Yonghesuchus
Encyclopedia
Yonghesuchus is an extinct genus
of Late Triassic
archosauriform
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.
(the holotype
) and one with articulated cervical vertebrae. The holotype skull, known as IVPP
V 12378, has been deformed by compression during preservation so that it has become dorsoventrally flattened. The paratype skull, known as IVPP V 12379, has also experienced damage as a result of its preservation.
The premaxilla
, 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 premaxilla
is the maxilla
, which contains a small depression that forms part of the antorbital fossa
. This depression distinguishes Yonghesuchus from related archosauriforms such as Turfanosuchus
. As in other archosauriforms such as Turfanosuchus and Euparkeria
, the palate
is covered in very small teeth called denticles. Behind the palate, the basisphenoid bone (which forms the floor of the braincase) 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
, which passes through a foramen
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
(a euparkeriid
) and more derived
archosauriforms.
In the lower jaw, the dentary bone has two projections at its posterior end where it attaches to the mandible
, 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
. 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
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
n crocodylomorphs and rauisuchia
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
, or eye socket.
The cervical vertebrae, which are only known in the paratype, are amphicoelus, meaning that they are concave at both ends. These vertebrae bear small ribs that are similar to other archosauriformes, including crocodyliforms
.
, but rather a closely related advanced archosauriform. One feature that excludes it from Archosauria is its palatal teeth, which are not found in any archosaur. Yonghesuchus is considered to be more closely related to archosaurs than the related family
Proterochampsidae
based on the position of the foramen for the carotid artery on the basisphenoid bone, which in Yonghesuchus is 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 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
). A later phylogenetic 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 to Archosauria.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
archosauriform
Archosauriformes
Archosauriformes is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Late Permian...
reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
. Remains have been found from the early Late Triassic Tongchuan Formation in Shanxi
Shanxi
' is a province in Northern China. Its one-character abbreviation is "晋" , after the state of Jin that existed here during the Spring and Autumn Period....
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. It is named after Yonghe County
Yonghe County
Yonghe County is a county of Shanxi, China. It is under the administration of Linfen city.-References:*...
, 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 mandibleMandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
(the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
) and one with articulated cervical vertebrae. The holotype skull, known as IVPP
Institute of Vertebrate Paleontology and Paleoanthropology
The Institute of Vertebrate Paleontology and Paleoanthropology of China is a prominent research institution and collections repository for fossils, including many dinosaur and pterosaurand cat poo specimens...
V 12378, has been deformed by compression during preservation so that it has become dorsoventrally flattened. The paratype skull, known as IVPP V 12379, has also experienced damage as a result of its preservation.
The premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
, 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 premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
is the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
, which contains a small depression that forms part of the antorbital fossa
Antorbital fenestra
An antorbital fenestra is an opening in the skull, in front of the eye sockets. This skull formation first appeared in archosaurs during the Triassic Period. Living birds today possess antorbital fenestrae, but the feature has been lost in modern crocodilians...
. This depression distinguishes Yonghesuchus from related archosauriforms such as Turfanosuchus
Turfanosuchus
Turfanosuchus is a genus of archosauriform reptile which lived during the Middle Triassic of northwestern China. The type species, T. dabanensis, was described by C.C. Young in 1973, based on a partially complete but disarticulated fossil skeleton...
. As in other archosauriforms such as Turfanosuchus and Euparkeria
Euparkeria
Euparkeria was a small African reptile of the early Triassic period between 248-245 million years ago, close to the ancestry of the archosaurs.- Palaeobiology :...
, the palate
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 separate. The palate is divided into two parts, the anterior...
is covered in very small teeth called denticles. Behind the palate, the basisphenoid bone (which forms the floor of the braincase) 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
Internal carotid artery
In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....
, which passes through a foramen
Foramen
In anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.-Skull:...
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
Dorosuchus is an extinct genus of archosauriform that is possibly a member of 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 species is D...
(a euparkeriid
Euparkeriidae
Euparkeriidae is a family of small basal archosauromorph carnivores which lived from the Early Triassic to the Middle Triassic . Their fossil remains are known so far from South Africa and Russia...
) and more derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
archosauriforms.
In the lower jaw, the dentary bone has two projections at its posterior end where it attaches to the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
, 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
Ornithosuchus is an extinct genus of crurotarsan from the Late Triassic Lossiemouth Sandstone of Scotland...
. 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
Articular
The articular bone is part of the lower jaw of most tetrapods, including amphibians, sauropsids and early synapsids. In these animals it is connected to two other lower jaw bones, the suprangular and the angular...
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
Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Late Jurassic. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms, which include all living crocodilians.-Stratigraphic...
n crocodylomorphs and rauisuchia
Rauisuchia
Rauisuchia is a group of predatory and mostly large Triassic archosaurs. As a clade, Rauisuchia includes these Triassic forms and all crocodylomorphs, which are descendants of Triassic rauisuchians. The group in its traditional sense is paraphyletic, because it does not include crocodylomorph...
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
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
, or eye socket.
The cervical vertebrae, which are only known in the paratype, are amphicoelus, meaning that they are concave at both ends. These vertebrae bear small ribs that are similar to other archosauriformes, including crocodyliforms
Crocodyliformes
Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians."In 1988, Michael J. Benton and James M. Clark argued that all traditional names for well-known groups of animals should be restricted to their crown clades, that is, used only for...
.
Classification
Yonghesuchus is not considered to be a crown-group archosaurArchosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
, but rather a closely related advanced archosauriform. One feature that excludes it from Archosauria is its palatal teeth, which are not found in any archosaur. Yonghesuchus is considered to be more closely related to archosaurs than the related family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Proterochampsidae
Proterochampsidae
Proterochampsidae is a family of 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 Middle and Late Triassic....
based on the position of the foramen for the carotid artery on the basisphenoid bone, which in Yonghesuchus is 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 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
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
). A later phylogenetic 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 to Archosauria.
External links
- Yonghesuchus in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...