Skull osteology of Aetosauroides scagliai Casamiquela, 1960 (Archosauria: Aetosauria) from the Late Triassic of Brazil: New insights into the paleobiology of aetosaurs

Abstract

Aetosauroides scagliai, from the Ischigualasto Formation of Argentina and Santa Maria Supersequence of Brazil (Carnian-Norian), is one of the oldest members of Aetosauria, a diverse clade of armored crocodile-line archosaurs. Aetosauroides scagliai differs from other aetosaurs in having the maxilla excluded from the margin of the external nares, the length/width ratio of the postzygapophyses ≤ 0.75, and other features that place it as one of the earliest-diverging members of the clade. In this paper we provide a detailed description of the skull of A. scagliai based on a new Brazilian specimen, revealing that it lacks a pneumatic cavity on the medial surface of the maxilla and further differs from all other known aetosaurs by the presence of ≥ 12 dentary teeth. However, contra previous studies, the elongated posterior process of the jugal does articulate ventrally with the quadratojugal in A. scagliai, forming the posteroventral corner of the skull as in all other aetosaurs. Aetosauroides scagliai exhibits some characters typical of predatory archosaurs (like the recurved ziphodont teeth and mandibular articulation at the level of the tooth row), but was probably an omnivore, as it also shares several probable adaptations for herbivory with aetosaurs generally (i.e., edentulous anterior premaxilla and dentary) and stagonolepidoids specifically (e.g., shovel-shaped snout). This suggests that there was greater trophic diversity in this clade than usually recognized, at least early in their evolutionary history.

An unusually robust specimen attributed to Buriolestes schultzi (Dinosauria: Sauropodomorpha) from the Late Triassic of southern Brazil

“…The elements of CAPPA/UFSM 0244 were associated with disarticulated rhynchosaur bones and an articulated dinosaur, which is currently in study. Other fossils from the site include conchostracans (Jenisch et al, 2017), actinopterygian fishes (Perez & Malabarba, 2002), hybodontiforms (Perez & Malabarba, 2002), aetosaurs (Langer, Ribeiro, et al, 2007; Paes Neto et al, 2021), sauropodomorphs (Garcia et al, 2019), and Hyperdapedontinae rhynchosaurs (Langer, Ribeiro, et al, 2007). This fossil content places the site within the Hyperodapedon Assemblage Zone ( sensu Schultz et al, 2020), which is Carnian in age according to radiometric data (ca., 233 Ma; Langer et al, 2018).…”

Cranial osteology and paleoneurology of Tarjadia ruthae: An erpetosuchid pseudosuchian from the Triassic Chañares Formation (late Ladinian‐?early Carnian) of Argentina

“…In this species the ascending process of the maxilla is short and low, being restricted to the anterior margin of the antorbital fenestra and resembling the condition of aetosaurs (e.g., Paratypothorax coccinarum : SMNS 19003, Neoaetosauroides engaeus : PVL 4363) and ornithosuchids (e.g., Riojasuchus tenuisceps : PVL 3827, 3828; Ornithosuchus woodwardi : NHMUK PV R2409). Conversely, the ascending process of the maxilla is proportionally anteroposteriorly longer and broadly participates in the dorsal border of the antorbital fenestra in other erpetosuchids (e.g., Pagosvenator candelariensis : Lacerda et al, 2018; Erpetosuchus granti : Benton & Walker, 2002; Parringtonia gracilis : Nesbitt et al, 2018), some aetosaurs ( Desmatosuchus smalli : Small, 2002; Aetosauroides scagliai : Paes Neto et al, 2021), paracrocodylomorphs (e.g., Fasolasuchus tenax : PVL 3850, 3951; Saurosuchus galilei : PVL 2062; Postosuchus kirkpatricki : Weinbaum, 2011; Effigia okeeffeae : Nesbitt, 2007), gracilisuchids ( Gracilisuchus stipanicicorum : PVL 4597), some phytosaurs ( Mystriosuchus westphali : GPIT 261–001; Parasuchus hislopi : ISIR 42), proterochampsids (e.g., Tropidosuchus romeri : PVL 4601, 4604; Chanaresuchus romeri : Trotteyn & Ezcurra, 2020), and early avemetatarsalians (e.g., Seazzadactylus venieri : Dalla Vecchia, 2019; Eudimorphodon ranzii : Wild, 1978; Asilisaurus kongwe : Nesbitt et al, 2020; Herrerasaurus ischigualastensis : Sereno & Novas, 1994). Most of the lateral surface of the ascending process of the maxilla of Tarjadia ruthae is invaded by the antorbital fossa and forms an angle of approximately 30° with the posterior process.…”

“…This condition also occurs in deeply nested erythrosuchids ( Erythrosuchus africanus : Gower, 2003; Shansisuchus shansisuchus : Young, 1964), Erpetosuchus granti (Benton & Walker, 2002), Erpetosuchus sp. (Foffa et al, 2020), most phytosaurs (Butler et al, 2014b; Chatterjee, 1978; Stocker et al, 2017), gracilisuchids (MCZ 4117; IVPP V12378), Aetosauroides scagliai (Paes Neto et al, 2021), Prestosuchus chiniquensis (Mastrantonio et al, 2019), and Lewisuchus admixtus (Bittencourt et al, 2014). By contrast, the erpetosuchid Pagosvenator candelariensis has a posterior process of the jugal that fails extending posteriorly beyond the level of the infratemporal fenestra.…”

Garzapelta muelleri gen. et sp. nov., a new aetosaur (Archosauria: Pseudosuchia) from the Late Triassic (middle Norian) middle Cooper Canyon Formation, Dockum Group, Texas, USA, and its implications on our understanding of the morphological disparity of the aetosaurian dorsal carapace

“…Aetosaurs are a Late Triassic group of quadrupedal pseudosuchian archosaurs that are characterized by their osteoderm-covered bodies, stout forelimbs, triangular skulls with laterally facing supratemporal fenestrae, partially edentulous dentaries, and body sizes ranging from 1-to-5 m in length; currently, they are documented from every continent except Australia and Antarctica (Desojo et al, 2013). In recent years, the discovery of dentigerous material for various aetosaur taxa has highlighted the disparity of the dentition among the different species (Paes-Neto et al, 2021a;Reyes et al, 2020). This has prompted researchers (e.g., Biacchi Brust et al, 2018;Desojo et al, 2013;Desojo & Ezcurra, 2011;Desojo & Vizcaíno, 2009;Paes-Neto et al, 2021a;Reyes et al, 2020;Small, 2002;von Baczko et al, 2018von Baczko et al, , 2021 to hypothesize that aetosaurs likely exhibited omnivorous/ faunivorous feeding ecologies, rather than being strictly herbivorous (Walker, 1961).…”

“…In recent years, the discovery of dentigerous material for various aetosaur taxa has highlighted the disparity of the dentition among the different species (Paes-Neto et al, 2021a;Reyes et al, 2020). This has prompted researchers (e.g., Biacchi Brust et al, 2018;Desojo et al, 2013;Desojo & Ezcurra, 2011;Desojo & Vizcaíno, 2009;Paes-Neto et al, 2021a;Reyes et al, 2020;Small, 2002;von Baczko et al, 2018von Baczko et al, , 2021 to hypothesize that aetosaurs likely exhibited omnivorous/ faunivorous feeding ecologies, rather than being strictly herbivorous (Walker, 1961). Most currently recognized species are documented exclusively from the Chinle Formation and Dockum Group of the southwestern United States (U.S.; Desojo et al, 2013;Parker, 2016a).…”