Poposauroids
   HOME

TheInfoList



OR:

Poposauroidea is a
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of advanced
pseudosuchians Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...
. It includes poposaurids, shuvosaurids,
ctenosauriscid Ctenosauriscidae is an extinct family of pseudosuchian archosaurs within the clade Poposauroidea. Ctenosauriscids existed in Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 mill ...
s, and other unusual pseudosuchians such as '' Qianosuchus'' and ''
Lotosaurus ''Lotosaurus'' is an extinct genus of sail-backed poposauroid known from Hunan Province of central China. Discovery ''Lotosaurus'' is known from the holotype IVPP V 4881 (or possibly V 4880), an articulated and well-preserved s ...
''. It excludes most large predatory quadrupedal " rauisuchians" such as rauisuchids and " prestosuchids". Those reptiles are now allied with
crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably more ...
(crocodile ancestors) in a clade known as Loricata, which is 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 ...
to the poposauroids in the clade
Paracrocodylomorpha Paracrocodylomorpha is a clade of pseudosuchian archosaurs. The clade includes the diverse and unusual group Poposauroidea as well as the generally carnivorous and quadrupedal members of Loricata, including modern crocodylians. Paracrocodylomor ...
. Although it was first formally defined in 2007, the name "Poposauroidea" 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. It was phylogenetically defined in 2011 by Sterling Nesbitt as ''
Poposaurus gracilis ''Poposaurus'' is an extinct genus of pseudosuchian archosaur from the Late Triassic of the southwestern and eastern United States. It belongs to the clade Poposauroidea, an unusual group of Triassic pseudosuchians that includes sail-backed, bea ...
'' and all taxa more closely related to it than to '' Postosuchus kirkpatricki'', ''
Crocodylus niloticus The Nile crocodile (''Crocodylus niloticus'') is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries. It is widely distributed in sub-Saharan Africa, occurring mostly in the eastern, southern, and ce ...
'' (the Nile crocodile), '' Ornithosuchus woodwardi'', or '' Aetosaurus ferratus''. Poposauroids went extinct at the end of the
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
period along with other non-crocodylomorph pseudosuchians. They were among the most diverse and longest lasting members of non-crocodylomorph Pseudosuchia, with ''
Xilousuchus ''Xilousuchus'' is an extinct genus of poposauroid from lower Triassic (Olenekian stage) deposits of Fugu County of northeastern Shanxi Province, China. Xilousuchus is one of the oldest archosaurs known to date. Discovery and naming It is ...
'' (a ctenosauriscid) living near the very beginning of the
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
and '' Effigia'' (a shuvosaurid) surviving up until near the end of the Triassic. Despite the high level of diversity and anatomical disparity within Poposauroidea, certain features of the clade can be determined, particularly in the structure of the snout and
pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...
(hip). Many of these features are examples of
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
with
dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
, with bipedal poposauroids such as ''
Poposaurus ''Poposaurus'' is an extinct genus of pseudosuchian archosaur from the Late Triassic of the southwestern and eastern United States. It belongs to the clade Poposauroidea, an unusual group of Triassic pseudosuchians that includes sail-backed, bea ...
'' and shuvosaurids having been mistaken for
theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...
dinosaurs in the past.


Features

Poposauroidea was a diverse group of pseudosuchians, containing genera with many different ecological adaptations. Some (''Poposaurus'' and shuvosaurids) were short-armed
bipeds Bipedalism is a form of terrestrial locomotion where an animal moves by means of its two rear (or lower) Limb (anatomy), limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from ...
, while others (ctenosauriscids and ''Lotosaurus'') were robust
quadrupeds Quadrupedalism is a form of locomotion in which animals have four legs that are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four legs is said to be a quadruped (fr ...
with elongated neural spines, creating a '
sail A sail is a tensile structure, which is made from fabric or other membrane materials, that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails may b ...
' like that of certain "
pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile was used, and Pelycosauria was considered an order, but this is now thoug ...
s" (like ''
Dimetrodon ''Dimetrodon'' ( or ; ) is an extinct genus of sphenacodontid synapsid that lived during the Cisuralian (Early Permian) Epoch (geology), epoch of the Permian period, around 295–272 million years ago. With most species measuring long and ...
'') and
spinosaurids Spinosauridae (or spinosaurids) is a clade or family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. Spinosaurid fossils have been recovered worldwide, including Africa, Europe, South America, and Asia. Their remains have ...
. ''Lotosaurus'' and shuvosaurids were toothless and presumably beaked herbivores while ''Qianosuchus'', ''Poposaurus'' and ctenosauriscids were sharp-toothed predators. The ecological disparity of many members of this clade means that it is difficult to assess what the ancestral poposauroid would have looked like.


Skull and vertebrae

Poposauroids can be differentiated from other pseudosuchians by the structure of the tip of the snout, particularly the premaxillary bone which lies in front of the nares (
nostril A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...
holes). This bone possesses two bony extensions ("processes") which wrap around the nares. The anterodorsal process, which wraps above the nares to contact the
nasal bones The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...
on the top edge of the snout, is typically quite short in pseudosuchians. Poposauroids have elongated anterodorsal processes, longer than the main premaxillary body. The posterodorsal process, which wraps below the nares to contact the
maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
on the side of the snout, possesses the opposite state. It is much shorter in poposauroids (compared to other pseudosuchians), restricted to only a portion of the lower edge of the nares. This has the added effect of allowing the maxilla to form the rest of the hole's lower and rear edge, with the front edge of the maxilla becoming concave as well. Although these snout features are rare among pseudosuchians, they are much more common in certain avemetatarsalians (bird-line archosaurs) such as
pterosaurs Pterosaurs are an extinct clade of flying reptiles in the Order (biology), order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosau ...
and
saurischian Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
. The rear branch of the maxilla tapers in most poposauroids, with the exception of ''Qianosuchus''. This contrasts with loricatans, in which this branch is rectangular in shape. Poposauroids also possess several features which are unusual compared to archosaurs in general. For example, in most archosaurs each side of the
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...
possesses a pit from where the internal carotid arteries may exit the
brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...
. In early poposauroids, these pits migrated to the underside of the braincase, thereby resembling the primitive condition seen in archosaur relatives such as ''
Euparkeria ''Euparkeria'' (; meaning "Parker's good animal", named in honor of W. K. Parker) is an Extinction, extinct genus of archosauriform reptile from the Triassic of South Africa. ''Euparkeria'' is close to the ancestry of Archosauria, the reptile gro ...
'' and proterochampsians. Nevertheless, this reversion is undone in shuvosaurids (and possibly earlier, although no braincase material is known in ''Poposaurus'' or ''Lotosaurus''). In addition, most poposauroids possessed elongated necks, and all of them had long and thin cervical ribs. This second neck trait contrasts with the condition in other pseudosuchians, phytosaurs, and pterosaurs, which have short and stout cervical ribs. The neural spines of the dorsal (back)
vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
are thin and plate-like, even in members of Poposauroidea without sails. This differs compared to the vertebrae of most other early pseudosuchians (as well as ''Euparkeria'' and phytosaurs), which have neural spines that expand outward to form a flat, rectangular surface when seen from above.


Pelvis

Like other reptiles, the pelvis of poposauroids is formed by three plate-like bones: the ilium which lies above the
acetabulum The acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...
(hip socket), the pubis which is below and in front of the acetabulum, and the
ischium The ischium (; : is ...
which is below and behind the acetabulum. The ilium is a large, complex bone, with a forward-pointing (preacetabular) process, a rear-pointing (postacetabular) process, and a lower portion which forms the upper edge of the acetabulum. In most archosaurs, the lower portion of the ilium is wedge-shaped, forming the inner face of a "closed" acetabulum. In poposauroids the lower portion of the ilium is concave, creating a partially to completely "open" acetabulum formed by open space instead of bone. The only other archosaurs with open hip sockets are dinosaurs and (to a lesser extent) crocodylomorphs. The upper edge of the acetabulum is formed by a pronounced ridge on the ilium, known as a supraacetabular rim or crest. Although all poposauroids possessed open acetabula, most other specializations of the ilium did not evolve until the clade containing ''Poposaurus'' and the shuvosaurids. For example, the supraacetabular crest projects downward, rather than outward in this clade. This trait is rare in archosaurs, only evolving independently in a few early theropod dinosaurs such as ''
Coelophysis ''Coelophysis'' ( Traditional English pronunciation of Latin, traditionally; or , as heard more commonly in recent decades) is a genus of coelophysid Theropoda, theropod dinosaur that lived Approximation, approximately 215 to 201.4 million y ...
'' and ''
Dilophosaurus ''Dilophosaurus'' ( ) is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 186 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserv ...
''. Another feature is the presence of an additional diagonal crest which branches upward from the supraacetabular rim. Although such a crest evolved independently in a number of different archosaurs, this specific subset of poposauroids is unique in having the crest be inclined forward (rather than vertical) and confluent with the elongated preacetabular blade, which is another derived feature of the clade. The pubis and ischium were also specialized in poposauroids. In every other archosaur, the two bones contact each other on the lower edge of the acetabulum. In poposauroids other than ''Qianosuchus'' and ''Lotosaurus'', the bones did not touch, leaving the acetabulum open from the sides and below. The width of the pubis is variable at different parts of its shaft. The portion near the acetabulum is thickened, but the tip of the bone (except in ''Qianosuchus'') is very thin when seen head-on. In most other archosaurs, the pubis has a consistent width. Theropod dinosaurs and a few other archosaurs have a
distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...
part of the pubis which is thinner than the proximal part. Shuvosaurids and ''Lotosaurus'' also possessed ischia (on either side of the body) which were fused to each other at the midline of the body.


Sacrum

Although the ancestral archosaur only had two sacral (hip)
vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...
e, many different archosaur groups acquired additional sacral vertebrae over the course of their
evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...
. Nesbitt (2011) argued that additional sacral vertebrae formed between these two "primordial" vertebrae. He gave the well-preserved sacrum of the poposauroid '' Arizonasaurus'' as evidence to this process. Poposauroids have three to four sacral vertebrae, with the last and third-to-last vertebrae articulating with the ilium in a way similar to the two primordial vertebrae of more primitive
archosauriformes Archosauriformes (Ancient Greek, Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles encompassing Archosaur, archosaurs and some of their close relatives. It was defined by Jacques Gauthier (1994) as the clade stemmin ...
such as ''Euparkeria'' and phytosaurs. The second-to-last vertebra has a form unlike the vertebrae of these archosauriforms, and Nesbitt concluded that it was an "insertion", formed from the innermost sections of the two primordial vertebrae. Although this process is not unique to poposauroids, it is only known in a few other archosaur lineages, such as '' Batrachotomus'',
silesaurids Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compr ...
, and
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
s. Basal poposauroids such as ''Arizonasaurus'' and ''Qianosuchus'' only had three sacral vertebra, with the second vertebra being the 'insertion'. More advanced poposauroids such as ''Poposaurus'' and shuvosaurids have four sacral vertebrae, the third recognizable as the insertion. This means that the first vertebra must have been another addition, seemingly the last dorsal vertebra which had been repurposed and transformed into a sacral vertebra. This incorporated dorsal vertebra called a dorsosacral. They were irregularly distributed among archosaurs, known in a few ornithosuchids and
aetosaurs Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...
as well as a variety of dinosaurs (most commonly in
ornithischians Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...
and theropods) In almost all archosariforms, the sacral ribs of the first primordial sacral vertebra contact the ilium near the base of that bone, close to its contact with the pubis. Poposauroids had first primordial sacral ribs with additional forward branches, which lie on the inner edge of the ilium's preacetabular blade. In poposauroids more advanced than ''Qianosuchus'', the sacral vertebrae fuse into a single bone, the sacrum. This fusion occurred incrementally, at different portions of the vertebra. For example, the zygapophyses fused together as early as the ctenosauriscids. The centra (main cylindrical portion) of the sacral vertebrae also may have fused as early as the ctenosauriscids. The bases of the neural arches (the portion of the vertebrae above the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
) were fused in some ctenosauriscids (''Arizonasaurus'') but not others ('' Bromsgroveia''), and were also fused in all poposauroids more advanced than the ctenosauriscids.


Other

Unlike most pseudosuchians, poposauroids lack bony scutes known as
osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of Extant taxon, extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, Temnospondyli, ...
. The only exception to this is ''Qianosuchus'', which possessed numerous tiny osteoderms, lying in a row extending down the neck and body. In all poposauroids, the tip of the
fibula The fibula (: fibulae or fibulas) 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. ...
(outer shin bone) is symmetrical and straight when seen from the side, rather than slanted as in other non-crocodylomorph pseudosuchians. Those more advanced than ctenosauriscids had flattened hooflike pedal
unguals An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulates have ungual phalanx bones, phalanges, as did the sauropods and ceratopsia, horned dinosaurs. A claw i ...
(toe claws). Some poposauroids had very short arms compared to the length of their legs, although disarticulation in ''Qianosuchus'' and a lack of limb material in ctenosauriscids means that it is unknown whether this trait was basal to the group as a whole. Missing data for ctenosauriscids also obscures when certain traits of the
caudal vertebrae Caudal vertebrae are the vertebrae of the tail in many vertebrates. In birds, the last few caudal vertebrae fuse into the pygostyle, and in apes, including humans, the caudal vertebrae are fused into the coccyx. In many reptiles, some of the caud ...
and
ankle The ankle, the talocrural region or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joint. The ...
bones were gained or lost within Poposauroidea.


History

Franz Nopcsa Franz may refer to: People * Franz (given name) * Franz (surname) Places * Franz (crater), a lunar crater * Franz, Ontario, a railway junction and unorganized town in Canada * Franz Lake, in the state of Washington, United States – see Fran ...
first used the term Poposauridae in 1923 to refer to poposauroids. At this time, the sole member of the group was ''
Poposaurus ''Poposaurus'' is an extinct genus of pseudosuchian archosaur from the Late Triassic of the southwestern and eastern United States. It belongs to the clade Poposauroidea, an unusual group of Triassic pseudosuchians that includes sail-backed, bea ...
'', which was considered to be a
theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
. Over the following years, poposauroids were placed in various groups, including
Saurischia Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithi ...
,
Theropoda Theropoda (; from ancient Greek iktionary:θηρίον, , (''therion'') "wild beast"; wiktionary:πούς, , wiktionary:ποδός, (''pous, podos'') "foot" is one of the three major groups (Clade, clades) of Dinosaur, dinosaurs, alon ...
, and
Carnosauria Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Ca ...
. This classification existed up until the 1970s, when better remains indicated that ''Poposaurus'' was a
pseudosuchian Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...
rather than a dinosaur. Other genera such as '' Sillosuchus'' and ''
Shuvosaurus ''Shuvosaurus'' (meaning "Shuvo hatterjees lizard") is a genus of beaked, bipedal poposauroid pseudosuchian from the Late Triassic (early to middle Norian) of western Texas. Despite superficially resembling a Theropoda, theropod dinosaur, es ...
'' were later erected. Like ''Poposaurus'', ''Shuvosaurus'' was originally thought to be a theropod dinosaur.
Sankar Chatterjee Sankar Chatterjee (born May 28, 1943) is a paleontology, paleontologist, the Paul W. Horn Professor of Earth science, Geosciences at Texas Tech University and curator of Paleontology at the Museum of Texas Tech University. He earned his Doctor of ...
reclassified poposauroids as theropod dinosaurs with his description of the new genus '' Postosuchus'' in 1985. Chatterjee 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 A Murry noted that several specimens referred to ''Postosuchus'' were distinct from the holotype, and so they assigned those specimens to the new genera '' Lythrosuchus'' and '' Chatterjeea''. In 2005, Sterling Nesbitt noted that "ctenosauriscids" such as ''Arizonasaurus'', ''Bromsgroveia'', and ''Lotosaurus'' shared many similarities with "poposaurids" such as ''Poposaurus'', ''Sillosuchus'', and "''Chatterjeea''" (now known as ''
Shuvosaurus ''Shuvosaurus'' (meaning "Shuvo hatterjees lizard") is a genus of beaked, bipedal poposauroid pseudosuchian from the Late Triassic (early to middle Norian) of western Texas. Despite superficially resembling a Theropoda, theropod dinosaur, es ...
''). He proposed that they formed a clade (informally named "Group X") to the exception of other pseudosuchians. "Group X" was formally given the name "Poposauroidea" 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 In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
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. 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 In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...
, consisting of two major clades: Rauisuchoidea and Poposauroidea. The monophyly of Rauisuchia was not strongly supported in Brusatte ''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 were not previously placed in the group. One of these genera, ''Qianosuchus'', is unique among pseudosuchians in its semiaquatic lifestyle. In his massive revision of archosaurs which included a large
cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...
analysis, Sterling J. Nesbitt (2011) found ''
Xilousuchus ''Xilousuchus'' is an extinct genus of poposauroid from lower Triassic (Olenekian stage) deposits of Fugu County of northeastern Shanxi Province, China. Xilousuchus is one of the oldest archosaurs known to date. Discovery and naming It is ...
'' 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, with ''Qianosuchus'' as the most basal member of the group and ''Lotosaurus'' grouping with shuvosaurids instead of ctenosauriscids. The
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
below follows Nesbitt (2011) with clade names based on previous studies.


References


External links


Poposauroidea
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 ...
{{Taxonbar, from=Q7229460 Early Triassic first appearances Rhaetian extinctions Taxa named by Franz Nopcsa von Felső-Szilvás Fossil taxa described in 1923