Poposaurus
Encyclopedia
Poposaurus is a genus
of reptile
from the Late Triassic
of the southwestern United States
. It was a crurotarsan archosaur
which lived in what is now Wyoming
, Utah
, Arizona
and Texas
. The type species
, Poposaurus gracilis, was described by M. G. Mehl in 1915. The second species, P. langstoni was originally the type species of the genus Lythrosuchus, although the discovery of new specimens has led to it being reclassified within Poposaurus.
The discovery of a new specimen of P. gracilis suggests it was an obligate biped instead of a quadruped. This posture was likely an advancement on the semi-erect "high walk" of its quadrupedal ancestors, which is still seen in living crocodilians. Its bipedal locomotion is similar to that of many dinosaurs, but unlike dinosaurs, its hind legs were set in a "pillar-erect" position. The acetabulum
, a hole in the hip that fits into the head of the femur
, projects downward in Poposaurus so that the femur rests under the hip like a pillar. In dinosaurs, the acetabulum faces outward and the femur attaches to the side of the femur in a "buttress-erect" stance. Based on bone structures seen in the new specimen, the hind limb and pelvis musculature of P. gracilis was reconstructed in a 2011 study.
Poposaurus gives its name to Poposauridae, a family
of Late Triassic
crurotarsans
.
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 reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
from 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...
of the southwestern United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. It was a crurotarsan 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...
which lived in what is now Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
, Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
, 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 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...
. 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...
, Poposaurus gracilis, was described by M. G. Mehl in 1915. The second species, P. langstoni was originally the type species of the genus Lythrosuchus, although the discovery of new specimens has led to it being reclassified within Poposaurus.
The discovery of a new specimen of P. gracilis suggests it was an obligate biped instead of a quadruped. This posture was likely an advancement on the semi-erect "high walk" of its quadrupedal ancestors, which is still seen in living crocodilians. Its bipedal locomotion is similar to that of many dinosaurs, but unlike dinosaurs, its hind legs were set in a "pillar-erect" position. The acetabulum
Acetabulum
The acetabulum is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.-Structure:...
, a hole in the hip that fits into the head of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
, projects downward in Poposaurus so that the femur rests under the hip like a pillar. In dinosaurs, the acetabulum faces outward and the femur attaches to the side of the femur in a "buttress-erect" stance. Based on bone structures seen in the new specimen, the hind limb and pelvis musculature of P. gracilis was reconstructed in a 2011 study.
Poposaurus gives its name to Poposauridae, a family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of 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...
crurotarsans
Crurotarsi
The Crurotarsi are a group of archosauriformes, represented today by the crocodiles,...
.