Marine tetrapod feeding guilds using automated high-density 3D geometric morphometrics

Defining feeding guilds based on tooth morphology is an entire subfield in marine tetrapod science. However, these assessments have mostly been qualitative, relying on gross tooth shape, rarely preserved gut content, and killing behaviour. Moreover, some of the data at the foundation of these guilds have proven to be debatable and there is an ever clearer need for a testable, quantitative framework to assess feeding guilds.

We develop a novel protocol that incorporates the pseudo-landmarking technique into high-density geometric morphometrics procedures, sampling 3D surface models of tooth crowns automatically and densely (e.g. 2000 surface landmarks) after placing just 5 fixed landmarks on each tooth. A crushing-to-piercing transition is evident along the first axis of the PCA-based morphospace, while the presence and shape of carinae, as well as crown curvature, is captured by the second axis. This allows an efficient visualisation of tooth shapes with just two axes. Peculiar structures such as strong crown curvature or carinae are mostly recorded on medium-sized teeth, suggesting that a scaling factor is at play. We attempt a new definition of marine reptile feeding guilds based on tooth morphology and size, using extant polarizers.