Xilousuchus is an extinct genus

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 poposauroid

Poposauroidea

Poposauroidea is a clade of rauisuchians. It includes poposaurids, shuvosaurids, and ctenosauriscids, but excludes the large predatory quadrupedal rauisuchians such as rauisuchids and prestosuchids. Although it was first formally defined in 2007, the term has been used for many years...

 from lower Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 (Olenekian

Olenekian

In the geologic timescale, the Olenekian is an age in the Early Triassic epoch or a stage in the Lower Triassic series. It spans the time between 249.7 ± 0.7 Ma and 245 ± 0.7 Ma . The Olenekian follows the Induan and is followed by the Anisian.The Olenekian saw the deposition of a large part of the...

 stage) deposits of Fugu County

Fugu County

Fugu County is a county of Yulin, Shaanxi, China....

 of northeastern Shanxi Province, 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...

. It is known from 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...

, IVPP V 6026, a single well-preserved partial skeleton

Skeleton

The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...

 including the skull

Skull

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...

. It was found from the Heshanggou Formation of the Ordos Basin, Hazhen commune. It was first named by Xiao-Chun Wu in 1981

1981 in paleontology

-Newly named dinosaurs:Data courtesy of George Olshevsky's dinosaur genera list and Dr. Jeremy Montague's dinosaur genus database.-Plesiosaurs:* Carroll, R. C., 1981, Plesiosaur ancestors from the Upper Permian of Madagascar: Philosophical Transactions of the Royal Society, London B, v. 293,...

 and 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...

 is Xilousuchus sapingensis. Wu (1981) referred Xilousuchus to the Proterosuchia

Proterosuchia

Proterosuchia refers to one of the suborders of Thecodontia; specifically the most primitive and ancestral forms. These were primitive, vaguely crocodile-like, archosaurs that mostly lived during the Early Triassic period....

. Gower and Sennikov (1996) found it to be an erythrosuchia

Erythrosuchidae

Erythrosuchidae are a family of large basal archosauromorph carnivores that lived from the later Early Triassic to the early Middle Triassic . Their fossil remains are known so far from South Africa , the Perm region of Russia, and China...

n based strictly on the braincase. A more detailed re-description of the genus was provided by Nesbitt et al. (2010) and found poposauroid affinities. In his massive revision of archosaurs which included a large cladistic analysis, Sterling J. Nesbitt (2011) found Xilousuchus to be a poposauroid which is most closely related to Arizonasaurus

Arizonasaurus

Arizonasaurus was a ctenosauriscid archosaur from the Middle Triassic . Arizonasaurus is found in the Middle Triassic Moenkopi Formation of northern Arizona. A fairly complete skeleton was found in 2002 by Sterling Nesbitt. The taxon has a large sailback formed by elongate neural spines of the...

. Xilousuchus is the oldest archosaur

Archosaur

Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...

 to date, although Ctenosauriscus

Ctenosauriscus

Ctenosauriscus is an extinct genus of sail-backed poposauroid archosaur from Early Triassic deposits of Lower Saxony in northern Germany. It gives its name to the family Ctenosauriscidae, which includes other sail-backed poposauroids such as Arizonasaurus...

and Vytshegdosuchus

Vytshegdosuchus

Vytshegdosuchus is a genus of rauisuchid archosaur. It is known from fossil bones discovered from three localities along the Vychegda River in the Komi Republic of the European section of Russia. These fossils were found in rocks of the upper Yarenskian Gorizont, dating to the late Olenekian stage...

might be even older by less than one million year. Since Xilousuchus is a suchia

Suchia

Suchia is a clade of archosaurs that includes all pseudosuchians except ornithosuchids. It includes crocodilians and their extinct relatives. Paul Sereno defined Suchia as the least inclusive clade containing Aetosaurus ferratus, Rauisuchus tiradentes, Prestosuchus chiniquensis, Gracilisuchus...

n archosaur, its early age suggests that most of the major groups of archosaurs (ornithodirans, ornithosuchid

Ornithosuchidae

Ornithosuchidae is an extinct family of reptiles from the Triassic period that were distantly related to crocodilians. They are classified as crurotarsan archosaurs. Ornithosuchids were quadrupedal and facultatively bipedal, meaning they had the ability to walk on two legs for short periods of time...

s, aetosaur

Aetosaur

Aetosaurs are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae...

s, and paracrocodylomorphs

Paracrocodylomorpha

Paracrocodylomorpha is a clade of crurotarsan archosaurs that includes crocodylomorphs and several closely related Triassic forms. Erected in 1993, the clade usually contains early crurotarsan taxa like Poposauridae and Gracilisuchus. These groups are considered sister taxa of the clade Bathyotica,...

) developed by the Early Triassic, soon after the appearance of the first archosaur.

Phylogeny

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...

 after Nesbitt, 2010: