Cave bear cub skeletons from Barová (Czech Republic) and Goyet (Belgium) caves contribute to our understanding of cave bear palaeobiology

The early period of life is crucial for the development of species-specific traits and, as such, for a correct understanding of the evolutionary constraints and adults’ adaptations. However, this critical aspect of life history is usually inaccessible for extinct mammals. One of the exceptions is the cave bear ( Ursus spelaeus ), whose hibernacula have yielded a sufficient number of cub remains at various ontogenetic stages. Unfortunately, although they have been studied for over a century, there is no consensus regarding their interpretation, which hinders their unambiguous integration into palaeobiological models. New excavations in Barová Cave (Czech Republic) have yielded unique finds of several partially preserved bear skeletons of various ages. Along with the cub skeletons from the Goyet Cave (Belgium) and isolated juvenile long bones from both localities, they enabled us to critically assess our knowledge of cave bear development during first year of cave bear life and solve thus this long-time controversy. Our results reveal that: (i) cave bear cub skeletal development during the first active season was quicker than in brown bears; (ii) tooth eruption timing was generally the same for both species and, thus, one of the main mortality peaks of cave bear cubs took place late during their first active season; (iii) mortality patterns of cubs are the same for cave bear hibernacula from Spain to the Urals. We connected the mortality peak during the active season with an unsuccessful transition to an adult diet.