Monjurosuchus
Encyclopedia
Monjurosuchus is a genus
of choristoderan reptile
that lived in what is now China
and Japan
during the Early Cretaceous
. It has large eyes, a rounded skull, robust legs with short claws, and a long, thin tail. Fossils have been found that preserve soft tissue, showing that it had soft skin and webbed feet. Monjurosuchus has been placed in the family Monjurosuchidae
along with Philydrosaurus
, but the relationships of early choristoderes remains unclear.
. Named in 1940, the type species
M. splendens was the first reptile described from the Yixian Formation
. The holotype
specimen was lost during World War II
but was replaced in 2000 by a recently discovered neotype preserving soft tissue. In 2007, remains were described from the Okurodani Formation
of the Tetori Group of Japan. The Japanese material represents a different species of Monjurosuchus that has not yet been named.
Unlike related choristoderes, Monjurosuchus has a relatively short neck with eight vertebrae, one less than usual. The skull is rounded rather than pointed and is dorsoventrally flattened in all fossils. The eye sockets are large and prominent temporal regions extend from the back of the skull. The jaws are lined with small, sharp teeth, while the palate
is covered in closely spaced tooth batteries. One distinguishing feature of Monjurosuchus is the lack of a lower temporal fenestra, a hole in the back of the skull that is common in many other diapsid
reptiles, including most choristoderes. Monjurosuchus is also distinct in having small spikes on the edge of the squamosal
bone at the back of the skull.
Specimens from China preserve soft tissue, including scales and webbing between the toes of the feet. The scales of Monjurosuchus were small, giving the animal soft skin. Two rows of larger scute
s run along its back. The rest of the scales on the back are small, while the scales on the underside are slightly smaller. The skin of Monjurosuchus has a similar appearance to the living Chinese crocodile lizard
Shinisaurus.
The feet of Monjurosuchus are webbed, with skin covering all parts of the foot but the short claws. The limbs were robust and the hips are wide. The long, slender tail shows no adaptations for its presumed semi-aquatic lifestyle. Gastralia are present on the underside of Monjurosuchus and are much thinner than the ribs. Intestinal contents are preserved between the gastralia and ribs of one specimen. Most of the material is sediment, but there are also fragments of what may be arthropod cuticle
, indicating that Monjurosuchus may have fed on invertebrates.
choristodere that lies outside the more advanced Neochoristodera. When named in 1940, it was placed in its own family Monjurosuchidae
. Unlike Monjurosuchus, neochoristoderes have small, dorsally facing eyes and long snouts. Philydrosaurus
, another Early Cretaceous Chinese choristodere, was grouped with Monjurosuchus in Monjurosuchidae. A 2007 phylogenetic analysis of choristoderes found only weak support for this family, as Philydrosaurus seemed to be a more basal choristodere than Monjurosuchus. A close relationship was found between Monjurosuchus and the Miocene Lazarussuchus
, but this was only weakly supported.
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 choristoderan 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...
that lived in what is now 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...
and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
during the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
. It has large eyes, a rounded skull, robust legs with short claws, and a long, thin tail. Fossils have been found that preserve soft tissue, showing that it had soft skin and webbed feet. Monjurosuchus has been placed in the family Monjurosuchidae
Monjurosuchidae
Monjurosuchidae is a family of prehistoric reptiles belonging to the order Choristodera. Until the description of Philydrosaurus in 2005, the only genus in the family was Monjurosuchus. Both lived in what is now China during the Early Cretaceous....
along with Philydrosaurus
Philydrosaurus
Philydrosaurus is an extinct genus of choristoderan which existed in China during the Early Cretaceous. The type species P. proseilus was named in 2005. Philydrosaurus is closely related to the choristodere Monjurosuchus, and both have been placed in the same family Monjurosuchidae...
, but the relationships of early choristoderes remains unclear.
Description and history
Monjurosuchus was first found in China as part of the Early Cretaceous Jehol BiotaJehol Biota
The Jehol Biota includes all the living organisms - the ecosystem - of northeastern China between 133 to 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation and Jiufotang Formation. It is also believed to have left fossils in the Sinuiju series...
. Named in 1940, 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...
M. splendens was the first reptile described from the Yixian Formation
Yixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
. 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...
specimen was lost during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
but was replaced in 2000 by a recently discovered neotype preserving soft tissue. In 2007, remains were described from the Okurodani Formation
Okurodani Formation
The Okurodani 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...
of the Tetori Group of Japan. The Japanese material represents a different species of Monjurosuchus that has not yet been named.
Unlike related choristoderes, Monjurosuchus has a relatively short neck with eight vertebrae, one less than usual. The skull is rounded rather than pointed and is dorsoventrally flattened in all fossils. The eye sockets are large and prominent temporal regions extend from the back of the skull. The jaws are lined with small, sharp teeth, while 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 closely spaced tooth batteries. One distinguishing feature of Monjurosuchus is the lack of a lower temporal fenestra, a hole in the back of the skull that is common in many other diapsid
Diapsid
Diapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
reptiles, including most choristoderes. Monjurosuchus is also distinct in having small spikes on the edge of the squamosal
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
bone at the back of the skull.
Specimens from China preserve soft tissue, including scales and webbing between the toes of the feet. The scales of Monjurosuchus were small, giving the animal soft skin. Two rows of larger scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
s run along its back. The rest of the scales on the back are small, while the scales on the underside are slightly smaller. The skin of Monjurosuchus has a similar appearance to the living Chinese crocodile lizard
Chinese crocodile lizard
The Chinese crocodile lizard is a semi-aquatic lizard found only in cool forests in the Hunan, Guangxi Zhuang, and Guizhou provinces of China. The Chinese crocodile lizard spends much of its time in shallow water or in overhanging branches and vegetation, where it hunts its prey of fish, tadpoles,...
Shinisaurus.
The feet of Monjurosuchus are webbed, with skin covering all parts of the foot but the short claws. The limbs were robust and the hips are wide. The long, slender tail shows no adaptations for its presumed semi-aquatic lifestyle. Gastralia are present on the underside of Monjurosuchus and are much thinner than the ribs. Intestinal contents are preserved between the gastralia and ribs of one specimen. Most of the material is sediment, but there are also fragments of what may be arthropod cuticle
Arthropod cuticle
The cuticle forms the outer skeleton of arthropods, including insects.-Anatomy:The cuticle is made up of two layers; the epicuticle which is a thin and waxy water resistant outer layer and contains no chitin, and another layer under it called the procuticle...
, indicating that Monjurosuchus may have fed on invertebrates.
Classification
Monjurosuchus is a basalBasal (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:...
choristodere that lies outside the more advanced Neochoristodera. When named in 1940, it was placed in its own family Monjurosuchidae
Monjurosuchidae
Monjurosuchidae is a family of prehistoric reptiles belonging to the order Choristodera. Until the description of Philydrosaurus in 2005, the only genus in the family was Monjurosuchus. Both lived in what is now China during the Early Cretaceous....
. Unlike Monjurosuchus, neochoristoderes have small, dorsally facing eyes and long snouts. Philydrosaurus
Philydrosaurus
Philydrosaurus is an extinct genus of choristoderan which existed in China during the Early Cretaceous. The type species P. proseilus was named in 2005. Philydrosaurus is closely related to the choristodere Monjurosuchus, and both have been placed in the same family Monjurosuchidae...
, another Early Cretaceous Chinese choristodere, was grouped with Monjurosuchus in Monjurosuchidae. A 2007 phylogenetic analysis of choristoderes found only weak support for this family, as Philydrosaurus seemed to be a more basal choristodere than Monjurosuchus. A close relationship was found between Monjurosuchus and the Miocene Lazarussuchus
Lazarussuchus
Lazarussuchus is a genus of basal choristodere, a type of amphibious reptile, from the late Oligocene and early Miocene of France and the Czech Republic. Two species have been named: the type species L. inexpectatus from the late Oligocene of France; and L...
, but this was only weakly supported.