''Yonghesuchus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

. Remains have been found from the early Late Triassic Tongchuan Formation in

Shanxi Shanxi (; ; formerly romanised as Shansi) is a landlocked province of the People's Republic of China and is part of the North China region. The capital and largest city of the province is Taiyuan, while its next most populated prefecture-lev ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

. It is named after

Yonghe County Yonghe County () is a county in the southwest of Shanxi province, China, bordering Shaanxi province to the west across the Yellow River. It is under the administration of the prefecture-level city of Linfen, and located in its northwest corner. The ...

, 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.

Description

''Yonghesuchus'' is known from two skulls, one with an attached

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

(the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

) and one with articulated cervical

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

e. The holotype skull, known as

IVPP The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP; ) of China is a research institution and collections repository for fossils, including many dinosaur and pterosaur specimens (many from the Yixian Formation). As its name suggest ...

V 12378, has been deformed by compression during preservation so that it has become

dorsoventrally Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

flattened. The paratype skull, known as IVPP V 12379, has also experienced damage as a result of its preservation. 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 mammal has b ...

, the bone at the front of the snout, projects past the front teeth to form a small pointed tip at the end of the snout. Behind the

is the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates 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 t ...

, which contains a small depression that forms part of the

antorbital fossa 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 archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, birds ...

. This depression distinguishes ''Yonghesuchus'' from related archosauriforms such as ''

Turfanosuchus ''Turfanosuchus'' is a genus of archosauriform reptile, likely a Gracilisuchidae, gracilisuchid archosaur, which lived during the Middle Triassic (Anisian) of northwestern China. The type species, ''T. dabanensis'', was described by Yang Zhongjia ...

''. As in other archosauriforms such as ''Turfanosuchus'' and ''

Euparkeria ''Euparkeria'' (; meaning "Parker's good animal", named in honor of W.K. Parker) is an extinct genus of archosauriform from the Middle Triassic of South Africa. It was a small reptile that lived between 245-230 million years ago, and was close ...

'', the

palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sepa ...

is covered in very small teeth called denticles. Behind the palate, the basisphenoid bone (which forms the floor of the

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

) is long and narrows toward the front. This is another distinguishing characteristic of ''Yonghesuchus'', as other early archosauriforms have shorter and wider basisphenoid bones. Moreover, the entrance of the

internal carotid artery The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these b ...

, which passes through a

foramen In anatomy and osteology, a foramen (;Entry "foramen"
in

in the basisphenoid to supply blood to the brain, is in a different position than related genera. Its position is more similar to that of ''

Dorosuchus ''Dorosuchus'' is an extinct genus of archosauriform previously assigned to the family Euparkeriidae. It lived during the Anisian stage of the Middle Triassic. Fossil material is known from Sol-Iletsk in Orenburg Oblast, Russia. The type speci ...

'' (a euparkeriid) and more

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

archosauriforms. In the lower jaw, the

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

bone has two projections at its posterior end where it attaches to the

, the higher one being markedly longer than the lower one. The high projection comprises much of the upper margin of the mandibular fenestra, an opening along the side of the jaw. The mandibular fenestra is longer and narrower than those of related archosauriforms such as ''Turfanosuchus'', ''Euparkeria'', and ''

Ornithosuchus ''Ornithosuchus'' (meaning "bird crocodile") is an extinct genus of pseudosuchians from the Late Triassic (Carnian) Lossiemouth Sandstone of Scotland. It was originally thought to be the ancestor to the carnosaurian dinosaurs (such as ''Allosauru ...

''. At the back of the jaw is the retroarticular region, which extends backward from the jaw joint. On the dorsal surface of this region on the

articular The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals. Anatomy In most vertebrates, the articular bone is connected to two oth ...

bone is a prominent ridge that is not seen in other archosauriforms. There is a wing-like projection on the medial, or inner, surface of the articular which is called the medial process. This process is also seen in

sphenosuchia Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Middle Jurassic. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms, a ...

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. During Mesozoic and early Cenozoic times, cro ...

s and

rauisuchia "Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilia ...

ns. ''Yonghesuchus'', like ''Turfanosuchus'', has small, compressed, recurved premaxillary teeth in the front of the upper jaw. The maxillary teeth are larger, more compressed, and serrated. The largest of these are the fourth and fifth maxillary teeth (the ninth and tenth teeth from the tip of the jaw). Teeth behind these get progressively smaller and end below the

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

, or eye socket. The cervical vertebrae, which are only known in the paratype, are amphicoelous, meaning that they are concave at both ends. These vertebrae bear small ribs that are similar to other archosauriformes, including

crocodyliforms 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 ...

Classification

''Yonghesuchus'' was not considered to be a

crown-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

, but rather a closely related advanced archosauriform. One feature that excluded it from Archosauria was its palatal teeth, which are not found in any archosaur (but are known to vary in other cladesMahler, L., and M. Kearney. (2006) The palatal dentition in squamate reptiles: morphology, development, attachment, and replacement. Fieldiana 108:1-61.). ''Yonghesuchus'' was considered to be more closely related to archosaurs than the related

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Proterochampsidae Proterochampsidae is a family of proterochampsian archosauriforms. Proterochampsids may have filled an ecological niche similar to modern crocodiles, and had a general crocodile-like appearance. They lived in what is now South America in the Mid ...

based on the position of the foramen for the carotid artery on the basisphenoid bone, which in ''Yonghesuchus'' was presumably more similar to that seen in archosaurs. The position of the foramen has also been an indication that ''Yonghesuchus'' is more closely related to archosaurs than ''Turfanosuchus'', which has a foramen in a position that is

plesiomorphic In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and ...

in archosauriformes and similar to proterochampsids. Xu ''et al.'' (2001), the first to describe ''Yonghesuchus'', suggested that among non-archosaurian archosauriformes, ''Yonghesuchus'' was the most closely related, followed by Proterochampsidae, ''Turfanosuchus'', and ''Euparkeria''. Xu ''et al.'' supported this claim with the geological position of these taxa, which are successively older from ''Yonghesuchus'' (early Late Triassic) to ''Euparkeria'' (late

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

). A later

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis on basal archosauriforms by Dilkes and Sues (2009) placed proterochampsids in a more basal position than ''Turfanosuchus'' and ''Yonghesuchus'', which were considered successive

sister taxa In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

to Archosauria. In most recent analyses, ''Yonghesuchus'' has been recovered as in a well supported clade, the

Gracilisuchidae Gracilisuchidae is an extinct family of suchian archosaurs known from the early Middle Triassic to the early Late Triassic (Anisian – early Carnian) of China and Argentina. Distribution Currently, the oldest known gracilisuchid is '' Turfanos ...

within the

Pseudosuchia Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...

, along with ''Gracilisuchus'' and ''Turfanosuchus''.Butler, R.J. et al. (2014) New clade of enigmatic early archosaurs yield insights into early pseudosuchian phylogeny and the biogeography of the archosaur radiation. ''BMC Evolutionary Biology'' 14: 128, http://www.biomedcentral.com/1471-2148/14/128/abstract

References

External links

''Yonghesuchus''
in the

Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database (PBDB) originated in the NCEAS-funded Phanerozoic Marine Pale ...

{{Taxonbar, from=Q8055005 Triassic archosaurs Gracilisuchids Late Triassic reptiles of Asia Prehistoric pseudosuchian genera