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The first osteohistological study focused exclusively on rhynchosaurs (non-archosauriform archosauromorphs), based on the hyperodapedontines

the non-dinosaurian dinosauriform silesaurids are the closest relatives of crown-group dinosaurs and are thus, important for understanding the origins of that group. here, we describe the limb bone histology of the Late triassic silesaurid Sacisaurus agudoensis from the Candelária Sequence of the Santa Maria Supersequence, Rio Grande do Sul state, Brazil. The sampled bones comprise eight femora and one fibula from different individuals. The microscopic analysis of all elements reveals uninterrupted fibrolamellar bone tissue indicating rapid growth. A transition to slower growing peripheral parallel-fibered bone tissue in some individuals indicates a decrease in growth rate, suggesting ontogenetic variation within the sample. the osteohistology of Sacisaurus agudoensis is similar to that of other silesaurids and supports previous hypotheses that rapid growth was attained early in the dinosauromorph lineage. however, silesaurids lack the complex vascular arrangements seen in saurischian dinosaurs. Instead, they exhibit predominantly longitudinally-oriented primary osteons with few or no anastomoses, similar to those of some small early ornithischian dinosaurs. this simpler vascular pattern is common to all silesaurids studied to date and indicates relatively slower growth rates compared to most Dinosauria.

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-The 'Botucaraí Hill' outcrop yielded a diverse Late Triassic vertebrate fauna, including several dinosaur remains, but most collected specimens are represented only by isolated bones. We present here a new dinosaur tibia from that site, particularly notable for its small size. Anatomical comparisons and a phylogenetic analysis support a sauropodomorph affinity for the specimen. In addition, histological analyses on transverse sections of the tibial shaft revealed a very thin bone wall, characterized by woven matrix with high vascularization, and the complete absence of lines of arrested growth (LAGs). These features suggest that the specimen was undergoing rapid and uninterrupted bone growth prior to death. Indeed, the small size of the specimen, the poor ossification of the bone extremities, and the absence of LAGs indicate that it represents a juvenile individual, as not previously recorded for the Brazilian Upper Triassic dinosaur fauna.