Postcranial anatomy of Prestosuchus chiniquensis (Archosauria: Loricata) from the Triassic of Brazil

The first ontogenetic model for non-crocodylomorph loricatans, based on osteohistology of the ontogenetic series of Prestosuchus chiniquensis from the Middle Triassic of Brazil

Prestosuchus chiniquensis is an iconic non-crocodylomorph loricatan from the Brazilian Triassic beds and the best-known taxon, represented by several specimens. The completeness and preservation of its skeleton make it a valuable taxon for paleobiological studies. We explore the microstructure of bone tissues of appendicular elements and ribs of three specimens of Prestosuchus to access a variety of aspects of its paleobiology, such as histovariability, ontogeny, and growth patterns. Integrating our data and other osteohistologically studied P. chiniquensis specimens, we proposed for the first time an ontogenetic model for non-crocodylomorph loricatans. The model encompasses six distinct age classes (I-VI) that allow us to infer the growth patterns of P. chiniquensis and possibly expand to other phylogenetically close taxa. During early ontogeny (age classes I-II), sustained fast growth was maintained by a fibrolamellar complex. In mid ontogeny (age classes III-IV), highly vascularized parallel-fibered bone predominates, suggesting intermediary growth rates. A change for a poorly vascularized parallel-fibered/lamellar bone would mark the attainment of sexual (age classes IV-V) and skeletal maturity, comprising the age class VI. An external fundamental system (EFS) present in the outermost cortex is the main histological feature that characterize the age class VI. Major histovariability features are present between appendicular bones and ribs of skeletally immature individuals. The most prominent of them is the presence of fibrolamellar complex and highly vascularized parallel-fibered bone in appendicular bones and poorly vascularized parallel-fibered bone in ribs. In advanced ontogenetic stages, the histovariability between appendicular bones and ribs tends to be minor. Our data also support previous hypothesis of the presence of one new taxon among the specimens assigned to P. chiniquensis, increasing the diversity of non-crocodylomorph loricatans. The new taxon, represented by the specimen UFRGS-PV-0152-T, awaits a formal anatomical description. Our study advances the preliminary understand of the ontogeny and growth patterns of non-crocodylomorphs loricatans and Pseudosuchia as a whole.

Reassessment of the enigmatic "Prestosuchus" loricatus (Archosauria: Pseudosuchia) from the Middle-Late Triassic of southern Brazil

Our knowledge of the diversity and evolution of South American Triassic pseudosuchians has greatly improved in the past 15 years, due to new discoveries, but also to the revision of several historically important specimens. One of the earliest descriptions of pseudosuchians from the Triassic of Brazil stems from the classic work of Huene from the first half of the 20th century, who described several species, including such influential taxa as Rauisuchus tiradentes or Prestosuchus chiniquensis, which have recently been reviewed. The more poorly known proposed second species of Prestosuchus, P. loricatus, is the focus of the present work. The original material included some elements of the axial skeleton (cervical and caudal vertebrae, ribs, osteoderms) and the hindlimb (ischia, calcaneum, metatarsus), collected from the Dinodontosaurus Assemblage Zone of the Chiniquá area, west of São Pedro do Sul. "Prestosuchus" loricatus shows numerous differences to P. chiniquensis, including the shape of cervical neural spines, presence of epipophyses on the cervical vertebrae, presence of a pit in the iliac articulation of the ischium, lack of longitudinal furrows in the dorsolateral surface of the ischial shafts, the more slender calcaneal tuber and a less pronounced ventral pit in the calcaneum, and is thus referred to a new genus, Schultzsuchus gen. nov. Phylogenetic analysis indicates an early branching position within Poposauroidea for Schultzsuchus, making it the oldest known member of this clade in South America.

The dawn of an Era: New contributions on comparative and functional anatomy of Triassic tetrapods

The Triassic period stands as a crucial moment for understanding tetrapod evolution, marking the emergence and early diversification of numerous lineages that persist in today's ecosystems. Birds, crocodiles, testudines, lizards, and mammals can all trace their origins to the Triassic, which is distinguished by several adaptive radiation events that fostered unparalleled diversity in body plans and lifestyles. Beyond this macroevolutionary significance, the Triassic period serves as fertile ground for scientific inquiry, especially in tetrapod studies. The aim of this Special Issue is to assemble a diverse array of new contributions focused on continental Triassic tetrapods globally, encouraging collaboration among researchers across generations, pooling their efforts to comprehend this pivotal moment in tetrapod evolutionary history. This issue encompasses almost 40 varied contributions, spanning topics from comparative and functional anatomy, including descriptions of novel taxa, comprehensive anatomical reviews, systematic investigations, phylogenetic analyses, paleoneurological studies, biomechanical assessments, and detailed examinations of histology and ontogeny. Collectively, this Special Issue offers an extensive exploration of Triassic tetrapods from anatomical, ecological, and evolutionary perspectives, unveiling fresh insights into this intriguing moment in vertebrate evolutionary history.