New rhadinosuchine proterochampsids from the late Middle-early Late Triassic of southern Brazil enhance the diversity of archosauriforms

A new small-sized predatory pseudosuchian archosaur from the Middle-Late Triassic of Southern Brazil

Before the rise of dinosaurs and pterosaurs, pseudosuchians-reptiles from the crocodilian lineage-dominated the Triassic land ecosystems. This lineage diversified into several less inclusive clades, resulting in a wide ecomorphological diversity during the Middle and Late Triassic. Some giant pseudosuchians occupied the top of the trophic webs, while others developed extensive bony armor as a defense mechanism, which later evolved as a convergence in the avemetatarsalian lineage. On the other hand, there were groups like the Gracilisuchidae, which was composed of carnivorous forms with lightweight build and less than 1 m in length. The fossil record of gracilisuchids is geographically restricted to China and Argentina, with one ambiguous record from Brazil. In the present study, the first unambiguous gracilisuchid from Brazil is described. Parvosuchus aurelioi gen. et sp. nov. comes from the Dinodontosaurus Assemblage Zone of the Santa Maria Formation, which is associated with the Ladinian-Carnian boundary. Composed of a complete cranium, vertebrae, pelvic girdle and hindlimbs, the new species nests with Gracilisuchus stipanicicorum and Maehary bonapartei in a phylogenetic analysis. Its discovery fills a taxonomic gap in Brazilian pseudosuchian fauna and reveals the smallest known member of this clade from the Dinodontosaurus Assemblage Zone, highlighting the diversity of pseudosuchians during the moment that preceded the dawn of dinosaurs.

A new early-diverging probainognathian cynodont and a revision of the occurrence of cf. Aleodon from the Chañares Formation, northwestern Argentina: New clues on the faunistic composition of the latest Middle-?earliest Late Triassic Tarjadia Assemblage Zone

The Chañares Formation (Ischigualasto-Villa Unión Basin) is worldwide known by its exquisitely preserved fossil record of latest Middle-to-early Late Triassic tetrapods, including erpetosuchids, "rauisuchians," proterochampsids, gracilisuchids, dinosauromorphs, pterosauromorphs, kannemeyeriiform dicynodonts, and traversodontid, chiniquodontid and probainognathid cynodonts, coming from the Tarjadia (bottom) and Massetognathus-Chanaresuchus (top) Assemblage Zones of its lower member. Regarding cynodonts, most of its profuse knowledge comes from the traditional layers discovered by Alfred Romer and his team in the 1960s that are now enclosed in the Massetognathus-Chanaresuchus Assemblage Zone (AZ). In this contribution we focus our study on the probainognathian cynodonts discovered in levels of the Tarjadia Assemblage Zone. We describe a new chiniquodontid cynodont with transversely broad postcanine teeth (Riojanodon nenoi gen. et sp. nov.) which is related to the genus Aleodon. In addition, the specimen CRILAR-Pv 567 previously referred to cf. Aleodon is here described, compared, and included in a phylogenetic analysis. It is considered as an indeterminate Aleodontinae nov., a clade here proposed to included chiniquodontids with transversely broad upper and lower postcanines, by having a cuspidated sectorial labial margin and a lingual platform that is twice broader than a lingual cingulum. Cromptodon mamiferoides, from the Cerro de Las Cabras Formation (Cuyo Basin), was also included in the phylogenetic analysis and recovered as an Aleodontinae. The new cynodont and the record of Aleodontinae indet. reinforce the faunal differentiation between the Tarjadia and Massetognathus-Chanaresuchus Assemblage Zones, in the lower member of the Chañares Formation, and inform on the diverse chiniquodontid clade with both sectorial and transversely broad postcanine teeth.

The redescription of Malerisaurus robinsonae (Archosauromorpha: Allokotosauria) from the Upper Triassic lower Maleri Formation, Pranhita-Godavari Basin, India

Allokotosauria, a clade of non-archosauriform archosauromorphs with a broad diversity of body plans, plays a crucial role in better understanding the evolutionary history of early diverging stem-archosaurs. Here we provide a detailed redescription of Malerisaurus robinsonae, a malerisaurine allokotosaur from the middle Carnian-lowermost Norian lower Maleri Formation, Pranhita-Godavari Basin, India. The new anatomical information available from recently discovered and well-preserved skeletons of various allokotosaurs, such as Azendohsaurus madagaskarensis, Shringasaurus indicus, Puercosuchus traverorum, and Malerisaurus-like taxa, and their comparison with Malerisaurus robinsonae enriches our understanding of the anatomy of this species. To reassess the phylogenetic relationships of Malerisaurus robinsonae, we revised its scorings and included eight additional allokotosaurian species to the already most comprehensive phylogenetic dataset focused on Permo-Triassic archosauromorphs. We modified 70 scorings for Malerisaurus robinsonae and the new analysis recovered this species at the base of Malerisaurinae and this group as the earliest branch of Azendohsauridae. Pamelaria dolichotrachela is found as the earliest diverging non-malerisaurine azendohsaurid and sister taxon to the Shringasaurus indicus + Azendohsaurus spp. clade. Trilophosaurid interrelationships are well resolved, with Teraterpeton hrynewichorum, Coelodontognathus ricovi, and Rutiotomodon tytthos as their successive earliest-branching species. The position of Anisodontosaurus greeri as a sister taxon to Variodens inopinatus bolsters long ghost lineages in the Late Triassic trilophosaurid record. A disparity analysis of tooth crown morphology shows that Allokotosauria is the most disparate Permo-Triassic archosauromorph clade, exploring the almost complete range of basic crown morphologies. Trilophosaurids occupy an area of the dental morphospace unique among archosauromorphs.

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.