Intraskeletal variability in osteohistology and growth record in a single individual of Sclerocephalus nobilis (Temnospondyli; Early Permian)

Abstract The osteohistology and growth record of eight bones from a single individual of the Permian temnospondyl Sclerocephalus nobilis were analysed. This individual grew dominantly with a parallel-fibred matrix, which can be histologically differentiated into an early ontogenetic (larval) and a later ontogenetic (juvenile) stage. The histological observation of two life phases concurs with the morphological assessment of this individual as a late juvenile. The number of growth marks interpreted as being annual ranges from five (humerus) to 10 (tibia). The bones show a variety of growth marks with diverging sequences (single, double and multiple rest lines). Thus, the number of growth marks does not necessarily reflect actual age but may nevertheless provide an indication of the time involved. A cautious interpretation suggests that the two ontogenetic phases observed in this S. nobilis individual each lasted several seasons, possibly years. More speculatively, considering the relatively simple sequence of the growth marks of both humeri and the dermal bones, the larval stage may have persisted for 4 to 5 years, followed by a juvenile stage lasting for another year before death. The overall slow growth rate observed in this specimen of S. nobilis is probably related to a strong seasonal growth in a harsh environment.