Poposauroidea
Encyclopedia
Poposauroidea is a clade
of rauisuchia
ns. 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. The group has been referred to as Poposauridae by some authors, although this name is often used more narrowly to refer to the family that includes Poposaurus and its close relatives.
, which was considered to be a theropod dinosaur
. Over the following years, poposauroids were placed in various groups, including Saurischia
, Theropoda
, and Carnosauria
. This classification existed up until the 1970s, when better remains indicated that Poposaurus was a crurotarsan rather than a dinosaur. Other genera such as Sillosuchus
and Shuvosaurus
were later erected. Like Poposaurus, Shuvosaurus was originally thought to be a theropod dinosaur.
Sankar Chatterjee
reclassified poposauroids as theropod dinosaurs with his description of the new genus Postosuchus
in 1985. Chaterjee even considered poposauroids to be the ancestors of tyrannosaurs. Postosuchus was widely considered to be a poposauroid for the next ten years and was included in many phylogenetic analyses of Triassic archosaurs. In 1995, Robert Long and Phillip Murry showed that the original material of Postosuchus was a chimera (paleontology)
, or collection of bones from several different animals. According to Long and Murry, Chaterjee's Postosuchus material included bones of Poposaurus and Shuvosaurus, giving the impression that it was a poposauroid. Postosuchus has since been classified as a rauisuchid, and poposauroids are generally considered not to be theropod dinosaurs.
Poposauroidea was formally defined as a clade
by Jonathan C. Weinbaum and Axel Hungerbühler in 2007. In their paper, Weinbaum and Hungerbühler described two new skeletons of Poposaurus and incorporated several new characters of the genus into a phylogenetic analysis. Poposauroidea was recovered as a monophyletic grouping, while other rauisuchians (namely Rauisuchidae and Prestosuchidae) were placed as basal forms of a new group called Paracrocodyliformes.
In 2005, paleontologist Paul Sereno
defined Poposauridae as a stem-based taxon that includes all taxa more closely related to Poposaurus gracilis than to Crocodylus niloticus, the Nile crocodile
. This would encompass not just poposaurids like Poposaurus but also many other poposauroids, making it equivalent to Poposauroidea in Weinbaum and Hungerbühler's study.
Brusatte
et al. (2010) conducted a phylogenetic study of archosaurs that resulted in a grouping referred to as Poposauroidea. Unlike many recent studies, they found Rauisuchia to be monophyletic, consisting of two major clades: Rauisuchoidea and Poposauroidea. However, the monophyly of Rauisuchia was not strongly supported in Brutasse et al.s analysis. They noted that if their tree was enlarged by one step, Poposauroidea fell outside Rauisuchia to become the sister group of Ornithosuchidae
, which is thought to closely related to, but outside, Rauisuchia. In their tree, Poposauroidea included genera usually classified as poposauroids as well as several other genera that are not traditionally placed in the group. One genus, Yarasuchus
, was previously classified as a prestosuchid, but was found to be the most basal
poposauroid. Yarasuchus is unusual in that it has a relatively long neck and small size. The other genus, Qianosuchus
, is unique among crurotarsans in its semiaquatic lifestyle.
In his massive revision of archosaurs which included a large cladistic analysis, Sterling J. Nesbitt (2011) found Xilousuchus
to be a poposauroid most closely related to Arizonasaurus
. Nesbitt's analysis did not recover a monophyletic Rauisuchia or monophyletic Rauisuchoidea. Poposauroidea was found to be monophyletic, and more resolved than in previous analyses. The cladogram
below follows Nesbitt (2011) with clade names based on previous studies.
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of rauisuchia
Rauisuchia
Rauisuchia is a group of predatory and mostly large Triassic archosaurs. As a clade, Rauisuchia includes these Triassic forms and all crocodylomorphs, which are descendants of Triassic rauisuchians. The group in its traditional sense is paraphyletic, because it does not include crocodylomorph...
ns. 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. The group has been referred to as Poposauridae by some authors, although this name is often used more narrowly to refer to the family that includes Poposaurus and its close relatives.
History
Franz Nopcsa first used the term Poposauridae in 1923 to refer to poposauroids. At this time, the sole member of the group was PoposaurusPoposaurus
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...
, which was considered to be a theropod dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
. Over the following years, poposauroids were placed in various groups, including Saurischia
Saurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
, Theropoda
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
, and Carnosauria
Carnosauria
Carnosauria is a group of large predatory dinosaurs that lived during the Jurassic and Cretaceous periods. While it originally contained a wide assortment of giant theropods that were not closely related, the group has since been defined to encompass only the allosaurs and their closest kin...
. This classification existed up until the 1970s, when better remains indicated that Poposaurus was a crurotarsan rather than a dinosaur. Other genera such as Sillosuchus
Sillosuchus
Sillosuchus is a genus of poposaurid crurotarsans from the Late Triassic of Argentina.The generic name refers to Dr. William Sill, and "suchus", from Greek meaning crocodile. A reconstruction of the fossil was presented in 2008 by the National University of San Juan in Argentina, in an homage to Dr...
and Shuvosaurus
Shuvosaurus
Shuvosaurus is a genus of beaked reptile from the Late Triassic of Texas. It was described by Sankar Chatterjee in 1993 after it was discovered by his son Shuvo. It was initially interpreted as a Triassic member of the Cretaceous dinosaur family Ornithomimidae...
were later erected. Like Poposaurus, Shuvosaurus was originally thought to be a theropod dinosaur.
Sankar Chatterjee
Sankar Chatterjee
Sankar Chatterjee is a paleontologist, and is the Paul W. Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University. He earned his Ph. D. from the University of Calcutta in 1970 and was a Post-doctoral Fellow at the Smithsonian...
reclassified poposauroids as theropod dinosaurs with his description of the new genus Postosuchus
Postosuchus
Postosuchus, meaning "crocodile from Post ", was a basal archosaur that lived in what is now North America during the middle through to the late Triassic period...
in 1985. Chaterjee even considered poposauroids to be the ancestors of tyrannosaurs. Postosuchus was widely considered to be a poposauroid for the next ten years and was included in many phylogenetic analyses of Triassic archosaurs. In 1995, Robert Long and Phillip Murry showed that the original material of Postosuchus was a chimera (paleontology)
Chimera (paleontology)
In paleontology, a chimera is a fossil which was reconstructed with elements coming from more than a single species of animal. A now classic example of chimera is Protoavis.-List of paleontological chimeras:*Brontosaurus*Lametasaurus...
, or collection of bones from several different animals. According to Long and Murry, Chaterjee's Postosuchus material included bones of Poposaurus and Shuvosaurus, giving the impression that it was a poposauroid. Postosuchus has since been classified as a rauisuchid, and poposauroids are generally considered not to be theropod dinosaurs.
Poposauroidea was formally defined as a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
by Jonathan C. Weinbaum and Axel Hungerbühler in 2007. In their paper, Weinbaum and Hungerbühler described two new skeletons of Poposaurus and incorporated several new characters of the genus into a phylogenetic analysis. Poposauroidea was recovered as a monophyletic grouping, while other rauisuchians (namely Rauisuchidae and Prestosuchidae) were placed as basal forms of a new group called Paracrocodyliformes.
In 2005, paleontologist Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
defined Poposauridae as a stem-based taxon that includes all taxa more closely related to Poposaurus gracilis than to Crocodylus niloticus, the Nile crocodile
Nile crocodile
The Nile crocodile or Common crocodile is an African crocodile which is common in Somalia, Ethiopia, Uganda, Kenya, Egypt, Tanzania, Zambia, Zimbabwe, Gabon, South Africa, Malawi, Sudan, Botswana, and Cameroon...
. This would encompass not just poposaurids like Poposaurus but also many other poposauroids, making it equivalent to Poposauroidea in Weinbaum and Hungerbühler's study.
Stephen L. Brusatte
Stephen Louis Brusatte , is an American paleontologist.-Biography:He is the author of the 2002 book Stately Fossils: A Comprehensive Look at the State Fossils and Other Official Fossils and the 2008 book Dinosaurs...
et al. (2010) conducted a phylogenetic study of archosaurs that resulted in a grouping referred to as Poposauroidea. Unlike many recent studies, they found Rauisuchia to be monophyletic, consisting of two major clades: Rauisuchoidea and Poposauroidea. However, the monophyly of Rauisuchia was not strongly supported in Brutasse et al.s analysis. They noted that if their tree was enlarged by one step, Poposauroidea fell outside Rauisuchia to become the sister group of Ornithosuchidae
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...
, which is thought to closely related to, but outside, Rauisuchia. In their tree, Poposauroidea included genera usually classified as poposauroids as well as several other genera that are not traditionally placed in the group. One genus, Yarasuchus
Yarasuchus
Yarasuchus is an extinct genus of rauisuchian, a group of predatory and large Triassic archosaurs. It lived during the Anisian stage of the Middle Triassic of India. Being only 2 metres long, is was one of the smallest rauisuchians known...
, was previously classified as a prestosuchid, but was found to be the most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
poposauroid. Yarasuchus is unusual in that it has a relatively long neck and small size. The other genus, Qianosuchus
Qianosuchus
Qianosuchus is an extinct genus of aquatic archosaur from the middle Triassic Guanling Formation of Pan County, China. It is represented by two nearly complete skeletons and a crushed skull.-External links:...
, is unique among crurotarsans in its semiaquatic lifestyle.
Xilousuchus
Xilousuchus is an extinct genus of poposauroid from lower Triassic deposits of Fugu County of northeastern Shanxi Province, China. It is known from the holotype, IVPP V 6026, a single well-preserved partial skeleton including the skull. It was found from the Heshanggou Formation of the...
to be a poposauroid 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...
. Nesbitt's analysis did not recover a monophyletic Rauisuchia or monophyletic Rauisuchoidea. Poposauroidea was found to be monophyletic, and more resolved than in previous analyses. The 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...
below follows Nesbitt (2011) with clade names based on previous studies.
External links
- Poposauroidea 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...