Limb bones microstructure in Rauisuchia (Archosauria:Pseudosuchia): New insights in the growth strategies

DESOJO, JULIA B; FARIAS, B.D.M.; SCHEYER, TORSTEN; CERDA, IGNACIO; RIBEIRO, A. M.; SOARES, M. B.

Praga

Congreso; Congreso. 12th International Congress of Vertebrate Morphology.; 2019

ISVM

Recently discovered specimens of "Rauisuchia" have boosted interestin this enigmatic group of pseudosuchians, because they provide crucialinformation on major patterns and processes in continental Triassicarchosaur evolution. Here, we analyze limb bone histology ofDecuriasuchus quartacolonia MCNPV10.005b-X (humerus, ulna, radius,tibia) and Prestosuchus chiniquensis BSPG AS XXV 10, 11b, 35 (humerus,femur, fibula) from the Middle Triassic (Santa Maria Supersequence),southern Brazil, to establish their ontogenetic stage and infer growthdynamics. Both taxa exhibit cyclically deposited highly vascularized cortices.Whereas a maximum of four lines of arrested growth wererecorded in Prestosuchus, only one is preserved in Decuriasuchus. Whilethe cortical bone is formed by fibrolamellar tissue in Decuriasuchus, parallelfibered bone predominates in Prestosuchus. Evidence of secondaryremodeling is only observed in Prestosuchus. An outer circumferentiallayer (indicative of somatic maturity) is absent in all samples. Furthermore,since no clear reduction of the distance between growth marks isobserved, sexual maturity also seems to not be achieved. Comparingwith the large bodied ?rauisuchian? Batrachotomus which exhibits ahigher proportion of fibrolamellar bone, the relative growth rate of Prestosuchusappears to be lower. Comparison with Decuriasuchus is difficult,due to the younger condition of the sampled individual. Otherpseudosuchians such as Effigia, Terrestrisuchus, and Postosuchus grewfast in early development, as shown by fibrolamellar bone matrix in theinner cortex, changing to lamellar-zonal after reaching sexual maturity.This condition is also evident in the taxa sampled here, likely reflectingthe primitive condition for archosaurs. Bone histology thus argues forrauisuchians reaching massive body size during early developmentinstead of protracted longevity. Funding: PICT 2016-0159 (JBD)&2014-0609(JBD/IC).