New data on the palaeosteohistology and growth dynamic of the notosuchian Araripesuchus Price, 1959

Abstract

Notosuchian crocodyliforms represent an intriguing group since they are mainly terrestrial forms and therefore with completely different lifestyles than extant crocodylian, which is reflected in their particular skeletal anatomy. Although there are some inferences in the literature related to the palaeoecology of notosuchian, little is known about their biology (e.g. metabolism, growth dynamics). The palaeohistology allows us to perform interpretations about the growth dynamics and strategies of growth in these extinct forms. Here, we worked on specimens of Araripesuchus Price, 1959 (Notosuchia, Uruguaysuchidae), coming from La Buitrera Palaeontological Area, Río Negro Province (northern Patagonia, Argentina). We described for the first time the osteohistology of this taxon, based on thin sections of the stylopodium shaft (femur and humerus) of four specimens, providing an assumption of its growth dynamics. A general slow growth rate is inferred for Araripesuchus, based on the poorly vascularized parallel-fibred/lamellar bone matrix. An unusual pattern of bone deposition was observed in two specimens; we consider this tissue as evidence of a rapid growth event at some point in the ontogeny of these individuals. Finally, it can be interpreted that in Araripesuchus, sexual maturity could be reached at least between eight to thirteen years old. This study is a first step to provide insight into the life history of these terrestrial notosuchids and to provide new empirical evidence for the osteohistological variability and palaeoecology of this peculiar group of extinct crocodyliforms.