The tiny multituberculate, Filikomys, enters the LRT

Figure 1. Ptilodus, Filikomys and Catopsbaatar to scale (at 72 dpi screen resolution).

Figure 1. Ptilodus, Filikomys and Catopsbaatar to scale (at 72 dpi screen resolution).

Filikomys primaevus 
(Weaver et al. 2020; NMC 1890; Late Cretaceous; Figs. 1, 2) is a cimolodont multituberculate found with others of its kind in a multi-season burrow/nest. Filikomys was originally nested close to Ptilodus (Figs. 1, 3), but here is more closely related to the even smaller Catopsbaatar (Fig. 1).

From the Weaver et al. abstract:
“Taphonomic and geologic evidence indicates that F. primaevus engaged in multigenerational, group-nesting and burrowing behaviour, representing the first example of social behaviour in a Mesozoic mammal. That F. primaevus was a digger is further supported by functional morphological and morphometric analyses of its postcranium.”

Figure 1. Filikomys from Weaver et al. 2020 and colorized here.

Figure 1. Filikomys from Weaver et al. 2020 and colorized here.

The Weaver et al. abstract continues:
“The social behaviour of F. primaevus suggests that the capacity for mammals to form social groups extends back to the Mesozoic and is not restricted to therians.”

By contrast, in the large reptile tree (LRT, 1754+ taxa) Filikomys is a multituberculate and they nest within the clade Glires, not far from the aye-aye (Daubentonia), rat (Rattus) and mouse (Mus), all within the clade Placentalia. Weaver’s cladogram is typical of analyses that include multituberculates where members of the clade Glires are not employed.

Figure 3. Ptilodus, an arboreal multituberculate.

Figure 3. Ptilodus, an arboreal multituberculate.

Traditional taxon exclusion problems, like this,
are minimized in the LRT, which includes a wide gamut of taxa. Colleagues, do the work you are paid to do. Don’t rest on old myths and traditions, even if they are in current textbooks and lectures.

Figure 4. Catopsbaatar greatly enlarged.

Figure 4. Catopsbaatar greatly enlarged.

The Weaver et al. paper concentrates on the subject
of sociality, first seen in basal tetrapods in the Carboniferous. Burrows go back at least to therapsids in the Permian. Filikomys was found in Late Cretaceous deposits.

Weaver et al. report,
“The material described herein includes the first associated multituberculate skeletons from the Mesozoic of North America and represents the oldest-known case of burrowing capabilities in a Mesozoic multituberculate.”

“Multiple lines of evidence thus indicate that F. primaevus was a terrestrial, scratch-digging mammal, functionally analogous to the Least Chipmunk, Neotamias minims.”

 

The above episode of “Old News”
(love that name!) features Christian Kammerer talking about multituberculates with a focus on tiny Filikomys. Click to play.


References
Weaver LN et al. 2020. Early mammalian social behaviour revealed by
multituberculates from a dinosaur nesting site. Nature ecology & evolution. https://doi.org/10.1038/s41559-020-01325-8

wiki/Kryptobaatar
wiki/Ptilodus
wiki/Catopsbaatar
wki/Filikomys
wiki/Ptilodontoidea

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