Figure 13. Paramedian osteoderms of Archeopelta. A, articulated left row and right row in B, dors... more Figure 13. Paramedian osteoderms of Archeopelta. A, articulated left row and right row in B, dorsal and F, lateral views. Both rows in E, anterior and G, ventral views. C–D, close up of the first osteoderm of the left row in dorsal view. Abbreviations: aaf, anterior articular facet; ns, neural spine; p, pit; se, collateral serrations. Scale bar = 2 cm.
Figure 9. First primordial sacral vertebra of Archeopelta in A, anterior; B, dorsal; and C, poste... more Figure 9. First primordial sacral vertebra of Archeopelta in A, anterior; B, dorsal; and C, posterior views; and second primordial sacral in D, dorsal view. Abbreviations: hyp, hyposphene; nc, neural canal; ns, neural spine; os, osteoderm; poz, postzygapophysis; prz, prezygapophysis; sr, sacral rib; tp, transverse process; vc, vertebral centrum. Scale bar = 2 cm.
FIGURE 16. Right pes of Aetobarbakinoides brasiliensis in proximal (A), dorsal (B), ventral (C), ... more FIGURE 16. Right pes of Aetobarbakinoides brasiliensis in proximal (A), dorsal (B), ventral (C), lateral (D), medial (E), and distal (F) views. Abbreviations: I-V, metatarsal I-V; clf, collateral fossa. Scale bar equals 2 cm.
FIGURE 15. Right distal tarsal IV of Aetobarbakinoides brasiliensis in dorsal (A), ventral (B), l... more FIGURE 15. Right distal tarsal IV of Aetobarbakinoides brasiliensis in dorsal (A), ventral (B), lateral (C), medial (D), proximal (E), and distal (F) views. Scale bar equals 1 cm.
FIGURE 14. Right pes of Aetobarbakinoides brasiliensis in dorsal view. Abbreviations: IV-1, first... more FIGURE 14. Right pes of Aetobarbakinoides brasiliensis in dorsal view. Abbreviations: IV-1, first pedal phalanx of the fourth digit; dtIV, disal tarsal IV; mttI-V, metatarsal I-V. Scale bar equals 2 cm.
FIGURE 5. Last cervical and three first dorsal vertebrae of Aetobarbakinoides brasiliensis in lef... more FIGURE 5. Last cervical and three first dorsal vertebrae of Aetobarbakinoides brasiliensis in left lateral (A), ventral (B), right lateral (C), and posterior (D) views; and last cervical rib of Aetobarbakinoides brasiliensis in posterior view (E). Abbreviations: cn, centrum; cp, capitulum; dp, diapophysis; hy, hyposphene; os, osteoderms; poz, postzygapophysis; pp, parapophysis; tb, tuberculum. Scale bar equals 2 cm.
The postcranial skeleton of Neoaetosauroides (Archosauria: Aetosauria) from the Upper Triassic of... more The postcranial skeleton of Neoaetosauroides (Archosauria: Aetosauria) from the Upper Triassic of west-central Argentina . The postcranial skeleton of the aetosaur Neoaetosauroides Bonaparte, based on previously studied specimens and additional material, is described herein. The new material consists of proatlas, cervical vertebrae, and appendicular dermal scutes collected in the Los Colorados Formation, Ischigualasto-Villa Unión Basin. All these materials are compared with those of other aetosaur taxa and functionally significant characters of the pelvic girdle and hindlimbs are in particular discussed. This study reveals a great anatomical diversity (e.g. , differences in degree of pelvic expansion, femoral flexure, and crural and tarsal morphology) and suggests that Aetosauria might have included semi-erect and erect forms. This possible spectrum of locomotor postures, together with their wide size range, support previous propositions of more varied lifestyles among aetosaurs tha...
Aetosauroides scagliai, from the Ischigualasto Formation of Argentina and Santa Maria Supersequen... more Aetosauroides scagliai, from the Ischigualasto Formation of Argentina and Santa Maria Supersequence of Brazil (Carnian-Norian), is one of the oldest members of Aetosauria, a diverse clade of armored crocodile-line archosaurs. Aetosauroides scagliai differs from other aetosaurs in having the maxilla excluded from the margin of the external nares, the length/width ratio of the postzygapophyses ≤ 0.75, and other features that place it as one of the earliest-diverging members of the clade. In this paper we provide a detailed description of the skull of A. scagliai based on a new Brazilian specimen, revealing that it lacks a pneumatic cavity on the medial surface of the maxilla and further differs from all other known aetosaurs by the presence of ≥ 12 dentary teeth. However, contra previous studies, the elongated posterior process of the jugal does articulate ventrally with the quadratojugal in A. scagliai, forming the posteroventral corner of the skull as in all other aetosaurs. Aetosauroides scagliai exhibits some characters typical of predatory archosaurs (like the recurved ziphodont teeth and mandibular articulation at the level of the tooth row), but was probably an omnivore, as it also shares several probable adaptations for herbivory with aetosaurs generally (i.e., edentulous anterior premaxilla and dentary) and stagonolepidoids specifically (e.g., shovel-shaped snout). This suggests that there was greater trophic diversity in this clade than usually recognized, at least early in their evolutionary history.
Ornithosuchidae is a group of terrestrial quadrupedal pseudosuchian archosaurs from the Late Tria... more Ornithosuchidae is a group of terrestrial quadrupedal pseudosuchian archosaurs from the Late Triassic of South America and Europe. Riojasuchus tenuisceps is arguably one of the best representative species of this clade because it comprises very well-preserved three-dimensional, almost complete skeletons. However, R. tenuisceps was originally described 50 years ago and compared then only with Ornithosuchus woodwardi and their affinities were discussed in detail. Here, we provide a detailed description of the postcranial skeleton of R. tenuisceps, which exhibits several remarkable features within pseudosuchians. When a wide spectrum of pseudosuchian archosaurs are considered, the alleged character that linked ornithosuchids with dinosaurs resulted in convergences and some were registered in other pseudosuchian groups as well. Riojasuchus tenuisceps also provided crucial information about the 'crocodile-reversed' tarsus, which is a unique feature of ornithosuchids, but it is not completely preserved in O. woodwardi and it is unknown in Venaticosuchus rusconii. In addition, the first histological analysis of cervical and dorsal osteoderms of R. tenuisceps was carried out as well, in order to test the utility of these structures as skeletochronological tools. Finally, the phylogenetic context of Ornithosuchidae is discussed based on the latest phylogenetic studies, which show a close affinity with Erpetosuchidae.
Ornithosuchidae is one of the most enigmatic clades of Triassic pseudosuchians. The group is comp... more Ornithosuchidae is one of the most enigmatic clades of Triassic pseudosuchians. The group is composed by three carnivorous species that were excavated from Upper Triassic beds of Scotland and Argentina. We describe the first ornithosuchid from the Upper Triassic sediments of Brazil and explore its phylogenetic affinities and implications for the evolution of the group. Dynamosuchus collisensis gen. et sp. nov. was found as the sister taxon of the Argentinean form Venaticosuchus rusconii. These relationships reject a potential endemic radiation of ornithosuchids from the Ischigualasto-Villa Unión Basin and would better support multiple diversification events. Our findings with ornithosuchids is consistent with the pattern reported for proterochampsid and erpetosuchid archosauriforms from Ischigualasto-Villa Unión and the Paraná basins. In addition, the presence of an ornithosuchid in the Late Triassic of Brazil suggests that ornithosuchids were more widespread than previously thought in the southern hemisphere. The new ornithosuchid further demonstrates a faunistic link between the Argentinean and Brazilian basins during the Carnian. Finally, the discovery of the new species provides the first clue of a putative necrophagous vertebrate from the oldest dinosaur-bearing beds and expands our knowledge regarding the trophic structure of the Late Triassic of Brazil.
The paleoneuroanatomy of pseudosuchian archosaurs is poorly known, based on direct examination of... more The paleoneuroanatomy of pseudosuchian archosaurs is poorly known, based on direct examination of the internal morphology of braincases and a few artificial endocasts. Among aetosaurs, only one endocast has been described almost a century ago by Case (1921) corresponding to Desmatosuchus spurensis from the Chinle Formation (Norian) of Texas, US, based on a resin cast. Here, we describe the first natural endocast of an aetosaur, Neoaetosauroides engaeus from the Los Colorados Formation (Norian) of NW Argentina, and also developed the first digital endocast of this taxon including the encephalon, cranial nerves, inner ear, and middle ear sinuses. The neuroanatomy of Neoaetosauroides engaeus exhibits several differences from that of Desmatosuchus spurensis despite their phylogenetic proximity, which may be a reflection of their different habits. The information provided by the endocasts of Neoaetosauroides engaeus about its olfactory region and the orientation of its head, based on the...
We describe the new aetosaur Aetobarbakinoides brasiliensis gen. et sp. nov. from the early Late ... more We describe the new aetosaur Aetobarbakinoides brasiliensis gen. et sp. nov. from the early Late Triassic (late Carnian-early Norian) Brazilian Santa Maria Formation. The holotype is composed of a partial postcranium including several cer-vical and dorsal vertebrae and ribs, one anterior caudal vertebra, right scapula, right humerus, right tibia, partial right pes,and anterior and mid-dorsal paramedian osteoderms. Aetobarbakinoides is differentiated from other aetosaurs by the pres-ence of cervical vertebrae with widely laterally extended prezygapophyses, mid-cervical vertebrae with anterior articularfacet width more than 1.2 times wider than the posterior one, anterior caudal vertebrae with extremely anteroposteriorlyshort prezygapophyses, elongated humerus and tibia in relation to the axial skeleton, and paramedian osteoderms with aweakly raised anterior bar. A cladistic analysis recovered the new species as more derived than the South American generaAetosauroides (late Carnian-ea...
Riojasuchus tenuisceps Bonaparte 1967 is currently known from four specimens, including two compl... more Riojasuchus tenuisceps Bonaparte 1967 is currently known from four specimens, including two complete skulls, collected in the late 1960s from the upper levels of the Los Colorados Formation (Late Triassic), La Rioja, Argentina. Computed tomography (CT) scans of the skulls of the holotype and a referred specimen of Riojasuchus tenuisceps and the repreparation of the latter allows recognition of new features for a detailed analysis of its cranial anatomy and its comparison with a wide variety of other archosauriform taxa. The diagnosis of Riojasuchus tenuisceps is emended and two autapomorphies are identified on the skull: (1) a deep antorbital fossa with its anterior and ventral edges almost coinciding with the same edges of the maxilla itself and (2) a suborbital fenestra equal in size to the palatine-pterygoid fenestra. Also, the first digital 3D reconstruction of the encephalon of Riojasuchus tenuisceps was carried out to study its neuroanatomy, showing a shape and cranial nerve d...
Figure 13. Paramedian osteoderms of Archeopelta. A, articulated left row and right row in B, dors... more Figure 13. Paramedian osteoderms of Archeopelta. A, articulated left row and right row in B, dorsal and F, lateral views. Both rows in E, anterior and G, ventral views. C–D, close up of the first osteoderm of the left row in dorsal view. Abbreviations: aaf, anterior articular facet; ns, neural spine; p, pit; se, collateral serrations. Scale bar = 2 cm.
Figure 9. First primordial sacral vertebra of Archeopelta in A, anterior; B, dorsal; and C, poste... more Figure 9. First primordial sacral vertebra of Archeopelta in A, anterior; B, dorsal; and C, posterior views; and second primordial sacral in D, dorsal view. Abbreviations: hyp, hyposphene; nc, neural canal; ns, neural spine; os, osteoderm; poz, postzygapophysis; prz, prezygapophysis; sr, sacral rib; tp, transverse process; vc, vertebral centrum. Scale bar = 2 cm.
FIGURE 16. Right pes of Aetobarbakinoides brasiliensis in proximal (A), dorsal (B), ventral (C), ... more FIGURE 16. Right pes of Aetobarbakinoides brasiliensis in proximal (A), dorsal (B), ventral (C), lateral (D), medial (E), and distal (F) views. Abbreviations: I-V, metatarsal I-V; clf, collateral fossa. Scale bar equals 2 cm.
FIGURE 15. Right distal tarsal IV of Aetobarbakinoides brasiliensis in dorsal (A), ventral (B), l... more FIGURE 15. Right distal tarsal IV of Aetobarbakinoides brasiliensis in dorsal (A), ventral (B), lateral (C), medial (D), proximal (E), and distal (F) views. Scale bar equals 1 cm.
FIGURE 14. Right pes of Aetobarbakinoides brasiliensis in dorsal view. Abbreviations: IV-1, first... more FIGURE 14. Right pes of Aetobarbakinoides brasiliensis in dorsal view. Abbreviations: IV-1, first pedal phalanx of the fourth digit; dtIV, disal tarsal IV; mttI-V, metatarsal I-V. Scale bar equals 2 cm.
FIGURE 5. Last cervical and three first dorsal vertebrae of Aetobarbakinoides brasiliensis in lef... more FIGURE 5. Last cervical and three first dorsal vertebrae of Aetobarbakinoides brasiliensis in left lateral (A), ventral (B), right lateral (C), and posterior (D) views; and last cervical rib of Aetobarbakinoides brasiliensis in posterior view (E). Abbreviations: cn, centrum; cp, capitulum; dp, diapophysis; hy, hyposphene; os, osteoderms; poz, postzygapophysis; pp, parapophysis; tb, tuberculum. Scale bar equals 2 cm.
The postcranial skeleton of Neoaetosauroides (Archosauria: Aetosauria) from the Upper Triassic of... more The postcranial skeleton of Neoaetosauroides (Archosauria: Aetosauria) from the Upper Triassic of west-central Argentina . The postcranial skeleton of the aetosaur Neoaetosauroides Bonaparte, based on previously studied specimens and additional material, is described herein. The new material consists of proatlas, cervical vertebrae, and appendicular dermal scutes collected in the Los Colorados Formation, Ischigualasto-Villa Unión Basin. All these materials are compared with those of other aetosaur taxa and functionally significant characters of the pelvic girdle and hindlimbs are in particular discussed. This study reveals a great anatomical diversity (e.g. , differences in degree of pelvic expansion, femoral flexure, and crural and tarsal morphology) and suggests that Aetosauria might have included semi-erect and erect forms. This possible spectrum of locomotor postures, together with their wide size range, support previous propositions of more varied lifestyles among aetosaurs tha...
Aetosauroides scagliai, from the Ischigualasto Formation of Argentina and Santa Maria Supersequen... more Aetosauroides scagliai, from the Ischigualasto Formation of Argentina and Santa Maria Supersequence of Brazil (Carnian-Norian), is one of the oldest members of Aetosauria, a diverse clade of armored crocodile-line archosaurs. Aetosauroides scagliai differs from other aetosaurs in having the maxilla excluded from the margin of the external nares, the length/width ratio of the postzygapophyses ≤ 0.75, and other features that place it as one of the earliest-diverging members of the clade. In this paper we provide a detailed description of the skull of A. scagliai based on a new Brazilian specimen, revealing that it lacks a pneumatic cavity on the medial surface of the maxilla and further differs from all other known aetosaurs by the presence of ≥ 12 dentary teeth. However, contra previous studies, the elongated posterior process of the jugal does articulate ventrally with the quadratojugal in A. scagliai, forming the posteroventral corner of the skull as in all other aetosaurs. Aetosauroides scagliai exhibits some characters typical of predatory archosaurs (like the recurved ziphodont teeth and mandibular articulation at the level of the tooth row), but was probably an omnivore, as it also shares several probable adaptations for herbivory with aetosaurs generally (i.e., edentulous anterior premaxilla and dentary) and stagonolepidoids specifically (e.g., shovel-shaped snout). This suggests that there was greater trophic diversity in this clade than usually recognized, at least early in their evolutionary history.
Ornithosuchidae is a group of terrestrial quadrupedal pseudosuchian archosaurs from the Late Tria... more Ornithosuchidae is a group of terrestrial quadrupedal pseudosuchian archosaurs from the Late Triassic of South America and Europe. Riojasuchus tenuisceps is arguably one of the best representative species of this clade because it comprises very well-preserved three-dimensional, almost complete skeletons. However, R. tenuisceps was originally described 50 years ago and compared then only with Ornithosuchus woodwardi and their affinities were discussed in detail. Here, we provide a detailed description of the postcranial skeleton of R. tenuisceps, which exhibits several remarkable features within pseudosuchians. When a wide spectrum of pseudosuchian archosaurs are considered, the alleged character that linked ornithosuchids with dinosaurs resulted in convergences and some were registered in other pseudosuchian groups as well. Riojasuchus tenuisceps also provided crucial information about the 'crocodile-reversed' tarsus, which is a unique feature of ornithosuchids, but it is not completely preserved in O. woodwardi and it is unknown in Venaticosuchus rusconii. In addition, the first histological analysis of cervical and dorsal osteoderms of R. tenuisceps was carried out as well, in order to test the utility of these structures as skeletochronological tools. Finally, the phylogenetic context of Ornithosuchidae is discussed based on the latest phylogenetic studies, which show a close affinity with Erpetosuchidae.
Ornithosuchidae is one of the most enigmatic clades of Triassic pseudosuchians. The group is comp... more Ornithosuchidae is one of the most enigmatic clades of Triassic pseudosuchians. The group is composed by three carnivorous species that were excavated from Upper Triassic beds of Scotland and Argentina. We describe the first ornithosuchid from the Upper Triassic sediments of Brazil and explore its phylogenetic affinities and implications for the evolution of the group. Dynamosuchus collisensis gen. et sp. nov. was found as the sister taxon of the Argentinean form Venaticosuchus rusconii. These relationships reject a potential endemic radiation of ornithosuchids from the Ischigualasto-Villa Unión Basin and would better support multiple diversification events. Our findings with ornithosuchids is consistent with the pattern reported for proterochampsid and erpetosuchid archosauriforms from Ischigualasto-Villa Unión and the Paraná basins. In addition, the presence of an ornithosuchid in the Late Triassic of Brazil suggests that ornithosuchids were more widespread than previously thought in the southern hemisphere. The new ornithosuchid further demonstrates a faunistic link between the Argentinean and Brazilian basins during the Carnian. Finally, the discovery of the new species provides the first clue of a putative necrophagous vertebrate from the oldest dinosaur-bearing beds and expands our knowledge regarding the trophic structure of the Late Triassic of Brazil.
The paleoneuroanatomy of pseudosuchian archosaurs is poorly known, based on direct examination of... more The paleoneuroanatomy of pseudosuchian archosaurs is poorly known, based on direct examination of the internal morphology of braincases and a few artificial endocasts. Among aetosaurs, only one endocast has been described almost a century ago by Case (1921) corresponding to Desmatosuchus spurensis from the Chinle Formation (Norian) of Texas, US, based on a resin cast. Here, we describe the first natural endocast of an aetosaur, Neoaetosauroides engaeus from the Los Colorados Formation (Norian) of NW Argentina, and also developed the first digital endocast of this taxon including the encephalon, cranial nerves, inner ear, and middle ear sinuses. The neuroanatomy of Neoaetosauroides engaeus exhibits several differences from that of Desmatosuchus spurensis despite their phylogenetic proximity, which may be a reflection of their different habits. The information provided by the endocasts of Neoaetosauroides engaeus about its olfactory region and the orientation of its head, based on the...
We describe the new aetosaur Aetobarbakinoides brasiliensis gen. et sp. nov. from the early Late ... more We describe the new aetosaur Aetobarbakinoides brasiliensis gen. et sp. nov. from the early Late Triassic (late Carnian-early Norian) Brazilian Santa Maria Formation. The holotype is composed of a partial postcranium including several cer-vical and dorsal vertebrae and ribs, one anterior caudal vertebra, right scapula, right humerus, right tibia, partial right pes,and anterior and mid-dorsal paramedian osteoderms. Aetobarbakinoides is differentiated from other aetosaurs by the pres-ence of cervical vertebrae with widely laterally extended prezygapophyses, mid-cervical vertebrae with anterior articularfacet width more than 1.2 times wider than the posterior one, anterior caudal vertebrae with extremely anteroposteriorlyshort prezygapophyses, elongated humerus and tibia in relation to the axial skeleton, and paramedian osteoderms with aweakly raised anterior bar. A cladistic analysis recovered the new species as more derived than the South American generaAetosauroides (late Carnian-ea...
Riojasuchus tenuisceps Bonaparte 1967 is currently known from four specimens, including two compl... more Riojasuchus tenuisceps Bonaparte 1967 is currently known from four specimens, including two complete skulls, collected in the late 1960s from the upper levels of the Los Colorados Formation (Late Triassic), La Rioja, Argentina. Computed tomography (CT) scans of the skulls of the holotype and a referred specimen of Riojasuchus tenuisceps and the repreparation of the latter allows recognition of new features for a detailed analysis of its cranial anatomy and its comparison with a wide variety of other archosauriform taxa. The diagnosis of Riojasuchus tenuisceps is emended and two autapomorphies are identified on the skull: (1) a deep antorbital fossa with its anterior and ventral edges almost coinciding with the same edges of the maxilla itself and (2) a suborbital fenestra equal in size to the palatine-pterygoid fenestra. Also, the first digital 3D reconstruction of the encephalon of Riojasuchus tenuisceps was carried out to study its neuroanatomy, showing a shape and cranial nerve d...
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