cypress seeds were drawn since the most abundant seed-producers were likely conifers. I also drew Maiasaura’s nest in far distance showing another social behavior. The coevolution of social behavior was stunning!

The study was published on November 2020 in Nature Ecology & Evolution. Also, press released at Yale News.

Congratulations, Luke and Greg!!

Later, those figures were used for The Dinosaur Expo 2023 in Japan.

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