Meeting Abstract
The Cenozoic spread of grasslands drove morphological, physiological, and behavioral transitions in many mammal taxa, perhaps the most profound of which was the evolution of burrowing in rodents. While several rodent families underwent this transition, sciurids are of particular interest not only due to the diversity of ground squirrels, but to the range of locomotion within the Sciuridae. While the vast saga of squirrel evolution is well documented in the fossil record, this record consists largely of craniodental remains. Postcrania are more informative about locomotion, but are often found isolated from teeth and skulls, making them impossible to assign to species. An exception to this rule was uncovered in 2017 from McKay Reservoir, a Miocene locality in northeast Oregon. The specimen is referable to Otospermophilus mckayensis and includes a skull and jaws as well as most of the anterior portion of the skeleton. We calculated functional indices based on measurements of the forearm of O. mckayensis as well as extant taxa and less complete specimens of Oligo-Miocene squirrels. A discriminant function analysis of these data had a high success rate when placing modern taxa into locomotor categories, but the fossil taxa cannot be classified as arboreal, terrestrial, fossorial, or gliding with a high degree of confidence. We also compared individual indices between species and found that while many were nearly identical to those seen in modern ground squirrels, others differed significantly. Ongoing analyses will test whether this indicates mosaic evolution of the ground squirrel limb and what implications this might have for behavior and locomotion of the earliest squirrels to take to the soil.
