Shartegosuchidae
Encyclopedia
Shartegosuchidae is an extinct family
of Late Jurassic
and Early Cretaceous
crocodylomorphs. The family is named after the Late Jurassic Shar Teeg Beds
in southwestern Mongolia
, from which most shartegosuchid remains have been found. Four genera are currently assigned to Shartegosuchidae: Shartegosuchus
, Nominosuchus
, Kyasuchus
, and Adzhosuchus
. Shartegosuchus, Nominosuchus, and Adzhosuchus all come from Shar Teeg, while Kyasuchus is known from the Early Cretaceous of Russia
. Another genus from the Late Jurassic Morrison Formation
in the western United States
may belong to the family, but it has not yet been described and is thus a nomen nudum
.
. No remains of any other parts of the body have been found. Shartegosuchids share several distinct characteristics in the skull. On the palate
, the choana
e (holes where the nasal cavity
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
, lacrimal
, and quadrate
, are also distinctive. Unlike most other archosaurs, shartegosuchids lack an antorbital fenestra
, an opening in the skull in front of the eyes.
ns, mesosuchia
ns, and perhaps notosuchia
ns of atoposaurids.
"Fruitachampsa
", an informal name given to a crocodylomorph from the Morrison Formation in Colorado
, may be referable to a shartegosuchid. It is commonly known as the "Fruita
form", and consists of several nearly complete skeletons. It was first classified in the suborder Mesosuchia
, which has since been replaced by the clade
Mesoeucrocodylia
. Shartegosuchidae lies outside Mesosuchia, being a more basal
group of crocodyliforms, so "Fruitachampsa" would not belong to the family if this was the case. 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
, 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, 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 of the family. This means that it is more closely related to Shartegosuchidae than any other crocodyliform.
Below is a cladogram
based on the 2006 study, showing the relationships of members of the family:
during the Mesozoic
. These crocodyliforms, along with other Asiatic tetrapod
s, make up a fauna that may be unique to the region due to geographic isolation that existed since the Late Triassic
or Early Jurassic
. This isolation first occurred when the supercontinent
Pangaea
began to break apart, forming the smaller northern supercontinent of Laurasia
. 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.
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...
of 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...
and Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
crocodylomorphs. The family is named after the Late Jurassic Shar Teeg Beds
Shar Teeg Beds
The Shar Teeg Beds 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...
in southwestern 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...
, from which most shartegosuchid remains have been found. Four genera are currently assigned to Shartegosuchidae: Shartegosuchus
Shartegosuchus
Shartegosuchus is a genus of protosuchian-grade crocodylomorph. It is known primarily from PIN 4174/2, the partial deformed skull and jaws of a juvenile. This specimen was discovered in ancient lake deposits of the Tithonian-age Upper Jurassic Tsagaantsav Formation, southwestern Mongolia. ...
, Nominosuchus
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 4174/4, a partial skull. Nominosuchus was not...
, Kyasuchus
Kyasuchus
Kyasuchus is an extinct genus of shartegosuchid crocodylomorph. 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 Cretaceous...
, and Adzhosuchus
Adzhosuchus
Adzhosuchus is an extinct genus of crocodylomorph in the family Shartegosuchidae. Fossils have been found from southwestern Mongolia that date back to the Late Jurassic period....
. Shartegosuchus, Nominosuchus, and Adzhosuchus all come from Shar Teeg, while Kyasuchus is known from the Early Cretaceous of Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. Another genus from the Late Jurassic Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is 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 and limestone and is light grey, greenish...
in the western United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
may belong to the family, but it has not yet been described and is thus a nomen nudum
Nomen nudum
The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...
.
Description
Shartegosuchids are known only from cranial material, or parts of the skullSkull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
. No remains of any other parts of the body have been found. Shartegosuchids share several distinct characteristics in the skull. On 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...
, the choana
Choana
Choana is the posterior nasal aperture.The choanae are separated by the vomer.- Boundaries :It is the opening between the nasal cavity and the nasopharynx....
e (holes where the nasal cavity
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
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
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....
, nasal
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
, lacrimal
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
, and quadrate
Quadrate bone
The quadrate bone is part of a skull in most tetrapods, including amphibians, sauropsids , and early synapsids. In these animals it connects to the quadratojugal and squamosal in the skull, and forms part of the jaw joint .- Evolutionary variation :In snakes, the quadrate bone has become elongated...
, are also distinctive. Unlike most other archosaurs, shartegosuchids lack an antorbital fenestra
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...
, 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 protosuchiaProtosuchia
Protosuchia is a group of extinct Mesozoic crocodyliforms. They were small in size and terrestrial. In phylogenetic terms, Protosuchia is considered an informal group because it is a grade of basal crocodyliforms, not a true clade....
ns, 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...
ns, and perhaps notosuchia
Notosuchia
Notosuchia is a suborder of primarily Gondwanan mesoeucrocodylian crocodylomorphs that lived during the Cretaceous. Fossils have been found from South America, Africa, and Asia...
ns of atoposaurids.
"Fruitachampsa
Fruitachampsa
"Fruitachampsa" is an informal name for an as-yet undescribed genus of mesoeucrocodylian 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 than long, with a short...
", an informal name given to a crocodylomorph from the Morrison Formation in Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
, may be referable to a shartegosuchid. It is commonly known as the "Fruita
Fruita, Colorado
The City of Fruita is a Home Rule Municipality located in the western part of Mesa County, Colorado, in the United States. It is part of the Grand Junction Metropolitan Statistical Area and within the Grand Valley...
form", and consists of several nearly complete skeletons. It was first classified in the suborder 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...
, which has since been replaced by the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
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....
. Shartegosuchidae lies outside Mesosuchia, being a more basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
group of crocodyliforms, so "Fruitachampsa" would not belong to the family if this was the case. 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
Gobiosuchus
Gobiosuchus was a gobiosuchid crocodyliform described in 1972 by Polish palaeontologist Halszka Osmólska. It hails from the Late Cretaceous of Bayn Dzak , in the Gobi Desert of Mongolia....
and Zosuchus
Zosuchus
Zosuchus is a genus of basal, Late Cretaceous crocodyliform from the Redbeds of Zos Canyon in the Gobi Desert of Mongolia. It was discovered by expeditions organized by the American Museum of Natural History, and described by palaeontologists Diego Pol and Mark Norell.The type species is Z...
, was found to be outside Mesoeucrocodylia, but still more derived than Protosuchidae
Protosuchidae
Protosuchidae was a family of crocodylmorph reptiles from the Late Triassic, Jurassic, and Cretaceous time periods.-Distribution:Triassic protosuchids are known from Lesotho and Arizona. Jurassic protosuchids are known from Nova Scotia, Poland, South Africa, and Arizona...
, 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, 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 of the family. This means that it is more closely related to Shartegosuchidae than any other crocodyliform.
Below is a cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
based on the 2006 study, showing the relationships of members of the family:
Paleobiology
The shartegosuchids from Mongolia and Russia comprise a group of crocodyliforms that was endemic to Central AsiaCentral Asia
Central Asia is a core region of the Asian continent from the Caspian Sea in the west, China in the east, Afghanistan in the south, and Russia in the north...
during the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
. These crocodyliforms, along with other Asiatic tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s, make up a fauna that may be unique to the region due to geographic isolation that existed since the 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...
or Early Jurassic
Early Jurassic
The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...
. This isolation first occurred when the supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
began to break apart, forming the smaller northern supercontinent of Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
. 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.