The mandibular morphology of the Middle Pleistocene brown bear mandible from Postes cave (Spain) within the European Ursus arctos (LINNAEUS, 1758) morphological variation

Brown bears (Ursus arctos) originated in Asia and diverged from the spelaeoid line in the late early Pleistocene, but they do not appear in the European fossil record until half a million years ago. Middle and Late Pleistocene bears are referred to in Europe as U. arctos priscus (GOLDFUSS, 1818) and U. arctos (LINNAEUS, 1758), respectively. U. arctos priscus is larger than recent European brown bears. Recent U. arctos comprises three subspecies in Europe and presents a high variability. In the Iberian Peninsula the oldest brown bears are dated to the Late Middle Pleistocene and their remains are very scarce. The oldest brown bear mandible of the Iberian Peninsula was found in the Middle Pleistocene site of Postes cave, in the Natural Monument of Fuentes de León, Extremadura (Spain). The bearing has yielded 62 bear remains identified as U. arctos sealed by a speleothem dated by U/Th in 192,986 +15,451/-13,837 ka BP. The purpose of this study is to compare the Postes specimen with European Ursus arctos focusing on mandibular morphology. The sample comprised of Pleistocene brown bears from the Iberian Peninsula, Southern France, Austria and Italy; Holocene (from Neolithic to Iron Age) Iberian bears and recent bears (XX-XXI century) from Iberian Peninsula, Central Europe, Balkans and Caucasus. Comparisons were made using traditional and 3D geometric morphometric analyses. The mandibles were digitized with a 3D scan and traditional measurements were taken with a calliper. Statistical analyses were carried out to compare the difference in size between European brown bears from different chronologies and test its relationship with shape. A principal component analysis (PCA) with traditional measurements shows that most of the variation is distributed along PC 1, with a minimum overlap between Pleistocene and recent U. arctos. A geometric morphometric (PCA) shows that Pleistocene U. arctos are grouped together, unlike recent specimens which show a larger degree of morphological variation. This might be caused by the diverse geographic origin of the recent sample and/or by the larger size range of the specimens. Furthermore, Holocene specimens seem to have a different shape from Pleistocene bears. A regression analysis of the Procrustes coordinates onto logarithmic centroid size indicates significant allometry in the sample. A One-way ANOVA of the centroid size shows there are significant differences between the groups. Additionally, a Tukey’s pairwise test shows that the difference lies between the recent specimens and the fossils. The results of the MANOVA are consistent with the previous analysis. In summary, these results suggest that Pleistocene U. arctos are uniform in size and shape, but present a difference in size with respect to recent specimens. Postes specimen fits within Pleistocene bear variation in both size and shape.