BAYESIAN BIOGEOGRAPHIC ANALYSIS OF SQUIRREL EVOLUTION SUGGESTS AN ASIAN ORIGIN
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Date
2021-06
Authors
Banks, Anna
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Squirrels have an incredibly diverse lineage with a global distribution and have dispersed
over millions of years from a common ancestor approximately 40-50 MYA. The assumption
since the 1980’s has been that squirrels originated in North America and evolved from North
American tree squirrels about 34-39 MYA, but in a more recent study, the oldest giant flying
squirrel fossil was found in Oregon suggesting a possible eastward migration from Asia. This
study made me question the previously accepted hypothesis that squirrels originated in North
America and led to an exploration of squirrel evolution and origins. We used an R package
called BiogeoBEARS with Bayesian biogeographic analysis and a DEC+J model to get a better
picture of where squirrels were located at different points in their evolution. To run this analysis,
we input a phylogenetic tree file, representing 225 modern Sciuridae species, and a biogeography
file with each of their locations sorted into eight regions. My analysis resulted in a few
noteworthy findings regarding major biogeography changes and their timing: (1) we believe that
squirrels originated in Asia, (2) North American and Southern African squirrels came from Asia,
and (3) we found one long South American branch, genetically distant from all other South
American Sciuridae species and stemming from near the oldest common squirrel ancestor,
leading to just one species, Sciurillus pusillus, a modern species that has resided in South
America for about 37 Ma.
Description
30 pages
Keywords
North American tree squirrels, Evolution, Sciurillus pusillus, Asia