SCULPTURED CRANIUMS AND HOW TO DESCRIBE THEM IN FOSSIL VERTEBRATES

Captorhinids are an extinct group of Palaeozoic eureptiles, being model representatives of basal Reptilia. These non-synapsid amniotes represent the first major radiation of terrestrial vertebrates. They have a conservative skull anatomy with the presence of conspicuous skull sculpturing.

Morphological skull features are extensively used in phylogenetic analysis, particularly external cranial bone surface texture (skull sculpturing). However, in captorhinids there is no consensus on the definition and classification of this trait, and different authors use different words to describe similar character states. In addition, current technology provides previously undescribed structures in bone texture that require proper nomenclature definition in order to be used as phylogenetic characters.

Here we present a deep redescription of all captorhinid phylogenetic characters used in recent literature. We also propose a redefinition of skull sculpturing terminology, standardize correspondent character states, and define multiple new characters.

We used image analysis software (Krita and FIJI) for drawing the bone texture network and isolating individual polygons. The resulting data was analysed on RStudio, where we performed statistic tests to find differences in skull sculpturing patterns.

This new data allows to generate new phylogenetic analyses that include 23 captorhinid species. We also compare our findings with the most recent available phylogenetic data and discuss our results in the context of current literature.

Additionally, the methodology here developed can be easily applied for any other research on extant or extinct animals that also present sculpturing in their skull, bringing new light into the evolutionary history of this extremely curious anatomical trait.