Limb bone histology of Decuriasuchus quartacolonia (Archosauria: Paracrocodylomorpha) from Santa Maria Formation Southern of Brazil

FARIAS, B.D.M.; J.B. DESOJO; FERIGOLO, J.; RIVERO, L.; DE FRANCA, M; SOARES, M. B.

Teresina

Congreso; XI Simpósio Brasileiro de Paleontologia de Vertebrados; 2018

Decuriasuchus quartacolonia is known by an exclusively assemblage of nine associated individuals (MCNPV10.105a?i) and a partial disarticulated skull (MCN-PV10.004) from Santa Maria 1 Sequence (Santa Maria Formation). The material is housed at the Fundação Zoobotânica de Porto Alegre, Brazil, and represents the sister taxon of Batrachotomus kupferzellensis from Germany + Prestosuchus chiniquensis from Brazil. They represent the earliest evidence of gregarious behavior among archosaurs. Until now, only anatomical descriptions of the skull and post cranium were made for D. quartacolonia, so information about its biology and phylogenetic relationships are thus limited. The ontogenetic stage of all specimens was considered adult based on their similar size, closed neurocranial, and neurocentral sutures by the original description. However, new studies in the last years showed that these approaches are not reliable for all the archosaurs. In this contribution, we provide the first insights on the biological aspects of D. quatacolonia using bone histology, the most reliable method to access growth rates, growth patterns, age and life style of extinct vertebrates. One radius and one ulna of both MCN PV 10.105 B and MCN PV 10.105 X were sampled using standard paleohistological procedures. The bone microstructure of the radius and ulna of MCN PV 10.105 X are quite similar. The inner cortex is highly vascularized with random vascular canals, many of them being primary osteons. Several round and random osteocyte lacunae are present in the bone matrix, resulting in a fibro-lamellar complex. Secondary osteons were not found. Vascularization continues towards the mid cortex, but it is less intense reaching the outermost cortex. An external fundamental system is not observed, suggesting that this individual was not fully grown. The radius and ulna of MCN PV 10.105 B are badly preserved, but the few preserved regions show the same organization of vascular canals presented and bone tissue as in MCN-PV-10.105 X. This data set suggest that these two individuals of D. quartacolonia were still growing at high rates, contrasting with the previous conclusions that all ten individuals of D. quartacolonia found in the quarry were adults. Similar bone histology was found in juveniles of Batrachotomus kupferzellensis.