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Osteology of the archosauromorph Teyujagua paradoxa and the early evolution of the archosauriform skull Pinheiro, Felipe; Oliveira, Daniel; Butler, Richard

DOI: 10.1093/zoolinnean/zlz093 License: Other (please specify with Rights Statement)

Document Version Peer reviewed version Citation for published version (Harvard): Pinheiro, F, Oliveira, D & Butler, R 2020, 'Osteology of the archosauromorph Teyujagua paradoxa and the early evolution of the archosauriform skull', Zoological Journal of the Linnean Society, vol. 189, no. 1, pp. 378–417. https://doi.org/10.1093/zoolinnean/zlz093

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Download date: 04. Oct. 2021 Zoological Journal of the Linnean Society

Osteology of the archosauromorph Teyujagua paradoxa Pinheiro et al. 2016 and the early evolution of the archosauriform skull

Journal: Zoological Journal of the Linnean Society

Manuscript ID ZOJ-03-2019-3638.R1 Manuscript Type:ForOriginal Review Article Only Archosauromorpha < Taxa, Gondwana < Palaeontology, Triassic < Keywords: Palaeontology, phylogeny < Phylogenetics, skull < Anatomy

Archosauriformes are a major group of 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 Abstract: 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 revealed an early development of skull pneumaticity prior to the emergence of the antorbital fenestra. We use this 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.

Page 1 of 98 Zoological Journal of the Linnean Society

1 1 2 3 Archosauriformes are a major group of fossil and living reptiles that include the crown 4 5 6 group Archosauria (birds, crocodilians, and their extinct relatives) and closely related 7 8 taxa. Archosauriformes are characterized by a highly diagnostic skull architecture, 9 10 which is linked to the predatory habits of their early representatives and the 11 12 development of extensive cranial pneumaticity associated with the nasal capsule. The 13 14 15 evolution of the archosauriform skull from the more plesiomorphic configuration 16 17 present ancestrally in the broader clade Archosauromorpha was, until recently, elusive. 18 19 This began to change with the discovery and description of Teyujagua paradoxa, an 20 21 For Review Only 22 early archosauromorph from the Lower Triassic Sanga do Cabral Formation of Brazil. 23 24 Here, we provide a detailed osteological description of the holotype and thus far only 25 26 known specimen of T. paradoxa. In addition to providing new details of the anatomy of 27 28 T. paradoxa, our study also reveals an early development of skull pneumaticity prior to 29 30 31 the emergence of the antorbital fenestra. We use these new data to discuss the evolution 32 33 of antorbital openings within Archosauriformes. Reappraisal of the phylogenetic 34 35 position of T. paradoxa supports previous hypotheses of a close relationship with 36 37 38 Archosauriformes. The data presented here provide new insights into character 39 40 evolution during the origin of the archosauriform skull. 41 42 43 ADDITIONAL KEYWORDS: Archosauromorpha – Brazil – Gondwana – Lower 44 45 Triassic – phylogeny – skull. 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 2 of 98

2 1 2 3 INTRODUCTION 4 5 6 Archosauriformes are an extraordinarily diverse clade of diapsid reptiles that originated 7 8 during the Permian and underwent several pulses of adaptive radiation during the 9 10 11 Mesozoic Era (Gauthier, 1986; Brusatte et al., 2008; Claessens et al., 2009; Nesbitt, 12 13 2011; Ezcurra et al., 2014; Ezcurra & Butler, 2018). Representatives of this clade, such 14 15 as non-avian dinosaurs, birds, crocodilians and pterosaurs, have been major components 16 17 18 of tetrapod faunas since the Triassic Period, with birds comprising around a third of 19 20 extant tetrapod diversity (Jetz et al., 2012). Several classic anatomical features, such as 21 For Review Only 22 the external mandibular fenestrae, closed lower temporal bars, serrated teeth and 23 24 25 antorbital fenestrae characterize the archosauriform skull (Gauthier, 1986; Nesbitt, 26 27 2011; Ezcurra et al., 2016). However, the evolution of these characters from the typical 28 29 condition observed in early members of the more inclusive clade Archosauromorpha 30 31 was, until recently, elusive. The recent description of the archosauromorph Teyujagua 32 33 34 paradoxa from the Lower Triassic Sanga do Cabral Formation of Brazil, however, 35 36 started to shed light on this important evolutionary transition. Teyujagua paradoxa was 37 38 recovered by Pinheiro et al. (2016) as the sister-taxon to Archosauriformes, and this 39 40 41 species displays several intermediate character conditions that provide new insights into 42 43 the assembly of the archosauriform skull (Pinheiro et al. 2016). 44 45 46 Teyujagua paradoxa is known only from its holotype, UNIPAMPA 0653, an 47 48 almost complete skull articulated with lower jaws and cervicals I-IV (Figs 1, 2). This 49 50 51 specimen was only briefly described by Pinheiro et al. (2016). Since then, further 52 53 preparation of UNIPAMPA 0653 has exposed key features of the left side of the skull 54 55 and cervical vertebrae. In addition, X-ray micro-computed tomography imaging (µCT 56 57 scans) and 3D modeling of individual bones have revealed anatomical characters which 58 59 60 otherwise would be impossible to access. Here we present a complete description of the Page 3 of 98 Zoological Journal of the Linnean Society

3 1 2 3 holotype of T. paradoxa. We also reassess the phylogenetic relationships of T. paradoxa 4 5 6 using two different phylogenetic frameworks and discuss the early evolution of key 7 8 characters of archosauriform craniomandibular anatomy. 9 10 11 12 13 14 INSTITUTION ABBREVIATIONS 15 16 17 AMNH, American Museum of Natural History, New York, USA; BP, Evolutionary 18 19 Studies Institute (formerly Bernard Price Institute for Palaeontological Research), 20 21 University of the Witwatersrand,For Review Johannesburg, South Only Africa; CAPPA/UFSM, Centro 22 23 24 de Apoio à Pesquisa Paleontológica da Quarta Colônia, São João do Polêsine, Brazil; 25 26 FMNH, Field Museum of Natural History, Chicago, USA; GMPKU, Geological 27 28 Museum of Peking University, Beijing, China; ISIR, Indian Statistical Institute Reptiles, 29 30 Kolkata, India; IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, 31 32 33 Beijing, China; MCN, Museu de Ciências Naturais, Fundação Zoobotânica do Rio 34 35 Grande do Sul, Porto Alegre, Brazil; MCP, Museu de Ciências e Tecnologia da 36 37 Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, Brazil; MSNM, 38 39 40 Museo di Storia Naturale, Milano, Italy; NHMUK, Natural History Museum, London, 41 42 United Kingdom; NMK, Naturkundemuseum im Ottoneum, Kassel, Germany; NM QR, 43 44 National Museum, Bloemfontein, South Africa; PIMUZ, Paläontologisches Institut und 45 46 47 Museum der Universität Zürich, Zurich, Switzerland; PIN, Borissiak Paleontological 48 49 Institute of the Russian Academy of Sciences, Moscow, Russia; PVSJ, División de 50 51 Paleontología de Vertebrados del Museo de Ciencias Naturales y Universidad Nacional 52 53 de San Juan, San Juan, Argentina; RC, Rubidge Collection, Wellwood, Graaff-Reinet, 54 55 56 South Africa; SAM-PK, Iziko South African Museum, Cape Town, South Africa; UA, 57 58 University of Antananarivo, Antananarivo, Madagascar; UCMP, University of 59 60 California Museum of Paleontology, Berkeley, CA, USA; UFRGS, Universidade Zoological Journal of the Linnean Society Page 4 of 98

4 1 2 3 Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil; ULBRA, Universidade 4 5 6 Luterana do Brasil, Canoas, Brazil; UNIPAMPA, Universidade Federal do Pampa, São 7 8 Gabriel, Brazil; UTGD, School of Earth Sciences, University of Tasmania, Hobart, 9 10 Tasmania, Australia. 11 12 13 14 15 16 MATERIAL AND METHODS 17 18 19 X-RAY MICROTOMOGRAPHY ANALYSIS (µCT SCAN) AND 3D-MODELING 20 21 For Review Only 22 In order to better access the morphology of skull bones, especially those elements that 23 24 were not exposed by mechanical preparation, we conducted high-resolution x-ray 25 26 27 computed tomography (µCT scanning) of the holotype of Teyujagua paradoxa 28 29 (UNIPAMPA 653) using a Nikon XT H 225 ST X-ray tomography scanner at the 30 31 School of Earth Sciences, University of Bristol, UK. The scan was set with 224 kV of 32 33 X-ray energy, 163µA of current and 1.41 s of exposure time. A 0.5 mm tin filter was 34 35 36 used and 4x frame averaging was applied (4 frames/projection). To maximize 37 38 resolution, the specimen was scanned in two adjacent regions of interest, each part 39 40 taking approximately 5 h to scan. The scan data were reconstructed using CT Pro 3D 41 42 43 software, and the two regions of interest were combined using VG Studio Max. This 44 45 procedure resulted in 3,358 tomographic slices of the specimen, 3,297 of which contain 46 47 skull/vertebrae data. Unfortunately, limited x-ray penetration of the carbonaceous 48 49 50 matrix limited resolution of those bones deeply embedded in rock or surrounded by 51 52 particularly dense portions of the matrix. Virtual preparation and separation of skull 53 54 bones through segmentation of individual slices was performed using the software 55 56 Avizo. 57 58 59 60 Page 5 of 98 Zoological Journal of the Linnean Society

5 1 2 3 PHYLOGENETIC ANALYSES 4 5 6 The phylogenetic analyses conducted here aimed to test the relationships of Teyujagua 7 8 paradoxa among archosauromorphs. In particular, our aim was to assess the impact of 9 10 11 new character state scorings provided by our detailed anatomical description on the 12 13 phylogenetic position originally recovered by Pinheiro et al. (2016). Additionally, we 14 15 also wanted to reconstruct the evolution of key characters during the assembly of the 16 17 18 archosauriform skull. 19 20 21 We performedFor two different Review analyses, using Only two previously published datasets. 22 23 First, we updated the scores of T. paradoxa in the data matrix of Pinheiro et al. (2016) 24 25 (Analysis I). This resulted in 65% missing data for T. paradoxa, as opposed to 73% 26 27 28 missing data in the original data matrix. Although this dataset includes a limited taxon 29 30 sampling when compared to more recent analyses (e.g. Ezcurra, 2016), we choose to 31 32 include it for being the original data matrix for which the phylogenetic position of 33 34 Teyujagua was tested (Pinheiro et al., 2016), being relevant to access whether the new 35 36 37 scores impacted the original conclusions. The second analysis (Analysis II) was based 38 39 on the updated scores of T. paradoxa in the recent dataset of Butler et al. (2019), which, 40 41 in turn, represents a modification of the original data matrix of Ezcurra (2016). As the 42 43 44 raw dataset of Butler et al. (2019) is an exhaustive assessment of archosauromorph taxa, 45 46 including a large number of OTUs with a considerable amount of missing data and/or 47 48 with still unresolved taxonomic issues (see Ezcurra, 2016), we pruned a priori 35 49 50 51 terminals, namely: Dinocephalosaurus, Macrocnemus obristi, Fuyuanosaurus, 52 53 Pectodens, Protanystropheus, Trachelosaurus, Tanystropheus haasi, Eorasaurus, 54 55 Prolacertoides, ‘Archosaurus holotype’, ‘Archosaurus hypodigm’, ‘Panchet 56 57 proterosuchid’, Vonhuenia, Chasmatosuchus rossicus, Chasmatosuchus magnus, 58 59 60 Chasmatosuchus vjushkovi, Koilamasuchus, Kalisuchus, NMQR 3570, Shansisuchus Zoological Journal of the Linnean Society Page 6 of 98

6 1 2 3 kuyeheensis, Uralosaurus, ‘Osmolskina holotype’, ‘Osmolskina hypodigm’, ‘Otter 4 5 6 Sandstone archosaur’, Stagonosuchus, Dagasuchus, Hypselorhachis, ‘Waldhaus 7 8 poposauroid’, Vysthegdosuchus, Bystrowisuchus, Bromsgroveia, ‘Moenkopi 9 10 poposauroid’, Mandasuchus, Lutungutali and Nyasasaurus. The resulting dataset 11 12 comprises 151 taxa and 695 characters. The scoring of Teyujagua paradoxa in Butler et 13 14 15 al. (2019) used in Analysis II resulted in a proportion of missing data of 58%. 16 17 18 All datasets were edited using the software Mesquite v. 3.51 (Maddison & 19 20 Maddison, 2018). Heuristic searches were performed in TNT (Tree Analysis Using 21 For Review Only 22 New Technology) v. 1.5 (Goloboff & Catalano, 2016). We performed a first round of 23 24 25 analysis using the New Technology search of TNT (Ratchet and Tree Fusing, 100 hits). 26 27 This enables the software to continue parsing until the best result (i.e. lowest tree 28 29 length) is hit 100 times. Following this, we performed a second search using the tree 30 31 bisection reconnection (TBR) algorithm starting with the trees recovered in the first 32 33 34 round of searching. 35 36 37 38 39 40 RESULTS 41 42 43 SYSTEMATIC PALAEONTOLOGY 44 45 46 Diapsida Osborn sensu Laurin, 1991 47 48 49 Sauria McCartney, 1802 sensu Gauthier et al. 1988 50 51 52 Archosauromorpha Huene, 1946 sensu Gauthier et al. 1988 53 54 55 Teyujagua paradoxa Pinheiro et al. 2016 56 57 Holotype UNIPAMPA 653, the holotype and, so far, only known specimen of 58 59 60 Teyujagua paradoxa consists of an almost complete, well preserved skull articulated Page 7 of 98 Zoological Journal of the Linnean Society

7 1 2 3 with the complete lower jaws, the atlas-axis complex, cervical vertebrae III and IV, and 4 5 6 some tiny fragments of cervical vertebra V (Figs 1, 2). 7 8 Type horizon and locality UNIPAMPA 653 was recovered from a fine sandstone layer 9 10 11 with abundant carbonaceous concretions, about 5 m from the base of ‘outcrop 5’, Bica 12 13 São Tomé locality (Da Rosa et al., 2009), Lower Triassic Sanga do Cabral Formation 14 15 (SCF), Brazil (29°36ʹ 56″ S, 55°03ʹ 10″ W). The outcrop is dominated by fine reddish 16 17 18 sandstones intercalated with coarse sandstones and intraformational conglomerates, 19 20 indicating a vast alluvial plain occasionally flooded by shallow braided streams (Zerfass 21 For Review Only 22 et al., 2003; Da Rosa et al., 2009; Pinheiro et al., 2016; Dias-da-Silva et al., 2017). An 23 24 25 Induan–Olenekian age is inferred for SCF based on the presence of the parareptile 26 27 Procolophon trigoniceps, allowing the correlation between SCF and the upper Katberg 28 29 Formation of the South African Karoo Basin (Dias da Silva et al., 2006, 2017; Botha & 30 31 Smith, 2006). The type locality of Teyujagua paradoxa has already yielded the 32 33 34 capitosauroid temnospondyl Tomeia witecki (Eltink et al., 2017), still undescribed 35 36 archosauromorph remains and abundant cranial and postcranial procolophonoid bones, 37 38 including fairly complete skulls of P. trigoniceps (Da Rosa et al., 2009; Dias-da-Silva et 39 40 41 al., 2017; Silva-Neves et al., 2018). Tanystropheid archosauromorphs were also 42 43 reported for other classic SCF localities (Oliveira et al., 2018). 44 45 46 Emended diagnosis Teyujagua paradoxa differs from all other known 47 48 archosauromorphs on the basis of the following unique combination of characters 49 50 51 (autapomorphies indicated by *): large, confluent external nares; external antorbital 52 53 fenestrae absent; open lower temporal bars; lateral mandibular fenestrae present and 54 55 positioned beneath the orbits when the lower jaw is occluded*; premaxillae lack 56 57 anterodorsal processes; premaxillae bear posterodorsally directed palatal processes; 58 59 60 anterior maxillary foramina absent; medial antorbital fossae present in maxillae; nasals Zoological Journal of the Linnean Society Page 8 of 98

8 1 2 3 are completely dorsal elements; lacrimals are broad and fill the space between the 4 5 6 ascending and posterior processes of the maxillae; frontals have a small contribution to 7 8 orbital rims; posterolateral processes of parietals elevated well above the skull roof; 9 10 dorsal borders of the supratemporal fenestrae level with the dorsal margins of the orbits; 11 12 squamosals with elongate ventral processes that reach a point level with the ventral 13 14 15 margins of the orbits; wide, anteriorly open quadrate foramen; triangular supraoccipital; 16 17 splenials exposed in lateral view; surangular shelves present; labiolingually compressed 18 19 marginal teeth; marginal teeth distally carinated and bearing serrations; pterygoid 20 21 For Review Only 22 dentition with a single tooth row on zone T3, zone T2 with two rows and zone T4 23 24 present*; strong longitudinal lamina on the lateral surface of the axial centrum*; neural 25 26 spine of cervical vertebra III with a rounded posterior projection*. 27 28 29 30 31 32 COMPARATIVE DESCRIPTION 33 34 35 Skull 36 37 38 General skull morphology and major openings: The skull is 114.5 mm long, as 39 40 measured from the tip of the snout to the posterior ends of the quadrates. While the right 41 42 43 side of the skull is very well preserved (Fig. 1A), the left side experienced a 44 45 considerable degree of deformation and abrasion, with the lateral surface of the maxilla 46 47 obliquely compressed and a dorsomedially displaced left mandibular ramus (Fig. 1B). 48 49 50 Partial exposure of the skull prior to collection resulted in considerable damage to the 51 52 left postorbital bar and anterior left orbital margin. Teyujagua had a comparatively short 53 54 snout, with the preorbital region accounting for about 43% of the total skull length. In 55 56 dorsal view, the lateral margins of the snout initially diverge in the posterior direction at 57 58 59 an angle of about 24° to each other. Close to the anterior margins of the orbits, the skull 60 Page 9 of 98 Zoological Journal of the Linnean Society

9 1 2 3 abruptly expands laterally, reaching close to its maximum width at the level of the 4 5 6 postorbital bar (Fig. 1C). More posteriorly there is a very gentle further expansion until 7 8 the actual maximum width, located between the squamosals. 9 10 11 The skull and lower jaws present a unique pattern of major openings. The nares 12 13 are conjoined into a single, enlarged opening that faces dorsally and slightly anteriorly 14 15 (and is therefore not visible in lateral view) and which is equal in length to 20% of skull 16 17 18 length. The conjoined narial opening has a broadly rectangular outline in dorsal view, 19 20 with a ‘W’-shaped posterior margin. There is no antorbital fossa or fenestra on the 21 For Review Only 22 lateral surface of the skull. The orbits are comparatively large (anteroposterior length is 23 24 25 ~17% of skull length) and are located at about the anteroposterior mid length of the 26 27 skull. They face primarily laterally, but are also visible in dorsal view due to the lateral 28 29 placement of the jugal with respect to the skull roof. They are subcircular in outline in 30 31 lateral view. The infratemporal fenestrae are large and have open lower temporal bars 32 33 34 along their ventral margins. The main parts of these fenestrae have a trapezoidal outline, 35 36 being anteroposterior longer at their ventral margins than dorsally. A small 37 38 posteroventral extension of the infratemporal fenestra occurs beneath the ventral process 39 40 41 of the squamosal. The supratemporal fenestrae have chicken-egg-shaped outlines, are 42 43 broadly separated from one another by the parietals, have vertical margins and are not 44 45 surrounded by supratemporal fossae. There are also comparatively large, slit-like post- 46 47 48 temporal openings present on the occiput, between the posterolateral wings of the 49 50 parietals and the paroccipital processes. 51 52 53 In the lower jaw, well-developed lateral mandibular fenestrae are present. These 54 55 openings are unusually anteriorly positioned, being located beneath the orbits when the 56 57 lower jaw is in occlusion (Fig. 2A, B). They form long, oval slits, with estimated 58 59 60 lengths around 20% of total skull length. Zoological Journal of the Linnean Society Page 10 of 98

10 1 2 3 Premaxillae: Both premaxillae are preserved in UNIPAMPA 0653 (Fig. 3). They are 4 5 6 both essentially complete, although the left premaxilla is partially covered with 7 8 sediment and small parts are missing at its anterior end. The premaxillae are nearly in 9 10 articulation, but the left premaxilla has been displaced slightly dorsally and posteriorly, 11 12 and a very narrow (~1 mm) sediment-infilled gap separates them at the anterior midline. 13 14 15 The main bodies of these bones are anteroventrally inclined at about 20° with 16 17 18 respect to the alveolar margins of the maxillae, and they contact each other medially to 19 20 form a rounded snout in dorsal view (Fig. 3E, F). The anteroventral inclination of the 21 For Review Only 22 premaxillae observed in UNIPAMPA 0653 resembles the condition in some specimens 23 24 25 of Prolacerta (e.g. BP/1/471) (Modesto & Sues, 2004). Downturned premaxillae in 26 27 Prolacerta, however, may sometimes be a taphonomic artifact generated by the loose 28 29 connection between premaxillae and maxillae, and a straighter transition between these 30 31 bones is suggested by some other specimens (AMNH 9529, UCMP 37151) of this taxon 32 33 34 (Spiekman, 2018). The anteroventral inclination of the premaxillae in UNIPAMPA 35 36 0653 does not reach the extreme condition often observed in proterosuchid 37 38 archosauriforms (Ezcurra, 2017). Erythrosuchids display a moderate (Erythrosuchus 39 40 41 africanus, BP/1/5207) to strong (Garjainia prima, PIN 2394/5-1) ventral inclination of 42 43 the premaxillary alveolar margins, representing an intermediate condition between that 44 45 observed in UNIPAMPA 0653 and Proterosuchus (Gower, 2003; Ezcurra et al., 2019). 46 47 48 The contact between the two counterparts is relatively narrow dorsoventrally. 49 50 51 A well-developed and dorsoventrally compressed posterodorsal process forms a 52 53 considerable posterior extension of each premaxilla (Fig. 3A, B). This process 54 55 ventrolaterally forms a broad contact with the anterior margin of the maxilla and its 56 57 dorsomedial surface forms more than half of the lateral margin of the confluent external 58 59 60 naris, similar to the condition in the early rhynchosaur Mesosuchus (SAM-PK-6536; Page 11 of 98 Zoological Journal of the Linnean Society

11 1 2 3 Dilkes, 1998) and Prolacerta (BP/1/471) (Modesto & Sues, 2004). In Mesosuchus and 4 5 6 other rhynchosaurs, however, the posterodorsal processes laterally flank the nasals, and 7 8 contact the prefrontals posteriorly (Ezcurra et al, 2016). UNIPAMPA 0653 also differs 9 10 from early archosauriforms such as Proterosuchus (e.g. RC 846) and Garjainia (PIN 11 12 2394/5-1), in which the posterodorsal processes usually form the entire lateral margins 13 14 15 of the external nares. The posterodorsal processes taper posteriorly and form very small, 16 17 discrete contacts with the acute anterolateral processes of the nasals close to the mid- 18 19 length of the external naris (Fig 2C). This condition is unlike most non-archosauriform 20 21 For Review Only 22 archosauromorphs. In tanystropheids such as Tanystropheus (PIMUZ T 3901), the 23 24 contacts between the nasals and the premaxillae are located close to the posterior 25 26 borders of the external nares (Nosotti, 2007), whereas in the allokotosaurian 27 28 Azendohsaurus these bones probably contacted each other posterior to the external nares 29 30 31 (Flynn et al., 2010). Moreover, the premaxillae form much broader contacts with the 32 33 nasals in most other archosauromorphs. 34 35 36 The lateral surfaces of the premaxillae of UNIPAMPA 0653 are convex. A slit- 37 38 like gap, approximately 5 mm long, is present at the contact between the premaxilla and 39 40 41 maxilla on the right side (Fig 3E). It is unclear if this gap is a natural feature or a 42 43 taphonomic artifact generated by a slight anterior displacement of the premaxilla, which 44 45 seems to be only loosely connected with the maxilla. Indeed, overlapping joints appear 46 47 48 to have been present between premaxillae and maxillae, so that the dorsal margins of 49 50 the premaxillae stand out above the maxillae in lateral view. Gaps between premaxillae 51 52 and maxillae are relatively common in archosauromorphs. Among non-archosauriforms, 53 54 Azendohsaurus (FMNH PR 2751) possesses conspicuous grooves on the main bodies of 55 56 57 the premaxillae, which are connected to anteriorly-opening maxillary foramina (Flynn 58 59 et al., 2010). Mesosuchus (SAM-PK-5882) has a similar morphology, but also has a 60 Zoological Journal of the Linnean Society Page 12 of 98

12 1 2 3 second gap, dorsal to the anterior maxillary foramen and mainly formed by a notch in 4 5 6 the maxilla (Dilkes, 1998). Well-developed slit-like gaps are also present in most 7 8 specimens of Proterosuchus (e.g. RC 846). Potentially homologous structures are also 9 10 present in crownward archosauriforms, such as in erythrosuchids (e.g. Garjainia, PIN 11 12 2394/5-1), a number of “rauisuchians” (e.g. Prestosuchus, ULBRA-PVT-281; Lacerda 13 14 15 et al., 2016; Roberto-da-Silva et al., 2016, 2018), some early dinosaurs (e.g. 16 17 Herrerasaurus, PVSJ 407; Sereno and Novas, 1993) and pterosaurs (e.g. Dorygnathus, 18 19 Ösi et al., 2010). 20 21 For Review Only 22 There is no diastema or notch at the transition between the alveolar margins of 23 24 25 the premaxillae and the maxillae. Probably as a consequence of the development of 26 27 confluent external nares, the premaxillae of Teyujagua lack anterodorsal (nasal) 28 29 processes along the midline (Fig. 3B, D). Combined with the gentle transition between 30 31 the main body and the posterodorsal process, the absence of an anterodorsal process 32 33 34 gives the premaxillae a distinct sigmoid shape in lateral view (Fig. 3A). The absence of 35 36 an anterodorsal process and the consequent confluence of the external nares is an 37 38 unusual feature in archosauromorphs. Among non-archosauriforms, confluent nares are 39 40 41 apparently present in allokotosaurians, such as Pamelaria, Azendohsaurus and 42 43 Shringasaurus (Sen, 2003; Flynn et al., 2010; Sengupta et al., 2017), and this feature is 44 45 also a synapomorphy of the extremely specialized rhynchosaurs (Ezcurra et al., 2016). 46 47 48 In Azendohsaurus (FMNH PR 2751), although the premaxillae lack anterodorsal 49 50 processes, it is unclear if an internarial bar formed completely by the nasals was present. 51 52 As such, the condition in Teyujagua is more similar to that observed in Rhynchosauria, 53 54 as early members of this clade, such as Mesosuchus (SAM-PK-6536), already presented 55 56 57 confluent nares as a consequence both of the absence of the anterodorsal processes of 58 59 60 Page 13 of 98 Zoological Journal of the Linnean Society

13 1 2 3 the premaxillae and of the reduction of the anterior processes of the nasals (Dilkes, 4 5 6 1998). 7 8 A very shallow narial fossa is present on the main body of each premaxilla, 9 10 11 adjacent to the anterior edge of the confluent external nares. There are no obvious large 12 13 foramina in this fossa, or elsewhere on the lateral surface of the premaxilla, although 14 15 poor surface preservation makes it unclear whether smaller nutrient foramina were 16 17 18 present. As revealed by CT scans, the palatal surface of the right premaxilla is gently 19 20 concave, and this bone bears a well-developed and short, posterodorsally directed 21 For Review Only 22 palatal process (Fig. 3B, C, D). In ventral view, the lateral margin of this process 23 24 25 extends anteroposteriorly in a near parasagittal plane, whereas the medial margin 26 27 extends posterolaterally at an angle of about 32° away from its contact with the opposite 28 29 premaxilla (Fig. 3C). The palatal process tapers posteriorly to a pointed tip. The 30 31 presence of a palatal process is an interesting feature of Teyujagua, as this is a condition 32 33 34 typical of archosauriforms, and is also present in Prolacerta and Boreopricea (Benton 35 36 & Allen, 1997; Ezcurra, 2016), both close relatives of the clade. Each premaxilla bears 37 38 four tooth positions. The alveoli are oval in shape, with their labiolingual axes being 39 40 41 longer than their mesiodistal axes (Fig. 3C). Bone lamellae separating successive alveoli 42 43 are complete between tooth positions two and three and three and four, whereas the first 44 45 and second alveoli are confluent. In addition, the first alveolus is open medially, as is 46 47 48 the case for the posterior margin of the fourth and last premaxillary alveolus. 49 50 51 Maxillae: The maxillae are both completely preserved, although the right element is 52 53 better preserved and exposed than the left one (Fig. 4). They are broadly triangular in 54 55 shape and are primarily exposed in lateral view, forming the majority of the lateral 56 57 surface of the skull anterior to the orbit (Fig. 4E, F). Although they are mainly exposed 58 59 60 on the lateral surface, the maxillae also make a modest contribution to the skull table. Zoological Journal of the Linnean Society Page 14 of 98

14 1 2 3 Due to the flattening of the snout, the dorsal edges of the maxillae gently curve 4 5 6 medially, so that their straight sutures with the nasals can only be seen in dorsal view 7 8 (Fig. 2C), and the nasals are almost entirely hidden in lateral view. The sutures between 9 10 the maxillae and the nasals are not parasagittal, but are positioned slightly further 11 12 medially at their anterior ends than at their posterior ends; as a result, the maxillae form 13 14 15 slightly more of the skull table at their anterior ends than they do posteriorly (Fig. 2C). 16 17 In a highly unusual condition for archosauromorphs, the anterior ends of the maxillae 18 19 are located well anterior to the anterior ends of the nasals. This feature is only 20 21 For Review Only 22 widespread among rhynchosaurs and proterochampsids and is probably a consequence 23 24 of the confluent nares (despite the fact that, in proterochampsids, the external nares are 25 26 not confluent). 27 28 29 The lateral surface of the right, better preserved, maxilla is slightly concave 30 31 dorsoventrally, but there is no sign of an antorbital fossa or fenestra (Fig. 4A). The 32 33 34 maxillae bear posterodorsally oriented, tapering ascending processes. While in the left 35 36 maxilla the ascending process appears to end in a pointed tip, the better-exposed right 37 38 maxilla bears a small concavity that accommodates a small anterior projection of the 39 40 41 prefrontal. Among non-archosauriform archosauromorphs with well-preserved skulls, 42 43 only Prolacerta (e.g. BP/1/471), Boreopricea (PIN 3708/1) and the allokotosaurian 44 45 Azendohsaurus (FMNH PR 2751) possess lacrimals that separate the maxillae from the 46 47 48 prefrontals (Benton & Allen, 1997; Modesto & Sues, 2004; Flynn et al, 2010). 49 50 51 The posterior (jugal) processes of the maxillae are well developed, comprising 52 53 approximately half of the total anteroposterior length of these bones (Fig. 4A). The 54 55 posterior processes are posteriorly overlain dorsally by the anterior (maxillary) 56 57 processes of the jugals. As revealed by CT scans, the contact surfaces for the jugals are 58 59 60 marked by a relatively deep concavity that is laterally delimited by an oblique ridge Page 15 of 98 Zoological Journal of the Linnean Society

15 1 2 3 (Fig. 4A). Starting close to the contact with the jugal, the posterior process of the right 4 5 6 maxilla displays several longitudinal grooves parallel with each other and with the 7 8 alveolar margin (Fig. 4E). Sometimes these grooves appear to terminate in nutritive 9 10 foramina anteriorly and fade posteriorly. 11 12 13 The concave rims that separate the ascending and the posterior processes of the 14 15 maxillae articulate with the lacrimals, which completely fill the gap formed by the 16 17 18 confluence of these processes (Fig. 4F). The condition observed in UNIPAMPA 653 19 20 resembles that of Azendohsaurus (FMNH PR 2751; Flynn et al., 2010), as the common 21 For Review Only 22 condition in archosauromorphs is that the lacrimals contact only the posterior processes 23 24 25 of the maxillae. In Archosauriformes the ascending and posterior processes of the 26 27 maxillae are usually separated and border anterodorsally the antorbital fenestrae, so that 28 29 the antorbital openings probably evolved through a posterior retraction of the lacrimals. 30 31 Anterodorsally, the ascending processes of the maxillae are overlain by the 32 33 34 posterodorsal processes of the premaxillae (see above). CT scans reveal that the contact 35 36 surfaces for the premaxillae bear deep, posteriorly tapering concavities to accommodate 37 38 the posterodorsal processes of these bones (Fig. 4D). The contact between premaxillae 39 40 41 and nasals excludes the maxillae from the margin of the external nares. A contribution 42 43 of the maxillae to the external nares is moderately common among archosaurs (e.g. 44 45 pterosaurs, most aetosaurs, some “rauisuchians” and dinosaurs) (Nesbitt, 2011), but it is 46 47 48 unusual for early archosauromorphs, one exception being the tanystropheid 49 50 Macrocnemus (e.g. PIMUZ T 4822). The alveolar margins of the maxillae are distinctly 51 52 straight in lateral view; in ventral view, they curve laterally close to their contacts with 53 54 jugals (Fig. 4C). The right, completely prepared, maxilla has sixteen tooth positions, 55 56 57 located throughout the whole extension of the bone. The lateral surfaces of the maxillae 58 59 lack anterior maxillary foramina (sensu Modesto and Sues, 2004). The absence of 60 Zoological Journal of the Linnean Society Page 16 of 98

16 1 2 3 anterior maxillary foramina is usually regarded as synapomorphic for 4 5 6 Archosauriformes, and the foramina occur widely among non-archosauriform 7 8 archosauromorphs. 9 10 11 The medial surfaces of the maxillae, as revealed by CT scans, show deep fossae 12 13 (here referred to as the ‘medial antorbital fossae’), limited posteriorly by the concave 14 15 contacts with the lacrimals and extending anteriorly as far as the fifth maxillary tooth 16 17 18 positions (Fig. 4B). These fossae are arrowhead-shaped, with straight, anteriorly 19 20 converging ventral and anterodorsal margins. The anterodorsal margins of the medial 21 For Review Only 22 antorbital fossae extend along the entire height of the ascending processes of the 23 24 25 maxillae, and are well-delimited by a distinct ridge. In contrast, the ventral margins of 26 27 the fossae have rounded rims and extend posteriorly for approximately half the lengths 28 29 of the posterior maxillary processes. Although the maxillae are comparatively 30 31 mediolaterally thick, the lateral walls of the medial antorbital fossae are exceptionally 32 33 34 thin. Although the presence of medial antorbital fossae might appear to be a unique 35 36 feature of Teyujagua, at least one specimen of Prolacerta (BP/1/2675), in which 37 38 maxillae are exposed in medial view, bears a similar structure (see below). The medial 39 40 41 surfaces of the ascending processes bear distinct articulation facets for the nasals, in the 42 43 shape of a double ridge delimiting a longitudinal groove. 44 45 46 Nasals: The nasals (Fig. 5) are both completely preserved. They are broad and are major 47 48 elements of the skull table, being restricted to the dorsal surface of the snout (Fig. 2C) 49 50 51 and being almost completely hidden in lateral view (a tiny portion of the nasal may be 52 53 visible in lateral view dorsal to the maxilla-prefrontal suture). Having nasals that are 54 55 completely dorsal elements is an unusual condition among archosauromorphs, and is 56 57 most likely a consequence of the flattened snout and the dorsal position of the conjoined 58 59 60 nares. However, in other non-archosauriform archosauromorphs with mostly dorsally Page 17 of 98 Zoological Journal of the Linnean Society

17 1 2 3 positioned nares, such as Mesosuchus (SAM-PK-6536) and Azendohsaurus (UA-7-20- 4 5 6 99-653), the nasals are still exposed in lateral view. The restriction of the nasals to the 7 8 dorsal surface of the skull, as observed in Teyujagua, was independently achieved only 9 10 by more specialized rhynchosaurs (e.g. Hyperodapedon, UFRGS PV0132T; 11 12 Teyumbaita, UFRGS-PV-0232T) and proterochampsians (e.g. Proterochampsa nodosa, 13 14 15 MCP 1694 PV) (Barberena, 1981; Benton, 1983; Langer & Schultz, 2003; Dilkes & 16 17 Arcucci, 2012; Trotteyn et al., 2013). 18 19 20 The midline suture between the two nasals is not clearly visible. The nasals form 21 For Review Only 22 a flat to gently concave external surface. Anteriorly, each nasal bifurcates into two 23 24 25 processes, giving the posterior margin of the confluent nares a ‘W’-shaped outline in 26 27 dorsal view (Fig. 2C). The longest process is the lateral one, a very narrow and tapering 28 29 extension that forms approximately half of the lateral margin of the confluent nares and 30 31 that contacts the premaxilla anteriorly (Figs 2A, 5A). Anteromedially, each nasal has a 32 33 34 short blunt process that is sutured with its counterpart along the midline. This second 35 36 process is probably homologous to the anterior process of the nasal that contributes to 37 38 the separation of the external nares in most diapsids. The configuration of both 39 40 41 processes of the nasals of Teyujagua is very similar to the condition in Mesosuchus 42 43 (SAM-PK-6536), which also has short and blunt medial processes combined with 44 45 lateral processes that delimit a considerable portion of the external nares. 46 47 48 Tanystropheids (e.g. Tanystropheus, PIMUZ T 3901; Macrocnemus, GMPKU-P-3001) 49 50 appear to lack lateral processes of the nasals (Nosotti, 2007; Jaquier et al., 2017), and 51 52 the condition for allokotosaurians seems to be very short lateral processes and long 53 54 medial processes (e.g. Azendohsaurus, UA-7-20-99-653; Flynn et al., 2010). In early 55 56 57 archosauriforms, the septum dividing the nares is usually formed by anterodorsal 58 59 60 Zoological Journal of the Linnean Society Page 18 of 98

18 1 2 3 processes of the premaxillae, with a limited contribution of the medial processes of 4 5 6 nasals (e.g. Proterosuchus, NMQR 880). 7 8 The nasals form straight sutures with the maxillae anterolaterally (see above). 9 10 11 Posterolaterally, the nasal-maxilla contact is continuous with that between nasals and 12 13 prefrontals, but its orientation changes, such that it is more medially placed at its 14 15 posterior end than at its anterior end (Fig. 2C). As such, the lateral margins of the nasals 16 17 18 are convex in dorsal view. At their contacts with the maxillae, the lateral margins of the 19 20 nasals are deflected ventrally at an angle of about 20° with respect to the skull table. 21 For Review Only 22 The lateral surfaces of these ventral projections are completely overlapped, and thus 23 24 25 hidden, by the maxillae and each one bears a prominent longitudinal crest separating 26 27 two deep grooves, perfectly matching the double-ridged medial surface of the ascending 28 29 process of the maxilla (see above) (Fig. 5D). The contact between the nasals and 30 31 frontals is mostly obliterated by several fractures and considerable compression of the 32 33 34 skull table between the orbits and the external nares, but seems to be positioned level 35 36 with the anterior limits of the orbits, in a similar position to that occurring in the 37 38 rhynchosaur Mesosuchus (SAM-PK-6436) and Prolacerta (BP/1/5066). 39 40 41 Lacrimals: The lacrimals (Fig. 6) are preserved on both sides of the skull, although the 42 43 44 right one is better preserved. They are triangular elements with no dorsal exposure on 45 46 the skull roof. These bones completely fill the space between the ascending and 47 48 posterior processes of the maxillae (Fig. 2A). CT scans reveal that their anterior ends 49 50 51 form pointed tips that are laterally covered by the maxillae (Fig. 6A, B). The 52 53 posterodorsally broad lacrimals of Teyujagua differ from most non-archosauriforms. In 54 55 tanystropheids (e.g. Tanystropheus, PIMUZ T 3901), early rhynchosaurs (e.g. 56 57 Mesosuchus, SAM-PK-6536) and Prolacerta (BP/1/471, BP/1/3575), the lacrimals are 58 59 60 slim, anteroposteriorly elongated elements that contact only the posterior processes of Page 19 of 98 Zoological Journal of the Linnean Society

19 1 2 3 maxillae. In this respect, Teyujagua resembles Azendohsaurus, which also has large 4 5 6 lacrimals that contact both the posterior and ascending processes of the maxillae (Flynn 7 8 et al., 2010). 9 10 11 Dorsally, the broad contacts between the lacrimals and prefrontals stand out 12 13 from the dorsolateral surfaces of the snout as low ridges in front of the orbits. The 14 15 lateral surface of the right lacrimal is excavated by relatively deep, branched grooves. 16 17 18 Posteriorly, the lacrimals gently curve medially to contribute to the anterior border of 19 20 the orbits. In anterior and posterior view, the lacrimals have a sigmoid shape (Fig. 6E, 21 For Review Only 22 F). Medially these bones have moderately deep ridges, extending from anterodorsal-to- 23 24 25 posteroventral (Fig. 6B). These ridges increase the contact surface between the 26 27 lacrimals and maxillae. Similar to the condition displayed by tanystropheids (e.g. 28 29 Tanystropheus, PIMUZ T 3901; Macrocnemus, PIMUZ T 4822) and rhynchosaurs 30 31 (Mesosuchus, SAM-PK-6536), there are no contacts between the lacrimals and the 32 33 34 nasals. This contact, however, is present in Azendohsaurus (UA-7-20-99-653), 35 36 Boreopricea (PIN 3708/1), Prolacerta (e.g. BP/1/471) and most archosauriforms. The 37 38 lacrimals contact the jugals at the anteroventral margins of the orbits. The naso-lacrimal 39 40 41 duct is evident in both lacrimals as a moderately deep anterodorsally directed groove, 42 43 somewhat following the outline of the suture between the lacrimal and the main body of 44 45 the maxilla (Fig. 6A). 46 47 48 Jugals: The jugals are preserved on both sides of the skull (Figs 3, 7). On the left side 49 50 51 the ascending process of the jugal is badly abraded (Fig 1B), whereas on the right side 52 53 most of the posterior process has been lost (Fig. 8). The jugals are triradiate and contact 54 55 the maxillae anteriorly, the postorbitals dorsally and form the anteroventral and ventral 56 57 borders of the infratemporal fenestrae posteriorly. Further preparation of the specimen 58 59 60 revealed that the anterior process of the jugal contacts the lacrimals at the anteroventral Zoological Journal of the Linnean Society Page 20 of 98

20 1 2 3 margin of the orbit (contra Pinheiro et al., 2016). In dorsal view, the jugals are flared 4 5 6 laterally relative to the maxillae, with a strongly convex lateral surface, and the skull is 7 8 widest approximately at the level of the jugal-postorbital bar (Fig. 2C). The main bodies 9 10 of both jugals are ornamented by a series of anteriorly converging longitudinal ridges 11 12 that extend onto the bases of the posterior processes of the bones (Figs 1A, 8). The 13 14 15 anterior (maxillary) processes of the jugals taper in dorsoventral height and form an 16 17 extensive contact with the posterior processes of the maxillae. The contact between the 18 19 jugal and the maxilla curves gently dorsally in the anterior direction, and the anterior 20 21 For Review Only 22 process of the jugal is similarly curved, delimiting the rounded ventral margin of the 23 24 orbit (Fig. 8). Though a dorsal curvature of the anterior processes of jugals is 25 26 widespread among archosauromorphs, the condition observed in Teyujagua differs from 27 28 the pronouncedly curved jugals of tanystropheids (e.g. Tanystropheus, PIMUZ T 3901; 29 30 31 Macrocnemus, PIMUZ T 4822) and Prolacerta (BP/1/471), being more similar to early 32 33 rhynchosaurs such as Mesosuchus (SAM-PK-6536) and most archosauriforms. 34 35 36 The ascending processes of the jugals form about half of the postorbital bars, 37 38 and contact the postorbitals in long sutures that extend diagonally from posterodorsal to 39 40 41 anteroventral (Fig. 7G). The better-preserved ascending process of the right jugal has a 42 43 shallow longitudinal concavity on its lateral surface along its entire length. Although the 44 45 transition between the ascending process and the anterior process is gently rounded 46 47 48 (forming the posteroventral margin of the orbit), the long axes of the two processes are 49 50 oriented at almost 90 degrees to one another. The ascending processes of the jugals 51 52 form a smaller contribution to the postorbital bars in non-archosauriforms such as 53 54 tanystropheids and Prolacerta (PB/1/3575), and the condition present in Teyujagua is 55 56 57 more similar to early rhynchosaurs (e.g. Mesosuchus, SAM-PK-6536; Eohyosaurus, 58 59 SAM-PK-K10159; Dilkes, 1998; Butler et al., 2015) and most archosauriforms. In spite 60 Page 21 of 98 Zoological Journal of the Linnean Society

21 1 2 3 of this, the ascending processes form almost the entire anterior borders of the 4 5 6 infratemporal fenestrae in allokotosaurians and most rhynchosaurs. 7 8 The posterior process is broken at its base in the right jugal, but is completely 9 10 11 preserved on the left side of the skull (Fig. 8). This process tapers posteriorly to form an 12 13 incomplete lower temporal bar, terminating approximately level with the tip of the 14 15 ventral process of the squamosal. The dorsal margin of the posterior process is straight, 16 17 18 whereas the ventral one is gently convex at the base of the process, and gently concave 19 20 close to the termination of the process. Most non-archosauriforms have incomplete 21 For Review Only 22 lower temporal bars, with the notable exception of specialized rhynchosaurs (Ezcurra et 23 24 25 al., 2016). In addition, the posterior processes of the jugals fail to contact the 26 27 quadratojugals in some early archosauriforms that have an almost complete lower 28 29 temporal bar (e.g. Proterosuchus fergusi, SAM-PK-K10603; Ezcurra & Butler, 2015). 30 31 32 Prefrontals: Both prefrontals are preserved as parallelogram-shaped elements, and are 33 34 mostly restricted to the dorsal surface of the skull but also make a small contribution to 35 36 37 the lateral surface, immediately dorsal to the lacrimals (Figs 9C, 10). The prefrontals 38 39 contact both nasals and frontals medially, while their anterior and anterolateral limits 40 41 contact, respectively, the ascending processes of the maxillae and the lacrimals. The 42 43 44 posterolateral rims of the prefrontals form parts of the anterodorsal orbital margins. The 45 46 prefrontals form considerable parts of the anterior orbital margins in most 47 48 archosauromorphs. In tanystropheids (Macrocnemus, PIMUZ T 4822; Tanystropheus, 49 50 51 PIMUZ T 3901) and early rhynchosaurs (Mesosuchus, SAM-PK-6536; Howesia, SAM- 52 53 PK-5884), almost the entire anterior margins of the orbits are delimited by the 54 55 prefrontals, with only small anteroventral contributions from the lacrimals. In 56 57 Prolacerta (BP/1/471) and some early archosauriforms (e.g. Proterosuchus, NMQR 58 59 60 1484), about half of the anterior orbital margins are formed by the prefrontals, the other Zoological Journal of the Linnean Society Page 22 of 98

22 1 2 3 half being formed by the lacrimals. The contribution of the prefrontals to the orbital 4 5 6 margin varies widely within Archosauriformes. 7 8 The posterior extensions of the prefrontals fail to contact the postfrontals due to 9 10 11 the presence of a small contribution of the frontals to the dorsal margins of the orbits 12 13 (Fig. 9C). The dorsal surfaces of the prefrontals are ornamented by dense clusters of 14 15 small shallow pits and low rugosities (Fig. 10). This particular ornamentation pattern is 16 17 18 restricted to this bone, and does not spread onto the surrounding elements. 19 20 Circumorbital ornamentation was reported previously for several archosauromorphs, 21 For Review Only 22 and the prefrontal ornamentation of UNIPAMPA 653 resembles that illustrated by 23 24 25 Flynn et al. (2010) for Azendohsaurus. 26 27 28 Frontals: Both frontals are preserved and form the midpart of the skull table, between 29 30 the orbits (Fig. 9). The exact position of the nasal-frontal suture is uncertain, but it 31 32 seems most likely to be at a point level with the anterior margin of the orbits. At this 33 34 point the skull table has been slightly deformed and pushed inwards. Although the 35 36 37 posterior contacts with the parietals are also not clear, there is some evidence for 38 39 interdigitation, suggesting that the suture is a largely straight transverse contact 40 41 approximately level with the posterior margin of the orbit. In this respect, Teyujagua is 42 43 44 similar to proterosuchids (e.g. Proterosuchus, NMQR 1484) and early rhynchosaurs 45 46 (Mesosuchus, SAM-PK-6536; Howesia, SAM-PK-5885; Dilkes, 1995, 1998), as the 47 48 usual condition among non-archosauriform archosauromorphs is a W-shaped suture, 49 50 51 with medial processes of frontals fitting into a concavity formed by the parietals. The 52 53 anteroposterior length of the frontals is slightly greater than their combined width, and 54 55 the length of the frontals exceeds that of the nasals. The frontals are not fused to one 56 57 another, and their dorsal surfaces are mostly flat. Laterally the frontals are bordered 58 59 60 anteriorly by the prefrontals and posteriorly by the postfrontals. Unusually, there is only Page 23 of 98 Zoological Journal of the Linnean Society

23 1 2 3 a very small contribution of the frontals to the dorsal rim of the orbit (Fig. 9C). The 4 5 6 frontals form most of the dorsal margins of the orbits in most non-archosauriforms. 7 8 Among those, only in rhynchosaurs (e.g. Mesosuchus, SAM-PK-6536; Howesia, SAM- 9 10 PK-5885; Teyumbaita, UFRGS-PV-0232T) is the contribution of the frontals to the 11 12 dorsal orbital edge limited similarly to the condition in Teyujagua, and in some 13 14 15 rhynchosaurs (e.g. Brasinorhynchus, UFRGS-PV-0168-T) the frontals are completely 16 17 excluded from the orbital margin (Schultz et al., 2016). In most early archosauriforms 18 19 (e.g. proterosuchids, erythrosuchids), however, the frontals form only a small part of the 20 21 For Review Only 22 orbital margins (e.g. Ezcurra & Butler, 2015; Ezcurra et al., 2019). The extent of frontal 23 24 contribution to the orbital margin in Garjainia prima (PIN 2394/5-1), for instance, is 25 26 similar to the condition displayed by Teyujagua. 27 28 29 The surface of the frontal adjacent to the orbital rim has some fine, striated 30 31 ornamentation, similar to and continuous with that on the adjacent prefrontal and 32 33 34 postfrontal (Fig. 10). The frontals are excluded from the borders of the supratemporal 35 36 fenestrae by the presence of a contact between the parietals and the 37 38 postfrontals/postorbitals (Fig. 9C). As the ventral surface of the frontals could not be 39 40 41 accessed by CT data, nothing can be said about the olfactory duct and bulbs. 42 43 44 Parietals: The parietals are completely preserved on both sides of the skull (Fig. 9C). 45 46 The two elements are not fused to each other and show a clear median suture, as is 47 48 common among non-archosauriform archosauromorphs, with the exception of 49 50 51 rhynchosaurs (e.g. Dilkes, 1995; Dilkes, 1998; Montefeltro et al., 2010) and some 52 53 tanystropheids (e.g. Macrocnemus fuyuanensis, GMPKU-P-3001). The contribution of 54 55 the parietals to the skull table is roughly trapezoidal, and they are perforated at mid- 56 57 length by a small pineal foramen (Fig. 9A). The foramen is completely enclosed by the 58 59 60 parietals, which lack a pineal fossa. The presence of a pineal foramen is the usual Zoological Journal of the Linnean Society Page 24 of 98

24 1 2 3 condition for basal archosauromorphs, and the loss of this opening presumably occurred 4 5 6 close to the origins of Archosauriformes. Prolacerta (BP/1/3574, BP/1/471) still has a 7 8 well-developed pineal foramen (Modesto & Sues, 2005), while Proterosuchus is 9 10 polymorphic for this feature, with some specimens displaying a vestigial parietal 11 12 foramen (e.g. NMQR 880, BP/1/3993; Ezcurra & Butler, 2015). An independent loss of 13 14 15 the pineal foramen also appears to have occurred within Rhynchosauria, given that 16 17 Mesosuchus (SAM-PK-6536), an early representative of this clade, still displays the 18 19 plesiomorphic condition of a large pineal opening perforating its fused parietals (Dilkes, 20 21 For Review Only 22 1998). 23 24 25 Although considerably long, the parietals are almost restricted to the postorbital 26 27 region of the skull, in a morphology that is typical for non-archosauriforms. The 28 29 parietals form all of the medial borders of the supratemporal fenestrae, but 30 31 supratemporal fossae are absent. Instead, the parietals show slightly elevated rims 32 33 34 bordering the supratemporal fenestrae. The posterolateral processes are plate-like, 35 36 mostly vertically oriented and elevated well above the main bodies of the parietals. 37 38 Among non-archosauromorphs, plate-like, subvertical posterolateral processes as 39 40 41 displayed by Teyujagua are present in allokotosaurians (Azendohsaurus, UA-7-20-99- 42 43 653), basal rhynchosaurs (e.g. Mesosuchus, SAM-PK-6536) and Prolacerta 44 45 (BP/1/3575). On the right side of the skull, where the temporal region is completely 46 47 48 exposed, the posterolateral process contacts the supratemporal in a region close to the 49 50 posterolateral corner of the supratemporal fenestra (Fig. 9). The parietals are 51 52 ornamented by delicate rugosities that converge into the regions close to the transition 53 54 between the main bodies and the posterolateral processes. 55 56 57 Postfrontal: The postfrontal is completely preserved on the right side, but absent on the 58 59 60 left (Figs 9C, 11). Although Pinheiro et al. (2016) identified the contact between the Page 25 of 98 Zoological Journal of the Linnean Society

25 1 2 3 postfrontal and the postorbital along the lateral edge of the skull table, it is not possible 4 5 6 to identify with certainly a suture in this region, although there is a slight break-in-slope 7 8 and change in the texture of the bone surface. Instead, based on CT data and 9 10 comparisons with other taxa we identify the suture as extending across the skull roof 11 12 from the anterior most part of the supratemporal fenestra to the posterodorsal corner of 13 14 15 the orbit (Figs 9C, 11C). There is a thin line of sediment in this contact, and the 16 17 postorbital has been slightly raised up relative to the postfrontal, presumably by post- 18 19 mortem distortion. 20 21 For Review Only 22 The postfrontal has a trapezoidal outline in dorsal view (Fig. 10). Medially it 23 24 25 contacts the frontal along an anteroposteriorly straight suture. As revealed by CT data, 26 27 the articulation surface with the frontal is dorsoventrally broad and bears a double ridge 28 29 (Fig. 11B). Posteriorly the postfrontal contacts the parietals and the postorbital, and is 30 31 excluded from the anterior margin of the supratemporal fenestra, and laterally it 32 33 34 contacts the postorbital (Fig. 9C). In a small sample of non-archosauriforms (e.g. 35 36 Tanystropheus, Jesairosaurus, Trilophosaurus) the postfrontals contribute to the 37 38 anterior margins of the supratemporal fenestrae (Ezcurra, 2016). 39 40 41 The postfrontal of UNIPAMPA 653 forms the posterodorsal corner of the orbital 42 43 44 margin. Its dorsal surface is ornamented with fine striations, similar to those of the 45 46 frontal and prefrontal, and these are best developed immediately adjacent to the orbit 47 48 (Fig. 10). The size of the postfrontal with respect to the postorbital in UNIPAMPA 653 49 50 51 is very similar to the condition in Prolacerta (BP/1/471) and Proterosuchus (e.g. 52 53 NMQR 1484). Allokotosaurians (Azendohsaurus, UA-7-20-99-653) and the 54 55 tanystropheid Macrocnemus (e.g. PIMUZ T 4822) have postfrontals rivaling the 56 57 postorbitals in size, whereas rhynchosaurs (e.g. Mesosuchus, SAM-PK-6536) show an 58 59 60 intermediate condition. Zoological Journal of the Linnean Society Page 26 of 98

26 1 2 3 Postorbital: The postorbital is completely preserved on the right side, but only small 4 5 6 parts of its internal surface and parts of the posterior process are present on the left side 7 8 (Fig. 8). The postorbital forms the majority of the gently curved posterior margin of the 9 10 orbit. It is a triradiate bone, with a medial process that contacts the postfrontal adjacent 11 12 to the orbit (Fig. 11). The sutural contact with the postfrontal is a straight contact, 13 14 15 extending from anterolateral-to-posteromedial, as described above. The posterior 16 17 process of the postorbital extends along the anterior two thirds of the lateral margin of 18 19 the supratemporal fenestra. It laterally overlaps the anterior process of the squamosal. 20 21 For Review Only 22 The posterior process tapers not far posterior to its contact with the squamosal. This 23 24 condition is similar to that displayed by Mesosuchus (SAM-PK-6536) and 25 26 tanystropheids (e.g. Macrocnemus, PIMUZ T 4822), whereas the condition for most 27 28 rhynchosaurs, Azendohsaurus (UA-7-20-99-653), Prolacerta (BP/1/471) and most early 29 30 31 archosauriforms is a much longer posterior process, extending close to or beyond the 32 33 posterior border of the supratemporal opening. The posterior process ends in a broadly 34 35 rounded tip (proportionately shorter than in Prolacerta, BP/1/471) (Fig. 11A, B). The 36 37 38 position of the posterior process of the postorbital with respect to the skull roof makes 39 40 the supratemporal fenestra comparatively tall dorsoventrally, with its dorsal border level 41 42 with the dorsal margin of the orbit. In this respect, UNIPAMPA 653 resembles the 43 44 45 condition observed in most archosauriforms (Ezcurra, 2016). By contrast, the usual 46 47 condition for non-archosauriform archosauromorphs is a ventrally positioned 48 49 supratemporal fenestra, with the upper temporal bar level with about mid-height of the 50 51 orbit (e.g. Prolacerta, BP/1/471; tanystropheids) (Modesto & Sues, 1998; Nosotti, 52 53 54 2007; Jaquier et al., 2017). Mesosuchus (SAM-PK-6536) and other rhynchosaurs show 55 56 a similar condition to that present in Teyujagua and Archosauriformes, with a dorsally 57 58 positioned upper temporal bar (Dilkes, 1998). 59 60 Page 27 of 98 Zoological Journal of the Linnean Society

27 1 2 3 As supratemporal fossae are absent in UNIPAMPA 653, there are no 4 5 6 excavations on the dorsal surface of the posterior process of the postorbital. Although 7 8 usually absent in early archosauriforms (e.g. Proterosuchus), excavated postorbitals 9 10 contributing to the supratemporal fossae are present in allokotosaurians (Flynn et al, 11 12 2010; Ezcurra, 2016) and early rhynchosaurs (e.g. Mesosuchus, SAM-PK-6536) 13 14 15 (Dilkes, 1998). The ventral process forms a long, gently curved suture with the jugal. 16 17 This process is broad anteriorly, where a deep longitudinal ridge marks the contact with 18 19 the jugal medially (Fig. 11B). Posterior to this ridge, the bone becomes a delicate 20 21 For Review Only 22 lamina that laterally overlies the dorsal process of the jugal. Similar to Prolacerta 23 24 (BP/1/2675), the ventral process has a weak longitudinal groove that gently curves 25 26 anteriorly, following the curvature of the process. As is typical among 27 28 archosauromorphs, the postorbital makes a similar contribution to the jugal to the 29 30 31 postorbital bar. The only exception to this is some tanystropheids such as Macrocnemus 32 33 (e.g. PIMUZ T 4822), in which the postorbital forms most of the postorbital bar 34 35 (Ezcurra, 2016; Jaquier et al., 2017). Ornamentation, in the form of fine striations, is 36 37 38 present on the bone adjacent to the postfrontal contact, and extending across the surface 39 40 of the bone to the border of the supratemporal fenestra (Fig. 10). 41 42 43 Squamosals: The squamosal is partially preserved on both sides of the skull, but is 44 45 heavily cracked and shattered on each side (Fig. 1A, B). On the left side parts of the 46 47 48 anterior process and the entire ventral process are preserved, but the medial process is 49 50 either missing or covered by sediment, and the posterior process of the bone is missing. 51 52 On the right side the anterior and medial processes are complete, but the ventral process 53 54 has largely broken away and the posterior process has shattered and no useful 55 56 57 anatomical information can be obtained (Fig 2A). The squamosal forms a small part of 58 59 the most posterolateral corner of the supratemporal fenestra. The anterior process is 60 Zoological Journal of the Linnean Society Page 28 of 98

28 1 2 3 transversely compressed and relatively deep dorsoventrally (Fig. 12A, B), and is 4 5 6 laterally overlapped by the posterior process of the postorbital. With respect to the 7 8 contribution of the anterior process to the lateral border of the supratemporal fenestra, 9 10 UNIPAMPA 653 is more similar to the typical condition among non-archosauriform 11 12 archosauromorphs than to that displayed by prolacertids and proterosuchid 13 14 15 archosauriforms. In the latter, the anterior process of the squamosal forms more than 16 17 half of the lateral border of the supratemporal fenestra. Erythrosuchids (Erythrosuchus, 18 19 BP/1/5207; Garjainia, PIN 2394/5) share with crownward archosauriforms a limited 20 21 For Review Only 22 contribution of squamosals to the lateral border of the supratemporal fenestrae. As 23 24 revealed by CT scans, the anterior end of the anterior process has a shallow depression 25 26 to accommodate the posterior process of the postorbital (Fig 12A). Posteriorly, the 27 28 transition between the anterior and the ventral processes is very gentle, giving the 29 30 31 infratemporal fenestra a rounded posterodorsal border, in a very similar condition to that 32 33 present in proterosuchid archosauriforms (e.g. Proterosuchus, NMQR 1484). With 34 35 some isolated exceptions (e.g. Protorosaurus, NMK S 180), the usual condition among 36 37 38 non-archosauriform archosauromorphs is a supratemporal fenestra with squared 39 40 posterodorsal borders. The medial process is short and triangular, and contacts the 41 42 supratemporal medially, forming only a short part of the posterior border of the 43 44 45 supratemporal bar. The ventral process is elongate, and extends nearly directly 46 47 ventrally, reaching a point level with the ventral margin of the orbit. This is an unusual 48 49 condition among non-archosauriform archosauromorphs, and occurs only in 50 51 hyperodapedontine rhynchosaurs (e.g. Teyumbaita, UFRGS-PV-0232T). The ventral 52 53 54 process is anteroposteriorly broad (similar to Proterosuchus, NMQR 1484), with a 55 56 gently convex anterior margin, and terminates ventrally in a broadly rounded tip. 57 58 Medially, the ventral process shows a dorsoventrally oriented ridge (Fig 12B), posterior 59 60 Page 29 of 98 Zoological Journal of the Linnean Society

29 1 2 3 to which the head of the quadrate is accommodated. Although only well preserved on 4 5 6 the right side, some fine surface ornamentation is present on the lateral surface of the 7 8 main body of the squamosal. 9 10 11 Supratemporal: The supratemporal is preserved on both left and right sides, although 12 13 the right element is better preserved (Fig. 9C). The supratemporal separates the 14 15 squamosal from the posterolateral wing of the parietal, and makes a small contribution 16 17 18 to the posterior border of the supratemporal fenestra. It also forms part of the 19 20 dorsolateral border of the post-temporal fenestra (Fig. 14) (see below). The 21 For Review Only 22 supratemporal is a narrow, rod-like element, with a long axis that extends from 23 24 25 anteromedial to posterolateral. The bone is flexed along this long axis so that the part 26 27 adjacent to the supratemporal fenestra is set more dorsally than the more posterolateral 28 29 part of the bone. In posterior view it forms a slightly interdigitating suture with the 30 31 posterolateral wing of the parietal (Fig. 14). Among non-archosauriform 32 33 34 archosauromorphs, supratemporals are present in rhynchosaurs and prolacertids 35 36 (Ezcurra, 2016). In archosauriforms, these bones were only reported for early members 37 38 of the clade (e.g. Proterosuchus, NMQR 1484). The slender nature of the 39 40 41 supratemporals of Teyujagua is similar to the condition displayed, for instance, by 42 43 prolacertids (e.g. Prolacerta, BP/1/471). 44 45 46 Quadrate: The quadrate is a robust element with a complex morphology (Fig. 13). The 47 48 left quadrate is completely preserved, but its right counterpart is missing except for 49 50 51 some scattered fragments that probably belong to this bone (Fig. 2A). The dorsal part of 52 53 the posterior margin of the quadrate is subvertical. Level with the ventral limit of the 54 55 squamosal, the quadrate bends posteriorly, so that the posterior margin of the ventral 56 57 part of the bone forms an angle of 138° with the posterior margin of the dorsal part of 58 59 60 the bone (Fig. 2B). Ventral to this, the posterior margin of the quadrate becomes gently Zoological Journal of the Linnean Society Page 30 of 98

30 1 2 3 convex, similar to the condition in Prolacerta (BP/1/3575). Although the quadrates of 4 5 6 allokotosaurians (e.g. Azendohsaurus, UA-7-20-99-653) also have posterior convexities 7 8 at their ventral ends, in these taxa this bone has a subvertical orientation. Subvertical 9 10 quadrates are also displayed by some specimens Proterosuchus (e.g. NMQR 1484). The 11 12 quadrate of UNIPAMPA 653 has a broad squamosal contact, articulating somewhat 13 14 15 loosely with the whole posterior margin of the ventral process of the squamosal. The 16 17 quadrate head is overlain by a small posterodorsal extension of the squamosal, but the 18 19 entire extension of the quadrate, including its head, is widely exposed in lateral view 20 21 For Review Only 22 (Fig. 13). The dorsal articulation with the squamosal is a blunt convexity, but does not 23 24 bend posteriorly, unlike the hook-shaped quadrate head of allokotosaurians (e.g. 25 26 Azendohsaurus, UA-7-20-99-653; Shringasaurus, ISIR 820; Flynn et al. 2010; Ezcurra, 27 28 2016; Sengupta et al. 2017). 29 30 31 The anterior margin of the quadrate is excavated at its mid-length to form a 32 33 34 wide, anteriorly open, quadrate foramen, similar to the one displayed by the 35 36 archosauriform Sarmatosuchus (PIN 2865/68-3; Ezcurra, 2016: fig. 24) (Fig. 13). The 37 38 ectocondyle is strongly laterally projected, but the entocondyle, as well as the medial 39 40 41 pterygoid flange, are still embedded in matrix and limited X-ray penetration hindered 42 43 their examination. Most interestingly, the quadrate apparently lacks articulation facets 44 45 for the quadratojugals. This later bone, not preserved in UNIPAMPA 0653, was either 46 47 48 very reduced or completely lost in Teyujagua, which is a highly unusual condition in 49 50 Archosauromorpha, apparently only mirrored by Tanystropheus (Nosotti, 2007; 51 52 Ezcurra, 2016). In addition to the absence of quadratojugal contacts on the quadrate of 53 54 UNIPAMPA 0653, the loss of quadratojugals in Teyujagua is supported by the fact that 55 56 57 this bone is not preserved on either side of the skull, even though the degree of 58 59 articulation of the holotype allowed the preservation of small structures, such as atlantal 60 Page 31 of 98 Zoological Journal of the Linnean Society

31 1 2 3 elements. The absence of quadratojugals in Teyujagua, however, can only be confirmed 4 5 6 by the discovery of further specimens. 7 8 Occiput: A considerable part of the occiput of UNIPAMPA 653 (Fig. 14) is hidden by 9 10 11 the atlas/axis complex. Among the exposed elements, the posterolateral processes of the 12 13 parietals have a wide contribution to the occipital region in the shape of their plate-like 14 15 posterior surfaces. The contribution of the parietals to the occiput is greater in 16 17 18 UNIPAMPA 653 than it is in Prolacerta (BP/1/3575) or Proterosuchus (NMQR 1484), 19 20 and is more similar to the condition displayed by Erythrosuchus (BP/1/4680; Gower, 21 For Review Only 22 2003). Although having a wide contribution of parietals to the occipital surface, 23 24 25 Azendohsaurus (UA-7-20-99-653) shows much deeper parietal plates than UNIPAMPA 26 27 653 (Flynn et al. 2010). The parietals apparently contact each other at the midline, with 28 29 no evidence for the presence of postparietals. Although postparietals are absent in 30 31 archosaurs and proterochampsids, they are widely spread among early archosauriforms 32 33 34 (Ezcurra, 2016), and are also present in the non-archosauriform Tasmaniosaurus 35 36 (UTGD 54655; Ezcurra, 2014). Laterally, the parietals articulate with the 37 38 supratemporals. 39 40 41 The supraoccipital is a triangular, anteroposteriorly sloping bone, with its apex 42 43 44 almost contacting the dorsal surface of the parietals. A triangular supraoccipital is also 45 46 present in Azendohsaurus (UA-7-20-99-653), while the condition for most 47 48 archosauromorphs is a rounded, plate-like bone. The ventral margin of the 49 50 51 supraoccipital dorsally limits a relatively large foramen magnum. The occipital condyle 52 53 is obscured by the anterior elements of the cervical series. The left opistothic is 54 55 represented by its anteroposteriorly flattened paroccipital process, which is 56 57 posterolaterally deflected from the anteroposterior axis of the skull and ventrolaterally 58 59 60 oriented in posterior view. Ventrally-deflected paroccipital processes are also known for Zoological Journal of the Linnean Society Page 32 of 98

32 1 2 3 Prolacerta (BP/1/3575) and Azendohsaurus (UA-7-20-99-653). In Proterosuchus (e.g. 4 5 6 NMQR 1484), Garjainia (PIN 2394/5-1) and most rhynchosaurs (e.g. Teyumbaita, 7 8 UFRGS-PV-0232T), however, the paroccipital process is mostly horizontally oriented. 9 10 The distal end of the paroccipital process is broader than its contact with the 11 12 supraoccipital, and apparently does not contact the parietals or supratemporals, although 13 14 15 this may reflect a slight posterior displacement of the paroccipital process. The post- 16 17 temporal fenestra, which is only visible on the left side, is a large, slit-like aperture, 18 19 ventrally bordered by the paroccipital process, dorsally by the parietal, and 20 21 For Review Only 22 dorsolaterally by the supratemporal (Fig. 14). The post-temporal fenestra of 23 24 UNIPAMPA 653 differs both from the extremely dorsoventrally constricted condition 25 26 present in Proterosuchus (NMQR 1484) and Erythrosuchus (BP/1/4680) (Gower, 27 28 2003), and the rounded opening of allokotosaurians with known skulls (e.g. UA-7-20- 29 30 31 99-653). Rhynchosaurs display a trend towards developing exceptionally wide post- 32 33 temporal fenestra, but this is seemingly not the case for the early representatives of the 34 35 clade (e.g. Mesosuchus; Dilkes, 1998). The lack of contact between the paroccipital 36 37 38 process and parietals/supratemporals means that the post-temporal fenestra is open 39 40 laterally as preserved. 41 42 43 Lower jaw 44 45 46 General morphology: The lower jaw (Fig. 15) is a comparatively slender element 47 48 anteriorly, especially throughout the length of the dentary. Ventral to the orbits, 49 50 51 however, the lower jaw expands dorsoventrally, becoming much deeper. The two 52 53 mandibular rami run parallel and almost contacting each other until close to the sixth 54 55 maxillary tooth position, where they start to diverge, following the pronounced lateral 56 57 expansion of the skull. The mandibular symphysis seems, therefore, to be weak and 58 59 60 restricted to the anteriormost portion of the dentaries (Fig. 15A, B). The external Page 33 of 98 Zoological Journal of the Linnean Society

33 1 2 3 mandibular fenestrae are slit-like openings located ventral to the orbits, being mostly 4 5 6 bordered by surangulars (posterodorsally) and angulars (anteroventrally), with a small 7 8 anterior contribution of the dentaries (Fig. 15D). The anterior position of the mandibular 9 10 fenestrae is unusual. Among most archosauriforms, including early representatives of 11 12 the clade, these openings are posteriorly displaced, with their anterior borders ending 13 14 15 level with the mid length of the orbits. In some specimens of Proterosuchus (e.g. RC 16 17 846), the external mandibular fenestrae are reduced to small ellipsoid openings ending 18 19 posterior to the anterior borders of the infratemporal fenestrae. In addition, the 20 21 For Review Only 22 contribution of the dentary to the anterior border of the mandibular fenestra is more 23 24 extensive in most early archosauriforms, such as Proterosuchus (e.g. NMQR 1484), 25 26 Erythrosuchus (BP/1/5207), Garjainia (PIN 2394/5-8) and Euparkeria (SAM-PK-5867) 27 28 (Ewer, 1965; Gower, 2003; Ezcurra et al., 2019). As the lower jaw was preserved in 29 30 31 occlusion, most of its dorsal and medial surfaces are still covered by cranial bones, and 32 33 rock matrix, but were partly accessed by CT scans (Fig. 15A-C). Unfortunately, poor X- 34 35 ray penetration in the rock matrix that embeds the posterior part of the medial surface of 36 37 38 the lower jaw prevented access to the morphology of the coronoid and prearticular. 39 40 41 Dentaries: Both dentaries are preserved, but their alveolar surfaces are still 42 43 hidden by matrix. They are comparatively short, slender bones, contributing to less than 44 45 half of the anteroposterior extension of the lower jaw, in contrast to the 46 47 48 anteroposteriorly long dentaries displayed by proterosuchids, Erythrosuchus 49 50 (BP/1/5207), Garjainia (PIN 2394/5-8) and Euparkeria (SAM-PK-5867). Prolacerta 51 52 (BP/1/471) shows a condition somewhat intermediate between UNIPAMPA 653 and 53 54 these latter species, whereas Mesosuchus (SAM-PK-6536) shows short dentaries in a 55 56 57 condition more similar that present in Teyujagua. The two dentaries meet close to their 58 59 anterior end, forming a weak symphysis. Externally, the posteroventral borders of the 60 Zoological Journal of the Linnean Society Page 34 of 98

34 1 2 3 dentaries curve dorsally to accommodate the splenials, but this upward bending is 4 5 6 revealed to be more abrupt under CT imaging, indicating that the splenials partially 7 8 cover the dentaries laterally (Fig. 15A, C). The tapering posterior ends of the dentaries 9 10 make small contributions to the anterior borders of the external mandibular fenestrae 11 12 (Fig. 15D). The dentaries of UNIPAMPA 553 lack posterocentral or posteroventral 13 14 15 processes, and their posterior ends are very similar to the condition observed in 16 17 Prolacerta (e.g. BP/1/471). The presence of a posterocentral process is widespread 18 19 among early archosauriforms, whereas a posteroventral process is present in 20 21 For Review Only 22 erythrosuchids and some crownward clades (Ezcurra, 2016). As revealed by CT images, 23 24 the right dentary bears sixteen tooth positions (Fig. 15A-C), in contrast to the twenty 25 26 alveoli displayed by the upper jaws (combined count for premaxilla and maxilla). As a 27 28 result, the dentary tooth rows end well anterior to the maxillary ones, in a position close 29 30 31 to the 11th maxillary alveolus. The dentary count of UNIPAMPA 653 is low in 32 33 comparison to Prolacerta and Proterosuchus, being more similar to erythrosuchids and 34 35 euparkeriids, among others (Gower, 2003; Modesto & Sues, 2004; Ezcurra, 2016, 36 37 38 Ezcurra et al., 2019). 39 40 41 Splenials: The splenials are mostly medial components of the mandibular rami. They 42 43 are anteroposteriorly long, extending from about the posterior border of the external 44 45 mandibular fenestrae until close to the anterior end of the lower jaw. Throughout their 46 47 48 whole extension, the splenials form most of the ventral surfaces of both mandibular 49 50 rami, gently giving way to the dentaries anteriorly. The contribution of the splenials to 51 52 the symphysis is unclear. The splenials are exposed in lateral view, ventral to the 53 54 contact between the angular and the dentary, filling the space left by the gentle dorsal 55 56 57 curvatures of these bones (Fig. 15D). Although the splenials are major components of 58 59 the lower jaw of most archosauromorphs, the lateral exposure of these bones is an 60 Page 35 of 98 Zoological Journal of the Linnean Society

35 1 2 3 unusual feature for this clade. One exception is the tanystropheid Macrocnemus 4 5 6 (PIMUZ T 4822, GMPKU-P-3001), which has a wide exposure of the splenials on the 7 8 lateral surfaces of the mandibular rami, surpassing the condition displayed by 9 10 UNIPAMPA 653. The splenials also seem to have a limited lateral exposure in the 11 12 lower jaws of the early rhynchosaur Mesosuchus (SAM-PK-5882), and this is also 13 14 15 widespread among several other rhynchosaurs (e.g. Rhynchosaurus, NHMUK PV 16 17 R1236; Teyumbaita, UFRGS-PV-0232T; Hyperodapedon, UFRGS-PV-0132T). 18 19 Prolacerta (e.g. BP/1/471), Proterosuchus (e.g. NMQR 1484) and Euparkeria (SAM- 20 21 For Review Only 22 PK-5867) share the usual condition for Archosauromorpha, in which the splenials are 23 24 restricted to the medial surfaces of the lower jaw. Among erythrosuchids, at least 25 26 Garjainia prima (PIN 2394/5-8) displays a modest contribution of splenials to the 27 28 lateral surface of the mandible. In archosauriforms, lateral exposure of splenials is also 29 30 31 present in phytosaurs (e.g. Machaeroprosopus, AMNH 3060) and proterochampsians 32 33 (e.g. Proterochampsa barrionuevoi, PVSJ 77) (Colbert, 1947; Dilkes & Arcucci, 2012; 34 35 Ezcurra, 2016). 36 37 38 Angulars: The angulars are long and narrow, having wide lateral exposures on 39 40 41 the posterior halves of the mandibular rami (Fig. 15D). These bones apparently make 42 43 small contributions to the retroarticular processes at their posterior ends, gradually 44 45 expanding dorsoventrally to reach their widest portion ventral to the infratemporal 46 47 48 fenestrae. Anterior to this, the angulars narrow again to form a long anterodorsally- 49 50 directed process that ventrally border the external mandibular fenestrae, gently 51 52 ascending and contacting the dentaries anteriorly while laterally overlapping the 53 54 splenials. This gives the dorsal margins of the angulars a sigmoid outline, and this is a 55 56 57 widespread condition among archosauromorphs, being common in archosaurs (e.g. 58 59 Prestosuchus, UFRGS-PV-0629-T; Decuriasuchus, MCN-PV10.105a; França et al., 60 Zoological Journal of the Linnean Society Page 36 of 98

36 1 2 3 2013; Mastrantonio et al., 2019) and non-archosaurian archosauriforms (e.g. Garjainia, 4 5 6 PIN 2394/5-8; Proterosuchus, RC 846), and also present in a small sample of non- 7 8 archosauriform archosauromorphs (e.g. Prolacerta, BP/1/471). In Teyujagua and 9 10 archosauriforms, where an external mandibular fenestra is present, the slender, upward- 11 12 directed anterior ramus shapes the round ventral border of this opening. The 13 14 15 participation of the angulars to the medial surfaces of the mandibular rami is still 16 17 obscured and could not be accessed by CT data. 18 19 20 Surangulars: The surangulars are large bones, composing most of the external posterior 21 For Review Only 22 halves of the mandibular rami and with their maximum dorsoventral depth level with 23 24 25 the postorbital bars (Fig. 15D). Anterior to this, the anteroventral margins of the 26 27 surangulars gently bend dorsally, composing the entire posterodorsal margins of the 28 29 mandibular fenestrae. The dorsal margins of the surangulars are slightly convex. Just 30 31 ventral to the dorsal margins, the lateral surfaces of the surangulars possess step-like 32 33 34 anteroposterior shelves that probably accommodated the posterior rami of the jugals. 35 36 The surangular shelves are well-developed and display nearly straight lateral edges. The 37 38 presence of surangular shelves is an interesting character of UNIPAMPA 0653, as this 39 40 41 structure is almost completely absent in non-archosauriforms, with the exception of the 42 43 low ridges observed in the surangulars of most rhynchosaurs (Ezcurra, 2016, character 44 45 286). Ridged surangulars or well-developed surangular shelves is, thus, a typical feature 46 47 48 of Archosauriformes, and the condition in UNIPAMPA 0653 is similar to that in 49 50 Euparkeria (SAM-PK-5867). Posterior to their maximum depth, the ventral margins of 51 52 the surangulars also curve gently dorsally, to accommodate the main bodies of the 53 54 angulars. Because the angulars deepen posteriorly, the ventral borders of the surangulars 55 56 57 are not entirely convex, having rather a sigmoid shape, in a similar condition to 58 59 Prolacerta (BP/1/471) and Proterosuchus (RC 846). As the articulars are displaced 60 Page 37 of 98 Zoological Journal of the Linnean Society

37 1 2 3 medially from the lateral surfaces of the lower jaw, the surangulars apparently make 4 5 6 only limited contributions to the retroarticular processes. A small, posteriorly-directed 7 8 foramen pierces the lateral surface of the posterior end of the right surangular. Posterior 9 10 surangular foramina are present in Azendohsaurus (FMNH PR 2751), Eohyosaurus 11 12 (SAM-PK-K10159), Prolacerta (e.g. BP/1/3575) and a wide range of taxa within 13 14 15 Archosauriformes (Ezcurra, 2016, character 289). Poor preservation, however, hinders 16 17 the recognition of this same structure on the left surangular. 18 19 20 Articulars: The articulars are preserved on both sides of the skull, but the left element 21 For Review Only 22 is broken and medially displaced. The main feature of the articulars is the presence of 23 24 25 very well-developed retroarticular processes, with the right, better preserved one, 26 27 extending approximately 8 mm posterior to the glenoid fossa (Fig. 15D). The anterior 28 29 part of the right retroarticular process follows the outline of the ventral margin of the 30 31 angular. Posterior to this, it develops a dorsomedially directed hook-shaped extension 32 33 34 which is medially displaced from the lateral margin of the main body of the articular. 35 36 Well-developed, upturned retroarticular processes are widely distributed among 37 38 archosauromorphs, and the condition displayed by UNIPAMPA 0653 resembles that in 39 40 41 Proterosuchus (RC 846; Ezcurra & Butler, 2015) and Euparkeria (SAM-PK-5867; 42 43 Ewer, 1965). By contrast, erythrosuchids (Garjainia, PIN 2394/5-8), Mesosuchus 44 45 (Dilkes, 1998), Prolacerta (BP/1/471) and crownward archosauriforms have rather 46 47 48 blunt retroarticular processes. The medial surface of the right articular is still embedded 49 50 in matrix. The left articular apparently lacks a medial foramen, although poor 51 52 preservation complicates assessment of this character. While absent in most early 53 54 archosauromorphs, a medial articular foramen is typical of archosauriforms (Ezcurra, 55 56 57 2016, character 294). 58 59 60 Dentition Zoological Journal of the Linnean Society Page 38 of 98

38 1 2 3 Marginal dentition Only the marginal dentition of the right premaxilla and maxilla were 4 5 6 completely exposed by preparation (Fig. 16C). A few replacement teeth are visible in 7 8 CT images. Some posterior teeth of the left maxilla are exposed (Fig. 16B), whereas the 9 10 anterior teeth (as well as the left premaxillary teeth) remain embedded in matrix. The 11 12 dentary dentition is only accessible through CT data (Fig.15A-C). 13 14 15 Both premaxillae bear four teeth, whereas the maxillae bear sixteen teeth each 16 17 18 (Fig. 17A, C, D). Among non-archosauriforms, the premaxillary tooth count present in 19 20 UNIPAMPA 0653 is only mirrored by the allokotosaurians Azendohsaurus (FMNH PR 21 For Review Only 22 2751), Shringasaurus (ISIR 793) and Pamelaria (ISIR 316/1) (Sen, 2003; Flynn et al., 23 24 25 2010; Sengupta et al., 2017). With the exception of Mesosuchus (two premaxillary teeth 26 27 SAM-PK-5882; Dilkes, 1998), Protorosaurus (three premaxillary teeth; NMK S 180; 28 29 Gottman-Quesada & Sander, 2009) and derived rhynchosaurs, all other non- 30 31 archosauriform archosauromorphs display five or more premaxillae teeth, and the same 32 33 34 is true for early archosauriforms (Ezcurra, 2016). The maxillary tooth count present in 35 36 UNIPAMPA 0653 is also low when compared to most non-archosauriform 37 38 archosauromorphs and early archosauriforms. The maxillae of Prolacerta (BP/1/471), 39 40 41 for example, bear up to 25 tooth positions (Modesto & Sues, 2004), and a high 42 43 maxillary tooth count is also reported for Proterosuchus, reaching more than 30 44 45 positions in larger specimens (e.g. RC 846; Ezcurra & Butler, 2015). 46 47 48 All the marginal teeth display typical ziphodont morphologies, with sharp, 49 50 51 distally curved crowns (Fig. 16). Most of the teeth are labiolingually compressed, the 52 53 only exception being the anterior most premaxillary teeth, which are circular in cross 54 55 section. Labiolingual compression of the marginal dentition is typical of 56 57 archosauriforms. Among early, non-archosauriform archosauromorphs, labiolingually 58 59 60 compressed teeth seem only to be present in azendohsaurids (e.g. Azendohsaurus, UA Page 39 of 98 Zoological Journal of the Linnean Society

39 1 2 3 8-29-97-160), Tasmaniosaurus and Prolacerta (e.g. BP/1/2675) (Ezcurra, 2015, 2016). 4 5 6 The marginal dentition of azendohsaurids, however, displays characteristic adaptations 7 8 for herbivory, such as leaf-shaped expanded crowns and coarse serrations (Flynn et al., 9 10 2010, Sengupta et al., 2017). 11 12 13 The premaxillary teeth increase in size distally, with the most mesial tooth pair 14 15 having short, anteriorly procumbent, crowns. The anterior maxillary teeth are the 16 17 18 largest, and the maxillary teeth decrease in size distally (Fig. 16C). The second and 19 20 fourth maxillary tooth positions on the right side, as well as the first and fourth positions 21 For Review Only 22 on the left side, are occupied by small replacement teeth. The marginal teeth are distally 23 24 25 carinated, but their mesial margins are blunt. When visible, the tooth carinae bear very 26 27 fine serrations, with approximately ten denticles per millimeter (Fig. 16B). Serrated 28 29 teeth were, prior to the initial description of Teyujagua, considered unique to 30 31 Archosauriformes (e.g. Nesbitt, 2011; Ezcurra et al., 2014). However, aside from 32 33 34 Teyujagua, serrated teeth are present in Azendohsaurus (UA 8-29-97-160), and were 35 36 also reported for Pamelaria (Ezcurra, 2016, character 304) and Shringasaurus 37 38 (Sengupta et al., 2017). The coarse serrations of the teeth of Azendohsaurus, however, 39 40 41 strongly differ from the minute denticles displayed by UNIPAPA 0653. The presence of 42 43 serrations on the distal tooth margin alone is also characteristic of proterosuchid 44 45 archosauriforms (Ezcurra, 2016). 46 47 48 Although Pinheiro et al. (2016) recognized thecodont tooth implantation for the 49 50 51 marginal teeth of UNIPAMPA 653, cross sections of alveoli made with CT data show 52 53 that tooth roots are ankylosed to the surrounding bone, indicating an ankylothecodont 54 55 implantation (Fig. 16A). Considering the phylogenetic position of Teyujagua among 56 57 early archosauromorphs (Pinheiro et al., 2016; see below), an ankylothecodont tooth 58 59 60 implantation is expected. A fully thecodont dentition is displayed by some Zoological Journal of the Linnean Society Page 40 of 98

40 1 2 3 erythrosuchids (e.g. Garjainia prima, PIN 2394/5), Erythrosuchus (BP/1/2529) and 4 5 6 crownward archosauriforms, whereas ankylothecodont dentition is observed in 7 8 allokotosaurians, rhynchosaurs, Prolacerta and the earliest archosauriforms (Ezcurra, 9 10 2016; Ezcurra et al., 2019). 11 12 13 Although still enclosed in matrix, dentary dentition was accessed by CT scans 14 15 (Fig. 15A-C). The better preserved right dentary bears sixteen alveoli, a low tooth count 16 17 18 when compared to most non-archosauriform archosauromorphs and early 19 20 archosauriforms. Early rhynchosaurs, such as Howesia (SAM-PK-5884) and 21 For Review Only 22 Mesosuchus (SAM-PK-5882) had dentaries with multiple rows of numerous blunt teeth 23 24 25 (Dilkes, 1995, 1998), and the tanystropheid Macrocnemus (e.g. GMPKU-P-3001) could 26 27 bear up to 40 small conical teeth on each dentary. Similarly, dentary tooth count is 28 29 comparatively high in Prolacerta (e.g. BP/1/471), and Proterosuchus (RC 846), whose 30 31 dentaries had room for up to 30 teeth. Dentary teeth are apparently similar to the 32 33 34 maxillary ones but have more circular cross-sections. The dentary tooth row ends 35 36 posteriorly well anterior to the posterior end of the maxillary series – the posterior most 37 38 dentary tooth is level with the 11th maxillary teeth. Although the dentary teeth bear 39 40 41 distal carinae, CT scans do not allow the recognition of possible serrations. 42 43 44 Palatal dentition Although still hidden by matrix, the palate of UNIPAMPA 0653, as 45 46 recovered by CT scans, shows an extensive presence of teeth (Fig. 17). Limited X-ray 47 48 penetration hindered the delimitation of palatal bones. However, the palatal dentition is 49 50 51 apparently associated with the pterygoids, palatines and vomers. The pterygoid 52 53 dentition consists of three distinct zones (Fig. 17B). One of these, tooth zone T4 of 54 55 Welman (1998) extends through the medial border of the palatal ramus. Although tooth 56 57 zone T4 comprises small, regularly spaced, blunt teeth on the left pterygoid, it shows 58 59 60 well developed fang-like teeth on the right side. On both sides, the apicobasal axes of Page 41 of 98 Zoological Journal of the Linnean Society

41 1 2 3 T4 tooth crowns are medially directed. The presence of tooth zone T4 in UNIPAMPA 4 5 6 0653 is remarkable, as a row of teeth on the medial surface of the palatal process of the 7 8 pterygoid is restricted to early archosauriforms (e.g. Proterosuchus, NMQR 1484) and 9 10 closely-related taxa, such as Prolacerta (e.g. BP/1/2675), Boreopricea and 11 12 Tasmaniosaurus (UTGD 54655) (Ezcurra, 2016). 13 14 15 Tooth zone T3 is composed of a single row of small teeth extending throughout 16 17 18 the ventral surface of the pterygoid. A single tooth row on zone T3 is uncommon among 19 20 early archosauromorphs, being thus far only reported for tanystropheids (Ezcurra, 2016, 21 For Review Only 22 character 197). Posteriorly, the T3 row begins in a region close to the presumed contact 23 24 25 with the ectopterygoid, extending through the palatal ramus. T3 teeth are rounded and 26 27 blunt posteriorly, but gradually become slightly bigger and pointed towards the anterior 28 29 end of the palatal ramus. Tooth zone T2 consists of two posteriorly converging rows of 30 31 considerably developed pointed teeth, the medial one apparently being continuous with 32 33 34 the palatine dentition. Due to poor X-ray penetration, tooth zone T2 can be consistently 35 36 identified only on the left pterygoid. The disposition of ventral pterygoid teeth into two 37 38 distinct fields (T2 and T3) is characteristic of early archosauromorphs, observable, for 39 40 41 instance, in Mesosuchus (SAM-PK-6536), Macrocnemus (PIMUZ T 1559), Prolacerta 42 43 (BP/1/5066) and Proterosuchus (NMQR 1484) (Ezcurra, 2016). However, the presence 44 45 of two tooth rows on field T2 was, among archosauromorphs, only reported for 46 47 48 Macrocnemus and Howesia (Dilkes, 1995; Ezcurra, 2016). Teeth corresponding to tooth 49 50 zone T1 of Welman (1998), which would be concentrated on the posterior border of the 51 52 palatine process of the pterygoid, are apparently absent in UNIPAMPA 0653. Among 53 54 non-archosauriform archosauromorphs, tooth zone T1 is absent in Jesairosaurus, 55 56 57 tanystropheids and rhynchosaurs (Ezcurra, 2016, character 202). 58 59 60 Zoological Journal of the Linnean Society Page 42 of 98

42 1 2 3 The combination of i) a single tooth row on zone T3; ii) presence of zone T4; iii) 4 5 6 zone T2 composed by two tooth rows and iv) absence of zone T1 is unique among 7 8 Archosauromorpha, making the pterygoid of UNIPAMPA 0653 highly diagnostic. 9 10 11 Anterolaterally to pterygoid tooth zone T2, the palatal teeth abruptly change in 12 13 shape from relatively tall and pointed to short and blunt. In addition, the teeth become 14 15 roughly oriented into two poorly defined anteromedially directed rows (Fig. 17B: ‘pld’). 16 17 18 This change in morphology probably marks the transition between the pterygoid and the 19 20 palatine, and the blunt teeth are probably associated with this latter bone. The presence 21 For Review Only 22 of teeth on the palatine is plesiomorphic for diapsids, being the usual condition among 23 24 25 archosauromorphs. Exceptions to this include erythrosuchids, most rhynchosaurs, 26 27 Prolacertoides (IVPP V3233), Trilophosaurus, and several clades of crownward 28 29 archosauriforms (Ezcurra, 2016). The vomerine dentition is oriented as a single row of 30 31 irregularly spaced fang-like teeth with medially oriented apicobasal axes (Fig. 17A). 32 33 34 Vomerine teeth are absent in specialized rhynchosaurs and Prolacertoides, whereas 35 36 Pamelaria and Prolacerta show multiple rows of teeth on the vomer (Sen, 2003; 37 38 Ezcurra, 2016, character 187). 39 40 41 Cervical vertebrae 42 43 44 General remarks: The atlas-axis and cervical vertebrae III and IV are completely 45 46 47 preserved and lie adjacent to the occiput (Figs 2C, 18). In addition, some very small 48 49 fragments of cervical vertebra V can be seen in articulation with the fourth element. 50 51 Although close to natural position, the cervicals are rotated along their main axis, so 52 53 that their left lateral surfaces are mainly exposed in dorsal view of the specimen. 54 55 56 Preparation exposed the left side of the vertebrae, but the right surface is still embedded 57 58 in the hard, mainly calcium carbonate concretion. As bone density in this particular part 59 60 of the specimen is exceedingly similar to matrix density, our attempts to reconstruct the Page 43 of 98 Zoological Journal of the Linnean Society

43 1 2 3 overall surface of vertebrae based on CT scan images failed. At least on the left side, 4 5 6 cervical ribs are still in articulation (Fig. 18). 7 8 Atlas: At least two atlantal elements lie in close association with the axis and are 9 10 11 exposed on the left side of the cervical series (Fig. 18). The dorsal one is here identified 12 13 as the atlas neural arch. It is a slender bone in lateral view, thicker ventrally and 14 15 gradually tapering in the dorsal direction, where it curves anteriorly, somewhat 16 17 18 following an anterior overhang of the axial neural spine. As preserved, the atlantal 19 20 neural arch does not present a posterior wing-like expansion to articulate with the axis, 21 For Review Only 22 as displayed, for example, by Azendohsaurus (UA 7-20-99-653; Nesbitt et al., 2015). 23 24 25 Additionally, there is a ventral, wedge-shaped element, positioned at the same level as 26 27 the axis centrum. This small bone is consistent in morphology with a crescent-shaped 28 29 intercentrum exposed in lateral view, and is here identified as the atlantal intercentrum. 30 31 32 Axis: The axis is a robust element, with a strong neural spine shaped as a wide plate 33 34 (Fig. 18). Anteriorly and in close association with the axis, there is an additional wedge- 35 36 37 shaped bone with a tapering posteroventral projection. This bone is here identified as 38 39 the axial intercentrum, and the posteroventral projection may correspond to the axial 40 41 parapophysis. As the anterodorsal part of this bone is still obscured by matrix and 42 43 44 atlantal elements, the presence of a fused odontoid process could not be confirmed. 45 46 47 The axial neural spine is longer than tall. It differs from the comparatively low 48 49 axial neural spines of tanystropheids (e.g. Tanystropheus, MSNM BES SC 265; Nosotti, 50 51 2007) and Prolacerta (Camp, 1945; Ezcurra, 2016). Although mainly rectilinear, its 52 53 dorsal surface is notched close to the mid length of the neural spine, which may be a 54 55 56 taphonomic artifact. Excluding this notch, the neural spine maintains a similar height 57 58 throughout its anteroposterior extension, differing from the anterodorsally expanded 59 60 axial neural spine of tanystropheids (e.g. Tanystropheus, MSNM BES SC 265). The Zoological Journal of the Linnean Society Page 44 of 98

44 1 2 3 anterodorsal corner of the axial neural spine is rounded, so that the transition from the 4 5 6 dorsal to the anterior surface is more or less gentle. The neural spine has a distinct 7 8 anterior overhang, as its outline abruptly curves posteroventrally, shaping a strong 9 10 concavity. In the way the elements are disposed, this anterior concavity accommodates 11 12 the atlantal neural arch. In this respect, the axial neural spine of UNIPAMPA 653 is 13 14 15 somewhat similar to that in Azendohsaurus (FMNH PR 3823). In this latter taxon, 16 17 however, the dorsal edge of the neural spine increases in height posteriorly (Nesbitt et 18 19 al. 2015). The axial neural spine of Prolacerta maintains its height throughout its 20 21 For Review Only 22 extension, but its anterior overhang tapers to form an acute projection (Camp, 1945). 23 24 25 The dorsal surface of the axial neural spine thickens posteriorly, forming a 26 27 swollen posterodorsal corner. In addition to this swelling, the dorsal surface of the 28 29 neural spine is slightly transversely expanded throughout its whole extension. In the 30 31 ventral direction, the neural spine widens to form the postzygapophysis. The 32 33 34 postzygapophysis articular facet is horizontally oriented, almost parallel to the dorsal 35 36 surface of the neural spine. There is no epipophysis, whereas this structure is present in 37 38 the axis of Azendohsaurus (FMNH PR 3823) and, apparently, Tanystropheus (MSNM 39 40 41 BES SC 265). Similar to UNIPAMPA 0653, epipophyses are absent on the axis of 42 43 Prolacerta (Camp, 1945) and early archosauriforms (e.g. Proterosuchus, NMQR 1484; 44 45 Garjainia, PIN 2394/5-10). A small prezygapophysis articulates with the atlantal neural 46 47 48 arch. Posteriorly to the prezygapophysis, there is a low lamina that fades long before the 49 50 mid length of the neural arch, not forming an interzygapophyseal lamina. 51 52 53 The centrum is anteroposteriorly short when compared to Azendohsaurus 54 55 (FMNH PR 3823), Tanystropheus (MSNM BES SC 265) and Prolacerta (Camp, 1945), 56 57 being more or less compatible with Proterosuchus (NMQR 1484). Close to its anterior 58 59 60 limit, it bears a ventrolaterally directed diapophysis, posterior to which a strong lamina Page 45 of 98 Zoological Journal of the Linnean Society

45 1 2 3 extends throughout its entire length, reaching the articulation facet with the third 4 5 6 cervical vertebra. Ventral to this lamina, the centrum is laterally compressed. The way 7 8 the vertebrae are preserved precludes the identification of a possible ventral keel. The 9 10 posterior articulation facet of the axis is positioned slightly ventral to the anterior one. 11 12 13 Cervical vertebrae III and IV: There are no intercentra associated with the third and 14 15 fourth cervical vertebrae. These elements display slender, vertically oriented neural 16 17 18 spines, approximately twice as tall as they are long (Fig. 18). Similarly, tall neural 19 20 spines are present in the anterior postaxial cervicals of Proterosuchus (NMQR 1484) 21 For Review Only 22 and Garjainia (PIN 2394/5-10), as well as in most archosauriforms (Ezcurra, 2016; 23 24 25 Ezcurra et al., 2019). On the other hand, the anterior postaxial cervicals of 26 27 tanystropheids, Azendohsaurus (FMNH PR 2791) and Prolacerta (e.g. BP/1/2675) 28 29 display low, anteroposteriorly elongated neural spines. Although the anterior margins of 30 31 the neural spines are straight, the posterior margin bears a well-developed projection 32 33 34 close to the mid-point between the dorsal margin of the neural spine and the beginning 35 36 of the postzygapophysis in cervical vertebra III. The neural spine of the fourth cervical 37 38 is dorsally broken and scattered, but a similar projection seems to be present. The dorsal 39 40 41 surface of the neural spine lacks a transverse expansion in the third cervical, but in the 42 43 fourth element this condition is unclear. This condition contrasts with Prolacerta (e.g. 44 45 BP/1/2675) and proterosuchids (e.g. Proterosuchus, NMQR 1484), which have neural 46 47 48 spines gradually expanding towards their distal ends. The prezygapophyses are 49 50 anteroposteriorly long and transversely wide, with mainly horizontal articulation 51 52 surfaces. The postzygapopophysis of cervical vertebra III is approximately at the same 53 54 level as the prezygapophysis, whereas in cervical IV the postzygapophysis is placed 55 56 57 considerably dorsally to the prezygapophysis. What seems to be a weak 58 59 interzygapophyseal lamina is present in cervical III. A similar lamina is present on the 60 Zoological Journal of the Linnean Society Page 46 of 98

46 1 2 3 third cervical vertebra of Prolacerta (BP/1/2675). Although the bone surface in this 4 5 6 region is poorly preserved both in cervical III and IV, shallow depressions are present at 7 8 the bases of the neural spines of these elements. Excavations at the base of the neural 9 10 spine are present in the anterior cervicals of Prolacerta, Proterosuchus, erythrosuchids 11 12 and other crownward archosauriforms (Ezcurra, 2016, character 337). 13 14 15 The centra are slightly anteroposteriorly expanded, and their anterior and 16 17 18 posterior articulation surfaces are positioned approximately at the same level (the 19 20 posterior articulation surface is slightly ventrally displaced in cervical IV). The 21 For Review Only 22 diapophyses and parapophyses are located approximately at the dorsoventral midpoints 23 24 25 of the centra in both cervicals III and IV. A longitudinal lamina extending posteriorly 26 27 from the diapophysis is present in both elements, although this structure seems to be 28 29 better developed in cervical IV, in which it dorsally limits a deep depression on the 30 31 centrum. Similar laminae are present in Proterosuchus (NMQR 1484), and are widely 32 33 34 expanded in some other early archosauriform taxa (e.g. Chasmatosuchus, PIN 35 36 2252/381). Delicate, horizontally-directed, cervical ribs are associated with cervicals III 37 38 and IV. No neurocentral suture is distinguishable. 39 40 41 42 43 44 PHYLOGENETIC ANALYSES 45 46 47 Our first analysis (updated scores of Teyujagua paradoxa in the data matrix of Pinheiro 48 49 50 et al. 2016) resulted in eight most parsimonious trees (MPTs) of 879 steps (differing 51 52 from two MPTs of 872 steps in the original analysis), with CI = 0.34, RI = 0.62. The 53 54 strict consensus of these trees (Fig. 19) displays the same relationships recovered by 55 56 Pinheiro et al. (2016) for non-archosauriform archosauromorphs: Tanystropheidae 57 58 59 (Tanystropheus + Macrocnemus) is recovered in a clade together with (Protorosaurus + 60 Page 47 of 98 Zoological Journal of the Linnean Society

47 1 2 3 Aenigmastropheus); Rhynchosauria is recovered as monophyletic, but the relationships 4 5 6 between the three included representatives of this clade are unresolved; Prolacerta is 7 8 recovered as the sister-taxon to (Teyujagua + Archosauriformes); and Teyujagua is 9 10 consistently placed as the sister-taxon to Archosauriformes (Bremer support 3 for this 11 12 node). Relationships among Archosauriformes are, however, mainly unresolved, with a 13 14 15 major polytomy including proterosuchid taxa, Chanaresuchus, Koilamasuchus, 16 17 Fugusuchus, (Vancleavea + Doswellia), Euparkeridae, Erythrosuchidae and 18 19 Archosauria (which is recovered as monophyletic). 20 21 For Review Only 22 Synapomorphies of the clade (Teyujagua + Archosauriformes) in the consensus 23 24 25 tree of analysis I include: serrations on marginal tooth crowns (character 4); trapezoidal 26 27 infratemporal fenestrae (character 17); presence of a palatal process on the premaxillae 28 29 (character 25); absence of an anterior maxillary foramen (character 29); absence of a 30 31 posterolateral process on the frontal (character 42); reduced postfrontals (character 43); 32 33 34 presence of an external mandibular fenestra (character 105); and presence of a lateral 35 36 shelf on the surangular (character 110). 37 38 39 Archosauriformes, on the other hand, is supported by three unambiguous 40 41 synapomorphies: presence of antorbital fenestrae (character 12); complete lower 42 43 44 temporal bar (character 19); and posteroventral process of premaxilla extending 45 46 posterior to the external naris (character 252) 47 48 49 Analysis II (updated scores of T. paradoxa in the dataset of Butler et al., 2019, 50 51 which is, by its turn, derived from the original data matrix of Ezcurra, 2016) resulted in 52 53 44 trees of 3599 steps in the first round of searches using the New Technology option of 54 55 56 TNT (FUSE algorithm, 100 hits). A second round of TBR starting from the trees 57 58 recovered in the first round, found 54 trees of 3599 steps, CI = 0.25; RI = 0.65. The 59 60 strict consensus of the most parsimonious trees produced by analysis II shows that Zoological Journal of the Linnean Society Page 48 of 98

48 1 2 3 Teyujagua is consistently nested as the sister group of a clade formed by 4 5 6 Tasmaniosaurus triassicus and Archosauriformes (Fig. 20). The clade (Teyujagua + 7 8 (Tasmaniosaurus triassicus + Archosauriformes)) is supported by the absence of an 9 10 anterior maxillary foramen (character 52); presence of a distinct ascending process with 11 12 a posterior concave margin on the maxilla (character 58); upper temporal bar level with 13 14 15 the dorsal margin of the orbit (character 126); gentle transition between the anterior and 16 17 ventral processes of squamosal (character 139); squamosal contributes with more than a 18 19 half of the posterior border of the infratemporal fenestra (character 146); presence of an 20 21 For Review Only 22 external mandibular fenestra (character 262); serrated teeth (character 304) and 23 24 excavation at the base of postaxial neural spines (character 337). 25 26 27 Notably, given the node-based definition of Archosauriformes (Nesbitt, 2011; 28 29 Ezcurra, 2016), the inclusion of Tasmaniosaurus triassicus in the dataset of Butler et al. 30 31 (2019) makes this enigmatic archosauromorph the sister-taxon to Archosauriformes 32 33 34 (contra Pinheiro et al., 2016), even though it closely resembles proterosuchid 35 36 archosauriforms in several aspects (Ezcurra, 2014). Synapomorphies supporting 37 38 (Tasmaniosaurus + Archosauriformes) are: presence of antorbital fenestrae (character 39 40 41 13); sheet-like postparietal (character 171) and presence of a posterocentral process on 42 43 the dentary (character 273). 44 45 46 In addition, the strict consensus recovered by analysis II agrees with previous 47 48 assessments of archosauromorph phylogeny (e.g. Ezcurra, 2016; Sengupta et al., 2017; 49 50 51 Butler et al., 2019). Jesairosaurus lehmani is the sister taxon to a monophyletic 52 53 Tanystropheidae, and the clades Allokotosauria, Rhynchosauria, Erythrosuchidae, 54 55 Proterochampsia and Archosauria were recovered. Notably, there is a polytomy 56 57 including Boreopricea, (Kadimakara + Prolacerta) and (Teyujagua + (Tasmaniosaurus 58 59 60 + Archosauriformes)). Page 49 of 98 Zoological Journal of the Linnean Society

49 1 2 3 4 5 6 DISCUSSION 7 8 9 IMPLICATIONS FOR THE EARLY EVOLUTION OF ARCHOSAURIFORMES 10 11 12 Shaping the archosauriform skull. The archosauriform body plan was classically 13 14 characterized by a series of key cranial characters presumably related to hypercarnivory 15 16 17 (Gauthier, 1986; Nesbitt; 2011; Ezcurra et al. 2014). Even though the clade and its 18 19 characteristic morphology had already evolved by the latest Permian (Ezcurra et al., 20 21 2014), adaptations to carnivoryFor Review provided archosauriforms Only with the opportunity to 22 23 24 replace large synapsids as apex predators during the aftermath of the end-Permian mass 25 26 extinction (Ezcurra & Butler, 2018). As such, in the Karoo Basin of South Africa, 27 28 where Permian-Triassic sequences are well-preserved and extensively studied, the 29 30 archosauriform Proterosuchus is the first new taxon to appear in the lowermost Triassic 31 32 33 rocks following the extinction (Botha & Smith, 2006). 34 35 36 Since the discovery of Teyujagua paradoxa, however, it has become clear that 37 38 some characteristic features of Archosauriformes evolved in a mosaic fashion before the 39 40 emergence of this clade (Pinheiro et al., 2016). Similar to non-archosauriform 41 42 43 archosauromorphs, Teyujagua lacks antorbital fenestrae and still retains open lower 44 45 temporal bars. However, Teyujagua also displays cranial features that were previously 46 47 regarded as synapomorphic for Archosauriformes, such as serrated teeth and external 48 49 50 mandibular openings. The inclusion of Teyujagua in a broader phylogenetic dataset of 51 52 Archosauromorpha makes it possible to track the origins of these key features. 53 54 55 As discussed above, although the overall morphology of Tasmaniosaurus 56 57 triassicus closely resembles those of proterosuchids (Ezcurra, 2014), the node-based 58 59 phylogenetic definition of Archosauriformes proposed by Nesbitt (2011) excludes this 60 Zoological Journal of the Linnean Society Page 50 of 98

50 1 2 3 species from the clade. This means that Teyujagua is the sister taxon of 4 5 6 (Tasmaniosaurus + Archosauriformes), and not the sister taxon to Archosauriformes, as 7 8 previously proposed by Pinheiro et al. (2016). The distribution of character states 9 10 among archosauriforms and closely related taxa reveals that classic synapomorphies of 11 12 Archosauriformes, most of them regarding skull morphology, in fact appear earlier 13 14 15 among its successive sister taxa (e.g. Teyujagua, Tasmaniosaurus). Serrated teeth, 16 17 external mandibular fenestrae and an elevated upper temporal bar (related to the 18 19 enlargement of the adductor chamber) characterize the clade formed by Teyujagua, 20 21 For Review Only 22 Tasmaniosaurus and Archosauriformes. Remarkably, all those features are linked to the 23 24 development of carnivory, making archosauriforms and its close sister taxa pre-adapted 25 26 to fill the role of apex predators already during the Permian, when they were minor 27 28 components of terrestrial faunas. 29 30 31 In addition to dietary adaptations, the clade composed of Tasmaniosaurus and 32 33 34 archosauriforms further developed facial pneumaticity, which was already incipient in 35 36 Teyujagua and Prolacerta (see below), also evolving some secondary skull features, 37 38 such as a sheet-like postparietal and posterocentral processes on the dentaries. Finally, 39 40 41 in this new phylogenetic framework, only two synapomorphies support 42 43 Archosauriformes: the presence of interdental plates and dorsally curved dentaries. This 44 45 is probably a result of the fragmentary nature of Tasmaniosaurus holotype, as the 46 47 48 ubiquitous presence of missing data in the taxon makes ambiguous several 49 50 Archosauriformes potential synapomorphies. 51 52 53 54 55 56 The origin of the antorbital fenestrae. The antorbital fenestra has been consistently 57 58 found as a synapomorphy of Archosauriformes or a node more basal (e.g. Gauthier et 59 60 al., 1988; Nesbitt, 2011; Pinheiro et al., 2016; Ezcurra, 2016), being classically Page 51 of 98 Zoological Journal of the Linnean Society

51 1 2 3 considered as the main diagnostic feature of this clade (Witmer, 1997). The antorbital 4 5 6 fenestrae are openings in the skull positioned anterior to the orbits, which are often large 7 8 in size, and which are mostly delimited by the maxillae and lacrimals, although 9 10 sometimes with contributions from the nasals and/or jugals (Witmer, 1997). The 11 12 internal antorbital fenestrae (sensu Witmer, 1997) are usually surrounded by the 13 14 15 antorbital fossae, which are normally most extensively developed on the maxillae, but 16 17 which can also excavate other adjacent bones. The development of additional openings 18 19 within the antorbital fossa is also common in archosauriforms – for example, the 20 21 For Review Only 22 promaxillary foramen of many theropod dinosaurs (Witmer, 1997). 23 24 25 The function of the antorbital fenestrae, fossae and accessory openings remained 26 27 elusive until detailed anatomical study by Witmer (1987, 1995a, 1997), which applied 28 29 the extant phylogenetic bracket approach (Witmer, 1995b) to convincingly argue that 30 31 these structures housed paranasal air sinuses, epithelial air sacs that outgrow the 32 33 34 cartilaginous nasal capsule, partially filling the nasal cavity and pneumatizing facial 35 36 bones. Although they fall outside the phylogenetic bracket formed by extant birds and 37 38 crocodilians (both of which display prominent paranasal sinuses), early archosauriforms 39 40 41 such as Proterosuchus and Euparkeria already display all the osteological correlates for 42 43 these soft tissue structures, and the evidence for intense pneumatization in early 44 45 archosauriform skulls is compelling. 46 47 48 Proterosuchus, the earliest archosauriform for which the cranial anatomy is well 49 50 51 understood, displays large antorbital fenestrae bounded by the maxillae and lacrimals, 52 53 with a small contribution to the posteroventral corners of the fenestrae from the 54 55 maxillary rami of the jugals. Shallow lacrimal antorbital fossae are present, indicating 56 57 that paranasal air sacs partially covered the lateral surfaces of these bones, but antorbital 58 59 60 fossae are absent from the lateral surface of maxillae (Ezcurra, 2016). Wider and Zoological Journal of the Linnean Society Page 52 of 98

52 1 2 3 deeper antorbital fossae excavating the maxillae laterally in addition to the lacrimals 4 5 6 appear for the first time among erythrosuchids such as Erythrosuchus and Garjainia 7 8 (Gower, 2003; Ezcurra, 2016; Ezcurra et al., 2019), where they occur primarily upon the 9 10 ascending processes of the maxillae, and in early crown archosaurs the antorbital fossae 11 12 are most extensive, extending onto the horizontal process of the maxilla along the entire 13 14 15 ventral margins of the antorbital fenestrae. 16 17 18 Although it lacks antorbital fossae or fenestrae on the external surface of the 19 20 skull, given its phylogenetic position the morphologies of the facial bones of Teyujagua 21 For Review Only 22 may shed light on the initial development of these key anatomical features. As 23 24 25 described above, the medial surfaces of the maxillae of Teyujagua bear deep, 26 27 arrowhead-shaped depressions, lateral to which the maxillary wall is exceptionally thin 28 29 (Fig. 21A, C). These depressions, which we here refer to as medial antorbital fossae, are 30 31 contiguous with similar excavations on the nasals and lacrimals. Together, they 32 33 34 probably formed a single functional structure. Prolacerta, which was generally 35 36 considered as the sister-taxon to Archosauriformes prior to the description of 37 38 Teyujagua, possesses very similar arrow-shaped medial antorbital fossae on the 39 40 41 maxillae (BP/1/2675) (Fig. 21B). 42 43 44 Topological similarities and phylogenetic congruence lead us to hypothesize 45 46 homology between the medial antorbital fossae of Teyujagua and Prolacerta and the 47 48 antorbital fenestrae and associated fossae of archosauriforms. In this framework, skull 49 50 51 pneumaticity associated with the lateral expansion of epithelial air sacs from the nasal 52 53 capsule appeared internally on the medial surfaces of the facial bones, before it became 54 55 expressed laterally via the antorbital fenestrae. Thus, integrating new data from 56 57 Teyujagua and Prolacerta with existing knowledge of the morphological diversity of 58 59 60 facial bones among Archosauriformes, we recognize five, not necessarily Page 53 of 98 Zoological Journal of the Linnean Society

53 1 2 3 interdependent, steps in the evolution of archosauriform antorbital fenestration (Fig. 4 5 6 22): 7 8 I) Lateral outgrowth of epithelial sinuses from the cartilaginous nasal capsule. 9 10 11 Air sacs are restricted to the nasal chamber, and not expressed on the lateral surfaces of 12 13 the skull. Osteological correlates are the presence of medial excavations on facial bones, 14 15 forming the medial antorbital fossae described above. Of the two taxa known to show 16 17 18 these fossae, Teyujagua differs from Prolacerta in having broader lacrimals that display 19 20 medial excavations, possibly also as a consequence of skull pneumatization. In 21 For Review Only 22 Prolacerta, therefore, the air sacs would be more restricted to the maxillary portion of 23 24 25 the snout than in Teyujagua. 26 27 28 II) Opening of the antorbital fenestrae. Continued growth of lateral sinuses 29 30 would drive facial bones to ossify surrounding the air sacs, resulting in the appearance 31 32 of antorbital fenestrae on the lateral surfaces of the skull. This would be driven by the 33 34 reduction in size of the lacrimals (broad in Teyujagua), and also by the development of 35 36 37 a separation between the ascending and the horizontal or posterior processes of the 38 39 maxillae. This condition could result from the formation of a fontanelle between the 40 41 lacrimals and maxillae that would remain open in later ontogenetic stages, as was 42 43 44 observed by Witmer (1995) for extant birds. At this stage only the lacrimals display 45 46 shallow fossae, as observed for example in some specimens of Proterosuchus (e.g. RC 47 48 846). 49 50 51 III) Lateral excavation of bones surrounding the antorbital fenestrae. The 52 53 paranasal sinuses invade the lateral surface of the skull, resulting in deep excavations 54 55 56 with well-defined rims on some facial bones. These excavations, the antorbital fossae, 57 58 are usually located on the lacrimals and maxillae, but can sometimes extend onto the 59 60 nasals and/or jugals. Deep antorbital fossae with well-defined rims are characteristic of Zoological Journal of the Linnean Society Page 54 of 98

54 1 2 3 the clade formed by erythrosuchids and Eucrocopoda (euparkeriids, Proterochampsia 4 5 6 and archosaurs), and expand further such that they extend along the entire horizontal 7 8 process of the maxilla in crown archosaurs (Nesbitt, 2011; Ezcurra, 2016). 9 10 11 IV) Emergence of accessory cavities. The development of secondary epithelial 12 13 diverticula associated with the main corpus of the paranasal sinus creates a series of 14 15 recesses in the bones that surround the antorbital fenestrae (Witmer, 1997). These 16 17 18 accessory openings are reasonably common among dinosaurs (especially theropods), 19 20 but also occur in pterosaurs, some loricatans (Witmer, 1997) and in at least one basal 21 For Review Only 22 sauropodomorph (Macrocollum itaquii, CAPPA/UFSM 0001a; Müller et al., 2018). 23 24 25 V) Reduction of the antorbital complex/closure of the antorbital fenestrae. 26 27 28 Several clades experienced the reductions of the antorbital fossae and fenestrae and 29 30 eventual closure of the latter as the result of different selective pressures and 31 32 biomechanical contingencies (Witmer, 1997). A number of representatives of the non- 33 34 archosaurian archosauriform clade Proterochampsia display reduced, dorsally- 35 36 37 positioned antorbital fenestrae with poorly developed antorbital fossae (e.g. Trotteyn et 38 39 al., 2013). This trend may be a result of the susceptibility of dorsoventrally compressed 40 41 skulls to torsion loads, as was proposed by Witmer (1997) for crocodylomorphs. The 42 43 44 apparently fully aquatic proterochampsian Vancleavea reached the extreme of 45 46 completely lacking external antorbital openings (Nesbitt et al., 2009), a condition later 47 48 independently acquired by neosuchian crocodylomorphs. Among Neosuchia, the 49 50 51 reduction and latter closure of the antorbital cavities was probably linked to the 52 53 formation of a secondary palate, as well as platyrostry (Witmer, 1997). Ornithischian 54 55 dinosaurs also display a strong trend towards reduction and eventual loss of the 56 57 antorbital openings, probably as a consequence of the development of specialized 58 59 60 feeding apparatus (Witmer, 1997). In addition, the lack of antorbital fossae is the usual Page 55 of 98 Zoological Journal of the Linnean Society

55 1 2 3 condition for pterosaurs, with the exception of some few early representatives (Nesbitt 4 5 6 & Hone, 2010), and the confluence of the nasal and antorbital fenestrae is characteristic 7 8 of Pterodactyloidea (Kellner, 2003; Unwin, 2003). 9 10 11 12 13 14 On the presence of external mandibular fenestrae in non-archosauriform 15 16 archosauromorphs. The recent recognition of external mandibular openings in 17 18 Teyujagua paradoxa (Pinheiro et al. 2016) made this taxon the only non-archosauriform 19 20 21 archosauromorph in whichFor this Reviewclassic archosauriform Only feature is unequivocally present 22 23 (the condition in Tasmaniosaurus is dubious). The recovered phylogenetic relationships 24 25 of Teyujagua implies that the presence of external mandibular fenestrae is a 26 27 28 synapomorphy of Teyujagua + (Tasmaniosaurus + Archosauriformes). 29 30 The tanystropheid Macrocnemus fuyuanensis, however, was proposed as 31 32 33 possibly possessing external mandibular openings. The brief description of the holotype 34 35 by Li et al. (2007) only mentioned the presence of “mandibular fossae”, not implying 36 37 the presence of actual openings. However, in a subsequent description of a better- 38 39 40 preserved specimen (Jiang et al., 2011), a small slit-like opening between the angular 41 42 and the surangular was mentioned and illustrated, although the potential implications of 43 44 the presence of external mandibular fenestrae in a tanystropheid were not discussed. 45 46 47 Our examination of several specimens of Macrocnemus, however, revealed that 48 49 50 the posterior mandibular bones are often disarticulated and were probably only loosely 51 52 connected in life. Indeed, some European specimens of Macrocnemus, such as PIMUZ 53 54 T 1559 (attributed to M. aff. M. fuyuanensis by Jaquier et al., 2017), show that a similar 55 56 opening to that illustrated by Jiang et al. (2011) can be artificially created by the 57 58 59 combined effects of slightly displaced posterior mandibular elements and fragmentation 60 Zoological Journal of the Linnean Society Page 56 of 98

56 1 2 3 of some bones (Fig. 23). In PIMUZ T 1559, the surangular is anteriorly and ventrally 4 5 6 abraded, and most of the angular and part of the splenial seem to be displaced from their 7 8 original positions, creating an artificial lateral opening in the lower jaw. In addition, the 9 10 presumed mandibular fenestra of M. fuyuanensis is biased by the misinterpretation by 11 12 Jiang et al. (2010) of the splenial as a posteroventral ramus of a bifurcated dentary 13 14 15 (Torsten Scheyer, personal communication, 2018). We note that posteriorly bifurcated 16 17 dentaries are the typical condition for archosauriforms, but that among non- 18 19 archosauriform archosauromorphs, only basal rhynchosaurs and Tasmaniosaurus show 20 21 For Review Only 22 this feature (Ezcurra, 2014). The revaluation of M. fuyuanensis by Jaquier et al. (2017) 23 24 did not identify external mandibular fenestrae in any of the specimens attributed to this 25 26 taxon. As such, we consider it most likely that external mandibular fenestrae were not 27 28 present in M. fuyuanensis. 29 30 31 CONCLUSIONS 32 33 34 Teyujagua paradoxa, as represented by its holotype and thus far only known specimen, 35 36 37 has a unique morphology that distinguishes it from all other known archosauromorphs. 38 39 In addition, T. paradoxa reveals the emergence of anatomical features that culminated 40 41 in the assemblage of the typical archosauriform skull architecture, including the early 42 43 44 development of cranial pneumaticity associated with the paranasal air sinuses. CT-based 45 46 anatomical description of T. paradoxa provided a wealth of new information, allowing a 47 48 reassessment of its phylogenetic relationships. The cladistic analysis performed here 49 50 51 supported T. paradoxa as the sister taxon of (Tasmaniosaurus + Archosauriformes), in a 52 53 similar position to that recovered by Pinheiro et al. (2016). In addition to adding 54 55 information on character evolution during the origins of Archosauriformes, T. paradoxa 56 57 plays an important role in the understanding of terrestrial ecosystems in the aftermath of 58 59 60 the end-Permian mass extinction in western Gondwana. Page 57 of 98 Zoological Journal of the Linnean Society

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62 1 2 3 Langer MC, Schultz CL. 2003. A new species of the Late Triassic rhynchosaur 4 5 6 Hyperodapedon from the Santa Maria Formation of South Brazil. Palaeontology 43: 7 8 633–652. 9 10 11 Li C, Zhao L, Wang L. 2007. A new species of Macrocnemus (Reptilia: Protorosauria) 12 13 from the Middle Triassic of southwestern China and its palaeogeographical implication. 14 15 Science in China Series D: Earth Sciences 50: 1601–1605. 16 17 18 Maddison WP, Maddison DR. 2018. Mesquite: a modular system for evolutionary 19 20 21 analysis. Version 3.51For http://www.mesquiteproject.org. Review Only 22 23 24 Mastrantonio BM, von Baczo MB, Desojo JB, Schultz, CL. 2019. The skull anatomy 25 26 and cranial endocast of the pseudosuchid archosaur Prestosuchus chiniquensis from the 27 28 Triassic of Brazil. Acta Palaeontologica Polonica 64. 29 30 31 Modesto SP, Sues H-D. 2004. The skull of the Early Triassic archosauromorph reptile 32 33 Prolacerta broomi and its phylogenetic significance. Zoological Journal of the Linnean 34 35 36 Society 140: 335–351. 37 38 39 Montefeltro FC, Langer MC, Schultz CL. 2010. Cranial anatomy of a new genus of 40 41 hyperodapedontine rhynchosaur (Diapsida: Archosauromorpha) from the Upper Triassic 42 43 of southern Brazil. Earth and Environmental Science Transactions of the Royal Society 44 45 46 of Edinburgh 101: 27–52. 47 48 49 Müller RT, Langer MC, Dias-da-Silva S., 2018. An exceptionally preserved 50 51 association of complete dinosaur skeletons reveals the oldest long-necked 52 53 sauropodomorphs. Biology Letters 14: 20180633. 54 55 56 Nesbitt SJ. 2011. The early evolution of archosaurs: relationships and the origin of 57 58 major clades. Bulletin of the American Museum of Natural History 352: 1–292. 59 60 Page 63 of 98 Zoological Journal of the Linnean Society

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64 1 2 3 Roberto-da-Silva L, Müller RT, França MAG, Cabreira SF, Dias-da-Silva S. 2018. 4 5 6 An impresive skeleton of the giant top predator Prestosuchus chiniquensis 7 8 (Pseudosuchia: Loricata) from the Triassic of Southern Brazil, with phylogenetic 9 10 remarks. Historical Biology. 11 12 13 Schultz CL, Langer MC, Montefeltro FC. 2016. A new rhynchosaur from south 14 15 Brazil (Santa Maria Formation) and rhynchosaur diversity patterns across the Middle- 16 17 18 Late Triassic boundary. Paläontologische Zeitschrift 90: 593–609. 19 20 21 Sen K. 2003. PamelariaFor dolichotrachela Review, a new prolacertidsOnly reptile from the Middle 22 23 Triassic of India. Journal of Asian Earth Sciences 21: 663–681. 24 25 26 Sengupta S, Ezcurra MD, Bandyopadhyay S. 2017. A new horned and long-necked 27 28 herbivorous stem-archosaur from the Middle Triassic of India. Scientific Reports 7: 29 30 8366. 31 32 33 Sereno PC, Novas FE. 1993. The skull and neck of the basal theropod Herrerasaurus 34 35 36 ischigualastensis. Journal of Vertebrate Paleontology 13: 451–476. 37 38 39 Silva-Neves E, Modesto SP, Dias-da-Silva. 2018. A new, nearly complete skull of 40 41 Procolophon trigoniceps Owen, 1876 from the Sanga do Cabral Supersequence, Lower 42 43 Triassicof Southern Brazil, with phylogenetic remarks. Historical Biology. 44 45 46 Spiekman SN. 2018. A new specimen of Prolacerta broomi from the lower Fremouw 47 48 49 Formation (Early Triassic) of Antarctica, its biogeographical implications and a 50 51 taxonomic revision. Scientific Reports 8: 17996. 52 53 54 Trotteyn MJ, Arcucci AB, Raugust T. 2013. Proterochampsia: an endemic 55 56 archosauriform clade from South America. In: Nesbitt SJ, Desojo JB, Irmis RB, eds. 57 58 59 60 Page 65 of 98 Zoological Journal of the Linnean Society

65 1 2 3 Anatomy, phylogeny and palaeobiology of early archosaurs and their kin. London: 4 5 6 Geological Society, Special Publication 379, 59–90. 7 8 Unwin DM. 2003. On the phylogeny and evolutionary history of pterosaurs. In: 9 10 11 Buffetaut E, Mazin J-M, eds. Evolution and Palaeobiology of Pterosaurs. London: 12 13 Geological Society, Special Publications 217: 139–190. 14 15 16 Welman J. 1998. The taxonomy of the South African proterosuchids (Reptilia, 17 18 Archosauromorpha). Journal of Vertebrate Paleontology 18: 340–347. 19 20 21 Witmer LM. 1987. TheFor nature Review of the antorbital fossa Only of archosaurs: Shifting the null 22 23 24 hypothesis. In: Currie PJ, Koster EH, eds. Fourth Symposium on Mesozoic Terrestrial 25 26 Ecosystems, Short Papers. Drumheller: Royal Tyrrell Museum of Palaeontology: 230– 27 28 235. 29 30 31 Witmer LM. 1995a. Homology of facial structures in extant archosaurs (birds and 32 33 crocodilians), with special reference to paranasal pneumaticity and nasal conchae. 34 35 36 Journal of Morphology 225: 269–327. 37 38 39 Witmer LM. 1995b. The extant phylogenetic bracket and the importance of 40 41 reconstructing soft tissues in fossils. In: Thomason JJ, ed. Functional Morphology in 42 43 Vertebrate Paleontology. New York: Cambridge University Press: 19–33. 44 45 46 Witmer LM. 1997. The evolution of the antorbital cavity of archosaurs: A study in 47 48 49 soft-tissue reconstruction in the fossil record with an analysis of the function of 50 51 pneumaticity. Journal of Vertebrate Paleontology 17(Supplement): 1–73. 52 53 54 Zerfass H, Lavina EL, Schultz CL, Garcia AJV, Faccini UF, Chemale F. 2003. 55 56 Sequence stratigraphy of continental Triassic strata of southermost Brazil: a 57 58 59 60 Zoological Journal of the Linnean Society Page 66 of 98

66 1 2 3 contribution to southwestern Gondwana paleogeography and paleoclimate. Sedimentary 4 5 6 Geology 161: 85–105. 7 8 9 10 11 APPENDIX 12 13 14 Updated scorings of Teyujagua paradoxa in the dataset of Pinheiro et al. (2016): 15 16 17 101110000? 20--121131 1000111000 1021001110 0010000001 100010-000 -- 18 19 20 11201??? ?100????0? 2????????? ?????????? ?001100011 ?121??1?20 0??1?????? 21 For Review Only 22 ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? 23 24 ?????????? ?????????? ?????????? ?????????? ?????????? 00 25 26 27 Updated scorings of Teyujagua paradoxa in the dataset of Butler et al. (2019): 28 29 30 0?00000010 110-011011 1011?01210 000-20000 1200100-1- ?00---1100 1--000-000 31 32 1000310000 -0-010-00 00100-0001 0000-00000 000000-0-? ?1000100-0 1000100010 33 34 35 0000010000 ------1100 -0-1110110 2-10012000 010???2000 ?10?012?1? ?2?????010 36 37 ?0101????? ?????????? ?????????? ?????????? ?0???????? 011?00000? 010-0-0000 38 39 0021?10?10 01?00??110 10011000?1 ?01??????0 0--??0?001 0?10?01?10 0000?1??10 40 41 42 ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? 43 44 ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? 45 46 ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? 47 48 49 ?????????? ?????????? ???????0------?? ??????000- 000------00-000000 0-000- 50 51 0?0? 0?????00-0 1?0?0?00?? ?????????? ??????0000 ?????????0 010?? 52 53 54 55 56 57 58 59 60 Page 67 of 98 Zoological Journal of the Linnean Society

67 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 For Review Only 22 23 24 25 26 27 28 29 30 Figure captions 31 32 33 Figure 1. UNIPAMPA 653, holotype of Teyujagua paradoxa, skull in right lateral (A), 34 35 left lateral (B) and dorsal (C) views. 36 37 38 Figure 2. UNIPAMPA 653, holotype of Teyujagua paradoxa, interpretative drawings 39 40 of skull in right lateral (A), left lateral (B) and dorsal (C) views. Abbreviations: an, 41 42 43 angular; ar, articular; ax, axis; cv, cervical vertebra; d, dentary; emf, external 44 45 mandibular fenestra; f, frontal; j, jugal; la, lacrimal; m, maxilla; n, nasal; p, parietal; pm, 46 47 premaxilla; po, postorbital; pof, postfrontal; pp, paroccipital process; prf, prefrontal; q, 48 49 50 quadrate; sa, surangular; so, supraoccipital; sp, splenial; sq, squamosal; st, 51 52 supratemporal. Artwork by Joana Bruno. 53 54 55 Figure 3. Premaxilla of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right 56 57 premaxilla in lateral (A), medial (B), ventral (C) and dorsal (D) views; anterior skull 58 59 bones in dorsolateral view (E, F); rendering of the right premaxilla with teeth inserted 60 Zoological Journal of the Linnean Society Page 68 of 98

68 1 2 3 (G). Abbreviations: I-IV, premaxillary tooth positions I-IV; d, dentary; m, maxilla; n, 4 5 6 nasal; nfo, nasal fossa; pdp, posterodorsal process of premaxilla; pm, premaxilla; ptp, 7 8 palatal process of premaxilla. 9 10 11 Figure 4. Maxilla of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right 12 13 maxilla in lateral (A), medial (B), ventral (C) and dorsal (D) views; photograph (E) and 14 15 interpretative diagram (F) of anterior skull bones in right lateral view. Abbreviations: 16 17 18 afj, articulation facet with jugal; afn, articulation facet with nasal; afpm, articulation 19 20 facet with premaxilla; an, angular; apm, ascending process of maxilla; d, dentary; j, 21 For Review Only 22 jugal; la, lacrimal; m, maxilla; maf, medial antorbital fossa; pm, premaxilla; po, 23 24 25 postorbital; ppm, posterior process of maxilla; prf, prefrontal; sa, surangular; sp, 26 27 splenial. 28 29 30 Figure 5. Nasal of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right nasal in 31 32 dorsal (A), ventral (B), medial (C) and lateral (D) views. Abbreviations: afm, 33 34 articulation facet with maxilla; afpf, articulation facet with prefrontal; apn, anterior 35 36 37 process of nasal; lpn, lateral process of nasal. Arrows indicate anterior direction. 38 39 40 Figure 6. Lacrimal of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right 41 42 lacrimal in lateral (A), medial (B), dorsal (C), ventral (D), anterior (E) and posterior (F) 43 44 views. Abbreviations: apl, anterior process of lacrimal; nld, nasolacrimal duct. Arrows 45 46 47 indicate anterior direction. 48 49 50 Figure 7. Jugal, postorbital and postfrontal of holotype of Teyujagua paradoxa 51 52 (UNIPAMPA 653). Right jugal in lateral (A), medial (B), anterior (C), posterior (D), 53 54 dorsal (E) and ventral (F) views; jugal in articulation with postorbital and postfrontal in 55 56 lateral (G) view. Abbreviations: apj, ascending process of jugal; j, jugal; mpj, maxillary 57 58 59 60 Page 69 of 98 Zoological Journal of the Linnean Society

69 1 2 3 process of jugal; po, postorbital; pof, postfrontal; ppj, posterior process of jugal. Arrows 4 5 6 indicate anterior direction. 7 8 Figure 8. Holotype of Teyujagua paradoxa (UNIPAMPA 653). Photograph (A) and 9 10 11 interpretative diagram (B) of posterior skull bones in left lateral view. Abbreviations: 12 13 an, angular; la, lacrimal; m, maxilla; nld, nasolacrimal duct; po, postorbital; prf, 14 15 prefrontal; q, quadrate; sa, surangular; sp, splenial; sq, squamosal. 16 17 18 Figure 9. Holotype of Teyujagua paradoxa (UNIPAMPA 653). Frontals and parietals 19 20 21 in dorsal view (A); photographFor Review(B) and interpretative Only diagram (C) of posterior skull 22 23 bones in dorsal view. Abbreviations: f, frontal; j, jugal; m, maxilla; p, parietal; pf, 24 25 parietal foramen; pof, postfrontal; po, postorbital; prf, prefrontal; sq, squamosal; st, 26 27 28 supratemporal; stf, supratemporal fenestra. 29 30 Figure 10. Holotype of Teyujagua paradoxa (UNIPAMPA 653). Dorsal view of the 31 32 33 skull detailing circumorbital ornamentation (arrowheads). 34 35 36 Figure 11. Postorbital and postfrontal of holotype of Teyujagua paradoxa 37 38 (UNIPAMPA 653). Right postorbital and postfrontal in right lateral (A), medial (B), 39 40 dorsal (C), ventral (D), anterior (E) and posterior (F) views. Abbreviations: pofr, 41 42 43 postfrontal; ppo, posterior process of postorbital; vppo, ventral process of postorbital. 44 45 Arrows indicate anterior direction. 46 47 48 Figure 12. Squamosal of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right 49 50 squamosal in lateral (A), medial (B), dorsal (C), ventral (D), posterior (E) and anterior 51 52 53 (F) views. Abbreviations: aps, anterior process of squamosal; mps, medial process of 54 55 squamosal; vps, ventral process of squamosal. 56 57 58 Figure 13. Posterolateral photograph (A) and interpretative diagram (B) of the skull of 59 60 holotype of Teyujagua paradoxa (UNIPAMPA 653), detailing the left quadrate and Zoological Journal of the Linnean Society Page 70 of 98

70 1 2 3 squamosal. Abbreviations: ecte, ectepicondyle; q, quadrate; qf, quadrate foramen; sq, 4 5 6 squamosal. 7 8 Figure 14. Posterodorsal photograph (A) and interpretative diagram (B) of holotype of 9 10 11 Teyujagua paradoxa (UNIPAMPA 653) detailing occipital bones. Abbreviations: cv, 12 13 cervical vertebrae; fm, foramen magnum; p, parietal; pp, paroccipital process; ptf, post- 14 15 temporal fenestra; so, supraoccipital; st, supratemporal. 16 17 18 Figure 15. Lower jaw of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right 19 20 21 dentary and articulatedFor splenial Review after rendering in Onlylateral (A), dorsal (B) and medial (C) 22 23 views; interpretative diagram (D) of lower jaw in right lateral view, with artificial 24 25 insertion of dentary rendering Abbreviations: an, angular; ar, articular; d, dentary; sa, 26 27 28 surangular; sp, splenial. 29 30 Figure 16. Marginal dentition of holotype of Teyujagua paradoxa (UNIPAMPA 653). 31 32 33 Tomographic slice of marginal dentition in transverse section (A), arrows indicate bone 34 35 striae ankylosing the teeth to surrounding alveoli; photograph of posterior maxillary 36 37 teeth in lateral view (B), the arrow indicates serrations associated with the distal carina; 38 39 40 marginal maxillary and premaxillary dentition in right lateral view (C). 41 42 43 Figure 17. Marginal and palatal dentition of holotype of Teyujagua paradoxa 44 45 (UNIPAMPA 653). Dentition in palatal view (A); teeth associated with left pterygoid 46 47 and palatine in palatal view (B); dentition in right lateral (C) and left lateral (D) views. 48 49 50 Arrows indicate anterior end of the skull; dashed line indicates inferred pterygoid 51 52 outline. Abbreviations: T2-T4, pterygoid tooth fields according to Welman (1998); md, 53 54 maxillary dentition; pd, palatal dentition; pld, palatine dentition; vd, vomerine dentition. 55 56 57 Figure 18. Photograph (A) and digital rendering (B) of cervical vertebrae of holotype of 58 59 Teyujagua paradoxa (UNIPAMPA 653) in left lateral view. Abbreviations: ain, axis 60 Page 71 of 98 Zoological Journal of the Linnean Society

71 1 2 3 intercentrum; ana, atlas neural arch; at, atlas; ati, atlas intercentrum. ax, axis; cr, cervical 4 5 6 rib; cv III, cervical vertebra III; cv IV, cervical vertebra IV; dp, diapophysis; ns, neural 7 8 spine; poz, postzygapophysis. 9 10 11 Figure 19. Strict consensus tree recovered by heuristic analysis of the dataset of 12 13 Pinheiro et al. (2016) including updated scores for Teyujagua paradoxa. Artwork by 14 15 Márcio L. Castro. 16 17 18 Figure 20. Strict consensus tree recovered by heuristic analysis of the dataset of Butler 19 20 21 et al. (2019) includingFor updated Reviewscores for Teyujagua Only paradoxa. Artwork by Márcio L. 22 23 Castro. 24 25 26 Figure 21. Maxilla of Teyujagua paradoxa (UNIPAMPA 654) (A) (mirrored) and 27 28 Prolacerta broomi (BP/1/2675) (B) in medial view; µCT-based rendering of rostrum of 29 30 UNIPAMPA 653 in right lateral view (C), depicting internal structure of the skull. Not 31 32 33 to scale. Abbreviation: maf, medial antorbital fossa. Photograph of Prolacerta courtesy 34 35 of Martín Ezcurra. 36 37 38 Figure 22. Simplified phylogenetic relationships of selected archosauromorphs, 39 40 displaying key steps of antorbital fenestrae evolution within the clade. Artwork of skulls 41 42 43 by Márcio L. Castro. 44 45 46 Figure 23. Macrocnemus aff. fuyuanensis (PIMUZ T 1559). Photograph (A) and 47 48 interpretative diagram (B) of lower jaw in left lateral view. Abbreviations: an, angular; 49 50 ar, articular; c, coronoid; d, dentary; pa, prearticular; sa, surangular; sp, splenial. 51 52 53 Figure 24. Dawn of the Triassic in southwestern Gondwana. Artistic representation of 54 55 Sanga do Cabral Formation fauna, with the parareptile Procolophon in the foreground, 56 57 58 Teyujagua in the midground and several individuals of the temnospondyl Tomeia in the 59 60 background. Artwork copyright Mark Witton. Zoological Journal of the Linnean Society Page 72 of 98

72 1 2 3 Table 1. Measurements of holotype UNIPAMPA 653 4 5 Skull 6 7 Total length (from the rostral end of premaxilla to the ectocondyle of the left 114.5 mm 8 9 quadrate) 10 11 Maximum height (from the ventral edge of the right jugal to the posterior limits of 35 mm 12 13 the posterolateral process of parietal) 14 15 Maximum width (between the lateral borders of both jugals) 62.5 mm 16 17 Maximum diameter of the supratemporal opening (right side of skull) 21.2 mm 18 19 Maximum height of the infratemporal opening (left side of skull) 22.6 mm 20 21 Orbital length (right orbit)For Review Only 21.25 mm 22 23 Orbital height (right orbit) 19.1 mm 24 25 Nasal opening maximum length 30.3 mm 26 27 Nasal opening maximum width 12.9 mm 28 29 Premaxilla 30 31 Total length (from the anterior border of the alveolar margin to the posterior end of 22 mm 32 the posterodorsal process) 33 34 Main body length 12.6 mm 35 36 Maximum height (from the ventral surface of the alveolar margin to the dorsal 11.5 mm 37 38 margin of the posterodorsal process) 39 40 Maximum width (from the medial suture to the lateral margin of the main body) 6.5 mm 41 42 Maxilla 43 44 Total length (from the contact with premaxilla to the posterior end of the jugal 56.7 mm 45 46 process) 47 48 Maximum height (from the alveolar margin to the dorsal end of the ascending 17.3 mm 49 50 process) 51 52 Nasal 53 54 Maximum length (form the anterior tip of the lateral process to the presumed suture 29.3 mm 55 56 with frontal – right element) 57 58 Maximum width 9.5 mm 59 60 Page 73 of 98 Zoological Journal of the Linnean Society

73 1 2 3 Lacrimal 4 5 Maximum exposed length (right element) 12.6 mm 6 7 Maximum exposed height (right element) 12 mm 8 9 Jugal 10 11 Total length (left element) 40 mm 12 13 Maximum height (right element) 21.7 mm 14 15 Prefrontal 16 17 Total length (right element) 19.8 mm 18 19 Maximum width 6.8 mm 20 Frontal 21 For Review Only 22 Total length 21.9 mm 23 24 Maximum width (from the medial suture to the orbital margin) 10.3 mm 25 26 Parietal 27 28 Maximum length (from suture with frontal to the posterior border of the 22 mm 29 30 posterolateral process – right element) 31 32 Maximum width (from medial suture to the most lateral border) 13.5 mm 33 34 Minimum width between the supratemporal openings 9.8 mm 35 36 Postfrontal 37 38 Maximum transverse width (right element) 12.1 mm 39 40 Posteromedial-anterolateral length (right element) 6.15 mm 41 42 Postorbital 43 44 Height (from the ventral tip of the jugal process to the dorsal margin of the main 20.1 mm 45 46 body – right element) 47 48 Anteroposterior length (main body – right element) 17.4 mm 49 Squamosal 50 51 Exposed anteroposterior length (right element) 18.6 mm 52 53 Height (left element) 24 mm 54 55 Supratemporal 56 57 Length (right element) 11.9 mm 58 59 Width (between the posterolateral process of parietal and the squamosal – right 3.75 mm 60 Zoological Journal of the Linnean Society Page 74 of 98

74 1 2 3 element) 4 5 Quadrate 6 7 Maximum height (left element) 20.1 mm 8 9 Maximum diameter of the quadrate foramen (left element) 6 mm 10 11 Maximum lateromedial width at the articular portion (left element) 10.7 mm 12 13 Occiput 14 15 Paroccipital process length (left element) 15.7 mm 16 17 Post-temporal fenestra length (left element) 15 mm 18 19 Post-temporal fenestra maximum height (left element) 4.1 mm 20 Lower jaw 21 For Review Only 22 Total length (from the anterior tip of the dentaries to the posterior limits of the 118 mm 23 24 articular – right mandibular ramus) 25 26 Dentary length (as exposed – right element) 45.38 mm 27 28 Mandibular fenestra length (left mandible) 24.7 mm 29 30 Mandibular fenestra height (left mandible) 8.3 mm 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 75 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 Figure 1. UNIPAMPA 653, holotype of Teyujagua paradoxa, skull in right lateral (A), left lateral (B) and 33 dorsal (C) views. 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 76 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 Figure 2. UNIPAMPA 653, holotype of Teyujagua paradoxa, interpretative drawings of skull in right lateral 33 (A), left lateral (B) and dorsal (C) views. Abbreviations: an, angular; ar, articular; ax, axis; cv, cervical 34 vertebra; d, dentary; emf, external mandibular fenestra; f, frontal; j, jugal; la, lacrimal; m, maxilla; n, 35 nasal; p, parietal; pm, premaxilla; po, postorbital; pof, postfrontal; pp, paraoccipital process; prf, 36 prefrontal; q, quadrate; sa, surangular; so, supraoccipital; sp, splenial; sq, squamosal; st, supratemporal. Artwork by Joana Bruno. 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 77 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 Figure 3. Premaxilla of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right premaxilla in lateral (A), medial (B), ventral (C) and dorsal (D) views; anterior skull bones in dorsolateral view (E, F); rendering of 35 the right premaxilla with teeth inserted (G). Abbreviations: I-IV, premaxillary tooth positions I-IV; d, 36 dentary; m, maxilla; n, nasal; nfo, nasal fossa; pdp, posterodorsal process of premaxilla; pm, premaxilla; 37 ptp, palatal process of premaxilla. 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 78 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 Figure 4. Maxilla of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right maxilla in lateral (A), medial 31 (B), ventral (C) and dorsal (D) views; photograph (E) and interpretative diagram (F) of anterior skull bones in right lateral view. Abbreviations: afj, articulation facet with jugal; afn, articulation facet with nasal; afpm, 32 articulation facet with premaxilla; an, angular; apm, ascending process of maxilla; d, dentary; j, jugal; la, 33 lacrimal; m, maxilla; maf, medial antorbital fossa; pm, premaxilla; po, postorbital; ppm, posterior process 34 of maxilla; prf, prefrontal; sa, surangular; sp, splenial. 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 79 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 Figure 5. Nasal of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right nasal in dorsal (A), ventral (B), 25 medial (C) and lateral (D) views. Abbreviations: afm, articulation facet with maxilla; afpf, articulation facet with prefrontal; apn, anterior process of nasal; lpn, lateral process of nasal. Arrows indicate anterior 26 direction. 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 80 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 Figure 6. Lacrimal of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right lacrimal in lateral (A), medial 26 (B), dorsal (C), ventral (D), anterior (E) and posterior (F) views. Abbreviations: apl, anterior process of 27 lacrimal; nld, nasolacrimal duct. Arrows indicate anterior direction. 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 81 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 Figure 7. Jugal, postorbital and postfrontal of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right jugal 24 in lateral (A), medial (B), anterior (C), posterior (D), dorsal (E) and ventral (F) views; jugal in articulation 25 with postorbital and postfrontal in lateral (G) view. Abbreviations: apj, ascending process of jugal; j, jugal; 26 mpj, maxillary process of jugal; po, postorbital; pof, postfrontal; ppj, posterior process of jugal. Arrows 27 indicate anterior direction. 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 82 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Figure 8. Holotype of Teyujagua paradoxa (UNIPAMPA 653). Photograph (A) and interpretative diagram (B) 19 of posterior skull bones Forin left lateral Review view. Abbreviations: Only an, angular; la, lacrimal; m, maxilla; nld, 20 nasolacrimal duct; po, postorbital; prf, prefrontal; q, quadrate; sa, surangular; sp, splenial; sq, squamosal. 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 83 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 Figure 9. Holotype of Teyujagua paradoxa (UNIPAMPA 653). Frontals and parietals in dorsal view (A); photograph (B) and interpretative diagram (C) of posterior skull bones in dorsal view. Abbreviations: f, 33 frontal; j, jugal; m, maxilla; p, parietal; pf, parietal foramen; pof, postfrontal; po, postorbital; prf, 34 prefrontal; sq, squamosal; st, supratemporal; stf, supratemporal fenestra. 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 84 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 Figure 10. Holotype of Teyujagua paradoxa (UNIPAMPA 653). Dorsal view of the skull detailing circumorbital 23 ornamentation (arrowheads). 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 85 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 Figure 11. Postorbital and postfrontal of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right postorbital 25 and postfrontal in right lateral (A), medial (B), dorsal (C), ventral (D), anterior (E) and posterior (F) views. 26 Abbreviations: pofr, postfrontal; ppo, posterior process of postorbital; vppo, ventral process of postorbital. 27 Arrows indicate anterior direction. 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 86 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 Figure 12. Squamosal of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right squamosal in lateral (A), 22 medial (B), dorsal (C), ventral (D), posterior (E) and anterior (F) views. Abbreviations: aps, anterior process 23 of squamosal; mps, medial process of squamosal; vps, ventral process of squamosal. 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 87 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 Figure 13. Posterolateral photograph (A) and interpretative diagram (B) of the skull of holotype of 23 Teyujagua paradoxa (UNIPAMPA 653), detailing the left quadrate and squamosal. Abbreviations: ecte, 24 ectepicondyle; q, quadrate; qf, quadrate foramen; sq, squamosal. 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 88 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 Figure 14. Posterodorsal photograph (A) and interpretative diagram (B) of holotype of Teyujagua paradoxa 23 (UNIPAMPA 653) detailing occipital bones. Abbreviations: cv, cervical vertebrae; fm, foramen magnum; p, 24 parietal; pp, paroccipital process; ptf, post-temporal fenestra; so, supraoccipital; st, supratemporal. 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 89 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Figure 15. Lower jaw of holotype of Teyujagua paradoxa (UNIPAMPA 653). Right dentary and articulated splenial after rendering in lateral (A), dorsal (B) and medial (C) views; interpretative diagram (D) of lower 39 jaw in right lateral view, with artificial insertion of dentary rendering Abbreviations: an, angular; ar, 40 articular; d, dentary; sa, surangular; sp, splenial. 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 90 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 Figure 16. Marginal dentition of holotype of Teyujagua paradoxa (UNIPAMPA 653). Tomographic slice of 26 marginal dentition in transverse section (A), arrows indicate bone striae ankylosing the teeth to surrounding 27 alveoli; photograph of posterior maxillary teeth in lateral view (B), the arrow indicates serrations associated 28 with the distal carina; marginal maxillary and premaxillary dentition in right lateral view (C). 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 91 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 Figure 17. Marginal and palatal dentition of holotype of Teyujagua paradoxa (UNIPAMPA 653). Dentition in 24 palatal view (A); teeth associated with left pterygoid and palatine in palatal view (B); dentition in right 25 lateral (C) and left lateral (D) views. Arrows indicate anterior end of the skull; dashed line indicates inferred 26 pterygoid outline. Abbreviations: T2-T4, pterygoid tooth fields according to Welman (1998); md, maxillary 27 dentition; pd, palatal dentition; pld, palatine dentition; vd, vomerine dentition. 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 92 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Figure 18. Photograph (A) and digital rendering (B) of cervical vertebrae of holotype of Teyujagua paradoxa 46 (UNIPAMPA 653) in left lateral view. Abbreviations: ain, axis intercentrum; ana, atlas neural arch; at, atlas; 47 ati, atlas intercentrum. ax, axis; cr, cervical rib; cv III, cervical vertebra III; cv IV, cervical vertebra IV; dp, diapophysis; ns, neural spine; poz, postzygapophysis. 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 93 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Figure 19. Strict consensus tree recovered by heuristic analysis of the dataset of Pinheiro et al. (2016) including updated scores for Teyujagua paradoxa. Artwork by Márcio L. Castro. 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 94 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Figure 20. Strict consensus tree recovered by heuristic analysis of the dataset of Butler et al. (2019) 41 including updated scores for Teyujagua paradoxa. Artwork by Márcio L. Castro. 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 95 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Figure 21. Maxilla of Teyujagua paradoxa (UNIPAMPA 654) (A) (mirrored) and Prolacerta broomi 39 (BP/1/2675) (B) in medial view; µCT-based rendering of rostrum of UNIPAMPA 653 in right lateral view (C), 40 depicting internal structure of the skull. Not to scale. Abbreviation: maf, medial antorbital fossa. Photograph 41 of Prolacerta courtesy of Martín Ezcurra. 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 96 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 Figure 22. Simplified phylogenetic relationships of selected archosauromorphs, displaying key steps of 33 antorbital fenestrae evolution within the clade. Artwork of skulls by Márcio L. Castro. 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 97 of 98 Zoological Journal of the Linnean Society

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 Figure 23. Macrocnemus aff. fuyuanensis (PIMUZ T 1559). Photograph (A) and interpretative diagram (B) of 24 lower jaw in left lateral view. Abbreviations: an, angular; ar, articular; c, coronoid; d, dentary; pa, prearticular; sa, surangular; sp, splenial. 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Zoological Journal of the Linnean Society Page 98 of 98

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 For Review Only 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Figure 24. Dawn of the Triassic in southwestern Gondwana. Artistic representation of Sanga do Cabral 44 Formation fauna, with the parareptile Procolophon in the foreground, Teyujagua in the midground and 45 several individuals of the temnospondyl Tomeia in the background. Artwork copyright Mark Witton. 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60