''Pseudochampsa'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of proterochampsid archosauriform known from the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

(

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...

) Cancha de Bochas Member of the

Ischigualasto Formation The Ischigualasto Formation is a Late Triassic fossiliferous formation and Lagerstätte in the Ischigualasto-Villa Unión Basin of the southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation ...

of San Juan Province, Ischigualasto-Villa Unión Basin in northwestern

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. It contains a single species, ''Pseudochampsa ischigualastensis'', originally named as a second species of the closely related '' Chanaresuchus'', based on a fairly complete articulated skeleton and

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

.Trotteyn et al., 2012 A revision of the remains concluded that it was best to move to species to its own genus, as no traits were found to unite ''P. ischigualastensis'' and the type species of ''Chanaresuchus'' to the exclusion of other proterochampsids. A

phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

places both species in a

polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...

with '' Gualosuchus'' as the most advanced members of

Proterochampsia Proterochampsia is a clade of early archosauriform reptiles from the Triassic period. It includes the Proterochampsidae (e.g. ''Proterochampsa'', ''Chanaresuchus'' and ''Tropidosuchus'') and probably also the Doswelliidae. Nesbitt (2011) define ...

.Trotteyn & Ezcurra, 2014

Discovery

''Pseudochampsa'' is known solely from the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

PVSJ 567, a nearly complete and articulated individual housed at the División de Paleontologia de Vertebrados del Museo de Ciencias Naturales y Universidad Nacional de San Juan, Argentina. The holotype consists of a

with fully occluded

lower jaw In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

s, a complete

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordate ...

lacking the outer half of the

tail The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammal ...

, several neck and back ribs, some haemal arches, some

gastralia Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In thes ...

, the pectoral girdle, both partially preserved

humeri The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a round ...

, a partial pelvic girdle, and both nearly complete hind-limbs including both

femora The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with t ...

, tibiae,

fibulae The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...

, tarsals and feet. PVSJ 567 was found at Valle Pintado, Hoyada de Ischigualasto of the

Ischigualasto Provincial Park Ischigualasto Provincial Park ( es, Parque Provincial Ischigualasto), also called ''Valle de la Luna'' ("Valley of the Moon" or "Moon Valley"), due to its moon like appearance, is a provincial protected area in the north-east of San Juan Provin ...

, San Juan Province. It was collected from the Cancha de Bochas Member of the

, of Ischigualasto-Villa Union Basin, dating to the late

to earliest Norian stages of the middle

Etymology

The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

of ''Pseudochampsa'' was first described and named by María J. Trotteyn, Ricardo N. Martínez and Oscar A. Alcober in

2012 File:2012 Events Collage V3.png, From left, clockwise: The passenger cruise ship Costa Concordia lies capsized after the Costa Concordia disaster; Damage to Casino Pier in Seaside Heights, New Jersey as a result of Hurricane Sandy; People gat ...

, as a second species of '' Chanaresuchus'', ''C. ischigualastensis''. The specific name refers to the

that yielded the holotype and only known specimen, with the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

suffix ''-ensis'', meaning "from". Trotteyn and Martín D. Ezcurra reassigned the species to its own genus in

2014 File:2014 Events Collage.png, From top left, clockwise: Stocking up supplies and personal protective equipment (PPE) for the Western African Ebola virus epidemic; Citizens examining the ruins after the Chibok schoolgirls kidnapping; Bundles of wat ...

, naming ''Pseudochampsa'' and creating the new combination ''Pseudochampsa ischigualastensis''. The new generic name is derived from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''pseudo'', meaning "false", and ''champsa'', meaning " crocodile", and refers to the crocodile-like body morphology of ''P. ischigualastensis''.

Description

The type species of ''Pseudochampsa'' was originally thought to be a member of '' Chanaresuchus''. Trotteyn ''et al.'' (2012) referred this species to ''Chanaresuchus'' and diagnosed ''Chanaresuchus'' based on the presence of

cranial Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

ornamentation by longitudinal crests and depressions on the upper surfaces of the

premaxillae The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

, maxillae and nasal bones, a side fossa on the centrum of the presacral

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

, a low deltopectoral crest on the humerus, and the absence of a fifth toe. However, Trotteyn and Ezcurra (2014) revised these supposed synapomorphies of ''Chanaresuchus'' and found them to represent synapomorphies of larger clades. Cranial ornamentation of this form as seen in ''Chanaresuchus bonapartei'' and ''P. ischigualastensis'' is also present in '' Gualosuchus reigi'' and '' Rhadinosuchus gracilis''. The shallow weakly-rimmed depression of the presacral centra in these species is also shared with '' Tropidosuchus romeri'', ''G. reigi'' and ''R. gracilis''. The low deltopectoral crest on the humerus is present in all known proterochampsids to the exclusion of ''R. gracilis'', in which it is unknown, and '' Proterochampsa barrionuevoi''. Finally, at least one other proterochampsid apart from ''C. bonapartei'' and ''P. ischigualastensis'' is known to lack a fifth toe - ''T. romeri''. The three established

autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

of ''C. bonapartei'' by Dilkes and Arcucci (2012), are either unknown in ''P. ischigualastensis'' or known to differ from it. In fact, two out of the three autapomorphies (a deep well-defined depression in front of the nostril, and an elongated oval supra

temporal fenestrae The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

with a back-side directed main axis) are absent in ''P. ischigualastensis'', in which this depression is shallow like in ''G. reigi'', and the supratemporal fenestra is near-triangular and aligned with the long axis of the skull. Thus, Trotteyn and Ezcurra (2014) found no synapomorphies that unite ''C. bonapartei'' and ''P. ischigualastensis'' exclusively, or support their

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

within ''Chanaresuchus'', requiring a new generic name for ''"C." ischigualastensis''. The

of Trotteyn and Ezcurra (2014) placed ''C. bonapartei'' and ''P. ischigualastensis'' in a

with ''G. reigi''. They also suggested that ''R. gracilis'', not included in the analysis, might be 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 ''C. bonapartei'', based on morphology, further supporting the exclusion of ''P. ischigualastensis'' from ''Chanaresuchus''. Trotteyn and Ezcurra (2014) distinguished ''P. ischigualastensis'' from other proterochampsids, including ''C. bonapartei'', based on a unique combination traits. These include a transversely broad basicranium with transversely oriented basal tubera, paroccipital processes with vertically expanded far end, the absence of a retroarticular projection on the

s, tail vertebrae with a mid longitudinal groove on the bottom surface of the centrum and with pre- and post- zygapophyses strongly divergent from the midline, the lack of

foramina In anatomy and osteology, a foramen (;Entry "foramen"
in

on the back groove of the

astragalus ''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...

, and finally,

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinc ...

ornamentation consisting solely of longitudinal grooving.

Phylogeny

The simplified

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

below follows Trotteyn and Ezcurra (2014) phylogenetic analysis, who used the data set of Dilkes & Arcucci (2012).

References

Bibliography

* * {{Portal bar, Paleontology Proterochampsians Prehistoric reptile genera Carnian genera Late Triassic reptiles of South America Triassic Argentina Fossils of Argentina Ischigualasto Formation Fossil taxa described in 2014