First histological and skeletochronological data on temnospondyl growth: palaeoecological and palaeoclimatological implications

Abstract

The metoposaurid Dutuitosaurus ouazzoui, from the Carnian (Upper Triassic) of southern Morocco is one of the best known temnospondyls; more than 75 specimens have been found, including 15 sub-complete skeletons of various sizes from ImiN'Tanoute, a mass mortality locality (Bull. Soc. Géol. Fr. 25 (1983) 623) in the Argana Basin, Western High Atlas. Ten femora, sampled from sub-complete skeletons belonging to a growth series, have been sectioned at the mid-diaphyseal level in order to perform histological and skeletochronological analyses. Sections from juveniles and adults show microstructures typical of aquatic stegocephalians (absence of a free medullary cavity, presence of an extensive spongiosa that merges gradually into a cortical compacta). Bone sections from juveniles reveal a relatively high initial growth rate (no secondary osteons, cortex with wide and densely vascularized growth zones, alternating with thin annuli or Lines of Arrested Growth—LAGs). Bone sections from adults indicate a decreased growth rate (less vascularized external cortex, osteocyte lacunae parallel to the cortical stratification), probably after the acquisition of sexual maturity, and a moderate amount of remodeling (presence of a few secondary osteons, of erosion bays in the cortical compacta). Growth marks are correlated with environmental changes, likely to be seasonal cycles. Compactness profiles have been quantified using ‘Bone profiler’. Comparison with profiles of extant taxa confirms the hypothesis that Dutuitosaurus was aquatic.