''Leptosuchus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of leptosuchomorph

phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...

with a complex taxonomical history.

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s have been found from the

Dockum Group The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Color ...

and lower

Chinle Formation The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In ...

outcropping in

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

, and

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, United States, and date back to the

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 227.3 ...

stage of the

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

. Currently there are believed to be four species of ''Leptosuchus''. All species share in common a similar position of the temporal arch below the skull roof and a posterior process of the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestra ...

that extends farther than the paroccipital process.Long, R. A., and Murry, P. A. (1995). "Late Triassic (Carnian and Norian) tetrapods from the southwestern United States". ''New Mexico Museum of Natural History and Science Bulletin'' 4:1-254. The type species is ''L. crosbiensis'', which was named in 1922 on the basis of material found from Texas. ''L. adamanensis'' was first described in 1930 as a species of ''

Machaeroprosopus ''Machaeroprosopus'' (from , 'large knife' and , 'bordering on') is an extinct genus of mystriosuchin leptosuchomorph phytosaur from the Late Triassic of the southwestern United States. ''M. validus'', once thought to be the type species of ''M ...

'' from the Blue Mesa Member of

Petrified Forest National Park Petrified Forest National Park is a national park of the United States in Navajo and Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassing semi-desert shrub steppe as wel ...

, along with the other two species, ''L. lithodendrorum'' and ''L. gregorii''. It was not until the publication of a 1995 paper on tetrapods of southwestern United States that these species were recognized as belonging to the genus ''Leptosuchus''. However, because of the distinctive size of the rostral crest in ''L. gregorii'', it was assigned to its own genus, '' Smilosuchus'', in that same paper. Despite this, ''L. gregorii'' has recently been seen as belonging to ''Leptosuchus'', as it is believed that the large, complete crest was independently developed in this particular species. The close relation of ''Leptosuchus'' and ''Machaeroprosopus'' with ''

Rutiodon ''Rutiodon'' (meaning "wrinkle tooth") is an extinct genus of mystriosuchine phytosaurs from the Late Triassic of the eastern United States. The type species of ''Rutiodon'', ''Rutiodon carolinensis'', encompasses a large number of skulls and as ...

'' has led some paleontologists to believe that the prior two were

synonymous A synonym is a word, morpheme, or phrase that means precisely or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are a ...

with ''Rutiodon'', with the latter's name having seniority. Differing features seen in the three phytosaurs have been attributed to sexual dimorphism, differing growth stages, or individual variation, while similarities could be seen in the rostral crest and the position of the nares. Previously it was believed that these were different genera due to the geographical isolation that could be seen in North American phytosaurs; ''Leptosuchus'' remains were found primarily in southern localities while ''Rutiodon'' remains could be found in more eastern localities. Other studies concluded that it was synonymous with ''Machaeroprosopus'' or ''

Phytosaurus ''Phytosaurus'' (meaning "plant lizard") is a dubious genus of extinct parasuchid phytosaur found in an outcrop of the Keuper (likely the Exter Formation) in Germany. ''Phytosaurus'' was the first phytosaur to be described, being done so by ...

''. A 1998 study again found ''Leptosuchus'' to be congeneric with ''Rutiodon'', but since then another study has suggested that its type species ''R. carolinensis'', while still very similar to ''Leptosuchus'', is synonymous with ''Angistorhinus''.Hungerbühler, A. and Sues, H.-D. (2001). Status and phylogenetic relationships of the Late Triassic phytosaur ''Rutiodon carolinensis''. ''Journal of Vertebrate Paleontology'' ''21''(3 suppl.):64A. ''L. imperfecta'' is known from a partial

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, UMMP 7523, from same locality as the holotype of ''L. crosbiensis''. It was collected as fragments and reassembled. Long and Murry (1995) considered it to be a

nomen nudum In Taxonomy (biology), taxonomy, a ''nomen nudum'' ('naked name'; plural ''nomina nuda'') is a designation which looks exactly like a scientific name of an organism, and may have originally been intended to be one, but it has not been published ...

, as there was never full formal documentation of this specimen. They referred it to ''L. adamanensis''. Camp (1930) and Ballew (1989) referred it to ''L. crosbiensis''. Stocker (2010) stated that the specimen is phylogenetically redundant and might be synonymous with ''L. crosbiensis'', because its traits are identical to those of ''L. crosbiensis''.

References

External links

''Rutiodon''
in the

Paleobiology Database The Paleobiology Database (PBDB) is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database originated in the NCEAS-funded Phanerozoic Marine Pale ...

(includes species of ''Leptosuchus'') {{Taxonbar, from=Q6528542 Phytosauria Prehistoric reptile genera Carnian genera Late Triassic reptiles of North America Triassic Arizona Paleontology in Arizona Triassic geology of New Mexico Paleontology in New Mexico Triassic geology of Texas Paleontology in Texas Chinle fauna Fossil taxa described in 1922 Taxa named by Ermine Cowles Case