A shrewd inspection of vertebral regionalization in large shrews (Soricidae: Crocidurinae)

The regionalization of the mammalian spinal column is an important
evolutionary, developmental, and functional hallmark of the clade.
Vertebral column regions are usually defined using transitions in external
bone morphology, such as the presence of transverse foraminae or rib
facets, or measurements of vertebral shape. Yet the internal structure of
vertebrae, specifically the trabecular (spongy) bone, plays an important
role in vertebral function, and is subject to the same variety of
selective, functional, and developmental influences as external bone
morphology. Here we investigated regionalization of external and
trabecular bone morphology in the vertebral column of a group of shrews
(family Soricidae). The primary goals of this study were to: 1) determine
if vertebral trabecular bone morphology is regionalized in large shrews,
and if so, in what configuration relative to external morphology; 2)
assess correlations between trabecular bone regionalization and functional
or developmental influences; and 3) determine if external and trabecular
bone regionalization patterns provide clues about the function of the
highly modified spinal column of the hero shrew Scutisorex. Trabecular
bone is regionalized along the soricid vertebral column, but the
configuration of trabecular bone regions does not match that of the
external vertebral morphology, and is less consistent across individuals
and species. The cervical region has the most distinct and consistent
trabecular bone morphology, with dense trabeculae indicative of the
ability to withstand forces in a variety of directions. Scutisorex
exhibits an additional external morphology region compared to unmodified
shrews, but this region does not correspond to a change in trabecular
architecture. Although trabecular bone architecture is regionalized along
the soricid vertebral column, and this regionalization is potentially
related to bone functional adaptation, there are likely aspects of
vertebral functional regionalization that are not detectable using
trabecular bone morphology. For example, the external morphology of the
Scutisorex lumbar spine shows signs of an extra functional region that is
not apparent in trabecular bone analyses. It is possible that body size
and locomotor mode affect the degree to which function is manifest in
trabecular bone, and broader study across mammalian size and ecology is
warranted to understand the relationship between trabecular bone
morphology and other measures of vertebral function such as intervertebral
range of motion.