Comparative functional skeletal morphology among three genera of shrews: implications for the evolution of locomotor behavior in the Soricinae (Eulipotyphla: Soricidae)

Abstract

The clade comprising the soricid tribes Blarinellini (Blarinella) and Blarinini (Blarina and Cryptotis) is notable within the Soricidae (Eulipotyphla) for the large proportion of reportedly semifossorial species. To better define locomotor modes among species in these two tribes, we quantified purported locomotor adaptations by calculating 23 functional indices from postcranial measurements obtained from museum specimens of Blarina and Blarinella and published measurements for 16 species of Cryptotis. We then analyzed relative ambulatory fossorial function of each species using principal component analyses and mean percentile rank (MPR) analysis of the indices. Species within the Blarinellini Blarinini clade exhibit a graded series of morphologies with four primary functional groupings that we classified as "ambulatory," "intermediate," "semifossorial," and "fossorial." To obtain a preliminary overview of evolution of locomotor modes in this group, we mapped MPRs on a composite phylogeny and examined the resulting patterns. That analysis revealed that the most recent common ancestor of the Blarinellini Blarinini clade most likely had an intermediate or semifossorial locomotor morphology. Individual subclades subsequently evolved either more ambulatory or more fossorial morphologies. Hence, evolution of locomotor traits within this clade is complex. Multiple shifts in locomotor mode likely occurred, and no single directional tendency is apparent either among the major modes or in levels of complexity.