Antediluvian Beasts of the East : Tamias aristus

First off, thanks for 300 views this past month! That blows my mind. I hope you enjoy the post, and thanks for reading!  Hike through any forest on the East Coast of the US today, and you’re bound to come across those small, fast sciurids we know as chipmunks. Back during the Pleistocene, however, chipmunks grew to much larger sizes, as evinced by the giant, or “noblest” chipmunk, Tamias aristus. The modern Eastern chipmunk, Tamias striatus, has been found to be T. aristus‘s closest relative (Ray, 1965), suggesting that the genus Tamias has an ancestry in the Eastern US. Based on the bones, T. aristus was around 30% larger then the modern Eastern chipmunk. Try thinking about that next time you go to see one of those cheesy Alvin and the Chipmunks movies! The type specimen of this animal was discovered at Ladd’s Quarry, which is a Pleistocene site in Georgia (Ray, 1965). Pleistocene Ice-Age tapir, Dire wolf, and even peccary fossils have been found at this site. A variety reptiles and amphibians were also present (Holman, 1985). Like the giant beaver Castoroides, which also inhabited the East Coast during the Pleistocene Ice Age (Hulbert et. al., 2014), Tamias aristus represents a super-sized relative of a modern species, which was a common trope during the Late Pleistocene. T. aristus may have had a slightly different lifestyle then its modern day-relative, but their overall skeletal similarities suggest that T. aristus occupied a similar niche. I’ve heard John Alroy estimated Ladd’s Quarry  to be around 300,000 years old based on the presence of the Vero tapir, but I haven’t seen any publications with this information. We can conclude, however, that Ladd’s Quarry represents an interglacial period with higher temperatures present then those of today. This conclusion is based on the presence of wetland animal remains, such as those of the Florida muskrat (Ray, 1967), at the site. Apart from these warmer-climate favoring species, a variety of other animals are found at Ladd’s Quarry which also are observed in the forests of the East Coast today. The Eastern Cottontail, White-tailed deer, and Opossum are just some of the animals which left their remains behind at Ladd’s (Ray, 1967). Larger animals, such as the horse Equus (Ray, 1965) and the giant ground sloth Megalonyx (Ray, 1967) are also present, and probably were the resident megafauna at Ladd’s Quarry during this interglacial period.

The environment which the noblest chipmunk called home would be similar to this modern forest in Connecticut. Photo by the author, 2015.

The environment which the noblest chipmunk called home would be similar to this modern forest in Connecticut. Photo by the author, 2015.

The noblest chipmunk (I’ll be referring to T. aristus as so from now on, as I find the name adorable) may also be known from Ice Age deposits in Florida. I can’t confirm the presence of this animal in Florida for lack of good references. However, the site fossilworks.org indicates T. aristus existed among the fauna of the Florida site Arredondo IIA, which dates to the Sangamonian interglacial stage. If the noblest chipmunk was present in Florida during the Sangamonian, it indicates that the chipmunk was able to survive through glacial periods, and also extends the noblest chipmunk’s temporal range by ~182,000 years (this is all based on if Ladd’s Quarry actually represents a 300,000 year old deposit, which some have argued against) . In Florida, the noblest chipmunk would have co-existed with many of the same species it came into contact with at Ladd’s. But let’s go back to the noblest chipmunk’s niche. As I said above, we think that the noblest chipmunk and the Eastern chipmunk had similar niches. The size of the noblest chipmunk, however, suggests that the noblest chipmunk had a slightly different lifestyle then T. striatus. I hypothesize, like some others, that the noblest was a year-round forager, taking advantage of its contemporaries’ hibernating needs. This lifestyle would equate to the animal possibly having larger fat layer, more hair for insulation in the cold, and an overall more robust body in life in order to withstand the extremes of winter. If this is the case, we might be looking at an effectively “woolly-chipmunk”. Keep in mind however, that this is wild speculation.

An Eastern Chipmunk foraging for Walnuts (Juglans sp.) stops to ponder at its larger relative, the noblest chipmunk Tamias aristus. Illustration by the author. Pencils on paper, 2015.

An Eastern Chipmunk foraging for Walnuts (Juglans sp.) stops to ponder at its larger relative, the noblest chipmunk Tamias aristus. Illustration by the author. Pencils on paper, 2015.

But this chipmunk’s reign as king of the forest floor was not to last. More extreme glacial intervals caused the forests of the East Coast to turn into grasslands. This specialist forager, who possibly depended on a year-round supply of food, slowly ran out of habitat, and eventually succumbed to extinction. The smaller, more adaptable Tamias species survived, an echo of an ancient arms-race. This grassland-killed hypothesis has been inferred by other folks as well, and seems to be our best shot at understanding how the noblest chipmunk’s extinction occurred.

Forests gave way to grassland during glacial periods. If you're an avid paleo-enthusiast, you might recognize that this photo is of Florissant Fossil Beds National Monument. Photo by the author, 2014.

Forests gave way to grassland during glacial periods. If you’re an avid paleo-enthusiast, you might recognize that this photo is of Florissant Fossil Beds National Monument. Photo by the author, 2014.

The noblest chipmunk is just another example of super-specialization eventually causing the extinction of a species. Yet during its heyday, Tamias aristus ruled the roost on the forest floors of Ice-Age Eastern US, its bones still preserving an ancient chipmunk legacy.

References 

1. Ray, .C. E. . 1965. “A new chipmunk, Tamias aristus, from the Pleistocene of Georgia.” Journal of Paleontology 39(5):1016-1022.

2. Hulbert, R.; Kerner, A.; Morgan, G. S. .2014. “Taxonomy of the Pleistocene giant beaver Castoroides (Rodentia: Castoridae) from the southeastern United States.” Bulletin of the Florida Museum of Natural History 53(2):26-43. 3.

3. Holman, J.A. .1985. “Herpetofauna of Ladds Quarry.” National Geographic Research 13: 423-436.

4. Ray, C. E. .1967. “Pleistocene mammals from Ladds, Bartow County, Georgia.” Bulletin of the Georgia Academy of Science 25(3):120-150.

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3 comments

  1. The presence of the Florida muskrat (Neofiber alleni) is evidence of warmer climate, not the presence of the muskrat (Ondatra zibithecus). The latter species lives as far north as Canada, while the Florida muskrat is restricted to Florida and extreme south Georgia. Despite the name, they are not closely related.

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