| Platyognathus Temporal range: Early Jurassic | |
|---|---|
 | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| Subclass: | |
| Infraclass: | |
| Superorder: | |
| Suborder: | |
| Genus: | Platyognathus Young, 1944 |
| Species | |
| |
Platyognathus is an extinct genus of protosuchian crocodyliform. Fossils are known from the Early Jurassic Lower Lufeng Formation in Yunnan, China and belong to the type and only species, P. hsui.
The skull of Platyognathus is small, being about 5 centimetres (2.0 in) in length. The snout is narrow and shorter than the remainder of the skull, as indicated by the anterior position of the antorbital fenestra. Two teeth, dentaries 5 and 6, are enlarged into caniniforms in the lower jaw. [1] Paired caniniform teeth are not seen in any other described crocodyliform taxa, but they have been recorded from an unidentified crocodyliform from the Lower Jurassic Kayenta Formation and from a protosuchid from the Lower Jurassic McCoy Brook Formation in Nova Scotia. [1] [2]
Platyognathus was first named by Chung-Chien Young in 1944 on the basis of a partial lower jaw found from the Dark Red Beds of the Lower Lufeng Formation in 1939. [3] [4] The material was first mentioned briefly four years earlier in a paper on Lufeng fossil vertebrates. [5] The holotype jaw consisted of 11 alveoli (tooth sockets) on the left side and 12 alveoli on the right side, in addition to one broken caniniform tooth. Several diagnostic features were mentioned, including an expansion at the tip of the jaw, a tooth cross section that is octangular in outline, and a lateral constriction of the jaw behind the caniniform tooth, which is followed by an expansion further back. The anterior teeth are small and angled forward, while there is evidence in the jaw of at least two caniniform teeth that were larger and oriented obliquely and anteriorly. Further back in the jaw, the posterior teeth are about the same size and project vertically. The entire jaw is well ossified, and sutures between the bones could not be identified in the holotype. The symphysis, the point where the two sides of the jaw come together, is represented by a broad ventral groove. [3]
Based on these features, Young found no close similarities between the jaw of Platyognathus and any other known early crocodylomorph such as Notochampsa , Sphenosuchus , Erythrochampsa , and Pedeticosaurus (at the time, these crocodylomorphs were collectively known as the "Pseudosuchia"). The jaw of Protosuchus richardsoni , described by Barnum Brown in 1933 from Arizona, is similar in size to that of Platyognathus, although it lacks many of the distinguishing features of the Asian form as described by Young. [6] Because Platyognathus differed from any other known pseudosuchian, Young suggested that it may belong to its own family. [3]
During World War II, the holotype was either lost or destroyed. The classification of the genus continued to be debated, as descriptions of the fragmentary jaw were all that was available to study. Platyognathus continued to be referred to Pseudosuchia in the following years, and was suggested to have a close relationship with Sphenosuchus. [7] [8] In 1955, it was suggested to have affinities with aetosaurs, and in 1956 Alfred Romer tentatively assigned it to the Notochampsidae (later synonymized with Protosuchidae). [9] [10]
In 1965, additional specimens from the Lower Lufeng were referred to Platyognathus. It was placed in a new pseudosuchian family, the Platyognathidae, and was considered to be intermediate between Pseudosuchia and Protosuchia. [11] Most later studies of Platyognathus were based on one specimen of the new material known as CUP 2083 which preserved the lower jaw. [1] Some of these studies concluded that Platyognathus was a pseudosuchian related to Sphenosuchus and Pedeticosaurus, [12] [13] but most considered it to be a protosuchian. [14] [15] [16] [17] [18] One 1986 study also considered the material to be from a protosuchian, but did not consider CUP 2083 to be from Platyognathus because the mandibular symphysis was elongate and unfused, unlike the holotype described by Young which was ossified. [19] Later that year, a new paper also concluded that the newer material did not represent Platyognathus, but considered the specimens and Platyognathus to belong to different basal crocodyliform taxa of uncertain affinities. In that paper, the validity of P. hsui was questioned on the basis of Young's description of the holotype [20]
In 1996, a newly described partial skull known as IVPP V8266 that was referable to Platyognathus was designated as a neotype. [1] It was collected in 1984 from the Lower Lufeng in Yunnan. The authors of the paper that described the neotype agreed with the previous studies that the material described in 1965 does not belong to Platyognathus because CUP 2083 lacks many of the features of the holotype. In CUP 2083, the mandibular symphysis is unfused, there is a single caniniform tooth in the dentary, and there is no groove along the symphysis. This contrasts with the holotype, which has a fused symphysis, at least two caniniform teeth, and a conspicuous trough along the symphysis. [3] The authors also mention that the holotype and CUP 2083 come from two different strata within the "Dark Red Beds" of the Lower Lufeng; the holotype is from stratum 6 of the Dahuangtian locality while CUP 2083 is from stratum 5 of the Dadi locality, about 400m southeast of the Dahuangtian locality. This shows that the two specimens are from different horizons and are likely to belong to different taxa. [1]
The new skull revealed an additional diagnostic feature of Platyognathus that distinguishes it from other protosuchians: the distinctive curvature of the jugal. Additional diagnostic characters were proposed by the authors, but their character-states cannot be determined in other protosuchian taxa. These characters include a width of the mandibular symphysis across the swellings of the caniniform teeth that is almost equal to the anteroposterior length of the symphysis and an anterolateral process of the ectopterygoid with an inverted V-shaped ridge on the dorsal surface. The shortness of the snout relative to the rest of the skull and the presence of a laterally and ventrally open notch between the premaxilla and maxilla indicate that Platyognathus is a member of Protosuchia as defined by Wu et al. (1994). Because the infratemporal fenestra of Platyognathus is very small and the mandibular symphysis extends posteriorly to the level of the seventh to ninth tooth, the genus is thought to be more derived than Orthosuchus . The authors of the description of the neotype suggested that Platyognathus may be closely related to the clade containing Protosuchidae and Shantungosuchus because it possesses a dentary tooth that fits into a notch between the premaxilla and maxilla. Because Platyognathus is known from such incomplete material, there is yet to be an adequate cladistic analyses that can determine a phylogenetic position for Platyognathus within Protosuchia. [1]
An unnamed mesosuchian from the Salt Wash Member of the Late Jurassic Morrison Formation of western Colorado in the United States possesses several features that are also seen in Platyognathus. [21] The dentition of the mesosuchian is similar to that of Platyognathus and like Platyognathus, the dentary is laterally expanded. However, the dentary of the unnamed mesosuchian is much broader and spatulate. [22]
Yunnanosaurus is an extinct genus of sauropodomorph dinosaur that lived approximately 199 to 183 million years ago in what is now the Yunnan Province, in China, for which it was named. Yunnanosaurus was a large sized, moderately-built, ground-dwelling, quadrupedal herbivore, that could also walk bipedally, and ranged in size from 7 meters (23 feet) long and 2 m (6.5 ft) high to 4 m (13 ft) high in the largest species.
Sinosaurus is an extinct genus of theropod dinosaur which lived during the Early Jurassic Period. It was a bipedal carnivore approximately 5.5 metres (18 ft) in length and 300 kilograms (660 lb) in body mass. Fossils of the animal were found at the Lufeng Formation, in the Yunnan Province of China.
Dianchungosaurus is an extinct genus of mesoeucrocodylian crocodyliform from the Early Jurassic of China. It was previously considered a dinosaur, but it was recently reclassified as a mesoeucrocodylian by Paul Barrett and Xing Xu (2005). It is probably the same animal as the informally named "Tianchungosaurus". The type species is D. lufengensis and it was described in 1982. A second species, D. elegans, was named in 1986, but it has since become a synonym of the type species.
Venaticosuchus is a genus of pseudosuchian archosaurs from the family Ornithosuchidae. Known from a single species, Venaticosuchus rusconii, this genus is described based on an incomplete skull and jaw collected from the Late Triassic (Carnian) Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina, which was deposited around 230 million years ago. This fossil material has been termed the holotype specimen PVL 2578. Venaticosuchus incorporated a myriad of features present in the other two genera of ornithosuchids, Ornithosuchus and Riojasuchus. However, it also had several unique traits, relating to the lower jaw.
Macroplata is an extinct genus of Early Jurassic rhomaleosaurid plesiosaur which grew up to 4.65 metres (15.3 ft) in length. Like other plesiosaurs, Macroplata probably lived on a diet of fish, using its sharp needle-like teeth to catch prey. Its shoulder bones were fairly large, indicating a powerful forward stroke for fast swimming. Macroplata also had a relatively long neck, twice the length of the skull, in contrast to pliosaurs.
Lukousaurus is an archosauromorph based on most of a small skull's snout, displaying distinctive lachrymal horns, found in the Early Jurassic-age Lower Lufeng Formation, Yunnan, China and was described by Chung Chien Young in 1940. The generic name refers to the Lugou Bridge, lit. “crossroads”, near Beijing, where the Sino-Japanese War started. L. yini is tentatively classified as a theropod dinosaur by some allied to ceratosaurs, by others a coelurosaur. Its skull is rather robust for its size though the teeth were described by the author as typically theropodan. Whatever Lukousaurus was, it was definitely an archosauromorph.
Heterodontosauridae is a family of ornithischian dinosaurs that were likely among the most basal (primitive) members of the group. Their phylogenetic placement is uncertain but they are most commonly found to be primitive, outside of the group Genasauria. Although their fossils are relatively rare and their group small in numbers, they have been found on all continents except Australia and Antarctica, with a range spanning the Early Jurassic to the Early Cretaceous.
Razanandrongobe is a genus of carnivorous ziphosuchian crocodyliform from the Middle Jurassic of Madagascar. It contains the type and only species Razanandrongobe sakalavae, named in 2004 by Simone Maganuco and colleagues based on isolated bones found in 2003. The remains, which included a fragment of maxilla and teeth, originated from the Bathonian-aged Sakaraha Formation of Mahajanga, Madagascar. While they clearly belonged to a member of the Archosauria, Maganuco and colleagues refrained from assigning the genus to a specific group because the fragmentary remains resembled lineages among both the theropod dinosaurs and crocodylomorphs.
Dianosuchus is an extinct genus of protosuchid crocodyliform. Fossils have been found from the Dark Red Beds of the Lower Lufeng Formation in Yunnan, China, dating back to the Sinemurian stage of the Early Jurassic. It is characterized by an unusually flattened snout compared to other protosuchians, conical isodont teeth that lacked striations, and very small antorbital fenestrae.
Eopneumatosuchus is an extinct genus of basal crocodyliform. Fossils have been found from two localities within the Kayenta Formation of Arizona. Both localities are around 20 miles southeast of the Grand Canyon and in close proximity to one another. The localities probably date back to the Early Jurassic, most likely during the Sinemurian stage.
Dimacrodon is an extinct genus of non-mammalian synapsid from the latest Early Permian San Angelo Formation of Texas. It is distinguished by toothless, possibly beaked jaw tips, large lower canines and a thin bony crest on top of its head. Previously thought to be an anomodont therapsid related to dicynodonts, it was later found to lack any diagnostic features of anomodonts or even therapsids and instead appears to be a 'pelycosaur'-grade synapsid of uncertain classification.
Eilenodon is an extinct genus of rhynchocephalian reptile from the Late Jurassic Morrison Formation of western North America, present in stratigraphic zone 4. The only known species of this genus was Eilenodon robustus. It was a member of a group of rhynchocephalians called the eilenodontines, which were large, herbivorous members of Rhynchocephalia, the order of reptiles which contains the modern tuatara (Sphenodon). The generic name "Eilenodon" is Greek for "packed teeth", in reference to its closely packed teeth. The specific name, "robustus", refers to the strong build of the jaws.
Microchampsa is an extinct genus of protosuchian crocodyliform that existed during the Early Jurassic. Fossils have been found from stratum 6 of the Dahuangtian locality, an outcrop of the Lower Red Beds of the Lufeng Formation in Yunnan, China.
Notochampsa is an extinct genus of protosuchian crocodyliform. Fossils have been found from the lower Clarens Formation of the Karoo Supergroup in South Africa, dating back to the Pliensbachian stage of the Early Jurassic. Notochampsa comes from a period of relative fossil scarcity, and is the youngest known occurrence of a crocodylomorph from the Karoo Basin of South Africa.
Zapatadon is an extinct genus of sphenodontid reptile from the end of the Early Jurassic in the lower part of La Boca Formation of Tamaulipas, Mexico. Is known from a nearly complete skull with mandible of a post-hatchling individual, and is one of the smallest skulls between the sphenodontians, with an estimated total length of 11.3 millimetres, a bit smaller than the hatchling individuals observed in the modern tuatara (Sphenodon); features like the oblique mandibular symphysis suggests that the holotype is from an individual in a relatively mature stage of ontogenic development. Zapatadon is diagnosed by their hatchling tooth series located in a depression in the anterior part of the dentary bone, the prefrontal bone surrounding the dorsal process of the maxilla and the broad jugal that extends over the maxillary suborbital process, been almost excluded of the orbit.
Yonghesuchus is an extinct genus of Late Triassic archosaur reptile. Remains have been found from the early Late Triassic Tongchuan Formation in Shanxi, China. It is named after Yonghe County, the county where fossils were found. Currently only one species, Y. sangbiensis, is known. The specific name refers to Sangbi Creek, as fossils were found in one of its banks.
Shartegosuchidae is an extinct family of Late Jurassic and Early Cretaceous crocodylomorphs. The family is named after the Late Jurassic Shar Teeg Beds in southwestern Mongolia, from which most shartegosuchid remains have been found. Five genera are currently assigned to Shartegosuchidae: Shartegosuchus, Nominosuchus, Kyasuchus, Adzhosuchus, and Fruitachampsa. Shartegosuchus, Nominosuchus, and Adzhosuchus all come from Shar Teeg, while Kyasuchus is known from the Early Cretaceous of Russia. Fruitachampsa is known from the Late Jurassic Morrison Formation of the western United States.
Pegomastax is a genus of heterodontosaurid dinosaur that lived during the Early Jurassic of South Africa. The only known specimen was discovered in a 1966-1967 expedition in Transkei District of Cape Province, but wasn't described until 2012 when Paul Sereno named it as the new taxon Pegomastax africana. The genus name is derived from the Greek for "strong jaw", and the species name describes the provenance of Africa; it was originally spelled africanus, was corrected to africana to align with the gender of the genus name.
Syntomiprosopus is an extinct genus of archosauriform, possibly a crocodylomorph from the Late Triassic period of Arizona. The type and only known species is S. sucherorum. Syntomiprosopus was unusually short-snouted, comparable to the Late Cretaceous notosuchian Simosuchus, and is regarded as an example of convergent evolution between Triassic stem-archosaurs and Cretaceous archosaurs.
Pachagnathus is an extinct genus of non-pterodactyloid pterosaur from the late Norian–early Rhaetian-aged Quebrada del Barro Formation of Argentina. It lived in the Late Triassic period, and is one of the only known definitive Triassic pterosaurs from the southern hemisphere. It is also one of the few known continental Triassic pterosaurs, indicating that the absence of early pterosaurs in both the southern hemisphere and terrestrial environments is likely a sampling bias, and not a true absence.
