Osteology of the archosauromorph Teyujagua paradoxa and the early evolution of the archosauriform skull

Abstract

Archosauriformes are a major group of fossil and living reptiles that include the crown group Archosauria (birds, crocodilians and their extinct relatives) and closely related taxa. Archosauriformes are characterized by a highly diagnostic skull architecture, which is linked to the predatory habits of their early representatives, and the development of extensive cranial pneumaticity associated with the nasal capsule. The evolution of the archosauriform skull from the more plesiomorphic configuration present ancestrally in the broader clade Archosauromorpha was, until recently, elusive. This began to change with the discovery and description of Teyujagua paradoxa, an early archosauromorph from the Lower Triassic Sanga do Cabral Formation of Brazil. Here, we provide a detailed osteological description of the holotype and, thus far, only known specimen of T. paradoxa. In addition to providing new details of the anatomy of T. paradoxa, our study also reveals an early development of skull pneumaticity prior to the emergence of the antorbital fenestra. We use these new data to discuss the evolution of antorbital openings within Archosauriformes. Reappraisal of the phylogenetic position of T. paradoxa supports previous hypotheses of a close relationship with Archosauriformes. The data presented here provide new insights into character evolution during the origin of the archosauriform skull.

A new archosauromorph from South America provides insights on the early diversification of tanystropheids

“…Until recently, the Sanga do Cabral Formation provided only few remains assigned to Archosauromorpha indet. Now, at least two independent lineages were reported for this unit ( [18,22,23,54] and this work). Although rare, these fossils demonstrate that archosauromorphs had already diversified in the Early Triassic of western Gondwana.…”

The cranial morphology ofTanystropheus hydroides(Tanystropheidae, Archosauromorpha) as revealed by synchrotron microtomography

“…MSNM BES SC 1018, PIMUZ T 2484; Nosotti, 2007). A similar postnarial process is also present in Prolacerta broomi, Azendohsaurus madagaskarensis, and Teyujagua paradoxa in which this process forms a simple articulation with the maxilla (Flynn et al, 2010;Pinheiro, Simão-Oliveira & Butler, 2019;Spiekman, 2018). The premaxilla of Macrocnemus bassanii also has an elongate postnarial process, but additionally bears a posteromedial process, and these two processes form a complicated articulation with the maxilla (Miedema et al, 2020).…”

“…From PIMUZ T 2819 it can be inferred that the pineal foramen was completely enclosed by the parietals on their anterior portion in Tanystropheus hydroides (figure 4B of Spiekman & Scheyer, 2019). This condition is common among early archosauromorphs, although the pineal foramen in Tanytrachelos ahynis (NMS G.2017.11.1), Prolacerta broomi (BP/1/5880), Proterosuchus fergusi (BP/1/3993), and Teyujagua paradoxa (Pinheiro, Simão-Oliveira & Butler, 2019) is positioned at approximately mid-length of the parietals, whereas the pineal foramen of Azendohsaurus madagaskarensis is enclosed posteriorly by the parietals and anteriorly by the frontals (Flynn et al, 2010). The large lateral extension of the anterolateral processes of the parietals in Tanystropheus hydroides is unique among non-archosauriform archosauromorphs but is somewhat reminiscent of the pronounced anterolateral processes seen in erythrosuchids (Butler et al, 2019a(Butler et al, , 2019bGower, 2003).…”

“…The prenarial process of Tanystropheus longobardicus and Macrocnemus spp. is also incipient, and has been reduced completely in rhynchosaurs, Teyujagua paradoxa, and the allokotosaurs Azendohsaurus madagaskarensis, Pamelaria dolichotrachela, and Shringasaurus indicus among early archosauromorphs (Dilkes, 1998;Flynn et al, 2010;Miedema et al, 2020;Nosotti, 2007;Pinheiro, Simão-Oliveira & Butler, 2019;Sengupta, Ezcurra & Bandyopadhyay, 2017). In contrast, the prenarial process is well-established and elongate in Protorosaurus speneri, Prolacerta broomi, Dinocephalosaurus orientalis, and Pectodens zhenyuensis (Gottmann-Quesada & Sander, 2009;Li et al, 2017;Modesto & Sues, 2004;Rieppel, Li & Fraser, 2008).…”

“…In contrast to the poorly known skull morphology of tanystropheids, largely complete and generally three-dimensionally preserved skulls are known from other early archosauromorphs. Their morphology has revealed valuable insights into archosauromorph palaeobiology and phylogeny, and has shed light on the acquisition of typical archosaur characters such as the presence of recurved teeth, an antorbital and mandibular fenestra, and the loss of the pineal foramen (Flynn et al, 2010;Pinheiro, Simão-Oliveira & Butler, 2019;Spiekman, 2018).…”