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Crurotarsi
 
 
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The Crurotarsi ("cross-ankles") are a group of archosaurs, whose name was erected as a node-based clade
Cladistics

Cladistics is the hierarchical classification of species based on evolutionary ancestry. Cladistics is distinguished from other taxonomic systems because it focuses on evolution rather than similarities between species, and because it places heavy emphasis on objective, quantitative analysis....
 by Paul Sereno
Paul Sereno

Paul Callistus Sereno is an United States paleontology who is the discoverer of several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco and Niger....
 in 1991 to supplant the old term Pseudosuchia
Pseudosuchia

Pseudosuchia is the name originally given to a group of prehistoric reptiles from the Triassic period. The name has been variously interpreted, and it is still sometimes, if infrequently, used in scientific literature today....
. Crurotarsi are by definition the sister group of the Avemetatarsalia
Avemetatarsalia

Avemetatarsalia is a clade name established by British palaeontologist Michael J. Benton in 1999 for all avesuchians that are closer to dinosaurs than to crocodiles....
 (all forms closer to birds than crocodiles).

Description
Crurotarsi is one of the two primary daughter clades of the Archosaur
Archosaur

Archosaurs are a group of diapsid reptiles represented by modern birds and crocodilians. This group also includes extinct non-avian dinosaurs, pterosaurs and relatives of crocodiles....
ia. The skull is often massively built, especially in contrast to ornithodires; the snout narrow and sometimes tending to be elongate, the neck is short and strong, and the limb posture ranging from typically reptilian sprawling to dinosaur or mammal-like erect (although this is achieved in a different way to dinosaurs and mammals).






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The Crurotarsi ("cross-ankles") are a group of archosaurs, whose name was erected as a node-based clade
Cladistics

Cladistics is the hierarchical classification of species based on evolutionary ancestry. Cladistics is distinguished from other taxonomic systems because it focuses on evolution rather than similarities between species, and because it places heavy emphasis on objective, quantitative analysis....
 by Paul Sereno
Paul Sereno

Paul Callistus Sereno is an United States paleontology who is the discoverer of several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco and Niger....
 in 1991 to supplant the old term Pseudosuchia
Pseudosuchia

Pseudosuchia is the name originally given to a group of prehistoric reptiles from the Triassic period. The name has been variously interpreted, and it is still sometimes, if infrequently, used in scientific literature today....
. Crurotarsi are by definition the sister group of the Avemetatarsalia
Avemetatarsalia

Avemetatarsalia is a clade name established by British palaeontologist Michael J. Benton in 1999 for all avesuchians that are closer to dinosaurs than to crocodiles....
 (all forms closer to birds than crocodiles).

Description


Crurotarsi is one of the two primary daughter clades of the Archosaur
Archosaur

Archosaurs are a group of diapsid reptiles represented by modern birds and crocodilians. This group also includes extinct non-avian dinosaurs, pterosaurs and relatives of crocodiles....
ia. The skull is often massively built, especially in contrast to ornithodires; the snout narrow and sometimes tending to be elongate, the neck is short and strong, and the limb posture ranging from typically reptilian sprawling to dinosaur or mammal-like erect (although this is achieved in a different way to dinosaurs and mammals). The body is often protected by two or more rows of armored plates. Many crurotarsans reached large size: approximately around three meters or more in length.

Evolution


Crurotarsans appeared during the late Olenekian
Olenekian

The Olenekian is a faunal stage of the Early Triassic epoch . It spans the time between 249.7 ? 0.7 annum and 245 ? 0.7 Ma . The Olenekian is divided into the Smithian and the Spathian age....
 (early Triassic
Triassic

The Triassic is a geologic period that extends from about 251 to 199 annum . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic....
); by the Ladinian
Ladinian

The Ladinian is a faunal stage of the Middle Triassic epoch . It spans the time between 237 ? 2 annum and 228 ? 2 Ma . The Ladinian was preceded by the Anisian Stage and succeeded by the Carnian Stage of the Late Triassic Period....
 (late Middle Triassic) they dominated the terrestrial carnivore
Carnivore

A carnivore , meaning 'meat eater' , is any animal with a diet consisting mainly of meat, whether it comes from animals living or dead .In a more general sense, an animal may be considered a carnivore if it prefers feeding on animal matter over plant matter....
 niches. Their heyday was the Late Triassic, during which time their ranks included erect-limbed rauisuchia
Rauisuchia

Rauisuchia are a poorly known assemblage of predatory and mostly large Triassic archosaurs. Originally it was believed that they were related to Erythrosuchidae, but it is now known that they are Crurotarsi....
ns, the crocodile-like phytosaur
Phytosaur

Phytosaurs - family Phytosauridae or Parasuchidae - were a group of large semi-aquatic predatory archosaurs that flourished during the Late Triassic Geologic period....
s, herbivorous
Herbivore

Herbivory is a form of predation in which an organism, known as an herbivore, heterotrophs principally autotrophs such as plants, algae and photosynthesizing bacteria....
 armoured aetosaur
Aetosaur

File:Aetosaur, PFNP.jpgThe aetosaurs are an extinct clade of heavily armoured, medium- to large-sized Late Triassic herbivore archosaurs. Two distinct subdivisions of aeotosaurs are currently recognized, the Desmatosuchinae and the Aetosaurinae, based primarily on differences in the morphology of the bony scutes of the two groups ....
s, the large predatory poposaurs
Poposauridae

The Poposauridae are a Family of large carnivore archosaurs which lived alongside dinosaurs during the Late Triassic. They are known from fossil remains from North and South America....
, the small agile crocodilians Sphenosuchia
Sphenosuchia

Sphenosuchia is the name of a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Middle Jurassic. Most were small, gracile animals with an erect limb posture....
, and a few other assorted groups.

At the end Triassic extinction
Triassic-Jurassic extinction event

The Triassic?Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, , and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans....
, all of the large crurotarsans died out. The cause of their extinctions is yet unknown, but it is believed that it may have been an asteroid impact, sudden climate change, or a planetary cataclysm. Futhermore, this allowed the dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s to succeed them as the dominant terrestrial carnivores and herbivores. Only the Sphenosuchia
Sphenosuchia

Sphenosuchia is the name of a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Middle Jurassic. Most were small, gracile animals with an erect limb posture....
 and the Protosuchia
Protosuchia

Protosuchians are early crocodilians that were small in size and Terrestrial animal....
 (Crocodylomorpha
Crocodylomorpha

The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now....
) survived.

As the Mesozoic
Mesozoic

The Mesozoic Era is one of three Geologic time scale of the Phanerozoic eon . The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' ....
 progressed, the Protosuchia gave rise to more typically crocodile-like forms. While dinosaurs were the dominant animals on land, the crocodiles flourished in rivers, swamps, and the oceans, with far greater diversity than they have today.

With the end Cretaceous extinction
Cretaceous-Tertiary extinction event

The Cretaceous?Tertiary extinction event, which occurred approximately , was a large-scale Extinction event of animal and plant species in a geologically short period of time....
 the dinosaurs became extinct, with the exception of the birds, while the crurotarsan crocodilians continued with little change.

Today, the crocodile
Crocodile

A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all members of the order Crocodilia: i.e....
s, alligators
Alligatoridae

Alligators and caimans are archosaurs, species of crocodilians and form the family Alligatoridae ....
, and gavials
Gavialidae

Gavialidae is a family of reptiles within the order Crocodilia. Gavialidae consists of only two surviving species, the gharial and the false gharial , which are each the sole living representatives of their genera....
 continue as the surviving representatives of this lineage.

Phylogeny

Cladogram after Parrish (1993), Nesbitt (2003 & 2005), and Nesbitt & Norell (2006). Crurotarsi |-?Doswellia
Doswellia

Doswellia is the name given to a genus of Crurotarsi from the Late Triassic . It lived in what is now North America. The type species, Doswellia kaltenbachi, was described by Weems in 1980....
 |-?Tarjadia |-?Parringtonia |-?Ctenosauriscidae
Ctenosauriscidae

The Ctenosauriscidae are a Family of large archosaurs which lived alongside dinosaurs during the Late Triassic. All species had large "sails" on their back....
 `--Crocodylotarsi |--Phytosauria `--Suchia |--Prestosuchidae
Prestosuchidae

Prestosuchidae are a group of Triassic carnivorous archosaurs. They were large active terrestrial apex predators, ranging from around 2.5 to 6 or 7 meters in length....
 |-?Turfanosuchus
Turfanosuchus

Turfanosuchus is a genus of archosauriform reptile which lived during the Middle Triassic of northwestern China. The type species, T. dabanensis, was described by Yang Zhongjian in 1973, based on a partially complete but disarticulated fossil skeleton ....
 `--Rauisuchiformes |-?Revueltosaurus
Revueltosaurus

Revueltosaurus is a genus of prehistoric crurotarsi from Late Triassic New Mexico and Arizona.According to William Parker, who discovered the partial skeleton, "we have pretty much erased the record of Triassic ornithischian dinosaurs from North America, Europe and worldwide, except for South America." His co-author Randall Irmis said,...
 |--Aetosauria `--Rauisuchia
Rauisuchia

Rauisuchia are a poorly known assemblage of predatory and mostly large Triassic archosaurs. Originally it was believed that they were related to Erythrosuchidae, but it is now known that they are Crurotarsi....
 |--Rauisuchidae
Rauisuchidae

Rauisuchidae are a group of large predatory Triassic archosaurs, and constitute advanced representatives of the larger group Rauisuchia. There is some disagreement over which genera should be included in the Prestosuchidae, which in Rauisuchidae, and which in the Poposauridae, and indeed whether these should even be thought of as separate F...
 `--Paracrocodylomorpha |--Gracilisuchus
Gracilisuchus

Gracilisuchus is an extinct genus of tiny crurotarsan from the Middle Triassic. It was a suchian close to the ancestry of crocodiles, and was at one time thought to be a dinosaur, but this hypothesis has since been rejected....
 |--Poposauridae
Poposauridae

The Poposauridae are a Family of large carnivore archosaurs which lived alongside dinosaurs during the Late Triassic. They are known from fossil remains from North and South America....
 `--Bathyotica |--Erpetosuchus
Erpetosuchus

Erpetosuchus is an extinct genus of crurotarsi from the Late Triassic. It was first described by E. T. Newton in 1894 for remains found in northeastern Scotland, with more remains found in the United States in recent years....
 `--Crocodylomorpha
Crocodylomorpha

The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now....


See also

  • List of crurotarsans
    List of crurotarsans

    This list of crurotarsans is a comprehensive listing of all Genus that have ever been included in the clade Crurotarsi, excluding purely vernacular terms....


External links