Hyperodapedon
Hyperodapedon is an extinct genus of rhynchosaur reptiles which lived during Late Triassic period. Like other rhynchosaurs, it was a heavily built archosauromorph, distantly related to archosaurs such as crocodilians and dinosaurs. Hyperodapedon in particular was part of the subfamily Hyperodapedontinae, a specialized rhynchosaurian subgroup with broad skulls, beaked snouts, and crushing tooth plates on the roof of the mouth.
Hyperodapedon remains one of the most widespread and well-understood rhynchosaurs due to its abundance of fossils on several continents. It was named and discovered by Thomas Henry Huxley in 1859, based on H. gordoni, a species from Scotland. It has also been reported from Africa, Asia, and North and South America, though some species were later split off into their own genera. An Indian species, H. huxleyi, is also known by the genus name Paradapedon. Some of the early South American finds were described under the name Scaphonyx, which is often considered a junior synonym of Hyperodapedon. Hyperodapedon fossils are abundant and biostratigraphically significant in strata of the late Carnian stage, such as the Ischigualasto Formation of Argentina and the Upper Santa Maria Formation of Brazil. It is generally considered a herbivore that used its beaked premaxilla and hindlimbs to dig for plants on land.
Discovery and species
''H. gordoni''
The first species of Hyperodapedon to be named and discovered was H. gordoni, from the Lossiemouth Sandstone near Elgin, Scotland. This species was named by Thomas Henry Huxley in honor of Rev. Dr. Gordon, the man who discovered the initial skeleton. Huxley initially named the species at an 1858 Geological Society of London conference. Huxley's correspondence was added as a postscript to Roderick Murchison's broader discussion on the age of the Elgin area sandstones. Hyperodapedon was the third reptile to be discovered in the area, behind Stagonolepis and "Telerpeton", and reinforced Huxley's new hypothesis that the Lossiemouth Sandstone was Mesozoic in age, rather than Paleozoic. Both Murchison's talk and Huxley's postscript were published in print in 1859. Huxley described Hyperodapedon gordoni in further detail in 1869 and 1887. Additional specimens were listed or described by Lydekker and Burckhardt. A complete redescription of all H. gordoni material was undertaken by Michael Benton in 1983.T.H. Huxley found many series of subcylindrical palatal teeth which was the main trait of Hyperodapedon. Huxley was able to distinguish Hyperodapedon from Rhynchosaurus ''articeps by the maxillary tooth rows. Later on, Lydekker realized that Hyperodapedon'' have more than two rows of teeth in both the maxilla and palatine.
''H. huxleyi (Paradapedon)''
Hyperodapedon huxleyi was named by English naturalist Richard Lydekker in 1881 based on fossils from the Lower Maleri Formation of India. It was described in more detail by the same author in 1885. Lydekker used the genus Hyperodapedon for the species, but German paleontologist Friedrich von Huene was of the opinion that it constituted a new genus closely related to Hyperodapedon. In 1938, von Huene established the new genus Paradapedon for the species. All fossils referred to Paradapedon were redescribed by Indian-American paleontologist Sankar Chatterjee in 1974.For much of the 20th century, Paradapedon huxleyi was entangled with debates over the validity of Parasuchus hislopi, a species which was first mentioned by Huxley and formally described by Lydekker. One of the syntype fossils of Parasuchus hislopi was a collection of bones including a partial braincase, osteoderms, teeth, and other associated material. The braincase was later identified as belonging to a rhynchosaur, but the other bones in the syntype are from a carnivorous phytosaur. This would make the syntype a chimera, comprising fossil material from two unrelated animal species.
To remedy this issue, von Huene elected to abandon the name Parasuchus hislopi, as he considered the name to apply to the rhynchosaur braincase first and foremost, which was certainly referrable to Paradapedon huxleyi. Chatterjee disagreed, noting that the braincase had no special status relative to the other fossils, as it was merely a syntype rather than a holotype. He separated the braincase from Parasuchus hislopi and named a phytosaur snout fragment as a new lectotype for the species. Assisted by the discovery of new complete skeletons, Parasuchus hislopi is still considered a valid phytosaur taxon to the present day.
Benton concluded that "Paradapedon" huxleyi should once again be considered a species of Hyperodapedon, thus rendering Paradapedon a junior synonym of Hyperodapedon.
''H. sanjuanensis (Scaphonyx)''
Fossils of Hyperodapedon sanjuanensis were previously described under the names Scaphonyx fischeri and Scaphonyx sanjuanensis prior to formally being referred to Hyperodapedon in 2000.Arthur Smith Woodward named a new genus and species, Scaphonyx fischeri, for a small number of reptile vertebrae and phalanges from the Upper Santa Maria Formation, in the Brazilian state of Rio Grande do Sul. The genus name Scaphonyx referred to the scoop-like shape of the reptile's claws, while the species name honors Dr. Jango Fischer, who discovered the fossils in 1902. At the time Woodward considered Scaphonyx fischeri to be a short-necked dinosaur closely related to Euskelosaurus. Further collection from the same area by Friedrich von Huene produced more extensive fossil material. Huene informally proposed multiple new names to describe the reptile fossils he had collected: Cephalonia, Cephalastron, Cephalostronius, and Scaphonychimus. By 1942, he had lumped all of these remains into either Cephalonia lotziana or Scaphonyx fischeri, while recognizing their rhynchosaurian affinities.
The name Scaphonyx sanjuanensis was established by Sill in reference to rhynchosaur fossils from the Ischigualasto Formation of Argentina. Sill also demonstrated the synonymy of Cephalonia lotziana and Scaphonyx fischeri, with fossils of the latter simply having been recrystallized into a more inflated state via diagenetic processes.
H. sanjuanensis is regarded as the most abundant fossil organism preserved in the Ischigualasto Formation, making up the majority of fossils found within the first of the formation.
''H. huenei''
Hyperodapedon huenei was named by Langer & Schultz, in the same publication which transferred H. sanjuanensis into the genus. The specific name honors Friedrich von Huene. H. huenei is another Brazilian species from the Upper Santa Maria Formation. The holotype is a large and well-preserved skull, UFRGS PV0132T. Only a few other maxilla and dentary fragments were referred to the species in its initial description.Diagnostic features of H. huenei include the absence of an infraorbital foramen, a single dentary blade, and fusion between the supraoocipital and opisthotic bones of the braincase. In addition, the rear portion of the maxillary tooth plate has a secondary wear groove alongside the main longitudinal groove, and the medial portion of the tooth plate is broader than the lateral portion. Both conditions are similar to more basal rhynchosaurs but unlike other species of Hyperodapedon.
''H. tikiensis''
Hyperodapedon tikiensis was named by Mukherjee & Ray from the Tiki Formation in the Rewa Basin of India. This diagnosis of this species relies on several features of the cranial and postcranial skeleton. Cranial autapomorphies include a basipterygoid process which is longer than wide and a crest-shaped maxillary cross section next to the main longitudinal groove. The lateral tooth field of the tooth plate is broader than that on the medial side, with three tooth rows versus two on the medial side. The rear edge of the tooth plate also has a broader angle compared to other species in the genus. The postcranial diagnostic features include ilium proportions, deeply excavated neural arches on the mid dorsal vertebrae, a long scapular blade, a pronounced deltopectoral crest, and a proximal humeral end which is broader at the distal end.Description
Hyperodapedon was a stocky and heavily built animal with thick limbs and a broad skull and body. H. gordoni had a total length around, with a skull length of. The largest species, H. huxleyi, had an estimated skull length around.Skull
Apart from its beak, it had several rows of teeth on each side of the upper jaw, and a single row on each side of the lower jaw, creating a powerful chopping action when it ate. The tooth rows of the upper jaw were hosted by tooth plates formed by the fusion of the maxilla and palatine bones. The tooth plates have even rows of small conical teeth, separated by a longitudinal groove which receives the teeth of the lower jaw. The teeth had open roots which could not be replaced like other reptiles.The upper temporal bar faces dorsally and is raised above the level of the ventral margin of the orbit. The braincase of Hyperodapedon had a longitudinal stapedial canal on the posterior side of the spatulate paroccipital process which the lagenar crest extended laterally to limit the posterior end. The pterygoid of Hyperodapedon lacks a pair of ridges present in other rhynchosaurs, as well as palatal dentition as a whole. The prefrontal is deeply concave on the dorsal side.