Functional morphology of the cave bear (Ursus spelaeus) cranium: a three-dimensional geometric morphometric analysis

The diet of the fossil bear Ursus spelaeus has been debated extensively. U. spelaeus is thought to have been herbivorous, but the exact composition of its diet remains unclear. To test this, the cranial morphology of U. spelaeus was analysed using 3D geometric morphometrics and compared to that of extant Ursidae. An approach including the Ursus species with a varied diet (brown, and American and Asiatic black bears) allows for a more precise focus on food items that are directly relevant to the question of the diet of U. spelaeus.Landmarks for 3D digitisation of the cranium were chosen to reflect functional morphology relating to the attachment of the musculus temporalis and m. masseter and general shape of the cranium. Extant Ursidae and the extinct U. spelaeus were digitised with a Microscribe G2. Generalised Procrustes superimposition was performed on the coordinates and allometry corrected for using pooled regression analysis. Principal Component Analysis (PCA) was conducted and interpreted with respect to diet.PCA differentiates between genera in Ursidae and known dietary composition in extant Ursus on principal components 1 and 2. The position of U. spelaeus in morphospace suggests more foliage intake, relative to the extant brown bear Ursus arctos. These results suggest that the diet of U. spelaeus likely consisted mostly of foliage. Two cave bear specimens from Moravský Kras and Merkensteinhöhle are separate from the others on PC2; this may be due to dietary differentiation, but the exact interpretation remains elusive, because precise geographical and temporal data are missing for the specimen from Moravský Kras.