Shartegosuchidae is an extinct

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

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the ...

and

Early Cretaceous The Early Cretaceous (geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pr ...

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. The family is named after the Late Jurassic Shar Teeg Beds in southwestern

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 millio ...

, from which most shartegosuchid remains have been found. Five genera are currently assigned to Shartegosuchidae: '' Shartegosuchus'', ''

Nominosuchus ''Nominosuchus'' is a genus of protosuchian-grade crocodylomorph. It is known from several specimens discovered in ancient lake deposits of the Tithonian-age Upper Jurassic Tsagaantsav Formation, southwestern Mongolia. The type specimen is PIN& ...

'', '' Kyasuchus'', '' Adzhosuchus'', and ''

Fruitachampsa ''Fruitachampsa'' is a genus of shartegosuchid crocodyliform from the Upper Jurassic Morrison Formation of Colorado. It is known from multiple specimens that show it to have been a relatively long-limbed terrestrial quadrupedal predator less tha ...

''. ''Shartegosuchus'', ''Nominosuchus'', and ''Adzhosuchus'' all come from Shar Teeg, while ''Kyasuchus'' is known from the Early Cretaceous of

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eigh ...

. ''Fruitachampsa'' is known from the Late Jurassic

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, siltstone, ...

of the western United States.

Description

Shartegosuchids are known only from cranial material, or parts of the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...

and some partial skeletons. Shartegosuchids share several distinct characteristics in the skull. On 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 s ...

, the

choana The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilia ...

e (holes where the

nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal ...

opens into the mouth) is placed within a deep depression of its midline. The palatal bones, located behind the choanae in what is known as the secondary palate, unite with each other at the midline of the palate. Shartegosuchids can also be diagnosed by the position of the teeth in their lower jaws, which are never found behind the mandibular fenestrae (holes found near the back of the jaw). The edges of the teeth are denticulated, or ridged. The shape and position of several bones of the skull, including the

frontal Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * ''The Front'', 1976 film Music *The Front (band), an American rock band signed to Columbia Records and active in the 1980s and ea ...

, nasal, lacrimal, and quadrate, are also distinctive. Unlike most other archosaurs, shartegosuchids lack an

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

, an opening in the skull in front of the eyes.

Classification

Shartegosuchids are considered to be basal crocodyliforms, but their classification within the group is still debated. At various times since the construction of the family, shartegosuchids have been considered to be protosuchians, mesosuchians, and perhaps

notosuchia Notosuchia is a suborder of primarily Gondwanan mesoeucrocodylian crocodylomorphs that lived during the Jurassic and Cretaceous. Some phylogenies recover Sebecosuchia as a clade within Notosuchia, others as a sister group (see below); if Sebec ...

ns or atoposaurids. ''

'', a crocodylomorph from the Morrison Formation in

Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

, is also referable to Shartegosuchidae. Before it was formally named in 2011, it was commonly known as the " Fruita form". The known material of ''Fruitachampsa'' consists of several nearly complete skeletons. It was first classified in the suborder Mesosuchia, which has since been replaced by the clade

Mesoeucrocodylia Mesoeucrocodylia is the clade that includes Eusuchia and crocodyliforms formerly placed in the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day. Diagnosis It was long known that M ...

. However, ''Fruitachampsa'' can be linked to shartegosuchids on the basis of similarities in the structure of the front of the palate and the choana. In a 2004 phylogenetic study, ''Fruitachampsa'', along with '' Gobiosuchus'' and ''

Zosuchus ''Zosuchus'' ("Zos anyoncrocodile") is a genus of basal, Late Cretaceous crocodyliform from the Mongolia. The type species is ''Z. davidsoni'', after preparator Amy Davidson. The name was emended to ''davidsonae'' in 2004. Discovery It was f ...

'', was found to be outside Mesoeucrocodylia, but still more derived than Protosuchidae, a family that is often thought to be closely related to shartegosuchids. A more recent study in 2006 found Shartegosuchidae to be the most basal clade of mesosuchians. A phylogenetic analysis found the family to be

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic ...

, meaning that it forms a true clade with a common ancestor from which only shartegosuchids are derived. "Fruitachampsa" was found to be outside Shartegosuchidae, but was the

sister taxon 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 ...

of the family. This means that it is more closely related to Shartegosuchidae than any other crocodyliform. Below is a

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

based on the 2006 study, showing the relationships of members of the family: Below is a

showing the phylogenetic placement of Shartegosuchidae from Clark (2011):

Paleobiology

The shartegosuchids from Mongolia and Russia comprise a group of crocodyliforms that was

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

Central Asia Central Asia, also known as Middle Asia, is a region of Asia that stretches from the Caspian Sea in the west to western China and Mongolia in the east, and from Afghanistan and Iran in the south to Russia in the north. It includes the former ...

during the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Creta ...

. These crocodyliforms, along with other Asiatic

tetrapod Tetrapods (; ) are four-limb (anatomy), limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant taxon, extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (p ...

s, make up a fauna that may be unique to the region due to geographic isolation that existed since the

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 ...

Early 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 ...

. This isolation first occurred when the

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which lea ...

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 millio ...

began to break apart, forming the smaller northern supercontinent of

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...

. The authors of a 2007 study of early crocodylomorphs did not include shartegosuchids in a phylogenetic analysis, indicating that they were so highly endemic to Asia that their relationship to other crocodylomorphs would be difficult to interpret.

References

{{Taxonbar, from=Q7490492 Mesozoic reptiles of Asia Jurassic crocodylomorphs Early Cretaceous crocodylomorphs Terrestrial crocodylomorphs Late Jurassic first appearances Early Cretaceous extinctions Prehistoric reptile families