Fossil Squirrels?

Good morning! What a wonderful morning it is! Punxsutawney Phil came out and told us all that spring is right around the corner, which is a very big deal. This is a North American "tradition" that was adapted from a similar German tradition (Dachstag: "Badger day") involving the European badger. American badgers would be far less amicable to this sort of treatment I think. In Pennsylvania, Phil is kind of a big deal him(her?)self. Groundhogs (Marmota monax) make a somewhat lucrative life for themselves in the state, even being endorsed by the state lottery as a spokes... hog named Gus. It is also quite hard to walk near any wooded area of Pennsylvania without running into at least a few of these large animals scurrying about the edge of the forest. But what are they really?

Fear is an acceptable response.

The animal has a lot of common names: groundhog, woodchuck, Canada marmot, and, my personal favorite, whistlepig, are just a few. Groundhogs, by any name, are not actually pigs or hogs (they are in the same genus as marmots, so that name has some basis, though they are certainly found south of Canada), but instead, they are actually some of the larger members of the squirrel family. Specifically, as some of their common names somewhat allude to, they are ground squirrels. Groundhogs can climb, despite their name, and a groundhog in a tree is something worth seeing.

When we think of oversized anything in the animal kingdom we tend to think that the only place to look is in the fossil record. That is, after all, where we find giant sloths, oversized wolves, dinosaurs, and enormous terror birds. We know that they are fantastic digging animals and spend a lot of time, including hibernation in a burrow. Was there, then, an even more giant ground squirrel that burrowed extensively in the history of life? Fossilized burrows are known from much earlier than the current era. The first burrows belong to very early animals, but if we are looking for the recent ancestors of giant squirrels, we do not need to go that far back.

Photo of Clarkia, Idaho squirrel fossil by
Bill Richards, North Idaho College

The first squirrels in North America appear in the Late Eocene, around 41 to 33 million years ago. Any "squirrel-like" fossils from before this are not squirrels.
The first ground squirrels appear shortly after the Eocene, in the early Oligocene, at approximately 30 million years ago in Europe. As far as the marmots themselves, there is no clear consensus on when this large group of ground squirrels first appear in the fossil record. They are evident by the Late Oligocene in North America. It is acknowledged that by the time we have a good fossil record, in the Mid-Miocene, the ground squirrels, particularly prairie dogs, are already well-represented within their modern range. The fact that we recognize their fossils as highly similar to their extant morphology does not really bode well for finding the origins of Punxsutawney Phil and Gus' family though. Truly, the fact of the matter is that squirrels, as long as we have known them in the extinct and extant capacity, have looked pretty much like squirrels. One could almost say that rodents are kind of like the cockroach of the mammal family in that they have existed long enough to have "survived anything and everything" that life can throw at them. We may see if this remains true in our own lifetimes, but let us hope that we do not.

For more reading:

Helgen, Kristofer M.; Cole, F. Russell; Helgen, Lauren E.; Wilson, Don E. (April 2009). "Generic Revision in the Holarctic Ground Squirrel Genus Spermophilus" (PDF). Journal of Mammalogy. 90 (2): 270–305. doi:10.1644/07-MAMM-A-309.1. Archived from the original (PDF) on 2011-10-22.

Kryštufek, B.; B. Vohralík (2013). "Taxonomic revision of the Palaearctic rodents (Rodentia). Part 2. Sciuridae: Urocitellus, Marmota and Sciurotamias". Lynx, n. s. (Praha). 44: 27–138.

Steppan, Scott J.; Storz, B.L. &; Hoffmann, R.S. (2004): "Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1". Mol. Phyl. Evol. 30(3): 703–719. doi:10.1016/S1055-7903(03)00204-5 PDF fulltext