title: Evolution and environmental correlates of craniodental morphology in the extinct cave bear Ursus spelaeus
Creators: name: Charters, D
Publisher: name: Liverpool John Moores University
Year: 2025

description: The cave bear Ursus spelaeus has been a focal species in Quaternary research for many years, being highly represented in the fossil record due to the high preservation of their remains in cave sites across Europe. Many studies over recent years through stable isotope and morphometric analyses of fossil assemblages have indicated that the cave bear was mostly herbivorous, with the species exhibiting skeletal morphological adaptations when exploiting varied environmental niches, be that spatially or temporally. Ecological diversity is very evident today in extant members of the genus Ursus, and appears to be key in explaining how they have thrived across vast ecological gradients. Here, I employ a multitude of methodologies to explore the evolution, adaptation, diet, palaeoecology and related environments of Ursus spelaeus in a single site. Geometric morphometrics stands as the backbone methodology for this series of studies, utilising phenotypic trajectory analysis, bioclimatic factors of extant species and d13C and d18O stable isotope analyses to explore temporal morphological and isotopic changes across the mandible and entire lower molar tooth row from the stratified temporal infilling of Scladina Cave, Belgium. I show that molar tooth size increases from Marine Isotope Stage (MIS) 5 – MIS 3, with shape changes in cusp position varying temporally in relation to a larger talonid grinding platform in the second and third molars in later time periods. The third molar suggests different evolutionary trajectories to that of M1 and M2 and appears much more responsive to environmental changes. Similarly in the mandible, Ursus species were discriminated with a high degree of accuracy through morphology, which showed intra and interspecific shape variation that was linked to climatic adaptations. This functional morphological variation in U. spelaeus suggested adaptations to a series of fluctuating environments through time. These climatic fluctuations were detected through varying d13C and d18O values through temporal units. Warmer environments are shown by higher d18O values correlated with lower d13C values as bears consume more d13C enriched plant sources in forest environments compared to those in colder, boreal or open steppe environments. An herbivorous, plant-dominant diet is suggested for Ursus spelaeus, irrespective of temporal position in the cave stratigraphy or inhabiting a temperate or steppic environment. However, findings show that cave bears may possess a degree of dietary plasticity, but in the general trophic context of herbivory. This helped to determine climatic classifications and assess previously proposed Marine Isotope Stages for chronostratigraphic sedimentary deposits in Scladina Cave. I suggest further work into temporal variation of well stratified sites in terms of understanding large Pleistocene fauna, through methodologies used herein. Further utilising other tools such as d15N and incorporating coeval species would provide an understanding of environmental stressors and the species subsequent adaptation across a complete trophic web.