New body mass estimates of British Pleistocene wolves: Palaeoenvironmental implications and competitive interactions

Body mass was reconstructed for early Middle Pleistocene Canis mosbachensis and late Middle to Late Pleistocene Canis lupus from key assemblages in Britain, to explore the presence of temporal size variability and whether size fluctuations were related to changes in climate and environment or to differences in Pleistocene carnivore community structure. Using the well-known body mass predictor of lower carnassial (m1) tooth length, combined with an extant canid dataset incorporating 25 species, least squares regression was used to assess allometric scaling prior to modelling the relationship between body mass and m1 length, producing a new predictive equation of Pleistocene canid body mass. The medium-sized C. mosbachensis had relatively stable body mass, with remarkable consistency in size compared to populations in the late Early Pleistocene of Europe. Periodical fluctuations in climatic conditions had a minimal effect on C. mosbachensis size over time, with the terrestrial connection between Britain and mainland Europe at this time key in promoting body mass stability by enabling movement away from less favourable conditions and to follow prey into refugia. Overall changes in carnivore guild structure were of minimal influence to C. mosbachensis in Britain, as the continued predominance of larger carnivores, in particular a larger canid, effectively constrained C. mosbachensis. In contrast, the body mass of larger-sized C. lupus was highly temporally varied, with an increasing size trend evident into the Devensian. Similar body size in the penultimate interglacial (MIS 7) and Middle Devensian (MIS 3) populations likely reflects palaeoenvironmental similarity and comparable carnivore community and prey spectrums, with larger predators effectively constraining C. lupus. However, the severely cold conditions of the Early Devensian (MIS 5a) may have caused a Bergmannian response in wolves, leading to their comparatively much larger size, with C. lupus further ecologically “liberated” by an absence of larger multiple larger predators at this time.