Leptosuchus
Encyclopedia
Leptosuchus is an extinct genus
of phytosaur
with a complex taxonomical history. Fossil
s have been found from the Dockum Group
and lower Chinle Formation
outcropping in Texas
, New Mexico
, and Arizona
and date back to the Carnian
stage of the Late Triassic
.
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
that extends farther than the paroccipital process. 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 from the Blue Mesa Member of Petrified Forest National Park
, 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
has led some paleontologists to believe that the prior two were synonymous
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
. One recent study has 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.
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 phytosaur
Phytosaur
Phytosaurs are an extinct group of large semi-aquatic Late Triassic archosaurs. Phytosaurs belong to the family Phytosauridae and the order Phytosauria. They were long-snouted and heavily armoured, bearing a remarkable resemblance to modern crocodiles in size, appearance, and lifestyle, an example...
with a complex taxonomical history. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found from the Dockum Group
Dockum Group
The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much...
and lower Chinle Formation
Chinle Formation
The Chinle is a geologic formation that is spread across the U.S. states of northern Arizona, Nevada, Utah, western New Mexico, and western Colorado. The Chinle is controversially considered to be synonymous to the Dockum Group in eastern Colorado, eastern New Mexico, southwestern Kansas, the...
outcropping in Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
, and Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
and date back to the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
stage of the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
.
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
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,...
that extends farther than the paroccipital process. 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 from the Blue Mesa Member of Petrified Forest National Park
Petrified Forest National Park
Petrified Forest National Park is a United States national park in Navajo and Apache counties in northeastern Arizona. The park's headquarters are about east of Holbrook along Interstate 40 , which parallels a railroad line, the Puerco River, and historic U.S. Route 66, all crossing the park...
, 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
Smilosuchus
Smilosuchus meaning "deadly-knife crocodile" is an extinct genus of phytosaur from the Late Triassic of North America. It was first described in 1995 as a replacement generic name for Leptosuchus gregorii...
, 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
Rutiodon is an extinct genus of archosaur belonging to the family Phytosauridae. It lived during the Late Triassic period, and was about 10 to 25 feet in length...
has led some paleontologists to believe that the prior two were synonymous
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
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
Phytosaurus is a dubious genus of phytosaur , and also the first phytosaur to be described, by G. Jaeger in 1828. It had a crocodile-like body structure, but its nostrils were on its forehead, not the tip of its snout...
. One recent study has 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.
External links
- Rutiodon in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...
(includes species of Leptosuchus)