Sunosuchus
Encyclopedia
Sunosuchus is an extinct genus
of goniopholidid mesoeucrocodylia
n. Fossils are known from China
, Kyrgyzstan
and Thailand
and are Jurassic
in age, although some may be Early Cretaceous
. Five species are currently assigned to the genus: the type species
S. miaoi and the species S. junggarensis, S. shartegensis, S. shunanensis, and S. thailandicus. All species are from China with the exception of S. thailandicus, which is from Thailand. The material from Kyrgystan has not been assigned to any species.
. Several characters help diagnose Sunosuchus and distinguish it from other taxa. For example, there are wide pits on the back of the frontal bone
. The frontal bone
also has a distinctive ridge along part of its midline. The lower jaw has a long symphysis
where the two halves come together. This symphysis is formed mostly from the mandible
s, but also partially by the splenial
s. Unlike other goniopholidids, the squamosal bone (which is found near the back of the skull) is narrow.
, which is very robust. The tip of the jaw is spoon shaped and wider than the portion of the jaw immediately behind it. The mandible was collected from the Phu Kradung Formation
near the town of Nong Bua Lamphu. This single specimen is the most well preserved vertebrate fossil that has been found from the formation; other vertebrates, including dinosaur
s, are known only from fragmentary remains. The age of the Phu Kradung Formation is uncertain. It was once thought to be Early Jurassic, which would make S. thailandicus the oldest species of Sunosuchus. However, the formation has more recently been considered to be Late Jurassic to Early Cretaceous in age. If so, S. thailandicus would be the youngest species of the genus. S. thailandicus shares features with both goniopholidids and pholidosaurid
s, and has been considered an indication of a close relation between the two groups.
S. junggarensis is the best known species of Sunosuchus. It was first described in 1996 from the Late Jurassic
Junggar Basin in Xinjiang
, China.
Material belonging to Sunosuchus was collected from Kyrgyzstan in the 1980s and was described in 2000. Many teeth were found, as well as a dorsal vertebra and some vertebral centra, some pelvic bones, part of a fibula and tibia
, a few metatarsals, and ventral and neck osteoderm
s. The only parts of the skull uncovered were squamosal bones. The squamosals are similar to those of other species of Sunosuchus but not those of other genera, which indicates that the material belongs to a species of Sunosuchus. While the specimens bear a strong resemblance to the bones of S. junggarensis, they have not been assigned to any species.
A fifth species, S. shunanensis, was described in 2005 from the Middle Jurassic of Zigong
in Sichuan
, China. Skulls were collected from the Dashanpu Dinosaur Quarry
in 1983, having been found in the Lower Shaximiao Formation. S. shunanensis has a longer snout than other species, being around three times the length of the postorbital region, or the portion of the skull behind the eyes. It also has a wider skull table than other species. The skull is widest at the back rather than between the eyes, a feature only seen in S. shunanensis. Near the back of each maxilla there is a distinct depression. There are unique ridges across the surface of the skull, one pair at the front of the eye socket on the lacrimal
s, and a second along the sides of the bacioccipitals and the undersurfaces of the exoccipitals at the base of the skull.
, although to a lesser degree than Sunosuchus. Despite the similarities with pholidosaurs, Sunosuchus shares several features with goniopholidids that ally it with the group. Among these features are small supratemporal fenestrae and openings at the front of the palate
. However, these features can also be considered plesiomorphic among Mesosuchia
, the group to which both goniopholidids and pholidosaurids belong. If this is the case, it is possible that Sunosuchus, or at least S. thailandicus, represents a primitive pholidosaur retaining old characteristics rather than an advanced goniopholidid.
or Late Triassic
, the Thai-Chan, Indochina, and South China
landmasses collided as part of the Indonesian orogeny to form these mountains. The resulting erosion resulted in the distinctive molasse
that remains of S. thailandicus have been found in. Also in these deposits are bivalves and other crocodyliform teeth, indicating that S. thailandicus inhabited a freshwater environment.
The material from Kyrgyzstan is the westernmost record of the geographic range of Sunosuchus. The strata from which this material has been found are similar to those of Mongolia
n and Chinese Middle and Late Jurassic strata. These areas shared a similar fauna that is characterized by crocodyliforms such as Sunosuchus as well as temnospondyl amphibian
s and xinjiangchelyid turtle
s, indicating freshwater environments across the region. Marine hybodont
shark
s and dipnoans are found in the Kyrgyzstan strata, suggesting that the area was estuarine at the time rather than entirely freshwater.
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 goniopholidid mesoeucrocodylia
Mesoeucrocodylia
Mesoeucrocodylia is the name of the clade that includes Eusuchia and the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day....
n. Fossils are known from 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...
, Kyrgyzstan
Kyrgyzstan
Kyrgyzstan , officially the Kyrgyz Republic is one of the world's six independent Turkic states . Located in Central Asia, landlocked and mountainous, Kyrgyzstan is bordered by Kazakhstan to the north, Uzbekistan to the west, Tajikistan to the southwest and China to the east...
and Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
and are Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
in age, although some may be Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
. Five species are currently assigned to the genus: the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
S. miaoi and the species S. junggarensis, S. shartegensis, S. shunanensis, and S. thailandicus. All species are from China with the exception of S. thailandicus, which is from Thailand. The material from Kyrgystan has not been assigned to any species.
Description
Sunosuchus has a long, narrow snout and a small skull tableSkull roof
The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...
. Several characters help diagnose Sunosuchus and distinguish it from other taxa. For example, there are wide pits on the back of the frontal bone
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
. The frontal bone
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
also has a distinctive ridge along part of its midline. The lower jaw has a long symphysis
Symphysis
A symphysis is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint.1.A symphysis is an amphiarthrosis, a slightly movable joint.2.A growing together of parts or structures...
where the two halves come together. This symphysis is formed mostly from the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
s, but also partially by the splenial
Splenial
The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side between the angular and suprangular....
s. Unlike other goniopholidids, the squamosal bone (which is found near the back of the skull) is narrow.
Species
S. thailandicus was described from northeastern Thailand in 1980. It is known only from the mandibleMandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
, which is very robust. The tip of the jaw is spoon shaped and wider than the portion of the jaw immediately behind it. The mandible was collected from the Phu Kradung Formation
Phu Kradung Formation
The Phu Kradung Formation is a Mesozoic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus.-See also:* List of dinosaur-bearing rock formations...
near the town of Nong Bua Lamphu. This single specimen is the most well preserved vertebrate fossil that has been found from the formation; other vertebrates, including dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, are known only from fragmentary remains. The age of the Phu Kradung Formation is uncertain. It was once thought to be Early Jurassic, which would make S. thailandicus the oldest species of Sunosuchus. However, the formation has more recently been considered to be Late Jurassic to Early Cretaceous in age. If so, S. thailandicus would be the youngest species of the genus. S. thailandicus shares features with both goniopholidids and pholidosaurid
Pholidosauridae
Pholidosauridae is an extinct family of mesoeucrocodylian crocodylomorphs. Fossils have been found in the United States, Canada, China, Kyrgyzstan, Africa and Spain...
s, and has been considered an indication of a close relation between the two groups.
S. junggarensis is the best known species of Sunosuchus. It was first described in 1996 from the Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
Junggar Basin in Xinjiang
Xinjiang
Xinjiang is an autonomous region of the People's Republic of China. It is the largest Chinese administrative division and spans over 1.6 million km2...
, China.
Material belonging to Sunosuchus was collected from Kyrgyzstan in the 1980s and was described in 2000. Many teeth were found, as well as a dorsal vertebra and some vertebral centra, some pelvic bones, part of a fibula and tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
, a few metatarsals, and ventral and neck osteoderm
Osteoderm
Osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs , crocodilians, phytosaurs, aetosaurs, placodonts, and hupehsuchians...
s. The only parts of the skull uncovered were squamosal bones. The squamosals are similar to those of other species of Sunosuchus but not those of other genera, which indicates that the material belongs to a species of Sunosuchus. While the specimens bear a strong resemblance to the bones of S. junggarensis, they have not been assigned to any species.
A fifth species, S. shunanensis, was described in 2005 from the Middle Jurassic of Zigong
Zigong
Zigong , ancient name Ziliujing and Gongjing, is a prefecture-level city and the third largest city in Sichuan Province, in southwest China.-Geography:...
in Sichuan
Sichuan
' , known formerly in the West by its postal map spellings of Szechwan or Szechuan is a province in Southwest China with its capital in Chengdu...
, China. Skulls were collected from the Dashanpu Dinosaur Quarry
Dashanpu Formation
The Dashanpu Formation is a Mid to Late Jurassic rock formation in China, most notable for the wealth of dinosaurs that have been excavated from the area...
in 1983, having been found in the Lower Shaximiao Formation. S. shunanensis has a longer snout than other species, being around three times the length of the postorbital region, or the portion of the skull behind the eyes. It also has a wider skull table than other species. The skull is widest at the back rather than between the eyes, a feature only seen in S. shunanensis. Near the back of each maxilla there is a distinct depression. There are unique ridges across the surface of the skull, one pair at the front of the eye socket on the lacrimal
Lacrimal
The term Lacrimal can refer to:*In typography:** A type of Stroke ending *In anatomy** Lacrimal apparatus** Lacrimal artery** Lacrimal bone...
s, and a second along the sides of the bacioccipitals and the undersurfaces of the exoccipitals at the base of the skull.
Classification
Sunosuchus was initially classified as a pholidosaurid because its jaws were long, making it a longirostrine, or long-snouted, crocodyliform. Most pholidosaurs are longirostrine, while goniopholidids usually have shorter snouts. The mandibular symphysis of S. thailandicus is similar to that of pholidosaurs in that it is long and the region around it is expanded to form a spoon shape. This expansion is also seen in the pholidosaurid SarcosuchusSarcosuchus
Sarcosuchus is an extinct genus of crocodyliform and distant relative of the crocodile that lived 112 million years ago. It dates from the early Cretaceous Period of what is now Africa and is one of the largest giant crocodile-like reptiles that ever lived...
, although to a lesser degree than Sunosuchus. Despite the similarities with pholidosaurs, Sunosuchus shares several features with goniopholidids that ally it with the group. Among these features are small supratemporal fenestrae and openings at the front of 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...
. However, these features can also be considered plesiomorphic among Mesosuchia
Mesosuchia
"Mesosuchia" is an obsolete name for a group of terrestrial, semi-aquatic, or fully aquatic crocodylomorph reptiles. The marine crocodile Metriorhynchus had paddle-like forelimbs, Dakosaurus andiniensis had a skull that was adapted to eat large sea reptiles, and Shamosuchus was adapted for eating...
, the group to which both goniopholidids and pholidosaurids belong. If this is the case, it is possible that Sunosuchus, or at least S. thailandicus, represents a primitive pholidosaur retaining old characteristics rather than an advanced goniopholidid.
Paleobiology
The presence of Sunosuchus in Thailand indicates that Southeast Asia had become part of Laurasia by the Jurassic. All other species of Sunosuchus have been found from China, and were thus living in Laurasia. Southeast Asia must have been in contact with Laurasia for Sunosuchus to migrate into Thailand, as it was likely a strictly freshwater animal. Based on the geology of the region, S. thailandicus most likely lived in an environment of lakes and rivers alongside a chain of mountains. During the MiddleMiddle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
or 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...
, the Thai-Chan, Indochina, and South China
South China (continent)
South China continent, also known as South China craton, South Chinese craton, or Yangtze craton, was an ancient continent that contained today's South and Southeast China , Indochina, and parts of Southeast Asia...
landmasses collided as part of the Indonesian orogeny to form these mountains. The resulting erosion resulted in the distinctive molasse
Molasse
The term "molasse" refers to the sandstones, shales and conglomerates formed as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse is deposited in a foreland basin, especially on top of flysch, for example that left from the rising Alps, or erosion in the Himalaya...
that remains of S. thailandicus have been found in. Also in these deposits are bivalves and other crocodyliform teeth, indicating that S. thailandicus inhabited a freshwater environment.
The material from Kyrgyzstan is the westernmost record of the geographic range of Sunosuchus. The strata from which this material has been found are similar to those of Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
n and Chinese Middle and Late Jurassic strata. These areas shared a similar fauna that is characterized by crocodyliforms such as Sunosuchus as well as temnospondyl amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s and xinjiangchelyid turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s, indicating freshwater environments across the region. Marine hybodont
Hybodontidae
Hybodontidae is an extinct family of sharks, first appearing in the Mississippian period, and disappearing during the Miocene....
shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s and dipnoans are found in the Kyrgyzstan strata, suggesting that the area was estuarine at the time rather than entirely freshwater.