Morphometry of lower cheek teeth of cave bears (Carnivora, Ursidae) and general remarks on the dentition variability

The variability of lower 6776 cheek teeth of spelaeoid (Ursus spelaeus, U. kanivetz, U. deningeri, U. kudarensis, U. savini and U. rossicus) and arctoid lineages (extant and extinct U. arctos) recovered from 176 palaeontological localities was analysed by methods of univariate and multivariate statistics. For comparison, teeth of U. minimus and U. etruscus species, which are ancestral taxa for cave bears and brown bear, were studied. The performed analyses indicate great variability of tooth crown in lower cheek teeth; no distinct general trend was identified in the changes, except for an increase in p4 roundness and in m3 size from U. minimus to big cave bears. Centroids of U. minimus and U. etruscus are at a great distance from those of cave bears; U. arctos occupies an intermediate position between the two groups. Molar characteristics in general are close in U. savini and U. rossicus. The bear species are differentiated in the morphospaces by morphometric variations in the lower cheek teeth but less markedly than in the morphospaces of the upper cheek teeth. A test of the inhibitory developmental cascade model showed that a linear relationship between lower molar dimensions became clear only after premolar p4 was included in the model. Evolutionary trends were found in the tooth changes with time (differently expressed in individual species and in different teeth) depending on environments, in particular on the elevation of the locality above the sea level. The allometric pattern differentiation does not always coincide with phylogenetic relationships between taxa, being most often revealed at the subspecies level. There is a dominant covariance between the upper and lower rows of teeth in accordance with the occlusion scheme. It may vary in manifestation depending on the particular species.