Research Training Program

Adrienne Sussman
Simon's Rock College of Bard
Great Barrington, Massachusetts

Richard Thorington, Ph.D.
Supervising Scientist
Vertebrate Zoology - Mammals

"I can not think of any way I would
rather have spent my summer."

The beautiful squirrel of South East Asia: cranial morphology and variation

In the rainforests in Malaysia and the Indonesian islands, one can see tree squirrels of all colors and sizes: black, gray, and brown, striped or solid, some twice as big as the others. However, as different as all of these animals might appear, they are all identified as being part of the same species, Callosciurus prevostii (Also known as Prevost's squirrel; Callosciurus means "beautiful squirrel"). At the moment, the squirrels are divided into 21 different subspecies, each with a unique appearance. This study investigated whether the variety between these subspecies is just a matter of different colorations, or whether the groups are distinct enough to be considered separate species. In order to measure how different each population is, skulls from the Smithsonian collection were measured. The skulls belonged to eight subspecies of C. prevostii from Sumatra, Borneo, the Malay Peninsula, and three smaller islands. On each skull, 33 distances were measured, and the skulls of the different subspecies were then compared using multivariate statistics. The results showed that the different subspecies could be identified to some degree by their skulls alone; in other words, more than color is changing between these groups. In addition, the changes in skulls did not seem to be related to changes in body size from group to group, indicating that the populations are different in shape, not just size. Overall, the evidence suggests that several of the C. prevostii subspecies are distinct, but not yet completely separate. Further consideration and analysis may cause C. prevostii to be reorganized into several species. The final decision in this case may help other scientists to make species classifications in the future. Learning about how the subspecies on each island are different will also help us to understand the history of C. prevostii's distribution in its habitat, contributing to our knowledge of the geographic history of South East Asia. Someday this research may even affect the squirrels themselves, as a new classification of all C. prevostii into smaller species groups might have an impact on the conservation status of the new species. By looking at their skulls, maybe we can help to keep all of the varieties of beautiful squirrels around forever!

This research was supported by a grant from the National Science Foundation Research Experiences for Undergraduates program, Award Number DBI-0243512.

Letter of gratitude