Comparing a Skeletal Squirrel to an Extant Flying Squirrel
If you’ve ever wondered how flying squirrels looked, this article will explain how they compared to extant skeletons and reconstructed their skeletons. Here, we’ll explore the differences between the skeletons of extant flying squirrels and the remains of a dead squirrel. This article will also cover how to identify bones and compare them with extinct flying squirrel skeletons.
Reconstruction of a squirrel skeleton
Scientists recently uncovered a fossil of a flying squirrel and its jawbone. This rodent, which had mandibles and cheek teeth, had evolved from tree squirrels some 31 million years ago. The team was surprised to find the fossil and its jawbones so close to those of flying squirrels today. The researchers hope the discovery will lead to a better understanding of how squirrels evolved over the past million years.
The oldest unquestionable flying squirrel, Miopetaurista neogrivensis, dates back to the middle/late Miocene boundary. The diagnostic wrist anatomy of this fossil allows the reconstruction of the time of origin for flying squirrels. Total evidence analysis estimates a time interval between 36.6 and 24.9 Ma, while node dating yields a younger estimate of 30.6 to 17.4 Ma. The fossil also demonstrates that flying squirrels have evolved into two separate subtribes.
A second set of craniometric data was recorded from the reconstruction. These measurements provided quantitative data about shifting between the jawbones and the mandible. Once these measurements were complete, the researchers assembled the skeleton of the flying squirrel. They also examined the final reconstruction to ensure anatomic accuracy. They found only a small gap in the right maxillary and zygomatic bone. There were no major fractures or reshaping of the bones that had occurred during the reconstruction process.
Characteristics of extant flying squirrels
The first occurrences of ‘flying squirrels’ in North America are associated with high mean global temperatures during the early Miocene. The early Miocene marks the Mid-Miocene climatic optimum. This period also coincides with the first records of new genera in Europe and North America. The species’ radiation would likely have been hindered if not impossible because of the lack of suitable habitats.
However, fossil data are needed to determine the phylogenetic position of older ‘flying squirrels’. Although independent estimates of the pteromyin divergence dates overlap, they are still significantly older than previous molecular results. The earliest ‘flying squirrel’ fossils are dated in the late Oligocene, which is the likely time when pteromyins diverged from other taxa.
The fossil record of ‘flying squirrels’ includes paleoclimatic data and morphological data from various species. The three genus include Miopetaurista neogrivensis, Douglassciurus jeffersoni, and Moxus adamanthus. In the graph below, the 95% highest posterior density intervals for the divergence dates for the flying squirrels are shown. These intervals overlap, and the darkest shading indicates the most likely time of the split.
In the fossil record, the genus Petaurista is separated from Miopetaurista by its dental characteristics. Despite their similarity, however, there are differences between these two groups. For instance, the Miopetaurista has a lower-crowned teeth than the Petaurista, and the two species share a prominent patellar groove on the femur.
Comparing a squirrel skeleton to an extant flying squirrel
The morphological characteristics of a flying squirrel differ from that of its closest relatives, including other mammals. The postcranial skeletons of Petaurista and Miopetaurista are nearly identical, although the former has a reduced lateral epicondylar ridge and has additional transverse lophules, whereas the latter has no longitudinal lophules. Comparing a squirrel skeleton to that of an extant flying squirrel can reveal many important differences, including morphological and behavioral similarities.
In a recent study, skeletal elements of M. neogrivensis were compared with those of other extant flying squirrels. This allowed researchers to reconstruct postcranial character states of extant flying squirrels and other mammals. The results of this study were published in the journal Zootaxa, and were confirmed by comparative anatomy and paleontological observations. Despite the difficulty in obtaining postcranial material, this study provides the earliest evidence of sciurid gliding locomotion.
The earliest flying squirrel, Douglassciurus, is the best candidate for comparison with extant flying mammals. Its postcranial skeleton contains abundant postcranial material, making it a possible outgroup for other flying squirrel groups. The fossil skeleton is dated to 11.66 million years ago, which allows us to recalibrate the divergence time between the tree squirrel and the flying squirrel.
Jessica Watson is a PHD holder from the University of Washington. She studied behavior and interaction between squirrels and has presented her research in several wildlife conferences including TWS Annual Conference in Winnipeg.