The aetosaur Stagonolepis from the Upper Triassic of Brazil and its biochronological significance

A new species of the rhynchosaur genus Hyperodapedon, namely H. tikiensis, is described from well-preserved skeletal elements that were collected from the Upper Triassic Tiki Formation of India. Hyperodapedon tikiensis is diagnosed on the basis of several cranial and postcranial features including longer than wide basipterygoid process, crest-shaped maxillary cross section lateral to the main longitudinal groove, deeply excavated neural arches of mid-dorsal vertebrae, long scapular blade, a pronounced deltopectoral crest, proximal humeral end much broader than distal end, iliac length greater than iliac height, equal pre-and postacetabular iliac lengths and circular femoral cross section. Two distinct morphotypes of the maxillary tooth plates can be discerned, which are attributed to ontogenetic variations. A maximum-parsimony analysis was carried out to show that the order Rhynchosauria is characterized by nine cranial and one postcranial character states. The analysis reveals that Otischalkia elderae is invalid and the basal forms, Howesia and Mesosuchus, are closely related. The Mid-Triassic genus Ammorhynchus is more derived and forms a sister group to the Late Triassic subfamily Hyperodapedontinae. Isalorhynchus and Teyumbaita are basal to the pandemic genus Hyperodapedon. Twenty-four characters that are not homoplasious document major patterns of skeletal evolution in rhynchosaurs. From laterally oriented scapula and slender propodials, the postcranial skeleton evolved into a more robust form as is evident from nearly vertical scapula and increase in the robustness of the propodials. Shortening of the femur is noted in the derived Late Triassic forms as exemplified in Hyperodapedon gordoni, Hyperodapedon huxleyi and H. tikiensis. for internal carotid artery; inf, intertrochanteric fossa; int, internal trochanter; lg, longitudinal groove on the posterodorsal surface of the maxillary tooth plate; na, neural arch; nc, neural canal; ns, neural spine; oc, occipital condyle; OcL, length of occipital condyle; OcW, width of occipital condyle; pbs, parabasisphenoid complex; pcf, femoral posterior condyle; pf, posterior flange of the femur;

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“…), Scotland (Huxley ; Benton ), Canada (Chatterjee ; Heckert and Lucas ) and the USA (Nesbitt and Whatley ; Lucas et al . ).…”

Section: Systematic Palaeontologymentioning

confidence: 97%

“…The lateral surface of the maxillary tooth plate is concave in contrast to the convex medial surface as in H. huxleyi (Chatterjee ), H. gordoni (Benton ), H. huenei (Langer and Schultz ), H. sanjuanensis (Lucas et al . ) and Teyumbaita sulcognathus (UFRGS‐PV‐0290T, Montefeltro et al . ).…”

Section: Osteological Descriptionmentioning

confidence: 99%

A new Hyperodapedon (Archosauromorpha, Rhynchosauria) from the Upper Triassic of India: implications for rhynchosaur phylogeny

Mukherjee

Ray

2014

Palaeontology

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“…Based upon plate morphology, Lucas & Heckert (2001) stated that Aetosauroides scagliai, which occurs in the Ischigualasto Formation, is conspecific with S. robertsoni, but plates alone are insufficient to determine species identity (Martz & Small, 2006, contra Parker, 2008b. The view of aetosaur evolution proposed here contradicts the suggestion that the Longosuchus biochron is earlier than the Stagonolepis biochron (Lucas & Heckert, 2001), because Stagonolepis is known from both sediments older and younger than Longosuchus. Diagnosis: Stagonolepis differs from Longosuchus and Desmatosuchus in the possession of premaxillary teeth, and the absence of strongly curved dorsolateral osteoderms with spines.…”

Section: Biostratigraphical Correlationmentioning

confidence: 99%

“…Although Lucas & Heckert (2001) reported various Stagonolepis osteoderms from Germany, Brazil, and Argentina, their assignments are mostly questionable, and particularly so those from Gondwanan localities. Isolated elements of dermal armour are difficult to assign correctly at the generic level (Martz & Small, 2006).…”

Section: Introductionmentioning

confidence: 99%

The skull of an early Late Triassic aetosaur and the evolution of the stagonolepidid archosaurian reptiles

Sulej

2010

Zoological Journal of the Linnean Society

126

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Disarticulated bones of several individuals recovered from the Late Triassic fluvial and lacustrine deposits at Krasiejów, Poland, are here described, allowing the restoration of the skull structure of a new aetosaurian archosaur: Stagonolepis olenkae sp. nov. The Krasiejów deposits probably correspond in age to the Lehrberg Beds (late Carnian) of Baden-Württemberg, Germany. The stratigraphical position of the new taxon combined with other available evidence is used to propose a model of aetosaurian evolution. The proposed phylogenetic position of Aetosaurus ferratus (Norian, Germany) as the basal aetosaurid is refuted and this species is instead proposed to be the most derived member of the Stagonolepis-Aetosaurus evolutionary lineage. Gradual change in several morphological characters can be observed from Stagonolepis robertsoni, through the new species from Krasiejów, to the stratigraphically youngest Aetosaurus ferratus. These changes include a decrease in the number of teeth and a decrease in the convexity of the ventral profile of the maxilla. The anterior elongation of the maxilla is associated with the expansion of the anterior tip of the maxilla towards the naris. In S. robertsoni and S. olenkae, the maxilla extends to middle of the naris, whereas in Aetosaurus, it reaches the anterior half of the naris.

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“…; Lucas et al . ; Mukherjee and Ray ). Two species of Hyperodapedon are known from two different Gondwana basins of peninsular India (Mukherjee and Ray ).…”

mentioning

confidence: 98%

New insights from bone microanatomy of the Late Triassic Hyperodapedon (Archosauromorpha, Rhynchosauria): implications for archosauromorph growth strategy

Mukherjee

2015

Palaeontology

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Bone microanatomy of multiple postcranial skeletal elements of several individuals of Hyperodapedon collected from India is reported. This reveals that fibrolamellar bone tissue is predominant in the mid-and inner cortices, whereas the peripheral region of the cortex is composed of either parallel-fibred and/or lamellar bone. The pattern of primary osteons mostly ranges between laminar and subplexiform. Such predominance of fibrolamellar bone tissue in the cortex suggests an overall fast growth, which slowed down considerably later in ontogeny. Four distinct ontogenetic stages are identified based on the bone microstructure. During the juvenile stage, growth was fast and continuous, but it became punctuated during the early and late sub-adult stages. In adult individuals, growth was slow and showed periodic interruption but did not stop completely, suggesting that Hyperodapedon had an indeterminate growth strategy. Interelemental histovariations affecting cortical thickness, organization of the vascular network, incidence of growth rings and extent of secondary reconstruction are noted.

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The aetosaur Stagonolepis from the Upper Triassic of Brazil and its biochronological significance

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A new Hyperodapedon (Archosauromorpha, Rhynchosauria) from the Upper Triassic of India: implications for rhynchosaur phylogeny

A new Hyperodapedon (Archosauromorpha, Rhynchosauria) from the Upper Triassic of India: implications for rhynchosaur phylogeny

The skull of an early Late Triassic aetosaur and the evolution of the stagonolepidid archosaurian reptiles

New insights from bone microanatomy of the Late Triassic Hyperodapedon (Archosauromorpha, Rhynchosauria): implications for archosauromorph growth strategy

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