Scaphonyx

''Hyperodapedon'' is a genus of rhynchosaurs (beaked, archosaur-like reptiles) from the Late Triassic period (Carnian stage). Fossils of the genus have been found in Africa, Asia, Europe and North and South America. Its first discovery and naming was found by Thomas Henry Huxley in 1859. ''Hyperodapedon'' was a herbivore that used its beaked premaxilla and hindlimbs to dig for plants in dry land.

Description

''Hyperodapedon'' was a heavily built, stocky, animal. ''H. gordoni'' had total length around with skull length of to , but largest species, ''H. huxleyi'' had lower jaw about and skull length is estimated about . Apart from its beak, it had several rows of heavy 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. It is believed to have been herbivorous, feeding mainly on seed ferns, and died out when these plants became extinct at the end of the Triassic. The diagnosis of ''Hyperodapedon'' relies on many features of the cranial and postcranial traits which include a longer than wide basipterygoid process, a crest-shaped maxillary cross section next to the main longitudinal groove, deep 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. The maxillary tooth plates are easily seen in ''Hyperodapedon'' and there are seven cranial, six postcranial, and three dentition synapomorphy traits.

''Hyperodapedon'' had jaws that allowed them to have a precision-shear bite to break down the tough plants that they ate. The beak-like premaxilla and hind limbs were used for digging up food. Teeth along the maxilla and dentary had open roots which could not be replaced like other reptiles. The forelimbs, on the other hand, were used for movement due to the rotation of; the humerus, however, the femur was not able to rotate. Another unique feature of ''Hyperodapedon'' was the large eyes with sclerotic plates, which allowed for good sense of vision. They had large nasal capsules to sense smell. Since ''Hyperodapedon'' lacked a tympanum, it was believed that they could sense sound by the skin near the quadrate.Benton, M. (1983). The Triassic reptile ''Hyperodapedon'' from Elgin: Functional morphology and relationships. ''Royal Society''. Hyperodapedons also appeared to have transverse rows of cone-shaped teeth along the lateral area of the maxilla.Huxley, T. (1887). Further Observations upon ''Hyperodapedon gordoni''. ''Quarterly Journal of the Geological Society,'' ''43'', 675–694.

''Hyperodapedon's'' closest relative is ''Rhynchosaurus'', and they both share a synapomorphy that the dentary is half the length of the lower jaw. ''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.Langer, M. C., & Schultz, C. L. (2003). A New Species Of The Late Triassic Rhynchosaur Hyperodapedon From The Santa Maria Formation Of South Brazil. ''Wiley Online Library,'' ''43''(4). Above the ventral margin of the orbit was the upper temporal bar which faced dorsally. A non-directional exploitation of morphospace from smaller ancestors with a smaller size restriction is responsible for a large body size in ''Hyperodapedon''. ''Hyperodapedon'' have a single row of teeth in mandible bites between their two rows of teeth fixed to a plate which is formed by a union of the maxilla with the palatine. Other key traits are the two maxillary grooves and a single dentary blade, along with missing the infraorbital foramen. The supraoccipital and opisthotics are fused together. ''Hyperodapedon'' had a pair of ridges which are absent on the pterygoid, they are missing the palatal dentition, and the prefrontal is concave deeply on the dorsal side.

Discovery

The first discovery was from Thomas Henry Huxley in 1859, who named ''Hyperodapedon gordoni'' in honor of Rev. Dr. Gordon's contributions in Elgin County.Burckhardt, R. (1900). I.—On ''Hyperodapedon gordoni''. ''Geological Magazine,7''(12), 529. doi:10.1017/s0016756800183529

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.

The type species of ''Scaphonyx'' (meaning ''canoe claw''), ''Scaphonyx fischeri'' that was once thought to be a dinosaur, is now known to be based on dubious material and therefore should be a ''nomen dubium''. The name ''Paradapedon'' was elected for the Indian species ''H. huxleyi'' (Lydekker, 1881). Benton, 1983, concluded that this rhynchosaur should be considered a species of ''Hyperodapedon''.

''Hyperodapedon'' is known from several species and has been found in many areas of the world, due to the continents being joined in the supercontinent Pangaea during the Triassic. Fossils from the various species have been identified from Argentina, Brazil, India, Scotland, Tanzania, Zimbabwe and possibly from Wyoming (United States).

Classification

Langer ''et al.'' (2000) defined ''Hyperodapedon'' as a stem-based taxon that includes all rhynchosaurs closer to ''Hyperodapedon gordoni'' than to ''"Scaphonyx" sulcognathus'' (now ''Teyumbaita''). The cladogram below follows their phylogenetic analysis of Mukherjee & Ray (2014).Mukherjee, D., Ray, S. (2014)
A new ''Hyperodapedon'' (Archosauromorpha, Rhynchosauria) from the Upper Triassic of India: implications for rhynchosaur phylogeny
''Palaeontology''. doi: 10.1111/pala.12113

Valid species that were first assigned to ''Scaphonyx''.

A quantitative phylogenetic analysis found a paraphyletic genus ''Rhynchosaurus'', with ''Rhynchosaurus brodiei'' more closely related to hyperodapedontines than to ''Rhynchosaurus articeps''. ''Hyperodapedon'' is the most commonly found tetrapod along the oldest dinosaur lineage which results in a broad biostratigraphic correlation.Ezcurra, M. D., Montefeltro, F., & Butler, R. J. (2016). The Early Evolution of Rhynchosaurs. ''Front. Ecol'' Rhynchosaurs are archosauromorph diapsids which is believed to ''Trilophosaurus'', and sister group to Prolacertiformes and Archosauria. A cladistic analysis of Rhynchosauria reveals that Hyperodapedontinae is a major subgroup of the late Triassic. ''Stenaulorhynchus'' and ''Rhynchosaurus'' are close outgroups to Hyperdapedontinae during the middle Triassic. They share the synapomorphy of the dentary is well over half the length of the lower jaw. Rhynchosaurs were basal archosauromorphs that were herbivorous on dry land in Triassic Pangea. Some rare forms are ''Mesosuchus'' and ''Howesia''. ''Hyperodapedon'' and ''Scaphonyx'' are included in the subfamily of Hyperodapedontinae.Huxley, T. (1869). On ''Hyperodapedon''. ''Quarterly Journal of the Geological Society,'' ''25'', 138–152. Hyperodapedontinae consist of ''Hyperodapedon huxleyi'' and ''Scaphonyx sulcognathus''.

Palaeoecology

''Hyperodapedon'' are commonly found in aeolian sand in Elgin, India, Brazil, and Argentina. They are a widely distributed tetrapod during the Upper Triassic and are present in locations where phytosaurs are absent. ''Hyperodapedon'' localities are found in the Popo Agie Formation in Wyoming that dates to the Otischalkian. They are also found in Scotland in the Lossiemouth Sandstone dating to the Adamanian, Maleri Formations in India, Pebbly Arkose Formation in Zimbabwe, Ischigualasto Formation in Argentina, and Santa Maria Formation in Brazil that vary between Otischalkian and Adamanian.Lucas, S. G. (2002). The ''Hyperodapedon'' Biochron, Late Triassic of Pangea. ''Albertiana''. Similarly, ''Rhynchosaurus'' is found in fluvial-intertidal deposits with desiccation along with aeolian deposits with common flash floods.Benton, M. J. (1990). The Species of ''Rhynchosaurus'', A Rhynchosaur (Reptilia, Diapsida) from the Middle Triassic of England. ''Philosophical Transactions of the Royal Society B: Biological Sciences,'' ''328''(1247), 213–306. doi:10.1098/rstb.1990.0114

Distribution

Fossils of ''Hyperodapedon'' have been found in:''Hyperodapedon''
at Fossilworks.org
* Ischigualasto Formation, Argentina
* Caturritas, Brazil
* Lower Maleri and Tiki Formation

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