Ontogeny/growth of (sub)modern brown bear (Ursus arctos) skeleton: A guideline to appraise seasonality for cave bear (Ursus spelaeus) sites?

Abstract

If cave bear (Ursus spelaeus) sites are suspected to be occupied during winters (hibernation), studies clearly demonstrating seasons of cave occupation by this species are still rare, and are mainly based on cementochronology. However, in numerous cave bear sites, postcranial elements belonging to non-adult individuals at different ontogenic stages are abundant and better preserved than are teeth.Studies on brown bear (Ursus arctos) skeletal growth have considered sequences of eruption and wear of deciduous teeth, and sometimes length of skulls or long bone epiphysation. In order to appraise seasons of cave occupation by Ursids, measurements have been taken on modern and subfossil complete brown bear skeletons. Those samples concern measurements taken from pictures (one 6-day old in Natural History Museum in Vienna (Austria), one 10-day old individual) or directly taken by the present authors (2 skeletons of Pyrenean modern 6-month old individuals in Natural History museum, Toulouse; an articulated skeleton belonging to the same stage of growth coming from the Mont Ventoux natural trap n°29 (MV29); and an articulated Pyrenean juvenile skeleton coming from the Trou Sylvain natural trap). Individual ages of those skeletons have been determined with eruption sequence of deciduous teeth and concern the first 2 years of brown bear life. Measurements on those samples have been taken and have been compared to the huge Holocene samples from 2 Mont Ventoux (MV2, MV4) natural traps, yielding each several hundred non-adult postcranial elements. As far as is known, those sites yield the largest brown bear populations from Europe. Seasonality has been previously studied from deciduous teeth eruption sequences. For postcranial elements, found discarded or mixed together, no analysis has been achieved. The goals of the current work are: 1) to match estimation of age from postcranial elements with the teeth eruption sequences; 2) to present rates of growth from appendicular elements during the first 2 years of life; 3) to evaluate evidence of sexual dimorphism during early life; and 4) to compare growth of brown bear postcranial skeleton with cave bear homologues. This work might provide interesting information on chronology of osseous growth and on seasons of cave occupations (winter vs annual occupation).