Turtles are a charismatic reptile group with a peculiar body plan, which most notably
includes the shell. Anatomists have often focused descriptive efforts on the shell
and other strongly derived body parts, such as the akinetic skull, or the cervical
vertebrae. Other parts of turtle osteology, like the girdles, limbs, and mandibles,
are documented with less rigor and detail. The mandible is the primary skeletal element
involved in food acquisition and initial food processing of turtles, and its features
are thus likely linked to feeding ecology. In addition, the mandible of turtles is
composed of up to seven bones (sometimes fused to as little as three) and has thus
anatomical complexity that may be insightful for systematic purposes and phylogenetic
research. Despite apparent complexity and diversity to the mandible of turtles, this
anatomical system has not been systematically studied, not even in search of characters
that might improve phylogenetic resolution. Here, we describe the mandibular osteology
for all major subclades of extant turtles with the help of digitally dissected 3D
models derived from high-resolution computed tomography (mu CT) scans of 70 extant
species. We provide 31 fully segmented mandibles, as well as 3D models of the mandibular
musculature, innervation, and arterial circulation of the cryptodire Dermatemys mawii.
We synthesize observed variation into 51 morphological characters, which we optimize
onto a molecular phylogeny. This analysis shows some mandibular characters to have
high systematic value, whereas others are highly homoplastic and may underlie ecological
influences or other factors invoking variation.
