Osteohistology of the silesaurid Sacisaurus agudoensis from southern Brazil (Late Triassic) and implications for growth in early dinosaurs

Abstract

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.

Growth and limb bone histology of aetosaurs and phytosaurs from the Late Triassic Krasiejów locality (sw Poland) reveals strong environmental influence on growth pattern

“…All dinosaurs, even the basal ones, grew throughout most of their life with flb (summarized in Chinsamy-Turan, 2005;Erickson, 2014). The strong phylogenetic signal in the growth of Silesaurus is confirmed by a similar fast uninterrupted growth in other silesaurids (i.e., Asilisaurus kongwe from the Middle Triassic of Tanzania, Griffin & Nesbit, 2016; Lewisuchus admixus from the Late Triassic of Argentina, Marsà et al, 2017; Sacisaurus agudoensis from Late Triassic of Brasil, Veiga et al, 2019).…”

Anatomy and phylogenetic affinities of a new silesaurid assemblage from the Carnian beds of south BrazilCitation for this article: Mestriner, G., Marsola, J. C. A., Nesbitt, S. J., Da-Rosa, A. A. S., & Langer, M. (2023) Anatomy and phylogenetic affinities of a new silesaurid assemblage from the Carnian beds of south Brazil. Journal of Vertebrate Paleontology . https://doi.org/10.1080/02724634.2023.2232426

“…In contrast, as pointed out by Veiga et al (2018), the vascular patterns of Silesauridae seems to approach that of some early ornithischians, such as the Fruitadens haagarorum and Scutellosaurus lawleri (Butler et al, 2010), which include predominantly longitudinally oriented vascular canals with few anastomoses (Butler et al, 2010;Padian et al, 2004;Veiga et al, 2018). Considering that more complex vascular patterns are associated with higher growth rates (Margerie et al, 2002;Padian & Lamm, 2013;Veiga et al, 2018), the simple vascular pattern of UFSM 11579O implies that, just like other silesaurids, this animal grew relatively slower than most early dinosaurs (Cerda et al, 2014;Klein & Sander, 2007;Marsola et al, 2019a;Padian et al, 2004).…”

“…The cortex is densely vascularized (Fig. 15D, E) and the bone tissues exhibit longitudinally oriented primary osteons and occasional anastomoses, a condition typically seen in silesaurids (Fostowicz-Frelik & Sulej, 2010;Griffin & Nesbitt, 2016;Veiga et al, 2018). The microstructure of the cortex is nearly uniform, with no discontinuities such as lines of arrested growth (LAGs-Fig.…”

“…Moreover, the simple vascular arrangement of longitudinally oriented primary osteons of UFSM 11579O and other silesaurids differs from that of most early dinosaurs, the vascular arrangements of which tend to include much more complex anastomoses, i.e., Massospondylus carinatus (Klein & Sander, 2007), Nhandumirim waldsangae (Marsola et al, 2019a), Herrerasaurus ischigualastensis (Padian et al, 2004). In contrast, as pointed out by Veiga et al (2018), the vascular patterns of Silesauridae seems to approach that of some early ornithischians, such as the Fruitadens haagarorum and Scutellosaurus lawleri (Butler et al, 2010), which include predominantly longitudinally oriented vascular canals with few anastomoses (Butler et al, 2010;Padian et al, 2004;Veiga et al, 2018). Considering that more complex vascular patterns are associated with higher growth rates (Margerie et al, 2002;Padian & Lamm, 2013;Veiga et al, 2018), the simple vascular pattern of UFSM 11579O implies that, just like other silesaurids, this animal grew relatively slower than most early dinosaurs (Cerda et al, 2014;Klein & Sander, 2007;Marsola et al, 2019a;Padian et al, 2004).…”

Osteohistology and growth dynamics of the Brazilian noasauridVespersaurus paranaensisLanger et al., 2019 (Theropoda: Abelisauroidea)

“…In recent years, studies on bone histology of dinosaurs in general and non-avian theropods in particular have provided new insights about growth and developmental strategies in relatively well-sampled taxa such as coelophysoids (Chinsamy, 1990), Tyrannosaurus rex Padian, Horner & Ricqlès, 2004;Lee & Werning, 2008) and Allosaurus agilis (Bybee, Lee & Lamm, 2006). In contrast, many dinosaur groups remain undersampled, with no well-known histological framework, especially those based on more incomplete taxa (Veiga et al, 2019). Among theropod dinosaurs, the Abelisauroidea is one such undersampled group.…”