Shartegosuchidae is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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 ...

and

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

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 ...

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

Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

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

Kyasuchus ''Kyasuchus'' is an extinct genus of Shartegosuchidae, shartegosuchid crocodyliform. Fossils have been found from the Ilek Formation outcropping in the Kemerovo Oblast of Russia, deposited during the Aptian and Albian stages of the Early Cretaceo ...

'', '' 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 country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

. ''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, siltston ...

of the western United States.

Description

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

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

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 sep ...

, the

choana The choanae (: choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the pharynx, in humans and other mammals (as well as crocodilians and most skinks). They ...

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 nas ...

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,

nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery * ...

, 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 Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...

, 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

protosuchia Protosuchia is a group of extinct Mesozoic crocodyliforms. They were small in size (~1 meter in length) and Terrestrial animal, terrestrial. In phylogenetic terms, Protosuchia is considered an informal group because it is a evolutionary grade, gr ...

ns,

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 ...

ns, and perhaps

notosuchia Notosuchia is a clade of primarily Gondwanan mesoeucrocodylian Crocodylomorpha, crocodylomorphs that lived during the Jurassic and Cretaceous. Some phylogeny, phylogenies recover Sebecosuchia as a clade within Notosuchia, others as a sister group ...

ns or atoposaurids. ''

'', a crocodylomorph from the Morrison Formation in

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

, is also referable to Shartegosuchidae. Before it was formally named in 2011, it was commonly known as the "

Fruita Fruita () is a home rule municipality located in western Mesa County, Colorado, United States. The city population was 13,395 at the 2020 United States census. Fruita is a part of the Grand Junction, Colorado Metropolitan Statistical Area and ...

form". The known material of ''Fruitachampsa'' consists of several nearly complete skeletons. It was first classified in the suborder

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 ...

, which has since been replaced by 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 ...

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 Me ...

. 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 Mongolia. The type species is ''Z. davidsoni'', after preparator Amy Davidson. The name was amended to ''davidsonae'' in 2004. Discovery It was found i ...

'', was found to be outside Mesoeucrocodylia, but still more derived than

Protosuchidae Protosuchidae is a family of basal crocodyliform reptiles that lived from the Late Triassic to the Late Cretaceous. This family should not be confused with Protosuchia, which is an informal evolutionary grade of primitive crocodiliforms Distr ...

, 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 biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

, 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 language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

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 only 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 foun ...

Central Asia Central Asia is a region of Asia consisting of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan. The countries as a group are also colloquially referred to as the "-stans" as all have names ending with the Persian language, Pers ...

during the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

. These crocodyliforms, along with other Asiatic

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

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 a ...

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� ...

. This isolation first occurred when the

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

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 period approximately 335 mi ...

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 Pa ...

. 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 Crocodyliformes Mesozoic reptiles of Asia Jurassic crocodylomorphs Early Cretaceous crocodylomorphs Terrestrial crocodylomorphs Late Jurassic first appearances Early Cretaceous extinctions Pseudosuchian families