See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/335794209

New Proterochampsid Specimens Expand the Morphological Diversity of the Rhadinosuchines of the Chañares Formation (Lower Carnian, Northwestern Argentina)

Article in AMEGHINIANA · June 2019 DOI: 10.5710/AMGH.25.05.2019.3230

CITATIONS READS 6 309

4 authors:

Martin Ezcurra M. Belen von Baczko Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"

174 PUBLICATIONS 3,780 CITATIONS 34 PUBLICATIONS 330 CITATIONS

SEE PROFILE SEE PROFILE

maría jimena Trotteyn Julia B Desojo National Scientific and Technical Research Council Universidad Nacional de La Plata

36 PUBLICATIONS 399 CITATIONS 116 PUBLICATIONS 1,968 CITATIONS

SEE PROFILE SEE PROFILE

Some of the authors of this publication are also working on these related projects:

Geochronologic constraints on early dinosaur evolution View project

Paleoneurology of the paracrocodylomorph archosaur Postosuchus kirkpatricki View project

All content following this page was uploaded by M. Belen von Baczko on 13 September 2019.

The user has requested enhancement of the downloaded file. NEW PROTEROCHAMPSID SPECIMENS EXPAND THE MORPHOLOGICAL DIVERSITY OF THE RHADINOSUCHINES OF THE CHAÑARES FORMATION (LOWER CARNIAN, NORTHWESTERN ARGENTINA)

MARTÍN D. EZCURRA 1,2 M. BELÉN VON BACZKO 2,3 M. JIMENA TROTTEYN 2,4 JULIA B. DESOJO 2,3

1Sección Paleontología de Vertebrados, CONICET–Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Avenida Ángel Gallardo 470, C1405DJR CABA, Argentina. 2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Avenida Rivadavia 1917, C1033AAJ CABA, Argentina. 3División Paleontología Vertebrados, Museo de La Plata, Facultad de Ciencias Naturales y Museo, Paseo del Bosque s/n, B1900FWA La Plata, Argentina. 4Instituto de Geología Emiliano P. Aparicio, INGEO-CIGEOBIO, Universidad Nacional de San Juan, Av. Ignacio de la Rosa 590 (oeste), J5402DCS San Juan, Argentina.

Submitted: September 25 th , 2018 - Accepted: April 25 th , 2019 - Published online: June 9 th , 2019

To cite this article: Martín D. Ezcurra, M. Belén Von Baczko, M. Jimena Trotteyn, and Julia B. Desojo (2019). New proterochampsid specimens expand the morphological diversity of the rhadinosuchines of the Chañares Formation (Lower Carnian, northwestern Argentina). Ameghiniana 56: 79–115. To link to this article: http://dx.doi.org/ 10.5710/AMGH.25.05.2019.3230

PLEASE SCROLL DOWN FOR ARTICLE

Also appearing in this issue:

New early Carnian rhadinosuchines Assemblages generated by owls New species of gastropods from Argentina show high record 14 species of rodents and reveal the presence of fauna morphological diversity and reveal quantitative differences with tropical affinities in intraspecific variation. with extant fauna. Central Argentina. AMEGHINIANA - 2019 - Volume 56 (2): 79–115 ARTICLES

ISSN 0002-7014

NEW PROTEROCHAMPSID SPECIMENS EXPAND THE MOR - PHOLOGICAL DIVERSITY OF THE RHADINOSUCHINES OF THE CHAÑARES FORMATION (LOWER CARNIAN, NORTHWESTERN ARGENTINA)

MARTÍN D. EZCURRA 1,2 , M. BELÉN VON BACZKO 2,3 , M. JIMENA TROTTEYN 2,4 , AND JULIA B. DESOJO 2,3

1Sección Paleontología de Vertebrados, CONICET–Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Avenida Ángel Gallardo 470, C1405DJR CABA, Argentina. [email protected] 2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Avenida Rivadavia 1917, C1033AAJ CABA, Argentina. 3División Paleontología Vertebrados, Museo de La Plata, Facultad de Ciencias Naturales y Museo, Paseo del Bosque s/n, B1900FWA La Plata, Argentina. be [email protected] ; [email protected] 4Instituto de Geología Emiliano P. Aparicio, INGEO-CIGEOBIO, Universidad Nacional de San Juan, Av. Ignacio de la Rosa 590 (oeste), J5402DCS San Juan, Ar gentina.

Abstract . The proterochampsids are crocodile-like, small- to medium-sized, quadrupedal and predatory stem-archosaurs. The rhadinosuchines are a clade of deeply nested proterochampsids that are the most abundant diapsids of the Massetognathus -Chanaresuchus Assemblage Zone of the Chañares Formation (lower Carnian) of north-western Argentina. Here, we describe two new rhadinosuchine proterochampsid specimens recently collected from the Massetognathus -Chanaresuchus Assemblage Zone of the Chañares Formation. These specimens are represented by an articulated partial skeleton and disarticulated cranial and postcranial bones, respectively. One of them is less complete, but its well-preserved disarticulated bones considerably expand the anatomical knowledge of certain regions of the rhadinosuchine skeleton. The combination of character-states present in both specimens and shared with other known rhadinosuchine species ( e.g. , Chanaresuchus bonapartei , Gualosuchus reigi , Rhadinosuchus gracilis ) results in an unexpected increase of the morphological diversity of the group ( e.g. , antorbital fossa on the horizon - tal process of maxilla, well-exposed antorbital fossa on lacrimal, X-shaped osteoderms). We conclude that the taxonomy of the currently known rhadinosuchine specimens should be revisited, including a careful reappraisal of the intraspecific variation and the post-mortem deformation that affected the specimens in different ways . Key words. Archosauriformes. Proterochampsidae. Ischigualasto-Villa Unión Basin. Triassic. South America.

Resumen. NUEVOS ESPECÍMENES DE PROTEROCHÁMPSIDOS EXPANDEN LA DIVERSIDAD MORFOLÓGICA DE LOS RHADINOSUQUINOS DE LA FORMACIÓN CHAÑARES (CARNIANO INFERIOR, NOROESTE DE ARGENTINA). Los proterochámpsidos son arcosauriformes no arcosauria - nos de tamaño mediano a pequeño, predadores y cuadrúpedos, parecidos a los cocodrilos. Los rhadinosuquinos son un clado profundamente anidado dentro de los proterochámpsidos y son los diápsidos más abundantes de la Zona de Asociación de Massetognathus -Chanaresuchus de la Formación Chañares (Carniano inferior) del noroeste de Argentina. Aquí describimos dos nuevos especímenes de proterochámspidos rhadi - nosuquinos recientemente colectados de la Zona de Asociación de Massetognathus-Chanaresuchus de la Formación Chañares. Estos especí - menes están representados por un esqueleto parcial articulado y huesos craneanos y poscraneanos desarticulados, respectivamente. Uno de ellos es menos completo, pero sus huesos desarticulados bien preservados incrementan considerablemente el conocimiento anatómico de ciertas regiones del esqueleto de los rhadinosuquinos. La combinación de estados de caracter presentes en ambos especímenes y com - partidos con otras especies conocidas de rhadinosuquinos ( e.g. , Chanaresuchus bonapartei , Gualosuchus reigi , Rhadinosuchus gracilis ) resulta en un incremento inesperado de la diversidad morfológica del grupo ( e.g. , fosa antorbital sobre el proceso horizontal del maxilar, fosa antorbital expuesta ampliamente sobre el lacrimal, oste odermos con forma de X). Concluimos que la taxonomía de los ejemplares de rhadinosuquinos actualmente conocidos debería ser revisada, in cluyendo una cuidadosa reevaluación de la variación intraespecífica y de la deformación post- mortem que afectó a los especímenes de diferentes maneras. Palabras clave. Archosauriformes. Proterochampsidae. Cuenca de Ischigualasto-Villa Unión. Triásico. América del Sur.

PROTEROCHAMPSIDAE is a clade of small- to medium-sized fos sil record restricted to the lower Upper Triassic rocks of quadrupedal, predatory, crocodile-like diapsids, with a South America (Trotteyn et al. , 2013). There is a general con -

AMGHB2-0002-7014/12$00.00+.50 79 AMEGHINIANA - 2019 - Volume 56 (2): 79–115 sensus that this group is one of the closest sister-taxa to les, Universidad Nacional de La Rioja, La Rioja, Argentina; crown group Archosauria ( e.g. , Benton and Clark, 1988; PVL, Paleontología de Vertebrados, Instituto Miguel Lillo, Sereno and Arcucci, 1990; Sereno, 1991; Parrish, 1993; Juul, San Salvador de Tucumán, Argentina; PVSJ, Paleontología 1994; Dilkes and Sues, 2009; Nesbitt, 2011; Ezcurra, 2016), de Vertebrados, Museo de Ciencias Naturales, Universidad but their phylogenetic proximity to the latter clade is still Nacional de San Juan, San Juan, Argentina; SAM-PK, Iziko under debate (Nesbitt, 2011; Ezcurra, 2016). A total of eight South African Museum, Cape Town, South Africa; SMNS, nominal species are currently known from the Ischigua - Staatliches Museum für Naturkunde, Stuttgart, Germany; lasto -Villa Unión Basin of north-western Argentina and the SNSB-BSPG, Staatliche Na tur wissenschaftliche Samm - Paraná Basin of southern Brazil (Huene, 1938; Price, 1946; lungen Bayerns-Bayerische Staatssammlung für Paläonto - Reig, 1959; Romer, 1971; Barberena, 1982; Arcucci, 1990; logie und Geologie, Munich, Germany; UFRGS, Universidade Trotteyn et al. , 2012). The proterochampsids are the most Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil. abundant diapsids of the Massetognathus -Chanaresuchus Assemblage Zone ( AZ ) ( sensu Ezcurra et al. , 2017) of the SYSTEMATIC PALEONTOLOGY Chañares Formation (Ischigualasto-Villa Unión Basin; north - western Argentina), and the species Chanaresuchus bona - DIAPSIDA Osborn, 1903 sensu Laurin (1991) partei is the most abundant (Mancuso et al. , 2014). Although ARCHOSAUROMORPHA Huene, 1946 sensu Dilkes (1998) more than ten specimens from Argentina and Brazil have ARCHOSAURIFORMES Gauthier, Kluge, and Rowe, 1988 sensu been referred to Chanaresuchus bonapartei in the last 50 Gauthier, Kluge, and Rowe (1988) years, some of them very well-preserved, a detailed taxo - PROTERCHAMPSIDAE Sill, 1967 sensu Trotteyn (2011a) nomic revision of this species is still lacking (Romer, 1971; RHADINOSUCHINAE Hoffstetter, 1955 sensu Ezcurra, Desojo, Hsiou et al. , 2002; Desojo et al. , 2011; Dilkes and Arcucci, and Rauhut (2015) 2012; Raugust et al. , 2013; but see Ezcurra et al. , 2015 for a taxonomic revision of the putative records of Chanaresuchus Gen. et sp. indet. bonapartei from Brazil). Here, we describe two new rhadi - Figures 1.3–4, 2–13; Tables 1–7 nosuchine proterochampsid specimens recently collected from the Massetognathus -Chanaresuchus AZ of the Chañares Materials . CRILAR-Pv 491 comprises a fairly complete skull Formation (Fig. 1). These specimens are represented by both and left hemimandible, two middle-posterior cervical ver - cranial and postcranial bones that expand our anatomica l tebrae, articulated last cervical and fourteen dorsal verte - knowledge of the group, because several elements are very brae and several of their respective osteoderms, articulated well preserved and completely disarticulated, which is an last dorsal, two sacral, and first three caudal vertebrae, unusual condition among rhadinosuchine specimens. These some presacral rib fragments, partial left iliac blade, right new specimens possess a combination of character-states pubis and probable ischium, left femur and proximal halves previously unknown in other rhadinosuchines, which re - of tibia and fibula, and some indeterminate fragments of sults in a conflicting mosaic of features—some of them bone (Figs. 1.3, 2–6; Tabs. 1–4). previously considered as diagnostic at species level—if we CRILAR-Pv 488 consists of a right maxilla, left quadrate, follow current taxonomic schemes (see Trotteyn et al. , left dentary, left atlantal neural arch, anterior to mid-cervi - 2013). Thus, the specimens reported here shed new light on cal neural arch, mid-cervical vertebra, four mid- to poste - the morphology and variation within this group, under - rior dorsal centra, second sacral vertebra and rib, three scor ing the need for its taxonomic revision. caudal vertebrae, four partial neural spines, left scapula, Institutional abbreviations . CRILAR-Pv, Paleontología de probable right radius without distal end, left partial pubic Vertebrados, Centro Regional de Investigaciones Científi - shaft, right ischium, distal half of left femur, left tibia, left cas y Transferencia Tecnológica, Anillaco, Argentina; MCZ, metatarsal V, and indeterminate bone fragments (Figs. 1.4, Museum of Comparative Zoology, Harvard University, Bos - 7–13; Tabs. 5–7). ton, USA; PULR, Paleontología, Museo de Ciencias Natura - Horizons and localities . CRILAR-Pv 488 was collected from

80 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

Figure 1. Geographic and stratigraphic provenance of the two new rhandinosuchine proterochampsid specimens described here ( CRILAR- Pv 488 and CRILAR-Pv 491). 1, Geological map indicating the occurrence of specimens; 2, stratigraphic column indicating the occurrence of specimens; 3, most preserved bones of CRILAR-Pv 491 in approximate dorsal view; 4, right maxilla of CRILAR-Pv 488 in lateral view. Scale bars= 2 km ( 1), 10 m ( 2), 3 cm ( 3), 1 cm ( 4). 1–2, Modified from Ezcurra et al. (2017).

81 AMEGHINIANA - 2019 - Volume 56 (2): 79–115 the lowermost levels of the Massetognathus -Chanaresuchus of Chanaresuchus bonapartei + Rhadinosuchus gracilis (Ezcurra, AZ of the Chañares Formation (Ischigualasto-Villa Unión 2016). The morphology of these two specimens suggests Basin) at the El Torcido locality, approximately 4 km east they very likely belong to the same species. from the “Chañares type” locality (= Far East Pocket locality of A. S. Romer). CRILAR-Pv 491 is from middle-upper levels DESCRIPTION of the Massetognathus -Chanaresuchus AZ of the Chañares The two new specimens (CRILAR-Pv 488, CRILAR-Pv Formation, approximately 600 m southwest from the 491) are described below and compared with other prote - “Chañares type” locality. Both localities are placed within rochampsids, with an emphasis on other rhadinosuchine the Talampaya National Park, La Rioja Province, north- specimens. western Argentina (Fig. 1). Comments . CRILAR-Pv 488 was found in a fine-grained grey CRILAR-Pv 491 sandstone, in levels lacking concretions, associated with a This specimen is represented by a partially articulated partial postcranium of Gracilisuchus stipanicicorum Romer, skeleton of a single individual (Fig. 1.3). The bones com - 1972a and a cynodont ilium. CRILAR-Pv 491 was collected monly possess weathered surfaces and, as a result, the from one of the typical concretions that have yielded most morphology of small or fragile features cannot be deter - of the specimens known from the Massetognathus -Chanare - mined. suchus AZ of the Chañares Formation (Romer, 1966; Rogers CRILAR-Pv 491 preserves a fairly complete, articulated et al. , 2001). skull and left hemimandible (Fig. 2; Tab. 1). The ventral half Comments on the taxonomic assignment . The two new pro - of the right quadrate, most of the pterygoids with the ex - terochampsid specimens described here are assigned to the ception of the anterior half of the anterior processes, most of proterochampsid subfamily Rhadinosuchinae ( sensu Ezcurra the right palatine, both ectopterygoids and parabasisphe - et al. , 2015) because of the presence of the following noid, and both prootics and laterosphenoids are not pre - synapomorphies of the clade (following Ezcurra, 2016): dor - served. The skull suffered dorsoventral compression during sal surface of nasals and frontals ornamented by ridges ra - fossilization, but to a lesser degree than the holotypes of diating from centres of growth (present in CRILAR-Pv 491, Chanaresuchus bonapartei and Pseudochampsa ischigualas - unknown in CRILAR-Pv 488); lateral margin of snout ante - tensis (Trotteyn and Ezcurra, 2014). As a result of this com - rior to prefrontal with a sharp edge along the maxilla, be - pression, the internarial bar of CRILAR-Pv 491 is placed tween the lateral and dorsal sides of this bone ( i.e. , box-like below the lateral borders of the external nares and the snout of Kischlat, 2000; present in CRILAR-Pv 491 and lat eral surface of the surangular faces more ventrally than CRILAR-Pv 488 ); anteriorly projecting, rounded spur on an - it would have during life. terior edge of ventral process of postorbital, indicating the The overall morphology of the skull of CRILAR-Pv 491 lower delimitation of the eye ball (present in CRILAR-Pv (Fig. 2.1–3, 2.5–6) resembles that of other rhadinosuchines, 491, unknown in CRILAR-Pv 488); and very thick parame - but it is distinctly more depressed than in the holotype of dian osteoderms (present in CRILAR-Pv 491, unknown in Gualosuchus reigi (PULR 05). The snout represents 55% of CRILAR-Pv 488). In addition, CRILAR-Pv 491 possesses a the total length of the skull, and the lateral borders of the fourth trochanter of the femur distally extended beyond skull diverge more abruptly in the postorbital region than in mid-shaft and well posteriorly developed, which Ezcurra the snout. The external nares are sub-oval, being antero - (2016) resolved as a synapomorphy of Gualosuchus reigi posteriorly longer than broad, and face directly dorsally, as Romer, 1971 + ( Chanaresuchus bonapartei Romer, 1971 + occurs in other proterochampsids. The antorbital fenestrae Rhadinosuchus gracilis Huene, 1938). It also possesses an open laterally and are sub-oval, being 3.8 times longer than antorbital fossa forming a distinct inset margin to the tall and extending along 26.8% of the length of the snout. antorbital fenestra on the lateral surface of the lacrimal, The orbits are sub-circular and mainly laterally, but also oc cupying almost half or more of the anteroposterior length slightly dorsally, oriented. This resembles the condition in of the ventral process of the bone, which is a synapomorphy other proterochampsids ( e.g. , Chanaresuchus bonapartei : PVL

82 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

Figure 2. Cranial remains of CRILAR-Pv 491. 1–3, 5, 6, Skull; 4, close-up of left maxillary antorbital fossa; 7–8, partial right quadratojugal and posterior end of hemimandible; 9–11, anterior two-thirds of the left hemimandible; 12–14, posterior third of the left hemimandible. Spec imen in 1, right lateral; 2, left lateral; 3, posterior; 4, 7, lateral; 5, 13, dorsal; 6, 8, ventral; 9–11, indeterminate; 12, ventrolateral; 14 , me - dial views. Abbreviations: anf, antorbital fenestra; bo, basioccipital; ch, choana; dmp, dorsomedial process; dt, dentary; en, external naris; exf, external mandibular fenestra; fm, foramen magnum; gf, glenoid fossa; itf, infratemporal fenestra; itfo, infratemporal fossa; l.anfo, lacrimal antorbital fossa; lr, lateral ridge; lsh, lateral shelf; m.anfo, maxillary antorbital fossa; or, orbit; pop, paroccipital process; pra, prearticular; qj, quadratojugal; sa, surangular; stf, supratemporal fenestra. Scale bars= 1 cm.

TABLE 1 – Measurements of the skull of CRILAR-Pv 491 in millimetres.

Length Height Width

Skull 151.7 27.9* 73.6

Snout 83.1 20.0 37.8

External naris 18.5 - 3.0

Antorbital fenestra 22.3 5.8 -

Orbit 21.1 21.6 -

Infratemporal fenestra 31.7 21.6 -

Supratemporal fenestra 16.6 - 9.1

Internal choana 31.0 - 4.2 Incomplete measurements indicated with an asterisk, the value given is the maximum measurable, and paired measurements are from the left side. Measurements were rounded to the nearest 0.1 mm.

83 AMEGHINIANA - 2019 - Volume 56 (2): 79–115

4586; Gualosuchus reigi : PULR 05), but is distinct from Pro - anterior process in front of the antorbital fenestra. This terochampsa spp., which has mainly dorsally oriented orbits process possesses a distinct longitudinal change in slope (Dilkes and Arcucci, 2012). The infratemporal fenestrae are that results in laterally and dorsally facing surfaces. As a laterally and slightly dorsally oriented and sub-trapezoidal, consequence, the snout acquires a box-like morphology that is being anteroposteriorly longer than tall and with a distinct characteristic of rhadinosuchine proterochampsids (Ezcurra notch in their posteroventral corner, as occurs in other pro - et al. , 2015). This change of slope coincides with the dorsal terochampsids (Dilkes and Arcucci, 2012). The supratem - border of the antorbital fossa and merges posteriorly with poral fenestrae open dorsally and are sub-oval, with an the sharp lateral edge formed by the ascending process of anteromedial to posterolateral long axis, resembling the the maxilla and the prefrontal. The horizontal process of the condition in Gualosuchus reigi (PULR 05, PVL 4576) and some maxilla maintains a constant height ventral to the antorbital specimens of Chanaresuchus bonapartei (PVL 4575, PVL fenestra and tapers only at its posterior end. The ascending 4586). By contrast, Pseudochampsa ischigualastensis (PVSJ process of the maxilla is mainly posteriorly and slightly dor - 567) and several specimens of Chanaresuchus bonapartei sally oriented, and very short, forming only the anterodor - (PULR 05, MCZ 4037, MCZ 4039, PVL 4647) possess a sal corner of the antorbital fenestra. The anterior border of straight to slightly convex anteromedial border of the the antorbital fenestra is concave and not pointed. The an - supratemporal fenestrae, which results in a subtriangular torbital fossa is well-developed anterior to the fenestra and opening in dorsal view. The posterolateral processes of the also extends onto the ascending process and the anterior parietals contact the paroccipital processes of the otoc - third of the horizontal process (Fig. 2.1: m.anfo , 2.4). The cip itals (= opisthotic fused to exoccipital) along their entire presence of an antorbital fossa on the horizontal process of length. Thus, if a posttemporal fenestra was present, it the maxilla also occurs in Rhadinosuchus gracilis , but it is would have been very small. In the palate, the choanae are ab sent in other proterochampsids (Ezcurra et al. , 2015). The very elongated, narrow, and placed in the posterior half of ventral margin of the antorbital fossa of CRILAR-Pv 491 is the snout. The morphology of the suborbital fenestra cannot rimmed by a thick and low longitudinal tuberosity. It cannot be determined because the lateral ramus of the pterygoids be determined if the posterior end of the horizontal process and most of the ectopterygoids are not preserved. of the maxilla contacted the ectopyterygoid. Premaxilla . The premaxillae are poorly preserved and their The medial surface of the maxilla possesses an antero - morphology is consistent with that of other proterochamp - posteriorly long palatal process, placed immediately dorsal sids ( e.g. , Romer, 1971; Dilkes and Arcucci, 2012; Ezcurra et to the interdental plates and does not contact its counter - al. , 2015). The bone is anteroposteriorly long and slightly part, as occurs in other non-archosaurian archosauriforms downturned. The postnarial process is slightly dorsally (Nesbitt, 2011; Ezcurra, 2016). The interdental plates are oriented and forms an oblique suture with the maxilla and pentagonal and well-separated from each other and form most of the lateral border of the external naris. The pre - part of a thecodont tooth implantation, as is the case in nar ial process is posteriorly oriented and contacts its coun - Middle Triassic erythrosuchids and other early eucrocopods terpart on the midline along its entire extension. As a result, (Ezcurra, 2016). The maxillary tooth count cannot be deter - the pair of nasals is separated from each other by the pre - mined confidently because of damage, but based on the maxillae in the midline. The prenarial processes form most preserved morphology of both maxillae a total of 15 tooth of the internarial bar. The dorsal surface of the premaxilla positions can be estimated. The same maxillary tooth count possesses a deep, but not well-rimmed, narial fossa ante - is present in some specimens of Chanaresuchus bonapartei rior to the external naris. The palatal process is long and (MCZ 4039), and a very similar count occurs in Gualosuchus contacts its counterpart on the midline. The premaxillary reigi (14 teeth; PULR 05, PVL 4576). The exposed maxillary tooth count cannot be determined because of damage, but tooth crowns are very poorly preserved. The crowns are a single, poorly preserved tooth is preserved in the right rel atively short and distally curved, but the presence of side. enamel ornamentation or serrated carinae cannot be deter - Maxilla . The maxilla possesses a long and anteriorly taper ing mined.

84 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

Nasal . The external surface of the nasals is not exposed, but 1971; Trotteyn et al. , 2013). The ventral process of the pre - preserved morphology of the bones is consistent with that frontal is slightly posteriorly oriented in lateral view. The ex - of other rhadinosuchines. The anteromedial process ar - ternal surface of the dorsal half of this process is subdivided tic ulates along an extensive, longitudinal suture with the by a thick, low ridge that separates a laterally facing surface postnarial process of the premaxilla and forms more than from a mainly posteriorly facing one. The latter surface half of the medial border of the external naris. The sutures forms the anterior wall of the orbital cavity. The ridge is con - with the maxilla, prefrontal, and its counterpart cannot be fluent dorsally with the lateral margin of the skull roof, in identified confidently. The suture with the frontal occurs the anterior margin of the orbit. This morphology of the ex - slightly anterior to the level of the anterior border of the ternal surface of the prefrontal is also present in other orbit and is strongly interdigitated. The nasals preserve rhadinosuchines ( e.g. , Chanaresuchus bonapartei : MCZ 4039). traces of the ornamentation pattern of their external sur - The sutures of the prefrontal with other bones of the skull face, and this condition is congruent with that of Rhadi - roof cannot be confidently determined because of damage. nosuchus gracilis (Ezcurra et al. , 2015), Pseudochampsa Jugal . The jugal possesses the typical triradiate morphology ischigualastensis (Trotteyn and Ezcurra, 2014), and speci - present in other archosauriforms (Ezcurra, 2016). The su - mens of Chanaresuchus bonapartei and Gualosuchus reigi tures between the jugal and the quadratojugal and pos - (Romer, 1971), in which ridges radiate from a centre, ante - tor bital cannot be identified because of poor preservation. riorly displaced in the bone, and two anteriorly projected The anterior process of the jugal is mostly straight and ridges form a V-shaped structure that extends to the an - dorsoventrally very low, resembling the condition in simi - teromedial and anterolateral processes. lar-sized specimens of Chanaresuchus bonapartei (MCZ Lacrimal . The lacrimal forms the posterodorsal corner of the 4039, PVL 4647) and Rhadinosuchus gracilis (Ezcurra et al. , antorbital fenestra and has a small contribution to the an - 2015). The anterior process contributes to the posteroven - teroventral border of the orbit. The bone is crescent-shaped tral corner of the antorbital fenestra. A sharp, very well- in lateral view, forming a gently concave margin of the an - de veloped, and laterally projected ridge extends along most torbital fenestra. The lateral surface of the ventral process of the ventral margin of the anterior process, not reaching and main body of the bone is subdivided by a sharp, slightly its anterior end at level with the contact with the lacrimal. anteriorly curved ridge that converges dorsally with the The ridge continues posteriorly along the main body of the lat eral margin of the skull roof. This ridge separates a con - jugal and the base of the posterior process to finish con - cave and well-exposed laterally antorbital fossa (Fig. 2.1: verging with the anteroventral border of the infratemporal l.anfo ) from a flat posterior half of the bone. The presence fenestra. This ridge is also strongly laterally developed and of an extensive, laterally exposed antorbital fossa in the converges posteriorly with the margin of the infratemporal lacrimal is also present in Rhadinosuchus gracilis (Ezcurra et opening in small-sized specimens of Chanaresuchus bona - al. , 2015) and some specimens of Chanaresuchus bonapartei partei (MCZ 4039). The posterior process of the jugal of (PULR 07, PVL 4647, MCZ 4039), but this fossa is absent or CRILAR-Pv 491 is barely dorsally bowed and forms together only marginally exposed in other proterochampsids (Ezcurra with the quadratojugal a fully closed lower temporal bar. et al ., 2015). The lacrimal of CRILAR-Pv 491 overlaps the The dorsal process of the jugal is oriented approximately ventral process of the prefrontal along an anterodorsal- perpendicular to the anterior and posterior processes, and a to- posteroventral suture. The contribution (or lack thereof) well-developed ridge runs along its anterior margin. This of the lacrimal to the skull roof and the morphology of its ridge extends ventrally onto the main body of the bone, but contact with the maxilla cannot be determined because of it does not converge with the longitudinal ridge, as also poor preservation. oc curs in Pseudochampsa ischigualastensis (Trotteyn and Prefrontal . The prefrontal forms the anterodorsal corner of Ezcurra, 2014), Chanaresuchus bonapartei (e.g. , PULR 07, PVL the orbit and a distinct, rounded lateral projection in front 4586, MCZ 4039), and Gualosuchus reigi (PULR 05, PVL of the orbit, as occurs in other proterochampsids (Romer, 4576).

85 AMEGHINIANA - 2019 - Volume 56 (2): 79–115

Frontal . The frontals are very poorly preserved, and most of ternal surface of the dorsal process of the quadratojugal, the bones are represented by a mould of their internal sur - posterior to the ridge, is flat and faces laterally and pos - face. Thus, the sutures with the parietals and postorbitals terodorsally. The posterior process of the quadratojugal is cannot be identified. The anterior end of the frontal pre - flange-like and overlaps most of the ventral end of the serves traces of predominantly longitudinal ridges that quadrate in lateral view. It is not possible to determine the form part of the ornamentation of the skull roof, as occurs degree of contribution of the quadratojugal to the quadrate in Pseudochampsa ischigualastensis (Trotteyn and Ezcurra, foramen because of poor preservation. 2014) and other rhadinosuchines (Romer, 1971; Ezcurra et Squamosal . The ventral process of the squamosal is broad, al. , 2015). The dorsal border of the orbit is elevated above plate-like, and forms most of the posterior border of the the dorsal surface of the snout, resembling the condition in infratemporal fenestra. This process is posteroventrally other proterochampsids ( e.g. , Romer, 1971; Dilkes and ori ented in lateral view and, as a result, its main axis forms Ar cucci , 2012; Trotteyn and Ezcurra, 2014). an angle of approximately 120° with that of the anterior Postorbital . The external surface of the postorbital is process, resulting in a widely concave posterodorsal corner weath ered. The ventral process of the bone possesses a of the infratemporal fenestra. This condition is also present vertical ridge on its anterior margin that extends from that in some specimens of Chanaresuchus bonapartei (MCZ 4037, of the ascending process of the jugal and merges dorsally MCZ 4039). The posterior process extends beyond the level with a laterally and slightly anteriorly oriented projection of the dorsal end of the quadrate. The dorsal surface of the on the posterodorsal corner of the orbit. This anteriorly squamosal is not preserved on both sides of the skull, and pro jecting spur probably delimited the eye ball posteroven - thus the morphology of the medial process is unknown. trally, and is also present in Pseudochampsa ischigualasten - Parietal . The parietals are strongly damaged and are not sis (Trotteyn and Ezcurra, 2014) and other rhadinosuchines very informative. There is a median opening that extends (e.g. , Chanaresuchus bonapartei : PULR 07, PVL 4586, PVL 4647, along the level of the supratemporal fenestrae and onto the MCZ 4039; Gualosuchus reigi : PULR 05, PVL 4576; Ezcurra, posterior margin of the skull roof. This opening probably 2016). The posterior process of the postorbital of CRILAR- in dicates the absence of a complete synostosis between Pv 491 tapers posteriorly, subdividing the squamosal in both parietals. The posterolateral processes form an acute lat eral view, and extends beyond the level of the posterior angle (73°) between each other in dorsal view. margin of the supratemporal fenestra. The shape of the Quadrate . The quadrate distinctly slants anterodorsally- an terior process cannot be determined. to- posteroventrally in lateral view, and the dorsal two- Quadratojugal . The quadratojugal is a triradiate bone that thirds of the bone are slightly posteriorly bowed. The forms the posteroventral corner of the infratemporal posterior surface of the ventral end of the bone is convex, as fen estra (Fig. 2.2–3, 5–7: qj ). This bone bears a distinct occurs in several other archosauromorphs (Nesbitt et al. , fossa that opens into the infratemporal fossa (Fig. 2.2, 7: 2015; Ezcurra, 2016). The lateral margin of the quadrate ex - itfo ) and is very well-defined by a sharp, U-shaped ridge, as tensively contacts the ventral process of the squamosal, also occurs in other proterochampsids (Dilkes and Arcucci, and ventrally the contact with the quadratojugal is ob - 2012). The ventral portion of this ridge runs posterodor - scured by poor preservation. The quadrate foramen is sally-to-anteroventrally on the lateral surface of the ante - placed on the ventral half of the quadrate, and its borders rior process of the bone. It is not possible to determine if the are damaged. Its size and position resemble those of other ridge extended anteriorly onto the jugal because the suture proterochampsids ( e.g. , Chanaresuchus bonapartei : MCZ 4037). with the latter bone cannot be traced, but it is restricted to Fragments of the pterygoid wing are preserved in the left the quadratojugal in Chanaresuchus bonapartei (PULR 07, quadrate. MCZ 4039) and Gualosuchus reigi (PULR 05). The dorsal por - Supraoccipital . The supraoccipital is fairly complete, lacking tion of the ridge runs along the anterior margin of the dor - only its dorsal tip. This bone is rhomboidal and its external sal process of the quadratojugal and reaches the contact surface faces posterodorsally. The dorsolateral margin of with the squamosal, but it does not extend onto it. The ex - the bone articulates with the posterolateral process of the

86 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION parietal and the ventrolateral margin articulates with the pterygoid posteriorly. The vomers are splint-like bones, as in otoccipital. The external surface of the bone is divided at the other archosauriforms (Ezcurra, 2016), and form the medial midline by a vertical, very low ridge. The supraoccipital border of the choanae. The posterior two-thirds of the left seems to have contributed to the dorsal border of the fora - vomer preserves a single row of tiny, conical palatal teeth men magnum, as occurs in other rhadinosuchines ( e.g. , (diameter= 0.5 mm), as occurs in other proterochampsids Chanaresuchus bonapartei : MCZ 4037). (e.g. , Chanaresuchus bonapartei : Romer, 1971); Protero - Otoccipital (opisthotic + exoccipital). The opithostic and ex - champsa barrionuevoi : Dilkes and Arcucci, 2012. oc cipitals cannot be differentiated from each other. Though Palatine . The palatine is a tetraradiate bone, as occurs in this condition may be a result of poor preservation, we non-phytosaurian archosauromorphs (Ezcurra, 2016). The de scribe these two bones as an otoccipital because of their pair of anterior processes are subequal in length, articu - complete fusion in other archosauriforms (Ezcurra, 2016). lat ing with the maxilla laterally and the pterygoid and vomer The left paroccipital process is the best preserved, but its medially, respectively, forming the posterior border of the margins are damaged, though it can be determined that the choana. The pair of posterior processes articulates with the end of the process contacts the posterior process of the jugal and, possibly, the maxilla laterally, and with the ptery - squamosal. The right paroccipital process preserves its goid medially, forming the posterior border of the suborbital ven tral surface, which shows the base of a broad and rela - fenestra. The ventral surface of the palatine possesses an tively shallow stapedial groove. The otoccipital forms the anterolaterally-to-posteromedially oriented ridge, as occurs lateral margin of the foramen magnum and lateral wall of in other proterochampsids (Dilkes and Arcucci, 2012; the posteriormost portion of the endocranial cavity. There Trotteyn et al. , 2013). This ridge bears a row of palatal teeth is a distinct, flange-like projection placed on the dorsolatera l in other proterochampsids (Romer, 1971), but they seem to corner of the margin of the foramen magnum, adjacent to not be preserved in CRILAR-Pv 491. the contact between the otoccipital and supraoccipital, Pterygoid . Most of the pterygoids are missing. The anterior which would have received the proatlas. It is not possible to half of the anterior process articulates laterally with the identify the suture between the otoccipital and basioccipital, vomer and palatine. The anterior end of the anterior process nor the opening(s) for the passage of the hypoglossal cranial of the right pterygoid is not preserved, thus it is not possi - nerve because of poor preservation. ble to determine if the pterygoids contacted each other an - Basioccipital . The basioccipital possesses an occipital teriorly. The anterior process of the pterygoid possesses a condyle separated from the rest of the bone by a distinct longitudinal row of tiny palatal teeth that is adjacent to neck. The basal tubera are completely separated from each the medial margin of the bone, as occurs in other prote - other and diverge in an obtuse angle in posterior view, as rochampsids and several other archosauromorphs (Ezcurra, occurs in other rhadinosuchines ( e.g. , Pseudochampsa is - 2016). chigualastensis : Trotteyn and Haro, 2012; Chanaresuchus Ectopterygoid . Fragments of a pair of plate-like bones are bonapartei : PULR 07, MCZ 4037). There is no well-rimmed preserved in contact with the medial surface of both jugals, depression on the ventral surface of the basioccipital, as respectively, symmetrically placed on both sides of the skull. oc curs in other proterochampsids ( e.g. , Trotteyn and Haro, These fragments probably correspond to lateral processes 2010, 2012). of the ectopterygoids because of their shape and position, Parabasisphenoid . Only the posterolateral corners of the but it cannot be determined if they also contacted the pos - parabasisphenoid are preserved. The preserved portions of terior end of the horizontal process of the maxilla. this bone contribute to the basal tubera and an anterome - Lower jaw . The lower jaw of CRILAR-Pv 491 is represented dially oriented ridge that is part of a V-shaped intertuberal by most of the left hemimandible (Fig. 2.7–11) and the gle - plate, as occurs in other proterochampsids (Trotteyn and noid region of the right one (Fig. 2.12–14), but in the former Haro, 2012). the dentary and splenial are badly damaged. Therefore, it is Vomer . The vomers articulate with the palatal process of the not possible to identify alveoli. Only the posterodorsal and premaxilla and maxilla anteriorly and with the palatine and posterior borders of the external mandibular fenestra, which

87 AMEGHINIANA - 2019 - Volume 56 (2): 79–115 are formed by the surangular and angular, are preserved. the anteriormost portion of the latter ridge to the ventral The external surface of the postdentary bones is poorly pre - margin of the lateral surface of the hemimandible at level served. The anteroventrally-to-posterodorsally oriented of the anterior end of the glenoid fossa. Thus, the ventral ridge that extends from the posterior border of the external margin of the posterior end of the hemimandible is formed mandibular fenestra in other proterochampsids (Dilkes exclusively by the surangular. A strongly laterally developed and Arcucci, 2012) is lower in CRILAR-Pv 491 than in other longitudinal shelf is present along the dorsolateral surface specimens of the clade, but this is probably a result of poor of the surangular and rises adjacent to the glenoid fossa, preservation. The surangular-angular suture extends from as occurs in other proterochampsids ( e.g. , Romer, 1971; Dilkes and Arcucci, 2012). It is not possible to determine the occurrence of a posterior surangular foramen. The suture between the surangular and articular cannot be identified, but the glenoid fossa would be composed of both bones (Fig. 2.12 –14), as it is in other diapsids (Romer, 1956). The glenoid fossa is formed by two rather symmetric convexities. The anterior portion of the retroarticular process is preserved, which possesses a well-developed medial pro - jection. The prearticular is dorsoventrally low and forms the ventromedial wall of the adductor fossa. The angular pos - sesses a distinct, longitudinal change in slope separating laterally and ventrolaterally facing surfaces, as occurs in other rhadinosuchines ( e.g. , Gualosuchus reigi : PVL 4576). Vertebral column . The cervical series is represented by two Figure 3. Two articulated middle-posterior cervical vertebrae of articulated mid- to posterior cervical vertebrae (Fig. 3; Tab. CRILAR-Pv 491 in 1, left lateral; 2, anterior; 3, dorsal; 4, right lateral; 5, posterior; and 6, ventral views. Abbreviations: aaf, anterior articu - 2) and the last cervical vertebra articulated to the dorsal lar facet; dp, diapophysis; ns, neural spine; pa, parapophysis; paf, pos - series (Figs. 4–5; Tab. 2). The neurocentral suture cannot terior articular facet; poz, postzygapophysis; prz, prezygapophysis. Scale bar= 5 mm. be distinguished in the cervical vertebrae.

TABLE 2 – Measurements of the cervical vertebrae of CRILAR-Pv 491 in millimetres.

Cv A Cv B Cv C

Centrum length 8.0 8.2 9.6

Centrum anterior height 6.0 - -

Centrum anterior width 5.9 - 9.1

Centrum posterior height - 5.9 -

Centrum posterior width - 7.3 6.9

Height of neural spine - 5.9* 8.2

Length of neural spine at base 5.9* 6.7 6.4

Maximum height 15.2* 16.2* 19.3

Length across zygapophyses 11.5 - 10.3 Incomplete measurements indicated with an asterisk and the value given is the maximum measurable. Measurements were rounded to the nearest 0.1 mm.

88 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

The two articulated vertebrae possess amphicoelous rochampsids ( e.g. , Chanaresuchus bonapartei : MCZ 4037; centra that are longer than tall (Fig. 3). The posterior ends of Gualosuchus reigi : PVL 4576). the centra are damaged, and as a result their complete The last cervical vertebra of CRILAR-Pv 491 possesses length cannot be determined. The centra are transversely a centrum that is 1.8 times longer than tall (9.6 mm length compressed around mid-length and have strongly convex and 5.2 mm posterior height) and represents 27% of the ventral and lateral surfaces. The ventral surface of at least maximum height of the element (19.1 mm; Fig. 4: lcv ). The the posterior vertebra lacks a longitudinal keel, whereas the proportions of this vertebra resemble those of the poste - ventral surface of the anterior elements is damaged and the rior cervical vertebrae of PVL 4575 (a referred specimen of absence of a keel cannot be determined confidently. Ven - Chanaresuchus bonapartei ), but contrast with the posterior tral longitudinal keels are present in the preserved/exposed cervical centra of some other rhadinosuchine specimens cervical vertebrae of Proterochampsa barrionuevoi (Dilkes and (e.g. , MCZ 4037, PVL 4576), which are approximately as Arcucci, 2012), Pseudochampsa ischigualastensis (Trotteyn and long as tall, or even slightly taller than long. The rest of the Ezcurra, 2014), Rhadinosuchus gracilis (Ezcurra et al. , 2015), morphology of the centrum is congruent with that of the and up to the sixth, eight, and ninth cervical vertebrae of Cha - posterior vertebra of the cervical sequence described pre - naresuchus bonapartei (MCZ 4037), Gualosuchus reigi (PVL vi ously. The diapophysis is longer and anteroposteriorly 4576), and Tropidosuchus romeri (PVL 4601), respectively. broader than in the anteriormost preserved cervical verte - The parapophyses of CRILAR-Pv 491 are short and placed brae, but placed at the same level in the neural arch. Short adjacent to the anterior margin and around the mid-height anterior and posterior centrodiapophyseal laminae extend of the centrum. A short anteroventrally-to-posterodorsally anteroventrally and posteroventrally, respectively, from the oriented ridge extends from the parapophysis towards the base of the diapophysis and delimit a large and relatively dorsolateral margin of the centrum. This ridge is longer in shallow centrodiapophyseal fossa. These laminae are also the posterior vertebra of the sequence and approximately present from the 10th to at least the 12th presacral verte - reaches where the neurocentral suture would have been brae of MCZ 4037 (Ezcurra, 2016). There is no depression placed. The diapophyses are placed completely on the neu - lateral to the neural spine, and the latter structure extends ral arch and at level of the roof of the neural canal. The left along the entire length of the neural arch at the midline. The diapophysis of the anterior vertebra is complete. It is shorter neural spine expands posteriorly towards its distal end— dorsoventrally than anteroposteriorly wide and slightly pos - the presence of an anterior expansion cannot be determined teriorly oriented. The shape and position of the parapophy - because of damage—and there is no transverse thickening ses and diapophyses of these two articulated vertebrae or expansion of the distal end, resembling the condition in closely resemble those in the seventh to ninth cervical ver - other rhadinosuchine proterochampsids ( e.g. , Chanaresuchus tebrae of referred specimens of Chanaresuchus bonapartei bonapartei : MCZ 4035, PVL 4575; Gualosuchus reigi : PVL (MCZ 4037) and Gualosuchus reigi (PVL 4576). The prezyga - 4576). The lateral surface adjacent to the distal margin of pophyses are anterodorsally oriented. They extend slightly the neural spine possesses a series of dorsoventrally and anterior beyond the level of the anterior margin of the cen - slightly anteroventrally oriented thin ridges, as occurs in trum, and their articular facets face dorsomedially. The other rhadinosuchine proterochampsids. prezygapophyses are broadly separated from each other The complete dorsal series is preserved in articulation and extend laterally slightly beyond the margins of the an - and maintains a rather consistent morphology through the terior rim of the centrum. The postzygapophyses are short, sequence; as a result, all the dorsal vertebrae are described posteriorly oriented, and form a dorsoventrally tall notch together (Figs. 4–5; Tab. 3). The neurocentral suture cannot with the centrum in lateral view. Only the base of the neu - be identified in the dorsal series. The centra are antero - ral spines is preserved. It extends along the entire dorsal pos teriorly longer than tall and their length increases to - surface of the neural arch at the mid line. The morphology wards the sacrum, resembling the condition present in PVL of the neural arches is consistent with those of the mid- to 4575. Indeed, the length of the centrum is 1.5–1.6 times posterior cervical vertebrae of other rhadinosuchine prote - the height of its anterior articular facet in the first to fourth

89 AMEGHINIANA - 2019 - Volume 56 (2): 79–115

Figure 4. Articulated last cervical vertebra and dorsal vertebrae of CRILAR-Pv 491 in 1, 3, right lateral; 2, 4, left lateral; 5–6, dorsal; 7–8, ven - tral views. Abbreviations: D1, first dorsal vertebra; D7, seventh dorsal vertebra; D14, fourteenth dorsal vertebra; lcv, last cervical vertebra; os, osteoderms. Scale bar= 3 cm.

90 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

TABLE 3 – Measurements of the dorsal, sacral and caudal vertebrae of CRILAR-Pv 491 in millimetres.

Centrum length Posterior width of centrum Height of neural spine Length across zygapophyses

D1 9.9 6.4 8.8 12.3

D2 10.1 6.5 8.9 13.7

D3 10.6 6.5 9.7 14.5

D4 - - 9.8 14.9

D5 - 7.1 - 14.8

D6 11.5 6.7 - 15.7

D7 11.7 - 9.5 16.4

D8 13.6 - 9.7 18.3

D9 12.4 - 9.6 17.8

D10 13.0 8.0 9.3 17.4

D11 12.5 - 9.3 15.6

D12 12.1 - 9.3 16.0

D13 13.5 - - 16.1

D14 11.4 - 9.2 15.1

D15 11.1 7.8 - -

S1 11.7 - 12.2 -

S2 - - 13.3 -

Ca2 12.0 - - - Vertebrae without preserved complete measurements were excluded from this table. Value given is the maximum measurable. Measurements were rounded to the nearest 0.1 mm.

dorsal vertebrae, 1.9–2.2 in the eighth to tenth dorsal ver - and moderately compressed around mid-length. The lateral tebrae, and 2.3–2.6 times in the eleventh to the last dorsal surface possesses a shallow, not well-rimmed depression vertebrae. The proportions of the posterior dorsal centra immediately on the dorsal half of the centrum, as occurs in re semble those of some specimens of Chanaresuchus bona - several non-archosaurian archosauriforms (Ezcurra, 2016). partei (PVL 4575, ratio= 2.1–2.4 in posterior dorsal verte - The parapophysis of the first dorsal vertebra is placed at the brae; PULR 07: ratio= 1.8 in a middle dorsal vertebra). By transition between the centrum and neural arch, whereas in contrast, the dorsal centra are proportionally shorter in the second dorsal it is placed entirely on the neural arch, an - other rhadinosuchine specimens ( e.g. , Chanaresuchus bona - teroventral to the diapophysis. The parapophysis migrates partei : PVL 6244, 1.2–1.3 from the eleventh to last dorsal; gradually towards the distal end of the diapophysis along Chanaresuchus bonapartei : MCZ 4037, 1.4 in the last dorsal; the dorsal series and remains as a distinct structure up to Gualosuchus reigi : PVL 4576, ratio= 1.0–1.1 in the first and the eleventh or possibly twelfth dorsal vertebra. The para - second dorsal vertebrae and 1.2 in the ninth dorsal verte - pophysis and diapophysis are separated from each other in bra). The anterior and posterior articular facets of the cen - the first and second dorsal vertebrae, but a paradiapophy - tra are approximately as tall as wide and D-shaped, with a seal lamina connects both structures from the second to, at rather straight dorsal margin and a strongly convex ventral least, the seventh dorsal vertebrae. The presence of this margin. The ventral surface is strongly transversely convex lamina from the eighth to twelfth dorsal vertebrae cannot

91 AMEGHINIANA - 2019 - Volume 56 (2): 79–115 be determined because of damage. A short posterior cen - the prezygapophysis and posteriorly along the anterior half trodiapophyseal lamina is present in the first dorsal verte - of the centrum. This facet is placed in a very short, laterally bra, being less posteroventrally extended than that of the projecting peduncle. The prezygapophysis is strongly dor - last cervical vertebrae. All the other vertebrae lack a poste - sally oriented, short, and does not exceed the level of the rior centrodiapophyseal lamina and all the dorsal vertebrae anterior margin of the centrum, as occurs in the middle- lack prezygodiapophyseal and postzygodiapophyseal lami - posterior dorsal vertebrae. The postzygapophyses of the nae, resembling the condition in several, disparate archo - first sacral vertebra are not exposed or preserved. The neu - sauromorph clades (Ezcurra et al. , 2014; Ezcurra, 2016). The ral spines are posterodorsally oriented, contrasting with the only complete diapophysis is the left one of the seventh vertical neural spines of the dorsal vertebrae. The neural dorsal vertebra, which is subrectangular, slightly longer spine of the first sacral vertebra is anteroposteriorly ex - than wide, and slightly posteriorly oriented in dorsal view. panded towards its distal end, resembling the condition in The base of the diapophyses is placed around the level of the dorsal vertebrae. This neural spine is too damaged to mid-length of the centrum and the roof of the neural canal. determine the presence of a transverse thickening or orna - The prezygapophyses are anterodorsally oriented, but mentation. The left rib of the first sacral vertebra is poorly towards the sacral region they become gradually more preserved, but it can be determined that it is anterolaterally dor sally oriented. As a result, the prezygapophysis does not oriented in dorsal view and articulated with the medial sur - extend beyond the level of the anterior margin of the cen - face of the ilium approximately at the level of the base of trum from the eighth dorsal vertebra. The postzygapophy - the preacetabular process, as in other archosauromorphs ses are short and extend beyond the level of the posterior (Nesbitt, 2011). margin of the centrum. There is no depression lateral to the The second sacral vertebra lacks most of the centrum, base of the neural spine. The neural spines extend along the transverse processes, left prezygapophysis, and postzy - entire length of the neural arch on the midline and are gapophyses. The right prezygapophyses and the anterodis - placed on the posterior two-thirds of the vertebra in lateral tal corner of the neural spine are damaged. The preserved view. The neural spines are taller dorsoventrally than an - regions of the second sacral vertebra possess a morphology teroposteriorly broad at their base and dorsally oriented. consistent with that previously described for the first sacral They are rather symmetrically and gradually expanded an - vertebra. The second sacral rib is poorly preserved, and it teroposteriorly towards their distal end, resulting in a fan- articulated with the ilium dorsal to the ischial peduncle and shaped spine in lateral view. The distal margin of the neural at the base of the postacetabular process, also resembling spines is only incipiently transversely thickened and orna - the ancestral archosauromorph pattern (Nesbitt, 2011). mented by short and low, slightly anteroventrally oriented The first three caudal vertebrae are represented by the ridges, as occurs in the last cervical vertebrae and other mould—together with some fragments of bone—of the left rhadinosuchine specimens ( e.g. , Chanaresuchus bonapartei : lateral surface and the base of the left transverse processes MCZ 4035, PVL 4575; Gualosuchus reigi : PVL 4576). There is (Fig. 5: cav ; Tab. 3). Thus, the anatomical information of no prespinal or postspinal fossa extending onto the margins these vertebrae is very limited, but their preserved overall of the neural spines. morphology resembles that of other rhadinosuchine prote - The sacrum is composed of two sacral vertebrae, which rochampsids ( e.g. , Chanaresuchus bonapartei : PVL 4575; Pseu - are more poorly preserved than the vertebrae of the dorsal dochampsa ischigualastensis : Trotteyn and Ezcurra, 2014). series (Fig. 5; Tab. 3). In the first sacral vertebra, the cen - The morphology of the centra is congruent with that of the trum is anteroposteriorly long and has a transversely con - posteriormost dorsal vertebrae. The base of the transverse vex ventral surface, lacking a ventral keel or groove. The rib processes is laterally and slightly dorsally oriented. The facet of this vertebra is exposed, indicating that the rib was prezygapophysis of the second caudal vertebra is an - not fused to it. The rib facet is placed adjacent to the ante - terodorsally oriented and does not seem to extend beyond rior margin of the dorsal two-thirds of the centrum and the the level of the anterior margin of the centrum. By contrast, base of the neural arch, extending dorsally onto the base of the prezygapophysis of the third caudal vertebra is more

92 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

Figure 5. Sacral region, osteoderms, and pelvis of CRILAR-Pv 491. 1, Left lateral articulated last dorsal, two sacral and first three caudal ver - tebrae, left sacral ribs, and left pelvic bones; 2, right lateral articulated last dorsal, two sacral and first three caudal vertebrae, left sacral ribs, and left pelvic bones; 3, close-up of middle-posterior osteoderms; 4–5, right pubis and ischium; 6–7, articulated last dorsal, two sacral and first three caudal vertebrae, left sacral ribs, and left pelvic bones. Specimen in 1, left lateral; 2, right lateral; 3, 6, dorsal; 4, anterior; 5, lateral; and 7, ventral views. Abbreviations: cav, caudal vertebrae; f.sr1, facet for the first sacral rib; il, ilium; ilpe , iliac peduncle; isc, ischium; ldv, last dorsal vertebra; os, osteoderms; poap, postacetabular process; pu, pubis; pu-isc, pubo-ischiatic plate; S1, first sacral vertebra; S2, second sacral vertebra; sr1, first sacral rib; sr2, second sacral rib; tp, transverse processes. Scale bars= 1 cm ( 1–2, 4–7 ), 5 mm ( 3).

anteriorly projected and extends beyond the anterior level thirds were mostly straight in lateral view. The postac - of the centrum. The neural spine of these anterior caudal etab ular process possesses a broad medial longitudinal vertebrae is strongly posterodorsally oriented, being pos - shelf that is slightly ventrally oriented likely as a result of teriorly extended distinctly beyond the level of the poste - deformation. A similar medial shelf is also present in other rior margin of their respective centra. proterochampsids ( e.g. , Chanaresuchus bonapartei : PVL 6244). Pelvic girdle . The pelvic girdle of CRILAR-Pv 491 is repre - The medial surface of the iliac blade is obscured by matrix sented by poorly preserved bones (Fig. 5). The left ilium only that could not be removed without compromising the spec - preserves its blade, lacking the preacetabular process, the imen. A large plate-like bone is preserved posterior to the dorsal margin of the blade at its central region, and the dis - left ilium and immediately above the third and fourth caudal tal end of the postacetabular process. The supraacetabular vertebrae. This bone may represent an ischium, but it is too crest is also missing. The preserved portions of the dorsal poorly preserved for a confident determination. margin of the iliac blade indicate that its posterior two- The proximal half of the right pubis is preserved imme -

93 AMEGHINIANA - 2019 - Volume 56 (2): 79–115

Figure 6. Hindlimb bones of CRILAR-Pv 491. 1–6, 11, left femur; and 7–10, 12, left tibia and fibula in 1, 10, anterior; 2, posteromedial; 3, 7, medial; 4, 8, lateral; 5, 9, posterior; 6, 12, proximal; 11, distal views. Abbreviations: amt, anteromedial tuber; br, broken area; cc, cnemial crest; fh, femoral head; fi, fibula; ft, fourth trochanter; gr, groove; plc, posterior lateral condyle; pmc, posterior medial condyle; pof, popliteal fossa; pt, posterior tuber; tc, tibial condyle; tfc, tibiofibular crest; ti, tibia. Scale bar= 1 cm.

94 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION diately next to a large, very poorly preserved, plate-like asymmetric, with the lateral one being placed approxi - bone that may represent a right ischium. The pubis strongly mately at the mid-depth of the proximal end, as occurs in bows ventrally in lateral view, resembling the condition in other rhadinosuchines ( e.g. , Chanaresuchus bonapartei : PVL other proterochampsids ( e.g. , Chanaresuchus bonapartei : 4575; Gualosuchus reigi : PVL 4576). The medial proximal PVL 6244). The preserved portion of the pubis apron is trans - condyle tapers distally, resembling the condition in some versely broad. rhadinosuchine specimens ( e.g. , Chanaresuchus bonapartei : Hindlimb . The available left femur does not preserve the PULR 07, PVL 4575). The tibial shaft becomes anteropos - lateral surface of the proximal half of the bone, the tibiofibu - teriorly deeper than transversely wide towards mid-length lar crest, or its proximal and distal surfaces (Fig. 6.1–6, 6.11; and possesses a flat medial surface. Tab. 4). The latter could be the result of poor preservation or Approximately the proximal third of the left fibula is pre - incomplete ossification. The femur is sigmoid in side view, served (Fig. 6.7–10; Tab. 4). This bone is very poorly pre - and its head is anteromedially oriented, poorly offset from served and there is no relevant morphology to describe. the shaft, and possesses distinct posterior and anterome - Osteoderms . There is a single row of osteoderms that is pre - dial tubers ( sensu Ezcurra, 2016). The presence of a pos - served articulated to the neural spines of the ninth to thir - teromedial tuber is uncertain because of damage. The teenth dorsal vertebrae; they are best preserved in the first fourth trochanter is mound-like and strongly proximodis - three vertebrae of this series (Fig. 4: os ). At least in the tenth tally developed, extending beyond mid-shaft, as occurs in dorsal vertebra it is very clear that there are three osteo - Gualosuchus reigi (PULR 05, PVL 4576) and Chanaresuchus derms articulating with its neural spine, as occurs in Chana - bonapartei (MCZ 4035, PVL 4575, PVL 6244) (Ezcurra, 2016). resuchus bonapartei (Trotteyn et al. , 2013) and a specimen As a result, the minimum circumference of the shaft is placed referred to Gualosuchus reigi (PVL 4576; contra Trotteyn et at the beginning of the distal three-quarters of the bone. al. , 2013). By contrast, two osteoderms are present per ver - The distal end possesses a short popliteal fossa, and the tebra in Tropidosuchus romeri (PVL 4601; contra Trotteyn et medial condyle is well developed posteriorly. The presence al. , 2013). The osteoderms of CRILAR-Pv 491 are dorsoven - of an extensor fossa cannot be undoubtedly confirmed be - trally thick, with a smooth, gently convex external surface, cause of damage. and overlap dorsally the anterior one-third of the subse - The proximal half of the left tibia is preserved (Fig. 6.7– quent element. The anteriormost preserved osteoderm is 10, 6.12; Tab. 4). The cnemial crest is low and straight, completely exposed in dorsal view; it is anteroposteriorly with a rounded anterior margin in proximal view, resembling longer than broad and possesses a X-shaped contour, the condition in other proterochampsids (Nesbitt, 2011; closely resembling the condition in Pseudochampsa ischi - Ezcurra, 2016). The proximal posterior condyles are strongly gualastensis (Trotteyn et al. , 2012; Trotteyn and Ezcurra,

TABLE 4 – Measurements of the hindlimb bones of CRILAR-Pv 491 in millimetres.

Femur Tibia Fibula

Length 91.8 47.5* 35.3*

Proximal width 17.7 7.9 5.1

Proximal depth 6.8 20.4 2.6

Distal width 10.0 - -

Distal depth 11.8 - - Incomplete measurements indicated with an asterisk and the value given is the maximum measurable. Measurements were rounded to the nearest 0.1 mm.

95 AMEGHINIANA - 2019 - Volume 56 (2): 79–115

2014). By contrast, the dorsal osteoderms of Chanaresuchus CRILAR-Pv 488 bonapartei have been described as wedge-shaped, those This specimen is represented by several cranial and of Gualosuchus reigi are oval, and those of Tropidosuchus postcranial bones (Figs. 7–13) that were found associated romeri are heart-shaped (Trotteyn et al. , 2013; Trotteyn and with a cynodont ilium and some postcranial bones referred Ezcurra, 2014). The transverse constriction of the osteo - to Gracilisuchus stipanicicorum (CRILAR-Pv 490). The prote - derms of CRILAR-Pv 491 is anteriorly displaced from the rochampsid bones are all larger than those of the other taxa mid-length of the elements, thus resulting in an anteropos - and of a size congruent with that expected for a single indi - teriorly asymmetric bone in dorsal view, contrasting with vidual. The bones are very well preserved and disarticulated, the symmetric osteoderms of Pseudochampsa ischigualas - allowing the description of several features usually obscure tensis (Trotteyn and Ezcurra, 2014). The osteoderms of in other articulated rhadinosuchine specimens from the Pseudochampsa ischigualastensis also differ from those of Chañares Formation. CRILAR-Pv 491 and other proterochampsids in the presence Skull . The maxilla lacks its anterior tip and the posterior half of a deep, well-defined longitudinal groove on their external of the horizontal process (Fig. 7.1–5). This bone is antero - surface (Trotteyn and Ezcurra, 2014). posteriorly elongated and dorsoventrally low, being at least

Figure 7. Cranial bones of CRILAR-Pv 488. 1–5, Right maxilla; 6–9, 14, right quadrate; 10, scanning electronic microscope photograph of erupt ing tooth crown indicated in figure 7.12; 11–12, 15–16, left dentary; 13, close-up of the mesial denticles of 7.10 in 1, 9, 11, lateral; 2, 8, 12, medial; 3, 15, dorsal; 4, 14, 16, ventral; 5, 7, anterior; 6, posterior; 10, 13, lingual views. Abbreviations: anfo , antorbital fossa; asp , ascending process; csl , change of slope; idp , interdental plates; f.pal, facet for palatine; lc , lateral condyle; Mc , roof of Meckelian canal; mc , me dial condyle; palp, palatal process. Scale bars= 1 cm ( 1–9, 11–12, 14–16 ), 0.1 mm ( 10 ), 0.5 mm ( 13 ).

96 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

2.5 times longer than its maximum height as preserved TABLE 5 – Measurements of the cranial bones of CRILAR-Pv 488 in (Tab. 5), resembling the general morphology of other pro - mil limetres. terochampsids (Trotteyn et al. , 2013). The maxilla forms the Length Height Width anterodorsal and anteroventral borders of the antorbital fenestra, forming an angle of approximately 30° between Maxilla 75.5* 27.4 12.7 them. The preserved lateral surface of the anterior and Quadrate distal end 8.3 15.4* 14.9* hor izontal processes of the maxilla is anteroposteriorly con - Dentary 41.9* 8.4* 5.0 cave and with some poorly inflated areas, one of them de - Incomplete measurements indicated with an asterisk and the value veloped as a longitudinal and incipiently ventrally bowed given is the maximum measurable. Measurements were rounded to the nearest 0.1 mm. ridge placed approximately at mid-height of the bone an - terior to the level of the antorbital fenestra. The lateral sur face of the maxilla possesses at least eight small and suboval, anteroposteriorly longer than tall, foramina. These is damaged, it cannot be determined whether it contacted foramina are arranged in a single longitudinal row placed 3.5 its counterpart or not. to 2.9 millimetres above the alveolar margin of the bone. The ascending process of the maxilla is posterodorsally The posterior two-thirds of the anterior process have a dis - oriented and twists along its length, in which the external tinct change of slope between dorsally and laterally facing surface faces mainly laterally posteriorly whereas it faces surfaces that defines a thick ridge along the dorsolateral mainly dorsally at its base. The external surface of this edge of the bone. This ridge extends posteriorly onto the process possesses a straight, longitudinal ridge placed base of the ascending process and borders the anterodorsal ap proximately at its mid-width. There is no antorbital fossa corner of the antorbital fenestra. As a result, the snout ac - on the ascending process of the maxilla. The preserved por - quires a distinct box-shape morphology, as occurs in the tion of the horizontal process slightly tapers posteriorly, as rhadinosuchines Rhadinosuchus gracilis (SNSB-BSPG AS XXV occurs in Rhadinosuchus gracilis (SNSB-BSPG AS XXV 50) and 50), Chanaresuchus bonapartei (PVL 4575, 4586), Pseudo - Tropidosuchus romeri (PVL 4606). By contrast, the horizontal champsa ischigualastensis (PVSJ 606), and Gualosuchus reigi process maintains the same dorsoventral height below the (PVL 4576), but not in other proterochampsids (Kischlat, antorbital fenestra in Chanaresuchus bonapartei (PVL 4575) 2000; Ezcurra et al. , 2015). and Gualosuchus reigi (PVL 4576). The horizontal process of The anterior process of the maxilla is subtriangular CRILAR-Pv 488 possesses an antorbital fossa below the an - with an anterior apex, and it is two times longer than the teroventral margin of the antorbital fenestra (Fig. 7.1: anfo ), ascending process (Tab. 1). The dorsal surface of the ante - as also occurs in Rhadinosuchus gracilis (SNSB-BSPG AS XXV rior process possesses a distinct facet for reception of the 50), but contrasting with the absence of an antorbital fossa postnarial process of the premaxilla, indicating that the in other proterochampsids ( Chanaresuchus bonapartei , Gualo - maxilla probably did not participate in the border of the ex - suchus reigi , Tropidosuchus romeri , Proterochampsa barrio - ternal naris, as occurs in other proterochampsids (Trotteyn nuevoi , Pseudochampsa ischigualastensis ; Ezcurra et al. , 2015) . et al. , 2013). The dorsal surface of the anterior process The antorbital fossa ends anterior to the broken margin of pos sesses a pair of longitudinal, very thin ridges at its pos - the horizontal process and is ventrally delimited by a thick terior third. The palatal process of the maxilla is dorsoven - ridge that increases in height posteriorly, up to the broken trally low, placed immediately above the interdental plates, end of the bone. The medial surface of the horizontal and directly medially projected. This process extends along process of the maxilla is anteroposteriorly and dorsoven - most of the anterior process of the maxilla, being four times trally convex below the antorbital fenestra. A distinct ar - longer than transversely wide (Tab. 1). The dorsal surface of tic ular facet for the reception of the palatine is placed on the the palatal process is flat, and the ventral one slightly trans - ventral half of the medial surface of the horizontal process versely concave. Because the maxilla was preserved disar - and is adjacent to the base of the interdental plates. The ticulated and the anteromedial margin of the palatal process posterior end of this facet extended onto the missing por -

97 AMEGHINIANA - 2019 - Volume 56 (2): 79–115 tion of the horizontal process. The palatine facet is distinctly the roof of the Meckelian canal (Fig. 7.16: Mc ). The dorsal mar - separated from the base of the palatal process, thus indi - gin of the preserved portion of the dentary is straight in latera l cating that the maxilla extensively contributed to the lateral view, as occurs in the central and posterior dentigerous re - border of the choana. The palatine facet is anteroposteriorly gion of the dentary of other rhadinosuchine proterochamp - elongated and tapers anteroventrally. The surface of this sids ( e.g. , Chanaresuchus bonapartei : MCZ 4037). The lateral facet is ornamented by low and thin anteroventrally-to- surface of the dentary is flat and generally smooth, with posterodorsally oriented striations on its ventral half and only a single anteroventrally to posterodorsally oriented, anteroposteriorly oriented ridges on its dorsal half. The facet thick tuberosity in the posterior third of the preserved por - is well delimited anterodorsally by a shelf that shallows tion of the bone. There is one oval, anteroposteriorly longer posteriorly. than tall, neurovascular foramen placed in the anterior third The maxilla preserves nine tooth positions, but the total of the preserved portion of dentary and slightly ventrally number of alveoli cannot be determined because the pos - displaced from mid-height. Most of the medial surface of terior end of the bone is missing. Tooth implantation is the - the dentary faced medially, but the dorsal end tilts laterally codont, and five teeth are preserved in their natural position. to generate a dorsomedially facing surface immediately The second alveolus (as preserved from anterior to poste - below the alveolar margin. The medially facing surface of rior) preserves the only fully erupted tooth, whereas the the bone that would have received the splenial is smooth, teeth of the first, sixth, and eighth alveoli present different being incipiently concave anteriorly and becoming flat pos - stages of eruption. The apex of a replacement tooth is ex - teriorly. There are eleven preserved alveoli, which are oval posed between the bases of the interdental plates of the and anteroposteriorly longer than broad in occlusal view. second alveolus. The preserved maxillary tooth crowns are The tooth implantation is thecodont and nine teeth with labiolingually compressed, slightly distally curved, and pos - dif ferent degrees of preservation are preserved in situ, in sess serrated mesial and distal carinae with six denticles per which only two erupting teeth preserve complete crowns. millimetre. The exposed surfaces of the enamel are smooth, The differences in the degree of dental eruption of these lacking ridges, wrinkles or wear facets. The alveoli are me - teeth indicate an alternate tooth replacement. The tooth dially defined by pentagonal interdental plates that do not crowns are labiolingually compressed, distally curved, and contact to each other. Their medial surface is smooth, lacking have small perpendicular denticles on both mesial and dis - ornamentation or foramina. tal carina (Fig. 7.10, 13). The medial wall of the alveoli is Only the ventral end of the right quadrate is preserved formed by triangular interdental plates that do not contact (Fig. 7.6–9, 14; Tab. 5). The anterior surface is transversely each other. concave and the posterior one is convex. The lateral and Atlantal neural arch . The left neural arch of the atlas is pre - medial surfaces are damaged and, as a result, the facet for served, lacking the medial margin of the bone anterior to the articulation with the quadratojugal is not preserved. The postzygapophysis and most of the epipophysis (Fig. 8.1–6). two ventral condyles are distinctly separated from each The bone is semilunate in lateral view, with a rather robust other by a posteromedially to anterolaterally oriented ventral peduncle. This resembles the condition in speci - groove. The medial ventral condyle is transversely narrower mens of Proterochampsa barrionuevoi (MCZ 3408; Dilkes and and considerably more ventrally projected than the lateral Arcucci, 2012: fig. 11a) and Gualosuchus reigi (PVL 4576) but one, as occurs in other rhadinosuchine specimens ( e.g. , contrasts with the proportionally more gracile peduncle of Chanaresuchus bonapartei : PVL 4575). The posterior margin the atlantal neural arch of specimens of Chanaresuchus of the articular surface is defined by a distinctive rim that bonapartei (MCZ 4037) and Tropidosuchus romeri (PVL 4601). suggests that the area was covered by cartilage in life. The atlantal neural arch of CRILAR-Pv 488 has a maximum The partial left dentary lacks its anterior and posterior preserved height of 13.0 mm and its ventral peduncle has a regions, and its ventrolateral margin is broken off (Fig. ventral anteroposterior depth of 6.1 mm and transverse 7.11–12, 15–16; Tab. 5). As a result, it is interpreted that width of 4.0 mm. The ventral articular end of the peduncle the preserved ventromedial margin of the bone represents of the neural arch is subdivided into two adjacent facets,

98 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION one on the anteroventral corner and the other on the ven - suchus reigi (PULR 05). The centrum is transversely com - tral surface. The anterior facet, which received the occipital pressed at mid-length and lacks a lateral fossa, resembling condyle, is concave and faces anteromedially and ventrally. the condition in Chanaresuchus bonapartei (PULR 07, MCZ The posterior facet, which articulated with the atlantal in - 4037) and Gualosuchus reigi (PVL 4576). The parapophyses tercentrum, faces ventrally and is anteroposteriorly convex. are placed on the anteroventral corner of the centrum, but The lateral surface of the ventral peduncle is smooth and not adjacent to the ventral rim. They project laterally, but convex. The medial surface possesses a very well developed they extend only slightly beyond the lateral margin of the anteroventrally to posterodorsally oriented ridge that ex - centrum. The articular facet of the parapophyses is subcir - tends from the facet for reception of the occipital condyle cular, flat, and faces laterally. The base of the neural arch is to a few millimetres from the postzygapophyseal facet. The preserved articulated to the centrum on the left side of the dorsal portion of the neural arch curves slightly ventrally vertebra, and the neurocentral suture is clearly visible. The and the postzygapophyseal facet is placed on its medial sur - base of the left diapophysis is preserved and placed entirely face. This facet faces ventromedially and is sub-oval, with on the neural arch. This vertebra lacks a posterior centro - an anteroposterior main axis. Only the base of the epipoph - di apophyseal lamina, and the presence of an anterior cen - ysis is preserved and the anterior (= uncinate) process, if trodiapophyseal lamina cannot be determined because of present, is broken off. The medial expansion on the pedun - damage. cle is well developed and forms part of the slightly concave The cervical neural arch lacks the central and posterior anterior articular surface for the occipital condyle. The ven - region of the left ventral peduncle (including the diapoph - tral articular surface of the peduncle is subtriangular in ysis), the posterior region of the right ventral peduncle, the shape and faintly concave. ends of the prezygapophyses, and the left postzygapoph - Postaxial cervical vertebrae . A centrum and a neural arch of ysis (Fig. 8.12–17; Tab. 6). This neural arch is interpreted to two anterior to mid-cervical vertebrae (third to fifth cervical be an anterior to mid-cervical vertebra because the di - vertebrae) are preserved. Both vertebrae preserve the an - apophysis is short and projects ventrolaterally, very slightly terior region of the left ventral peduncle of the neural arch, over the base of the neural arch, as occurs from the third to indicating that they belong to different elements. The cen - fifth cervical vertebrae of other proterochampsids ( e.g. , trum belongs to an anterior to mid-cervical vertebra be - Tropidosuchus romeri : PVL 4601; Chanresuchus bonapartei : cause of the strong ventral development and straight profile MCZ 4037; Gualosuchus reigi : PVL 4576). The preserved an - in lateral view of the longitudinal keel (Fig. 8.7–11; Tab. 6). terior portion of the articular facet for the centrum is flat The centrum is nearly as long as tall and very slightly para - and subtriangular, with a laterally projecting apex that ex - llelogram-shaped in lateral view, as occurs in the anterior tends close to the diapophyseal facet. The diapophyseal to mid-cervical vertebrae of Proterochampsa barrionuevoi facet faces ventrolaterally and slightly anteriorly, and it is (MCZ 3408) and rhadinosuchines ( e.g. , Chanaresuchus bona - distinctly smaller than the parapophyseal facet of the cer - partei : MCZ 4037; Gualosuchus reigi : PVL 4576). By contrast, vical centrum described above. The neural arch lacks prezy - the anterior to mid-cervical vertebrae of Tropidosuchus romeri godiapophyseal and postzygodiapophyseal laminae, as are proportionally longer and more parallelogram-shaped occurs in other proterochampsids ( e.g. , Chanaresuchus bona - (PVL 4601). The anterior and posterior articular facets of the partei : MCZ 4037; Tropidosuchus romeri : PVL 4601; Gualosu - cervical centrum of CRILAR-Pv 488 are shallowly concave chus reigi : PVL 4576). The presence of anterior and posterior and suboval, being dorsoventrally taller than broad. The centrodiapophyseal laminae cannot be determined in this ventral surface of the centrum possesses a well-developed, vertebra because the region ventral to the diapophysis is sharp median keel that extends along the entire length of not preserved. The roof of the neural canal possesses a me - the bone, resembling the condition in Rhadinosuchus gracilis dian longitudinal ridge that becomes thinner posteriorly. The (SNSB-BSPG AS XXV 50), Chanaresuchus bonapartei (PULR prezygapophyses are anterodorsally oriented and broadly 07), Proterochampsa barrionuevoi (Dilkes and Arcucci 2012: separated from each other, but connected at their bases by fig. 11a −d), Tropidosuchus romeri (PVL 4601), and Gualo - a dorsally concave bony platform. The postzygapophyses

99 AMEGHINIANA - 2019 - Volume 56 (2): 79–115

Figure 8. Cervical vertebrae of CRILAR-Pv 488. 1–6, Atlantal neural arch; 7–11, anterior-middle postaxial cervical vertebra; 12–17, anterior- middle postaxial cervical neural arch; 18–19, cervical or dorsal neural spine in 1, lateral; 2, medial; 3, 10, 14, anterior; 4, 11, 15, posterior; 5, 16, dorsal; 6, 9, 17, ventral; 7, 13, 19, left lateral; 8, 12, 18, right lateral views. Abbreviations: aaf, anterior articular facet; dp, diapophysis; ep, epipophysis; f.ai , facet for atlantal intercentrum; f.ce , facet for centrum; f.oc , facet for occipital condyle; ncs , neurocentral suture; ns , neu - ral spine; pa, parapophysis; paf, posterior articular facet; posf, postspinal fossa; poz, postzygapohysis; prsf, prespinal fossa; prz, prezy - gapoph ysis; ri , ridge; str , striations; vk , ventral keel; vpe , ventral peduncle. Scale bars= 2 mm ( 1–6 ), 5 mm ( 7–19 ).

are posterolaterally projected, and their articular facet faces and is distinctly less developed than the epipophyses ventrolaterally. The dorsal surface of the single preserved pres ent in several archosauromorph lineages ( e.g. , Nesbitt, postzygapophysis possesses a very low and thick, antero - 2011; Ezcurra, 2016). The base of each postzygapophysis medially to posterolaterally oriented tuberosity. This struc - is connected to its opposite by a V-shaped lamina with a ture does not extend beyond the postzygapophyseal facet ventrally oriented apex, but this is not interpreted as a hy -

100 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

TABLE 6 – Measurements of the cervical, dorsal, sacral and caudal vertebrae of CRILAR-Pv 488 in millimetres.

Cv A Cv B D A D B D C D D S2 Ca A Ca B Ca C

Centrum length 11.8 - 15.9 15.6 16.4 16.1 15.8 16.9 15.4 15.1

Centrum anterior 11.3 - 11.4 10.2 10.2 10.4 9.4 12.6 10.0* 9.2* height Centrum anterior 9.4 - 11,9 12.6 12.7 13.8 15.6 10.7 9.6 8.9* width Centrum posterior 11.0 - 10.5* 9.7 10.6 11.0 8.2 10.8* 11.0 12.2 height Centrum posterior 8.8 - 12.3 12.3 13.0 8.5* 12.7 9.9 8.9 10.6 width Height of neural ------8.2* - 5.6* 5.6* spine Length of neural - 9.6 - - - - 16.1 - 11.3 11.4 spine at base

Maximum height 15.0* 17.4* 12.3* 11.4* 11.3* 11.0* 20.9* 16.9* 21.0* 21.8*

Length across - 17.0* - - - - 19.5 - - - zygapophyses Incomplete measurements indicated with an asterisk and the value given is the maximum measurable. Measurements were rounded to the nearest 0.1 mm.

posphene. The base of the neural spine is broad and extends terior and posterior articular facets of the centra are placed along the entire midline of the neural arch. There is no fossa at the same level ( i.e. , the centra are not parallelogram- lateral to the base of the neural spine. The prespinal fossa shaped), are shallowly concave, and wider than tall. The dor - is sub-circular and moderately large. The postspinal fossa sal surface of each centrum is deeply excavated in an is sub-oval, dorsoventrally taller than broad, and larger than anteroposteriorly oriented deep and narrow furrow. The lat - the prespinal fossa. Both prespinal and postpinal fossae are eral and ventral surfaces are smooth and transversely con - deep, invading the neural arch ventral to the base of the cave, thus the centra are spool-shaped in ventral view. neural spine. There is no lateral fossa, similar to the condition in other Four dorsal isolated centra are preserved, probably be - proterochampsids ( e.g. , Chanaresuchus bonapartei : PVL 4575, longing to mid- or posterior dorsal vertebrae because of the PVL 6244; Tropidosuchus romeri : PVL 4606; Gualosuchus reigi : absence of a distinct ventral keel, a parapophysis on the PVL 4576; Proterochampsa barrionuevoi : PVSJ 606), but in centrum, and their elongated morphology (Fig. 9). The dor - contrast with the dorsal vertebrae o f Pseudochampsa ischi - sal centra of CRILAR-Pv 488 are 1.5–1.6 times longer than gualastensis that possess a very shallow lateral fossa the height of the anterior articular facet (Tab. 6). By contrast, (Trotteyn and Ezcurra, 2014). The facets for the articulation the mid- to posterior dorsal centra are proportionally shorter with the neural arch are well preserved in the four available in other rhadinosuchine specimens, such as a specimen of dorsal centra of CRILAR-Pv 488, indicating that the neuro - Chanaresuchus bonapartei that is larger in absolute size than central suture was open in life. The facet for reception of the CRILAR-Pv 488 (PVL 6244: ratio= 1.3) and a specimen of neural arch is formed by two anteroposteriorly concave sur - Gualosuchus reigi that is smaller in absolute size than faces separated by a subtriangular lip. This facet does not CRILAR-Pv 488 (PVL 4576: ratio= 1.2). The ventral surfaces extend onto the anterior end of the centrum. of the centra possess an incipient, almost indistinguishable, There are four distal ends of neural spines that may median longitudinal ridge on their central portion. The an - be long to the dorsal or cervical series (Fig. 8.18–19). These

101 AMEGHINIANA - 2019 - Volume 56 (2): 79–115 processes have several well-developed vertical striations ticular facet (Tab. 1) , resembling the condition in a specimen adjacent to their dorsal margin, as also occurs in the cervi - of Chanaresuchus bonapartei slightly larger than CRILAR-Pv cal and dorsal vertebrae of Chanaresuchus bonapartei (MCZ 488 (PVL 6244: ratio= 1.6). The anterior and posterior ar - 4037, PULR 07, PVL 6244). tic ular surfaces of the centrum are oval, 1.5 times wider The second sacral vertebra (lacking the left postzy - than tall, and shallowly concave, which is a similar condition gapophysis and the distal end of the neural spine) (Fig. to that of Chanaresuchus bonapartei (PVL 6244: ratio= 1.3). 12.1–6; Tab. 6) and the distal portion of the left second The ventral surface of the centrum is very slightly trans - sacral rib are preserved (Fig. 12.7–12). It is interpreted as versely convex and anteroposteriorly concave and lacks a the second sacral vertebra because the facets for articula - groove or keel. Most of the lateral surface of the centrum is tion with the sacral ribs extend along most of the length of occupied by the sacral rib facet, which extends onto the the bone and the posterior articular facet of the centrum is lat eral surface of the neural arch. This facet is placed on a placed slightly ventral to the level of the anterior facet, as very low transverse process. The portion of the sacral rib occurs in the second sacral vertebrae of other rhadinosu - formed by the centrum is slightly more anteriorly and dis - chine specimens ( e.g. , Chanaresuchus bonapartei : MCZ 4035, tinctly more posteriorly developed and dorsoventrally taller PVL 6244). By contrast, the rib facet is restricted to the an - than that portion of the facet placed on the neural arch. The terior half of the vertebra and the anterior and posterior ar - rib facet is cup-shaped and is fully exposed, indicating that ticular facets of the centrum are placed at the same level in the vertebra was not co-ossified to its respective ribs. The the first sacral vertebrae of other rhadinosuchines ( e.g. , latter condition also occurs in large rhadinosuchine speci - Chanaresuchus bonapartei : MCZ 4035, PVL 6244). The cen - mens ( e.g. , Chanaresuchus bonapartei : MCZ 4035, PVL 6244), trum is 1.8 times longer than the height of its posterior ar - suggesting that if a fusion between the second sacral ver -

Figure 9. Dorsal vertebrae of CRILAR-Pv 488 in 1, 7, 13, 19, left lateral; 2, 8, 14, 20, right lateral; 3, 9, 15, 21, dorsal; 4, 10, 16, 22, ventral; 5, 11, 17, 23, anterior; 6, 12, 18, 24, posterior views. Abbreviations: f.na, facet for neural arch. Scale bar= 5 mm.

102 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION tebra and rib occurred it would have been late in the on - does not extend onto the plate-like posterolateral corner of togeny. The neurocentral suture is open on both sides. The the bone. The anterior surface of the ventrodistal end of the floor of the neural canal is deeply depressed. bone possesses a small and suboval, with a dorsoventral The neural arch lacks laminae, and the portion below main axis (6.3 mm in dorsoventral height and 3.6 mm in the neural spine is shorter than the centrum. The prezy - transverse width), articular facet for contact with the first gapophysis is positioned dorsal to the level of the trans - primordial sacral rib. The proportionally narrow first sacral verse process and is short, projecting anteriorly, slightly rib facet indicates the presence of a large space between beyond the level of the anterior margin of the centrum. The sacral ribs in dorsal and ventral views. postzygapophyseal facet is sub-circular and faces dorso - Three elements are interpreted as anterior caudal ver - medially. The postzygapophysis is also short, projecting tebrae because the transverse processes and neural spines posteriorly very slightly beyond the level of the posterior of at least two of them are well-developed (Fig. 10; Tab. 6). margin of the centrum. The postzygapophyseal facet is The two most complete caudal vertebrae are shorter than sub oval, with an anteroposterior long axis, and faces ven - the other one, thus the latter is interpreted as more poste - trolaterally. There is no prespinal fossa, and the postspinal rior in the series. The more anterior vertebrae lack most of fossa is developed as a deep, narrow vertical furrow be - the transverse processes, zygapophyses, and neural spine. tween the postzygapophyses. It cannot be determined if the The other caudal vertebra preserves the centrum and the postspinal fossa extended onto the neural spine because of left side of the base of the neural arch. The centra of the two breakage. There is no fossa lateral to the base of the neural more anterior vertebrae are 1.5 times longer than their pos - spine. The base of the neural spine is subtriangular, nar - terior height, whereas the other caudal vertebra is 1.7 times rowing anteriorly, and extends along the entire length of the longer than tall (Tab. 6). The centrum of the more posterior midline of the neural arch, projecting anteriorly between the caudal vertebra is parallelogram-shaped, with the posterior prezygapophyses. The anterior and posterior edges of the facet slightly more ventrally placed than the anterior one. base of the neural spine are broken off. The ventral rim of the anterior facet of the other two centra The sacral rib lacks its proximal end and posterodorsal is broken off, and as a result, the shape of the centrum in (Fig. 12.7–12). This bone is interpreted as a second sacral lateral view cannot be determined. The centra are moderately rib because it expands anteriorly towards the distal end, ta - compressed towards the mid-length and acquire a spool- pers posterodorsally to form a plate-like process, and an shape in ventral view. The anterior and posterior articular anteriorly facing facet to contact the preceding sacral rib. facets are concave and sub-circular to oval, slightly taller This morphology is very similar to that of the second sacral than broad. The anterior two-thirds of the ventral surface ribs of other archosauriforms ( e.g. , Teleocrater rhadinus : of the centrum are transversely convex, whereas the pos - Nes bitt et al. , 2017: fig. 10; Nundasuchus songeaensis : Nes - terior third possesses a groove that partially divides the bitt et al. , 2014: fig. 4m, n, p) and has a preserved transverse bevelling that houses the flat articular facet for the haemal width of 14.4 mm. The anterodorsal surface of the sacral rib arch. The lateral surface is very shallowly concave and in possesses two well-defined, mainly transversely oriented two of these vertebrae the surface is collapsed, but there is grooves that reach the iliac articular surface of the bone. no evidence of a distinct lateral fossa. The neurocentral su - The anterodorsal surface is dorsoventrally convex and the ture is closed in these three caudal vertebrae, suggesting posteroventral surface concave. The iliac articular surface that the sequence of closure of the suture started in the is comma-shaped, tapers posterodorsally, and has a an terior caudal region in this specimen. dorsoventral main axis. This surface is slightly convex and The neural arches lack laminae, and the transverse has an anteroposterior length of 14.7 mm and a dorsoven - processes are placed at the mid-length level of the centrum tral height of 11.0 mm. There is a low, anterodorsally-to- and the floor of the neural canal. The base of the transverse posteroventrally oriented ridge that subdivides the anterior processes is posterolaterally oriented, and their anterior half of this articular facet and is slightly ventrally displaced margin is sharper than the posterior one, as usually occurs from mid-height. The dorsal end of the iliac articular surface in other archosauriforms ( e.g. , Tropidosuchus romeri : PVL

103 AMEGHINIANA - 2019 - Volume 56 (2): 79–115

Figure 10. Anterior caudal vertebrae of CRILAR-Pv 488 in 1, 7, 13, right lateral; 2, 8, 14, left lateral; 3, 9, 15, anterior; 4, 10, 16, posterior; 5, 11, 17, dorsal; 6, 12, 18, ventral views. Abbreviations: f.ha, facet for haemal arch; ns, neural spine; poz, postzygapophysis; prsf, prespinal fossa; prz, prezygapophysis; tp, transverse process. Scale bar= 1 cm.

4601; Chanaresuchus bonapartei : PVL 4575, PVL 6244). The facet for articulation with the coracoid is well-preserved, in - base of only one prezygapophysis is preserved, and it is dicating that these two bones were not fused to each other, an terodorsally oriented. There is a change in slope of the as occurs in specimens of Chanaresuchus bonapartei (MCZ lateral surface of the neural arch between the bases of the 4035, PVL 4575), Gualosuchus reigi (PVL 4576), and Tropido - transverse process and neural spine, which defines a ventral suchus romeri (PVL 4606). By contrast, the scapula and cora - laterally facing surface and a dorsal dorsolaterally facing coid are fused to each other in specimens of Proterochampsa surface. The neural spines are transversely narrow and ex - barrionuevoi (Trotteyn, 2011b), Pseudochampsa ischigualas - tend along most of the midline of the neural arch, but they tensis (Trotteyn and Ezcurra, 2014), and the holotype of do not extend between the prezygapophyses. The anterior Gualosuchus reigi (PULR 05). The proximal end of the scapula margin of the neural spines slants posterodorsally, and is strongly posteriorly expanded, which results in a glenoid the posterior one is mainly vertical. The prespinal fossa is fossa that is placed completely posterior to the level of the shallow and defined by the bases of the prezygapophyses scapular blade if the latter is vertically oriented. In addition, and neural spine. The postspinal fossa is developed as a the main axis of the proximal margin of the bone is deflected transversely narrow furrow that extends dorsally along the approximately 30° from the main axis of the scapular blade. base of the neural spine. This combination of features also occurs in Chanaresuchus Scapula . The left scapula of CRILAR-Pv 488 is preserved in bonapartei (MCZ 4035, PVL 6244), Gualosuchus reigi (PULR two pieces lacking the mid-section of the blade (Fig. 11.1– 05), Pseudochampsa ischigualastensis (PVSJ 567), and Prote - 8; Tab. 7). The anterior region of the proximal and distal rochampsa barrionuevoi (PVSJ 606). By contrast, the glenoid ends of the bone is broken off. The posterior portion of the region is poorly posteriorly projected and the main axes of

104 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

Figure 11. Shoulder girdle and forelimb bones of CRILAR-Pv 488. 1–8, Left scapula; 9–13, probable right radius in 1, 9, lateral; 2, 12, medial; 3, 13, posterior; 4, 10, anterior; 5, 11, proximal; 6, cross-section of proximal portion around mid-length of the scapular blade; 7, cross-section of distal portion around mid-length of the scapular blade; 8, distal views. Abbreviations: acp, acromion process; f.co, facet for coracoid; gf, glenoid fossa; ms, muscle scar; ri, ridge. Scale bars= 1 cm.

TABLE 7 – Measurements of the shoulder and pelvic girdle and limb bones of CRILAR-Pv 488 in millimetres.

Length Proximal width Proximal depth Distal width Distal depth

Scapula 73.1* 14.5 24.8 3.8 22.7*

Ulna 60.8* - - 9.2 5.9

Pubis 19.2* - - - -

Ischium 33.2* 12.7 17.8 - -

Femur 59.9* - - 17.4 21.0

Tibia 92.3 14.7 27.7 8.7 21.3

Metatarsal V 23.1* 10.4 10.9 - -

Incomplete measurements indicated with an asterisk and the value given is the maximum measurable. Measurements were rounded to the nearest 0.1 mm.

the proximal margin and scapular blade are approximately bling the condition in erythrosuchids and eucrocopodan ar - parallel to each other in Tropidosuchus romeri (PVL 4601, PVL chosauriforms (Ezcurra et al. , 2019). The glenoid fossa is D- 4604) and other Permo-Triassic archosauromorphs ( e.g. , shaped, with a straight ventral margin, a convex dorsal Shringasaurus indicus , Prolacerta broomi , Proterosuchus margin, and a concave lateral margin. The medial two-thirds alexanderi , Garjainia prima , Teleocrater rhadinus , Parasuchus of the glenoid fossa are dorsoventrally concave and the hislopi ; Ezcurra et al. , 2019). The glenoid fossa of CRILAR-Pv lat eral region is transversely convex. This fossa is well de - 488 faces mainly posteriorly and slightly laterally, resem - fined dorsally by a prominent supraglenoid lip. The anterior

105 AMEGHINIANA - 2019 - Volume 56 (2): 79–115 margin of the proximal end has a very well-developed, Radius? . A slender long bone is interpreted as a probable blade-like acromion process with a semi-circular profile in right radius missing its distal end (Fig. 11.9–13; Tab. 7). This anterior view (Fig. 11: acp ), as occurs in Chanaresuchus bona - bone is too slender to be a fibula, and the preserved end is partei (MCZ 4035, PVL 6244) and Gualosuchus reigi (PULR too compressed to be interpreted as a proximal end of ulna 05). By contrast, the acromion process is absent in Tropido - or distal end of ulna or radius. The interpretation of this suchus romeri (PVL 4604). The acromion process of CRILAR- bone as a forelimb element is also bolstered by the torsion Pv 488 is approximately parallel to the main axis of the of the main axis of the bone through its length. As inter - scapular blade in lateral view and the edge of this process is preted, the cross-section of the shaft, where it is broken off, rugose, indicating the probable attachment site of the M. is sub-oval, with a posterolaterally-to-anteromedially deltoides clavicularis , similar to that of crocodylians and ori ented main axis. Towards the proximal end of the bone, Sphenodon . The lateral surface of the proximal end of the the shaft narrows anteroposteriorly, forming a longitudinal bone, between the acromion process and glenoid fossa, is ridge on the posterior surface of the bone (Fig. 11.13: ri ). As strongly anteroposteriorly concave. a result, the radius acquires a comma-shaped profile in The scapular blade is posterodorsally oriented when the proximal view, with a tapering posterior margin and a shal - articular facet for the coracoid is horizontally oriented. The lowly concave medial surface. The proximal articular surface lateral surface of the base of the scapular blade has an oval, is slightly convex. rugose muscle scar that probably indicates the attachment Pubis . The left pubis is represented by the proximal portion area of the M. triceps longus lateralis (Fig. 11.1: ms ), as seen of the shaft, including a partial pubic apron with a damaged in extant crocodylians (Meers, 2003), Sphenodon , and Iguana symphyseal margin (Fig. 12.13, 16–18; Tab. 7). The mor - (Dilkes, 2000), and some extinct archosauriforms, such as phology of this bone is very similar to that of other rhadi - Halazhaisuchus qiaoensis (Sookias et al. , 2014), Nicrosaurus nosuchines ( e.g. , Chanaresuchus bonapartei : PVL 6244). The kapffi (SMNS 4060), Batrachotomus kupferzellensis (SMNS shaft is sub-cylindrical, with a slightly wider than dorsoven - 80271), and Saurosuchus galilei (Trotteyn et al. , 2011) . How - trally tall cross-section proximally that becomes more ever, this muscle scar differs from that of the above men - dorsoventrally compressed towards the distal end. The tioned taxa in its lateral orientation and central placement pre served portion of the shaft is straight in lateral view and on the lateral surface of the bone, rather than being pos - the lateral margin is concave in dorsal view, which agrees terolaterally facing and closer to the posterior margin. The with a reduction of the transverse width of the pubis in the base of the scapular neck is oval in cross-section, with an proximal portion of the shaft. The lateral surface of the shaft anteroposterior main axis. A shallow longitudinal groove is is strongly dorsoventrally convex and the proximalmost present on the medial surface. The posterior margin of the por tion possesses a muscle scar, probably for the attach - scapular blade is narrower than the more broadly convex ment of the M. ambiens (Fig. 12.13: ms ). The pubic apron anterior margin. The distal portion of the scapular blade is rises from the dorsomedial surface of the shaft. transversely flat and D-shaped in cross-section, in which Ischium . The right ischium, lacking the distal end and ven - the lateral surface is flat and the medial one slightly an - tral margin, is preserved (Fig. 12–15, 19–22; Tab. 7). The teroposteriorly convex based on the morphology of other proximal end is transversely thick and the bone narrows rhadinosuchine specimens ( e.g. , Chanaresuchus bonapartei : to wards the distal end. The proximal end possesses lateral MCZ 4035). This distal portion of scapular blade expands and medial facets separated by a distinct change in slope. moderately anteroposteriorly towards the distal margin of The medial facet is semilunate in proximal view, with a con - the bone, with the distal expansion being around three vex medial margin, and articulated with the ischiadic pe - times the width of the base of the blade, as occurs in duncle of the ilium. The lateral facet corresponds to the Chanaresuchus bonapartei (MCZ 4035), Gualosuchus reigi acetabular fossa and is twice as transversely broader as the (PULR 05), and Tropidosuchus romeri (PVL 4604). The distal iliac facet, slightly concave, faces dorsolaterally, and has a surface of the scapula has unfinished bone, suggesting a semi-circular profile in anterolateral view. The articular cartilaginous cover or incomplete ossification. facet for the pubis is not preserved. The dorsal margin of

106 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

Figure 12. Sacrum and pelvic girdle of CRILAR-Pv 488. 1–6, Second primordial sacral vertebra; 7–12, left second primordial sacral rib; 13, 16– 18, left pubis; 14–15, 19–22, right ischium in 1, right lateral; 2, left lateral; 3, 9, 17, anterior; 4, 10, 18, posterior; 5, 11, 22, dorsal; 6, 12, 21, ventral; 7, 13, 19, lateral; 8, 20, medial; 14, proximal; 15, distal views; 16, cross-section of pubic apron. Abbreviations: aaf, anterior articular facet; ac, acetabulum; f.il, facet for ilium; f.sr1, facet for first sacral rib; f.sr2, facet for second sacral rib; ms, muscle scar; ns, neural spine; pa, pubic apron; paf , posterior articular facet; pdp , posterodorsal process; poz , postzygapophysis; prz , prezygapophysis. Scale bar= 1 cm.

the ischium is strongly concave in lateral view, as occurs in Chanaresuchus bonapartei , Gualosuchus reigi , Tropidosuchus other proterochampsids ( e.g. , Tropidosuchus romeri : PVL romeri , Proterochampsa barrionuevoi , Pseudochampsa ischi - 4601; Chanaresuchus bonapartei : MCZ 4035). The dorsal sur - gualastensis ; Trotteyn et al. , 2013). The shaft is oval in cross- face of the bone is mostly flat and lacks the shallow, longi - section, with an anteroposteriorly oriented long axis. There tudinal groove present in some specimens of Chanaresuchus is a longitudinal groove on the lateral surface. However, this bonapartei (PVL 6244). The ischial shaft narrows ventrally groove seems to be an artefact as a result of the collapse and becomes a plate-like bone, a widespread condition of cortical bone and it is not present in other rhadinosuchine among non-archosaurian archosauromorphs (Nesbitt, proterochampsids ( e.g. , Chanaresuchus bonapartei : MCZ 4035, 2011; Ezcurra, 2016). The main axis of the shaft, where it is PVL 6244; Gualosuchus reigi : PVL 4576). The shaft lacks a broken off, is rotated approximately 20° with respect to posteromedial intermuscular line ( sensu Langer, 2003). The that of the proximal end of the bone and would have al - distal end is slightly anteroposteriorly and transversely ex - lowed the medial contact of the ischium with its counter - panded, but the collapse and cracks of the cortical bone on part along the ventral margin of the elements. the distal region of the femur suggests that this element Femur . The distal half of the left femur is preserved (Fig. has been taphonomically altered. As preserved the distal 13.1–5; Tab. 7). The preserved portion of the femur curves end of the femur of CRILAR-Pv 488 is slightly anteroposte - posteriorly, and when complete it was probably a sigmoid riorly deeper than transversely broad, whereas in other element in side view, as in other proterochampsids ( e.g. , rhadinosuchine specimens the distal end of the femur has a

107 AMEGHINIANA - 2019 - Volume 56 (2): 79–115

Figure 13. Hindlimb bones of CRILAR-Pv 488. 1–5, Left femur; 6–11, tibia; 12–16, metatarsal V in 1, 7, anterior; 2, 6, posterior; 3, 8, 14, la - teral; 4, 10, distal; 5, 11, 15, medial; 9, 16, proximal; 12, dorsal; 13, ventral views. Abbreviations: cc , cnemial crest; exf , extensor fossa; f.as , facet for astragalus; fc , fibular condyle; f.dt4 , facet for distal tarsal 4; lpt , lateral plantar tubercle; mp , medial process; ms , muscle scar; plc , pos - terior lateral condyle; pmc , posterior medial condyle; pof , popliteal fossa; pp , proximal process; tc , tibial condyle; tfc , tibiofibular crest. Scale bars= 1 cm ( 1–11 ), 5 mm ( 12–16 ).

108 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION transversely oriented long axis ( Chanaresuchus bonapartei : Tibia . The left tibia is complete, but it is slightly laterally MCZ 4035, MCZ 4039, PULR 07, PVL 4575, PVL 6244; compressed by deformation (Fig. 13.6–11; Tab. 7). Both Gualosuchus reigi : PULR 05, PVL 4576; Rhadinosuchinae proximal and distal ends are anteroposteriorly expanded, indet.: UFRGS-PV-0877-T). The most lateral portion of the and their main axes slightly twisted (ca. 10°) relative to one anterior surface of the femur possesses a series of longitu - another. The proximal end is 1.5 times deeper anteropos - dinal striations that extend along 2.2 cm. The posterior sur - teriorly than the distal one (Tab. 1). The lateral condyle of face of the tibial condyle possesses a shallow, sub-oval the proximal end of the tibia is strongly anteriorly offset depression (5.7 mm long and 3.3 mm wide) with longitudi - from the medial one, as occurs in other proterochampsids nal striations that is placed 7 mm proximal to the distal sur - and several early dinosauriforms (Nesbitt, 2011; Ezcurra, face of the bone (Fig. 13.2: ms ). The relatively small size of 2016). Because of the anterior displacement of the medial this depression resembles that of other non-archosaurian condyle, the tibia acquires a sub-triangular profile in proxi - archosauriforms and pseudosuchians, but differs from the mal view. The medial condyle tapers posteriorly and the much transversely broader and proximodistally longer scar lat eral condyle is semi-circular. The cnemial crest is sub- present in avemetatarsalians (Nesbitt et al. , 2017). The rectangular, transversely broader than anteroposteriorly tib ial condyle tapers posteromedially, has a straight medial long, straight, and its anterior surface possesses a shallow margin in distal view, and its distal articular surface is an - longitudinal depression, resembling the condition in a re - teroposteriorly convex. The fibular condyle has convex ferred specimen of Chanaresuchus bonapartei (MCZ 4035) lat eral and anterior margins, with a rather sharp edge on its and the holotype of Gualosuchus reigi (PULR 05). By contrast, anterolateral corner, in distal view. The fibular condyle is the cnemial crest has a semi-circular profile in proximal view ap proximately as wide as the tibial condyle, but it has a and lacks an anterior depression in several other rhadi - more convex articular surface. The fibular condyle extends nosuchine specimens ( Chanaresuchus bonapartei : PULR 07, anteriorly distinctly beyond the level of the tibial condyle, PVL 4575; Gualosuchus reigi : PVL 4576). The medial surface resembling the condition in some rhadinosuchine speci - of the proximal end has a median depression, but it is mens ( e.g. , Chanaresuchus bonapartei : PVL 4575, PVL 6244; prob ably a taphonomical artefact as a result of the collapse Gualosuchus reigi : PVL 4576). Nevertheless, in other speci - of cortical bone. The shaft is straight in side view and mens of the same species these condyles are sub-equally slightly laterally bowed in anterior or posterior view. The anteriorly projected ( e.g. , Chanaresuchus bonapartei : MCZ cross-section of the shaft around mid-length is D-shaped, 4035, MCZ 4039, PULR 07; Gualosuchus reigi : PULR 05). The with a flat lateral margin. The tibia narrows transversely tibiofibular crest is subtriangular, posteriorly and slightly along its distal half and the width of the distal end is 0.6 laterally oriented, and placed proximal to the distal surfaces times that of the proximal end. A longitudinal groove is of the tibial and fibular condyle. The tibiofibular crest and present along the lateral surface of the distal third of the the fibular condyle are not separated by a groove, but by a tibia and opens distally to form a notch in distal view, as change in slope. The articular surface of the tibiofibular crest oc curs in other proterochampsids and dinosauromorphs is slightly convex. The popliteal fossa is proximodistally (Nesbitt, 2011; Ezcurra, 2016). The distal articular surface short, as occurs in most other archosauriforms with the ex - of the tibia is reniform, slightly convex. It is asymmetric in ception of silesaurids (Nesbitt et al. , 2010). The extensor side view, facing anterodistally, as in other rhadinosuchines fossa is shallow and broad, resembling the condition in (e.g. , Chanaresuchus bonapartei : PULR 07, PVL 4575; Gualo - other rhadinosuchines ( e.g. , Chanaresuchus bonapartei : MCZ suchus reigi : PVL 4576). The anterior region of the distal end 4035, MCZ 4039, PULR 07, PVL 4575, PVL 6244; Gualo - is transversely narrower than the posterior one. suchus reigi : PULR 05, PVL 4576; Rhadinosuchinae indet.: Metatarsal V . The left metatarsal V is preserved; it has a UFRGS-PV-0877-T). There is a clear thin ridge around the damaged dorsal surface and ventrodistal end (Fig. 13.12– perimeter of the distal end of the femur that divides the 16; Tab. 7). This metatarsal is hook-shaped in dorsal or ven - lat eral surface from the distal articular facet, which would tral view, with a gradually medially curved proximal end, be covered by cartilage capsule. resembling the condition in Euparkeria capensis (SAM-PK-

109 AMEGHINIANA - 2019 - Volume 56 (2): 79–115

K8309). The proximal articular surface is cup-shaped, with ischigualastensis lack a fifth digit (Romer, 1972b; Trotteyn et a sub-circular profile, and faces proximomedially and very al. , 2013; Trotteyn and Ezcurra, 2014). probably articulated with the convex surface of the distal tarsal 4, as in other early archosauriforms ( e.g. , Euparkeria DISCUSSION capensis : SAM-PK-K8309). The metatarsal shaft is about The two new specimens described here expand the two times longer than its proximal width (Tab. 7) and sub - knowledge about the morphology of the rhadinosuchines oval in cross-section, with a transversely oriented long axis. because several elements are very well-preserved and The ventral surface of the shaft possesses a longitudinal, completely disarticulated ( e.g. , maxilla, sacral vertebra well-developed ridge that runs adjacent to the lateral mar - and rib, scapula, tibia, metatarsal V), which is an unusual gin of the bone and it is interpreted as a lateral plantar tu - condition for members of this group from the Chañares bercle. This ridge disappears gradually in the distal third of For mation. Despite the abundance of morphological infor - the bone. The distal half of the metatarsal V broadens mation available in CRILAR-Pv 488 and CRILAR-Pv 491, nei - slightly transversely and has a shallow groove on its apex. ther could be referred to known rhadinosuchine species Between the lateral plantar tubercle and the rim of the (i.e. , Chanaresuchus bonapartei and Gualosuchus reigi sensu proximal articular surface, there is a shallow ventral de - Trotteyn et al. , 2013; Pseudochampsa ischigualastensis sensu pression. A medial plantar tubercle is absent. The distal end Trotteyn and Ezcurra, 2014; Rhadinosuchus gracilis sensu is damaged and suboval in cross-section as preserved, with Ezcurra et al. , 2015). As discussed below, the combination a transverse main axis. The presence or absence of pha - of character-states present in these two specimens con - langes in the fifth digit cannot be determined, but Tropido - flicts with those listed in the diagnoses of some rhadinosu - suchus romeri , Chanaresuchus bonapartei , and Pseudochampsa chine species.

TABLE 8 – Selected lengths of rhadinosuchine specimens from the Chañares Formation in millimetres.

Current assignment Specimen Skull Snout Maxilla Femur Tibia

R. gracilis SNSB-BSPG AS XXV 50 - 76.8 - - -

C. bonapartei PVL 4586 136 80.8 74.8 - -

Gen. et sp. indet. CRILAR-Pv 491 151.7 83.1 74.6 91.8 -

C. bonapartei MCZ 4039 162.4 87.2 79.1 - -

G. reigi PVL 4576 169 93.5 90.6 93.1 65.5

Gen. et sp. indet. UFRGS- PV-0877-T - - - 113.4 88.1

C. bonapartei PVL 4575 163 92.7 83.4 119.6 82.2

Gen. et sp. indet. CRILAR-Pv 488 - - - - 92.3

C. bonapartei MCZ 4035 - - - 126.9 96.1

C. bonapartei PULR 07 212 127.5 100.4 - 91.3

C. bonapartei PVL 6244 - - - 152.6 -

C. bonapartei MCZ 4037 243 133.4 105.7 - -

P. ischigualastensis PVSJ 567 254 147.9 136.8 154.8 128.1

G. reigi PULR 05 330 186 161 172.0 -

Specimens are approximately arranged by size and PVL 4647 was not included because does not preserve any of the measured features. Measure - ments were rounded to the nearest 0.1 mm.

110 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

Antorbital fossa on the horizontal process of the maxilla fossa that does not reach the posteroventral corner of the The two rhadinosuchine specimens described here pos - antorbital fenestra. The same character-state has been sess a horizontal process maxilla with a distinct antorbital considered previously as restricted to the small- sized type

Figure 14. Comparison between different character-states present in CRILAR-Pv 488 and CRILAR-Pv 491 with their condition in other, selected rhadinosuchine specimens. 1, Chanaresuchus bonapartei (MCZ 4039, reversed); 2, Gualosuchus reigi (PVL 4576); 3, Rhadinosuchus gracilis (SNSB- BSPG AS XXV 50); 4, Chanaresuchus bonapartei (PVL 4586); 5, Chanaresuchus bonapartei (MCZ 4037); 6, Chanaresuchus bonapartei (PULR 07); 7, Chanaresuchus bonapartei (MCZ 4035, reversed); 8, Chanaresuchus bonapartei (PVL 4575); 9, Pseudochampsa ischigualastensis (PVSJ 567). 1–5 , Skull; 6–7, tibia (lateral to the right); 8–9, dorsal osteoderms in 1, left lateral (reversed); 2–3, right lateral; 4–5, 8–9, dorsal; and 6, proximal; 7, proximal (reversed) views. Abbreviations: l.anfo, lacrimal antorbital fossa; lr, lateral ridge on jugal; m.anfo, maxillary antorbital fossa; nthp, non-tapering horizontal process; oasq, obtuse-angled squamosal; scpmc, subcircular posterior medial condyle; sostf, suboval supratemporal fenestra; stpmc, subtriangular posterior medial condyle; ststf, subtriangular supratemporal fenestra; thp, tapering horizontal process; uds, un depressed surface; Xos, X-shaped osteoderms. Scale bars= 2 cm ( 1–5 ), 5 mm ( 6–9 ).

111 AMEGHINIANA - 2019 - Volume 56 (2): 79–115 specimen of Rhadinosuchus gracilis among prote rochamp - specimens of Chanaresuchus bonapartei (MCZ 4037, MCZ sids (Ezcurra et al. , 2015) (Fig. 14.3: m.anfo ; Tab. 8). 4039, PVL 4575, PVL 4647), and in Gualosuchus reigi (PULR 05, PVL 4576) (Fig. 14.2: oasq ; Tab. 8). By contrast, the ven - Horizontal process of the maxilla tapering posteriorly tral process of the squamosal is vertical and forms a square The anterior half of the horizontal process of the maxilla angle with the anterior process in other specimens of tapers posteriorly in CRILAR-Pv 488 and Rhadinosuchus gra - Chanaresuchus bonapartei (PULR 07, PVL 4586). cilis (Ezcurra et al. , 2015) (Fig. 14.3: thp ), but it maintains the same dorsoventral height below the antorbital fenestra in Sub-oval supratemporal fenestra CRILAR-Pv 491, Pseudochampsa ischigualastensis (PVSJ Trotteyn et al. (2013) listed the presence of a narrow and 567), and small and large specimens of both Chanaresuchus axially elongated supratemporal fenestra in the diagnosis bonapartei (MCZ 4037, MCZ 4039, PULR 07, PVL 4575, PVL of Gualosuchus reigi . This condition is also present in CRILAR- 4586) and Gualosuchus reigi (PULR 05, PVL 4576) (Fig. 14.1– Pv 491 and in a small referred specimen of Chanaresuchus 2: nthp ; Tab. 8). bonapartei (PVL 4586) (Fig. 14.4: sostf ). By contrast, the supratemporal opening is subtriangular, with a broad an - Lacrimal with a well-developed, laterally exposed an - teromedial margin, in Pseudochampsa ischigualastensis (PVSJ torbital fossa 567), UFRGS PV-0877-T, and most specimens of Chanare - This character-state was optimized as a synapomorphy suchus bonapartei (MCZ 4037, MCZ 4039, PULR 07, PVL of the clade that includes Chanaresuchus bonapartei and 4575, PVL 4647; Fig. 14.5: ststf ). Rhadinosuchus gracilis (Ezcurra et al. , 2015; Ezcurra, 2016), and it also occurs in CRILAR-Pv 491 (Fig. 14.1, 3: l.anfo ). Mid-to posterior dorsal centra more than 1.5–1.6 times Nevertheless, the most lateral surface of the lacrimal grows longer than the height of the anterior articular facet anteriorly over the antorbital fossa in one of the largest Proportionally elongated middle and posterior dorsal known specimens of Chanaresuchus bonapartei (MCZ 4037; centra (with a length-to-anterior height ratio lower than Tab. 8), resembling the condition present in specimens of 1.5) are present in CRILAR-Pv 488, CRILAR-Pv 491, and Gualosuchus reigi (PULR 05, PVL 4576; Fig. 14.2: uds ). small- to medium-sized specimens of Chanaresuchus bona - partei (PVL 4575, PULR 07; Tab. 8). By contrast, these dor - Well-developed and sharp lateral ridge on jugal, ap - sal centra are proportionally shorter in large specimens of proaching the anteroventral border of the infratemporal Chanaresuchus bonapartei (PVL 6244, MCZ 4037) and a fenestra spec imen of Gualosuchus reigi (PVL 4576; Tab. 8). This condition is present in CRILAR-Pv 491, Pseudo - champsa ischigualastensis (PVSJ 567), and some specimens Medial proximal condyle of the tibia tapering posteriorly of Chanaresuchus bonapartei (MCZ 4039, PVL 4586, PVL The medial condyle of the proximal end of the tibia of 4647) (Fig. 14.1: lr ). By contrast, the jugal of Gualosuchus reigi the two new specimens is subtriangular, tapering poste - (PULR 05, PVL 4576) (Fig. 14.2: lr ) and relatively large ri orly in proximal view. This condition is also present in the specimens of Chanaresuchus bonapartei (MCZ 4037, PULR holotype and a small referred specimen of Chanaresuchus 07, PVL 4575; Tab. 8) possess a less developed lateral ridge, bonapartei (PULR 07, PVL 4575) (Fig. 14.6: stpmc ; Tab. 8) which does not approach the margin of the infratemporal and UFRGS- PV-0877-T (the tibia is here reinterpreted as a fenestra. right element), but in a large-sized specimen of Chanare - suchus bonapartei (MCZ 4035) (Fig. 14.7: scpmc ; Tab. 8) and Obtuse angle between the anterior and ventral processes in Gualosuchus reigi (PULR 05, PVL 4576) the medial proxi - of the squamosal mal condyle of the tibia is semi-circular in proximal view. The presence of this character-state occurs in CRILAR- Pv 491, Pseudochampsa ischigualastensis (Trotteyn and X-shaped middle-posterior dorsal osteoderms Ezcurra, 2014), UFRGS PV-0877-T, some small and large CRILAR-Pv 491 possesses osteoderms with a X-shaped

112 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION profile in dorsal view, closely resembling the condition pre - mal condyle of tibia; development of the lateral ridge on viously interpreted as autapomorphic of Pseudochampsa is - the jugal), but others do not seem to be ( e.g. , profile of chigualastensis (Trotteyn et al. , 2012; Trotteyn and Ezcurra, supratemporal fenestra; angle between the anterior and 2014) (Fig. 14.9). Nevertheless, the osteoderms of the new ventral processes of the squamosal). In addition, the com - specimen differ from those of Pseudochampsa ischigualas - bination of character-states present in the two new speci - tensis in the absence of a longitudinal groove on the exter - mens described here is not completely consistent with that nal surface. The single preserved complete osteoderm of of any of the rhadinosuchine species. Thus, CRILAR-Pv 488 Rhadinosuchus gracilis is subrectangular in dorsal view, being and CRILAR-Pv 491 reveal an unexpected increase of the wider transversely than long anteroposteriorly (Ezcurra et morphological diversity of the rhadinosuchines of the Cha - al. , 2015). However, this osteoderm probably belongs to the ñares Formation. In addition, we found that the morphology anterior cervical series and the same morphology occurs in of at least some specimens of Chanaresuchus bonapartei , the osteoderms of this region of the axial skeleton in Chana - such as PVL 4586, is congruent with the list of character- resuchus bonapartei (PVL 4575). Trotteyn et al. (2013) listed states in the most recent diagnosis of Gualosuchus reigi the presence of wedge-shaped osteoderms, narrow anteri - pro posed by Trotteyn et al. (2013). As a result, based on the orly and broader posteriorly, as an autapomorphy of Chana - analysis presented here, we consider that the taxonomy of resuchus bonapartei and the presence of oval osteoderms as the currently known rhadinosuchine specimens should be part of the diagnosis of Gualosuchus reigi . The contour of the revised, an issue that goes beyond the scope of this paper. osteoderms of the rhadinosuchines is usually difficult to The proposed revision should test whether the holotypes of de termine if their anterior region is overlapped by their pre - Chanaresuchus bonapartei and Gualosuchus reigi can be dis - ceding osteoderm. The complete shape of the osteoderms tinguished from each other based on unique combinations can be determined if some elements are broken or disar - of character-states, or if they are individuals on opposite ticulated in the row. The latter occurs in a referred speci - extremes of a single ontogenetic trajectory. Otherwise, if men of Chanaresuchus bonapartei (PVL 4575), and the the latter hypothesis is rejected, it seems to be clear anyway outline of some middle-posterior dorsal osteoderms is X- that the current diagnoses of the rhadinosuchine species shaped in dorsal view, with a V-shaped anterior region (with seem to fail to account for the morphological diversity ob - lateral margins diverging anteriorly) that is usually covered served in the specimens of the group. Beyond these two by the preceding osteoderm (Fig. 14.8: Xos ), as occurs in scenarios, the information presented here shows that mul - CRILAR-Pv 491. tiple polymorphisms are present among the rhadinosuchine proterochampsids. Such a comprehensive revision of the Possible taxonomic implications rhadinosuchine taxonomy should consider the new anatom - The nine characters discussed above are intraspecifically ical information that became available in recent years and a variable within Rhadinosuchinae ( e.g. , maxilla with tapering detailed revision of historical specimens, with a careful horizontal process; lacrimal with a well-developed, laterally reappraisal of the intraspecific variation (ontogenetically re - exposed antorbital fossa; jugal with well-developed and lated and not) that may occur in the species of the clade, as sharp lateral ridge; squamosal with obtuse angle between well as the post-mortem deformation that affected speci - the anterior and ventral processes; middle-posterior dorsal mens in different ways. centra anteroposterior elongation; tibia with medial proxi - mal condyle tapering posteriorly), more widespread in the CONCLUSIONS clade than previously thought (maxilla with antorbital fossa We described two new rhadinosuchine specimens from on the horizontal process; X-shaped middle-posterior dor - the lower Carnian beds of the Chañares Formation in north - sal osteoderms), or both (sub-oval supratemporal fenestra). western Argentina. These new specimens provide novel Some intraspecific polymorphisms seem to be size-related anatomical information for the group and possess a combi - (e.g. , middle-posterior centra becoming proportionally nation of character-states previously unknown in other shorter towards somatic maturity; profile of medial proxi - rhadinosuchines. These new morphotypes result in a con -

113 AMEGHINIANA - 2019 - Volume 56 (2): 79–115 flicting mosaic of features—some of them previously con - reptiles. Philosophical Transactions of the Royal Society of London B 353: 501 541. sidered as diagnostic at species level—if we follow current − Dilkes, D.W. 2000. Appendicular mycology of the hadrosaurian di - taxonomic schemes (see Trotteyn et al. , 2013). We conclude nosaur Maiasaura peeblesorum from the Late Cretaceous (Cam - that the rhadinosuchine taxonomy should be revised on the panian) of Montana. Transactions of the Royal Society of Edinburgh, Earth Sciences 90: 87–125. light of the information presented here, along with a care - Dilkes, D.W., and Sues, H-D. 2009. Redescription and phylogenetic ful reappraisal of the intraspecific variation that may occur relationships of Doswellia kaltenbachi (Diapsida: Archosauri - formes) from the Upper Triassic of Virginia. Journal of Vertebrate in the clade and taphonomic artefacts that may affect in - Paleontology 29: 58 −79. terpretation of anatomical features. The hypothesis that Dilkes, D.W., and Arcucci, A. 2012. Proterochampsa barrionuevoi (Ar chosauriformes: Proterochampsia) from the Late Triassic Chanaresuchus bonapartei and Gualosuchus reigi correspond (Carnian) of Argentina and a phylogenetic analysis of Prote - to extremes of a single ontogenetic trajectory should be rochampsia. Palaeontology 55: 1–33. tested, and the alpha taxonomic richness of the rhadi - Ezcurra, M.D. 2016. The phylogenetic relationships of basal ar - chosauromorphs, with an emphasis on the systematics of pro - nosuchines should be reconsidered. In any case, it seems terosuchian archosauriforms. PeerJ 4: e1778. that the evolution of the rhadinosuchine proterochampsids Ezcurra, M.D., Scheyer, T.M., and Butler, R.J. 2014. The origin and early evolution of Sauria: reassessing the Permian saurian fossil was characterized by high levels of homoplasy, which could record and the timing of the crocodile-lizard divergence. PLoS be a result of high evolutionary rates or the presence of ONE 9: e89165. Ezcurra, M.D., Desojo, J.B., and Rauhut, O.W.M. 2015. Redescription longer ghost lineages than previously thought. and phylogenetic relationships of the proterochampsid Rhadi - nosuchus gracilis (Diapsida: Archosauriformes) from the early ACKNOWLEDGMENTS Late Triassic of southern Brazil. Ameghiniana 52: 391 −417. We thank the Secretaría de Cultura de La Rioja and the Adminis - Ezcurra, M.D., Fiorelli, L.E., Martinelli, A.G., Rocher, S., von Baczko, tración de Parques Nacionales for granting permits to work in the M.B., Ezpeleta, M., Taborda, J.R., Hechenleitner, E.M., Trotteyn, Talampaya National Park, the field crews of 2011—the year in M.J., and Desojo, J.B. 2017. Deep faunistic turnovers preceded which the specimens studied here were collected—and the rangers the rise of dinosaurs in southwestern Pangaea. Nature Ecology of the National Park for their help in the field. We thank the following & Evolution 1: 1477. curators, researchers, and collection managers that provided access Ezcurra, M.D., Gower, D.J., Sennikov, A.G., and Butler, R.J. 2019 . The to specimens under their care for the purpose of this research: M. osteology of the holotype of the early erythrosuchid Garjainia Moser and O. Rauhut (SNSB-BSPG); L. Fiorelli (CRILAR); J. Cundiff prima Ochev, 1958 (Diapsida: Archosauromorpha) from the (MCZ); E. Vaccari and G. Cisterna (PULR); J. Powell † and P. Ortiz (PVL); upper Lower Triassic of European Russia. Zoological Journal of R. Martínez (PVSJ); S. Kaal and R. Smith (SAM-PK); R. Schoch the Linnean Society 185: 717–783. (SMNS); and C.L. Schultz (UFRGS). CRILAR-Pv 488 was prepared by Gauthier, J.A., Kluge, A.G., and Rowe, T. 1988. Amniote phylogeny S. Reuil and CRILAR-Pv 491 was prepared by J. Kaluza. Scanning and the importance of fossils. Cladistics 4: 105 −209. electronic microscope photographs were taken by F. Tricárico at the Hoffstetter, R. 1955. Thecodontia. In: J. Piveteau (Ed.), Traité de MACN. We thank A. Arcucci, an anonymous reviewer, and the editor Paléontologie, Vol. 5: Amphibiens, Reptiles, Oiseaux . Masson et J. Wilson for their comments and suggestions, which improved the Cie, Paris, p. 665 −694. final version of the manuscript. This research was funded by the Hsiou, A.S., Abdala, F., and Arcucci, A. 2002. Novo registro de pro - Agencia Nacional de Investigaciones Científicas y Técnicas (PICT terocampsídeo (Reptilia-Archosauriformes) do Triássico médio– 2012-0925 and PICT 2014-0609 to J.B.D.) and Universidad Nacional superior do Brasil. Revista Brasileira de Paleontologia 3: 48–55. de San Juan (PROJOVI, and CICITCA UNSJ-SECITI to M.J.T.). Huene, F. von. 1938. Die fossilen Reptilien des südamerikanischen Gondwanalandes. Neues Jahrbuch für Mineralogie, Geologie und REFERENCES Paläontologie. Abteilung B 1938: 142 −151. Arcucci, A.B. 1990. Un nuevo Proterochampsidae (Reptilia-Archo - Huene, F. von. 1946. Die grossen Stämme der Tetrapoden in den sauriformes) de la fauna local de Los Chañares (Triasico Medio), geologischen Zeiten. Biologisches Zentralblatt 65: 268 −275. La Rioja, Argentina. Ameghiniana 27: 365 −378. Juul, L. 1994. The phylogeny of basal archosaurs. Palaeontologia Barberena, M.C. 1982. Uma nova espécie de Proterochampsa , P. no - Africana 31: 1–38. dosa sp. nov. do Triássico do Brasil. Anais da Academia Brasileira Kischlat, E-E. 2000. Tecodôncios: a aurora dos arcossáurios no de Ciências 54: 127 −141. Triássico. In: M. Holz, and L.F. De Ross (Eds.), Paleontologia do Benton, M.J., and Clark, J.M. 1988. Archosaur phylogeny and the re - Rio Grande do Sul . Universidade Federal do Rio Grande do Sul, lationships of the Crocodylia. In: M.J. Benton (Ed.), The phylogeny Porto Alegre, p. 273 −316. and classification of the Tetrapods. Volume 1. Amphibians, Rep - Langer, M.C. 2003. The pelvic and hindlimb anatomy of the stem- tiles, and Birds . Clarendon Press, Oxford, p. 295–338. sauropod Saturnalia tupiniquim . PaleoBios 23: 1 −40. Desojo, J.B., Ezcurra, M.D., and Schultz, C.L. 2011. An unusual new Laurin, M. 1991. The osteology of a Lower Permian eosuchian from archosauriform from the Middle −Late Triassic of southern Texas and a review of diapsid phylogeny. Zoological Journal of Brazil and the monophyly of Doswelliidae. Zoological Journal of the Linnean Society 101: 59 −95. the Linnean Society 161: 839 −871. Mancuso, A.C., Gaetano, L.C., Leardi, J.M., Abdala, F., and Arcucci, Dilkes, D.W. 1998. The Early Triassic rhynchosaur Mesosuchus A.B. 2014. The Chañares Formation: a window to a Middle browni and the interrelationships of basal archosauromorph Tri assic tetrapod community. Lethaia 47: 244–265.

114 EZCURRA ET AL .: NEW RHADINOSUCHINE SPECIMENS FROM THE CHAÑARES FORMATION

Meers, M.B. 2003. Crocodylian forelimb musculature and its rele - Sereno, P.C. 1991. Basal archosaurs: phylogenetic relationships and vance to Archosauria. The Anatomical Record 274A: 891–916. functional implications. Society of Vertebrate Paleontology Nesbitt, S.J. 2011. The early evolution of archosaurs: relationships Mem oir 2: 1 –53. and the origin of major clades. Bulletin of the American Museum Sereno, P.C., and Arcucci, A.B. 1990. The monophyly of crurotarsal of Natural History 352: 1 −292. archosaurs and the origin of bird and crocodile ankle joints. Nesbitt, S.J., Sidor, C.A., Irmis, R.B., Angielczyk, K.D., Smith, R.M.H., Neues Jahrbuch für Geologie und Paläontologie Abhandlungen 180: and Tsuji, L.A. 2010. Ecologically distinct dinosaurian sister- 21 –52. group shows early diversification of Ornithodira. Nature 464: Sill, W.D. 1967. Proterochampsa barrionuevoi and the early evolution 95 −98. of the Crocodilia. Bulletin of the Museum of Comparative Zoology Nesbitt, S.J., Sidor, C.A., Angielczyk, K.D., Smith, R.M.H., and Tsuji, 135: 415–446. L.A. 2014. A new archosaur from the Manda beds (Anisian, Sookias, R.B., Sullivan, C., Liu, J., and Butler, R.J. 2014. Systematics Mid dle Triassic) of southern Tanzania and its implications for of putative euparkeriids (Diapsida: Archosauriformes) from the character state optimizations at Archosauria and Pseudosuchia. Triassic of China. PeerJ 2: e658. Journal of Vertebrate Paleontology 34: 1357 −1382. Trotteyn, M.J. 2011a. The phylogenetic relationships and mono - Nesbitt, S.J., Flynn, J.J., Pritchard, A.C., Parrish, J.M., Ranivohari - phyly of Proterochampsidae. IV Congreso Latinoamericano de Pa - manana, L., and Wyss, A.R. 2015. Postcranial anatomy and re - leontología de Vertebrados (San Juan), Actas : 224. lationships of Azendohsaurus madagaskarensis . Bulletin of the Trotteyn, M.J. 2011b. Material postcraneano de Proterochampsa ba - American Museum of Natural History 398: 1 −126. rrionuevoi Reig, 1959 (Diapsida: Archosauriformes) del Triásico Nesbitt, S.J., Butler, R.J., Ezcurra, M.D., Barrett, P.M., Stocker, M.R., Superior del centro-oeste de Argentina. Ameghiniana 48: 424 – Angielczyk, K.D., Smith R.M.H., Sidor, C.A., Nied źwiedzki, G., 446. Sennikov, A.G., and Charig, A.J. 2017. The earliest bird-line ar - Trotteyn, M.J., and Haro, J.A. 2010. The braincase of a specimen of chosaurs and the assembly of the dinosaur body plan. Nature Proterochampsa Reig (Archosauriformes: Proterochampsidae) 544: 484–487. from the Late Triassic of Argentina. Paläntologische Zeitschrift Osborn, H.F. 1903. The reptilian subclasses Diapsida and Synap - 85: 1–17. sida and the early history of the Diaptosauria. Memoirs of the Trotteyn, M.J., and Haro, J.A. 2012. The braincase of Chanaresuchus American Museum of Natural History 1: 449 −519. ischigualastensis (Archosauriformes) from the Late Triassic of Parrish, J.M. 1993. Phylogeny of the Crocodylotarsi, with reference Argentina. Journal of Vertebrate Paleontology 32: 867 –882. to archosaurian and crurotarsan monophyly. Journal of Verte - Trotteyn, M.J., and Ezcurra, M.D. 2014. Osteology of Pseudo - brate Paleontology 13: 287–308. champsa ischigualastensis gen. et comb. nov. (Archosauri - Price, L.I. 1946. Sobre um novo pseudosuquio do Triássico Superior formes: Proterochampsidae) from the early Late Triassic do Rio Grande do Sul. Boletim Divisão de Geología e Mineralogía Ischigualasto Formation of northwestern Argentina. PLoS ONE 120: 1 −38. 9: e111388. Raugust, T., Lacerda, M., and Schultz, C.L. 2013. The first occurrence Trotteyn, M.J., Arcucci, A.B., and Raugust, T. 2013. Proterochampsia : of Chanaresuchus bonapartei Romer 1971 (Archosauriformes, an endemic archosauriform clade from South America. Geological Proterochampsia) of the Middle Triassic of Brazil from the San - Society, Special Publication 379: 59 –90. tacruzodon Assemblage Zone, Santa Maria Formation (Paraná Trotteyn, M.J., Desojo, J.B., and Alcober, O.A. 2011. Nuevo material Basin). Geological Society, Special Publication 379: 303 −318. postcraneano de Saurosuchus galilei Reig (Archosauria: Cruro - Reig, O.A. 1959. Primeros datos descriptivos sobre nuevos reptiles tarsi) del Triásico Superior del centro-oeste de Argentina. arcosaurios del Triásico de Ischigualasto (San Juan, Argentina). Ameghiniana 48: 13–27. Revista de la Asociación Geológica Argentina 13: 257 –270. Trotteyn, M.J., Martínez, R.N., and Alcober, O.A. 2012. A new prote - Rogers, R.R., Arcucci, A.B., Abdala, F., Sereno, P.C., and May, C.L. rochampsid Chanaresuchus ischigualastensis (Diapsida, Ar - 2001. Paleoenvironment and taphonomy of the Chañares For - chosauriformes) in the Early Late Triassic Ischigualasto mation tetrapod assemblage (Middle Triassic), northwestern Formation, Argentina. Journal of Vertebrate Paleontology 32: Argentina: spectacular preservation in volcanogenic concre - 485 –489. tions. Palaios 16: 461–481. Romer, A.S. 1956. Osteology of the reptiles . University of Chicago Press, Chicago, 772 p. Romer, A.S. 1966. The Chãnares (Argentina) Triassic reptile fauna: I. Introduction. Breviora 247: 1–14. Romer, A.S. 1971. The Chañares (Argentina) Triassic reptile fauna. XI: Two new long –snouted thecodonts, Chanaresuchus and Gualosuchus . Breviora 379: 1 –22. Romer, A.S. 1972a. The Chañares (Argentina) Triassic reptile fauna. doi: 10.5710/AMGH.25.05.2019.3230 XIII. An early ornithosuchid pseudosuchian, Gracilisuchus sti - panicicorum , gen. et sp. nov. Breviora 389: 1–24. th Romer, A.S. 1972b. The Chañares (Argentina) Triassic reptile fauna. Submitted: September 25 , 2018 th XII. The postcranial skeleton of the thecodont Chanaresuchus . Accepted: April 25 , 2019 Breviora 385: 1–21. Published online: June 9 th , 2019

115

View publication stats