limb bone structure

Mammals exhibit a diverse range of limb morphologies that are associated with different locomotor ecologies and structural mechanics. Biologists, however, have rarely investigated whether these factors have different effects on the external and internal morphologies of limb bones. Here, we used squirrels (Sciuridae) as a model clade to examine the effects of locomotor mode and allometry on the size, external shape, and internal structure of the humerus and femur. With over 278 species, Squirrels (family Sciuridae) are found across diverse habitats ranging from deserts, through tropical and temperate forests, to the arctic tundra. Furthermore, squirrels can be sorted into distinct ecotypes (i.e., ground, tree, and gliding) that invite questions about the adaptive significance of different body plans for these different niches.

#TeamSquirrel is lead by UW undergraduates Abby Burtner, Tate Linden, and Hannah Rickman!

We CT scanned squirrel humeri and femora and quantified their external shapes and internal structures. The above figure shows the pruned phylogeny of our 76 species overlaid with an ancestral state reconstruction of squirrel ecotype. 194 pseudolandmarks on the humeri and 152 pseudolandmarks on the femora were generated and applied to our sample using the PseudoLMGenerator and ALPACA modules in SlicerMorph. Bone structure variables were calculated using the SegmentGeometry module in Slicer. Cg = global compactness; DE = diaphysis elongation; CSS = cross-sectional shape.