Craniometric differentiation within wild-living cats in Scotland using 3D morphometrics

Due to the unknown effects of long-term sympatry and interbreeding with the domestic cat, there is an ongoing debate about the characterization and taxonomic status of the wildcat Felis silvestris in Europe. Recent results on the morphology of wild-living cats in Scotland had revealed two morphological groups, T1 and T2, defined from a discriminant function (based on intestine length and limb bone size). We compared wild-living cats of each of these types from Scotland, together with known domestic cats, using a new technique: geometric analysis of 3D landmarks, with the goal of formalizing a definition of wildcats that would assist with their conservation. Eighty-five landmarks were digitized on a set of 85 skulls and subjected to superimposition techniques and univariate and multivariate analyses. Results showed that T1 cats generally clustered together while, despite showing their own morphological characteristics, T2 cats seemed closer to domestic cats. T1 cats had the largest skulls, the lowest braincase capacity index and demonstrated the greatest sexual dimorphism. Domestic cats were more heterogeneous, exhibiting a wide overlap between males and females. Analysing individual landmarks, females showed more differences between the groups, particularly in the orbito-nasal region. Our results not only provide a completely independent verification of the T1/T2 categorization, but also show that, as a practical tool, skulls can be identified as T1 using six linear skull characters selected from the 85 landmarks. From current evidence it is not logically possible to state conclusively that T1 cats are wildcats, but our results firmly support the hypothesis that they are furthest from domestic cats. Thus, the distribution of T1 cats in Scotland provides a possible basis for wildcat conservation through protection by area.