A juvenile sauropodomorph tibia from the 'Botucaraí Hill', Late Triassic of Southern Brazil

Abstract

-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.

A Juvenile Specimen of Sauropodomorpha from the Lower Jurassic of China and a Brief Review of the Lufeng Sauropodomorph Fauna

“…The heavy vascularization of the tissue, presence of woven bone, and absence of LAGs and secondary osteons suggest that CVEB22001 was a juvenile with a fairly fast growth (de Ricqlè s, 1974;Chinsamy, 1993). Similar patterns with dense vascularization and primary osteons have been observed in several juvenile non-sauropodan sauropodomorphs, including Ignavusaurus (Knoll, 2010), Massospondylus, Mussaurus (Cerda et al, 2014) and MMACR-PV-028-T (Pretto et al, 2016).…”

“…The proximal articular surface is flat and, without considering the cnemial crest, suboval in outline. This shape differs from the circular one of the juvenile Yunnanosaurus robustus (Sekiya et al, 2014) and the subtriangular one of an indeterminate juvenile sauropodomorph from the Triassic of Brazil (Pretto et al, 2016).…”

“…A few specimens are still indeterminate to date, but most of them have been assigned to new or already existing genera. Non-sauropodan sauropodomorph juveniles attributed to six different genera, as well as one indeterminate specimen, were reported from Upper Triassic deposits: Efraasia (Galton and Bakker, 1985), Thecodontosaurus (Benton et al, 2000), Euskelosaurus (Durand, 2001), Mussaurus (Pol and Powell, 2007;Cerda et al, 2014), Pantydraco (Galton et al, 2007;Galton and Kermack, 2010), Plateosaurus (Hofmann and Sander, 2014), and MMACR-PV-028-T (Pretto et al, 2016).…”

Anatomy of the dinosaur Pampadromaeus barberenai (Saurischia—Sauropodomorpha) from the Late Triassic Santa Maria Formation of southern Brazil

“…Caudal to this furrow, the lateral surface bears a rugose rounded bump for the articulation of the fibula and attachment of the tibiofibularis ligament [28]. A foramen, possibly related to the nutritive tibial artery [28, 89–91], is observable distal to the rugose bump. The poorly preserved distal end of the left tibia is not significantly broader lateromedially than craniocaudally, suggesting that any transverse expansion of the bone only occurred distal to that.…”

On a skeletally immature individual of Unaysaurus tolentinoi (Dinosauria: Sauropodomorpha) from the upper Triassic of southern Brazil

“…Small, skeletally immature sauropodomorphs are relatively rare from Triassic beds of Brazil. Whereas most sauropodomorph specimens from Caturrita Formation may have not reached their maximum size (e.g., all the specimens have visible neurocentral sutures; Leal et al, 2004; Müller et al, 2018), individuals of a small size are unusual, restricted to a single isolated tibia (Pretto et al, 2016). Therefore, the new specimen provides an important new record for the Caturrita Formation, which is reported below.…”