Platyognathus
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''Platyognathus'' is an extinct
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
crocodyliform Crocodyliformes is a clade of Crurotarsi, crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the ...
of the superfamily
Gobiosuchoidea Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseudo ...
, representing the oldest representative of such, leaving a ghost lineage of aprox. 67 million years. Fossils are known from the
Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic ...
(
Sinemurian In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...
) Zhangjiawa Member of the Lower Lufeng Formation in
Yunnan Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
and belong to the
type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...
and only species, ''P. hsui''.


Description

Platyognathus was a small crocodyliform, roughly the size of "protosuchians" like ''Protosuchus'', with a skull about 5.6 cm long and an estimated body length of around 63 cm. Its well-preserved skeleton, though slightly compressed and cracked, includes a nearly complete skull, mandible, vertebrae, and parts of the limbs, with sculpted dorsal and ventral osteoderms suggesting a mature individual. The skull features a tall, narrow rostrum, broader than ''Protosuchus'' but less abruptly widening than some relatives. The lower
Canine tooth In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, eye teeth, vampire teeth, or fangs, are the relatively long, pointed teeth. In the context of the upper jaw, they are also known as '' fangs''. They can appear more f ...
, with polygonal cross-sections due to ridges and grooves, extend high, occluding outside a premaxilla-maxilla notch. The antorbital fossa is medially walled, potentially reducing or eliminating the antorbital fenestra. The snout is narrow and shorter than the remainder of the skull, as indicated by the anterior position of the
antorbital fenestra An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...
. The nares face forward, bordered mostly by the premaxillae, and the skull table is broad and flat, typical of crocodyliforms. The infratemporal fenestra is elongated and faces dorsolaterally, while the supratemporal fenestrae are obliquely oriented. The mandible is long, with fused dentaries forming a quarter-length symphysis. A unique, narrow fenestra lies between the dentary and angular. The dentition includes four premaxillary teeth, up to 12 maxillary teeth (with serrations on some), and prominent caniniforms in the dentary. 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 The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic–Jurassic extinction event, 201.3 Ma&nb ...
Kayenta Formation The Kayenta Formation is a geological formation in the Glen Canyon Group that is spread across the Colorado Plateau area of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Originally suggested as being Sinemur ...
and from a protosuchid from the Lower Jurassic McCoy Brook Formation in
Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...
. The vertebral column includes nine cervical and at least eight dorsal vertebrae, with articulated ribs and osteoderms. The limbs, including a nearly complete femur, humerus, and parts of the tibia, fibula, and tarsus, show slight bowing and robust articulations. Osteoderms are extensive, with sculpted dorsal ones wider than long and flat ventral ones, some possibly armoring the limbs.


History and classification


Holotype

''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. The material was first mentioned briefly four years earlier in a paper on Lufeng fossil vertebrates. The
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
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. Based on these features, Young found no close similarities between the jaw of ''Platyognathus'' and any other known early
crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably mor ...
such as '' Notochampsa'', '' Sphenosuchus'', '' Erythrochampsa'', and '' Pedeticosaurus'' (at the time, these crocodylomorphs were collectively known as the "
Pseudosuchia Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...
"). The jaw of ''
Protosuchus richardsoni ''Protosuchus'' (from , "first" and , "crocodile") is an extinct genus of carnivorous crocodyliform from the Early Jurassic. It is among the earliest animals that resemble crocodilians. ''Protosuchus'' was about in length and about in weight. ...
'', described by
Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. He discovered the first documented remains of ''Tyrannosaurus'' during a career that made him one of the most famous fossil ...
in 1933 from
Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...
, is similar in size to that of ''Platyognathus'', although it lacks many of the distinguishing features of the Asian form as described by Young. Because ''Platyognathus'' differed from any other known pseudosuchian, Young suggested that it may belong to its own family. During
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, 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''. In 1955, it was suggested to have affinities with
aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...
s, and in 1956
Alfred Romer Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution. Biography Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...
tentatively assigned it to the Notochampsidae (later synonymized with Protosuchidae).


New material

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. Most later studies of ''Platyognathus'' were based on one specimen of the new material known as CUP 2083 which preserved the lower jaw. Some of these studies concluded that ''Platyognathus'' was a pseudosuchian related to ''Sphenosuchus'' and ''Pedeticosaurus'', but most considered it to be a protosuchian. 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. 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 Crocodyliformes is a clade of Crurotarsi, crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the ...
taxa of uncertain affinities. In that paper, the validity of ''P. hsui'' was questioned on the basis of Young's description of the holotype. In 2025, the most complete known mature specimen was reported, with the describers classifying the genus as a member of their new crocodyliform clade
Gobiosuchoidea Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseudo ...
.


Neotype

In 1996, a newly described partial skull known as IVPP V8266 that was referable to ''Platyognathus'' was designated as a
neotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...
. 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. 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. The new skull revealed an additional diagnostic feature of ''Platyognathus'' that distinguishes it from other protosuchians: the distinctive curvature of the
jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...
. 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 The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
and
maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
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 In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
containing Protosuchidae and ''
Shantungosuchus ''Shantungosuchus'' is an extinct genus of Early Cretaceous crocodyliform found in China. It includes three species: ''Shantungosuchus chuhsienensis'' and ''S. brachycephalus'', which were both described by Yang Zhongjian – usually referre ...
'' 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. An unnamed
mesosuchia "Mesosuchia" is an obsolete name for a group of terrestrial, semi-aquatic, or fully aquatic crocodylomorph reptiles. Characteristics The marine crocodile '' Metriorhynchus'' had paddle-like forelimbs, '' Dakosaurus andiniensis'' had a skull that ...
n from the Salt Wash Member of the
Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...
Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltston ...
of western
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in the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
possesses several features that are also seen in ''Platyognathus''. 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.


References


External links


''Platyognathus''
in the
Paleobiology Database The Paleobiology Database (PBDB) is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database originated in the NCEAS-funded Phanerozoic Marine Pale ...
{{Taxonbar, from=Q7202680 Crocodyliformes Terrestrial crocodylomorphs Early Jurassic crocodylomorphs Early Jurassic reptiles of Asia Prehistoric pseudosuchian genera