Pseudosuchia
Encyclopedia
Pseudosuchia is the name originally given to a group of prehistoric reptiles from the Triassic
period. The name has been variously interpreted, and it is still sometimes, if infrequently, used in scientific literature today. A more commonly used name, Crurotarsi
, is often substituted for Pseudosuchia, as it generally includes the same taxa. Unlike Crurotarsi though, Pseudosuchia as used in recent literature is a stem-based taxon that includes crocodile
-line archosaur
s, or all archosaurs (including crocodilians) that are more closely related to crocodilians than bird
s.
in 1887-1890 to include three taxa (two aetosaur
s and Dyoplax
) that were superficially crocodilian-like, but were not actually crocodilian. Hence the name "false crocodiles".
In mid-twentieth century textbooks like Romer's Vertebrate Paleontology
and Colbert's Evolution of the Vertebrates
the Pseudosuchia constitute one of the suborders of the Thecodont
ia. Zittel's aetosaurs were now placed in their own suborder. For typical Pseudosuchians, Colbert uses the example of small lightly built archosaurs such as Ornithosuchus
and Hesperosuchus
, both of which were at the time reconstructed as bipeds like miniature (length about 1 meter) Theropods. These little animals were assumed to be the ancestors of all later archosaurs. The name however also became a sort of wastebasket taxon for all thecodonts that didn't fit in the other three suborders. Even Sharovipteryx
and Longisquama
have been regarded as pseudosuchians.
Under the cladistic system, Gauthier
and Padian
(1985) and Gauthier (1986) became the first to establish this name in a phylogenetic context, using it as a monophyletic stem-based taxon for crocodile-ancestors and their descendants. This made the name Pseudosuchia somewhat ironic, because true crocodiles are now included. Phylogenetic definitions of Pseudosuchia include "Crocodiles and all archosaurs closer to crocodiles than to birds" (Gauthier and Padian), "Extant crocodiles and all extinct archosaurs that are closer to crocodiles than they are to birds" (Gauthier 1986), and more recently "the most inclusive clade within Archosauria that includes Crocodylia but not Aves" (Senter 2005). As a stem-based taxon, Pseudosuchia is the sister taxon of another stem group, the Avemetatarsalia
. Avemetatarsalians are bird-line archosaurs, including pterosaur
s, non-avian dinosaur
s, and all modern birds.
A different definition was suggested by Benton
and Clark, 1988: the node-based taxon including the Rauisuchidae
and the aetosaur
s. However, relations between those two groups and other archosaurs are controversial, and so this clade may be invalid (or include living crocodiles).
Paul Sereno
rejects the term Pseudosuchia, and it is not often applied by him; his Crurotarsi
is more often used instead (another partial synonym is Benton and Clark's Crocodylotarsi). Crurotarsi, however, is defined as a node-based taxon, relying on the inclusion of groups such as Phytosauria, Aetosauria, and Crocodylomorpha
. Pseudosuchia and Crurotarsi have been considered partial synonyms because the latter clade encompasses all crocodile-line archosaurs in most phylogenetic analyses. However, some analyses such as Nesbitt (2011) place one crurotarsan group, Phytosauria, outside Pseudosuchia. Since the definition of Crurotarsi relies on phytosaurs, their placement outside Pseudosuchia (and thus Archosauria) means that the clade Crurotarsi includes both pseudosuchians and avemetatarsalians.
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period. The name has been variously interpreted, and it is still sometimes, if infrequently, used in scientific literature today. A more commonly used name, Crurotarsi
Crurotarsi
The Crurotarsi are a group of archosauriformes, represented today by the crocodiles,...
, is often substituted for Pseudosuchia, as it generally includes the same taxa. Unlike Crurotarsi though, Pseudosuchia as used in recent literature is a stem-based taxon that includes crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
-line 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...
s, or all archosaurs (including crocodilians) that are more closely related to crocodilians than bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s.
Taxonomic history
The name Pseudosuchia was coined by Karl Alfred von ZittelKarl Alfred von Zittel
Karl Alfred Ritter von Zittel was a German palaeontologist.-Biography:He was born at Bahlingen in Baden, and educated at Heidelberg, Paris and Vienna. For a short period he served on the Geological Survey of Austria, and as assistant in the mineralogical museum at Vienna...
in 1887-1890 to include three taxa (two aetosaur
Aetosaur
Aetosaurs are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae...
s and Dyoplax
Dyoplax
Dyoplax is an extinct genus of sphenosuchian crocodylomorph. Fossils have been found from the type locality within the upper Schilfsandstein Formation in Stuttgart-Feuerbach, Germany. The formation was deposited during the early Carnian stage of the Late Triassic 228 million years ago in a lagoonal...
) that were superficially crocodilian-like, but were not actually crocodilian. Hence the name "false crocodiles".
In mid-twentieth century textbooks like Romer's Vertebrate Paleontology
Vertebrate Paleontology (Romer)
Vertebrate Paleontology is an advanced textbook on vertebrate paleontology by Alfred Sherwood Romer, published by the University of Chicago Press. It went through three editions and for many years constituted a very authoritative work and the definitive coverage of the subject. A condensed...
and Colbert's Evolution of the Vertebrates
Evolution of the Vertebrates
Evolution of the Vertebrates, subtitled "A History of the Backboned Animals Through Time" is a basic paleontology textbook by Edwin H. Colbert, published by John Wiley & Sons.-Overview:...
the Pseudosuchia constitute one of the suborders of the Thecodont
Thecodont
Thecodont , now considered an obsolete term, was formerly used to describe a diverse range of early archosaurs that first appeared in the Latest Permian and flourished until the end of the Triassic period...
ia. Zittel's aetosaurs were now placed in their own suborder. For typical Pseudosuchians, Colbert uses the example of small lightly built archosaurs such as Ornithosuchus
Ornithosuchus
Ornithosuchus is an extinct genus of crurotarsan from the Late Triassic Lossiemouth Sandstone of Scotland...
and Hesperosuchus
Hesperosuchus
Hesperosuchus is an extinct genus of crocodylomorph reptile that contains a single species, Hesperosuchus agilis. Remains of this sphenosuchian have been found in Late Triassic strata from Arizona and New Mexico....
, both of which were at the time reconstructed as bipeds like miniature (length about 1 meter) Theropods. These little animals were assumed to be the ancestors of all later archosaurs. The name however also became a sort of wastebasket taxon for all thecodonts that didn't fit in the other three suborders. Even Sharovipteryx
Sharovipteryx
Sharovipteryx , was an early gliding reptile, from the middle-late Triassic period . Fossils have been found from the Madygen Formation of Kyrgyzstan along with the unusual reptile Longisquama...
and Longisquama
Longisquama
Longisquama insignis is an extinct lizard-like reptile known only from one poorly preserved and incomplete fossil. It lived during the middle or late Triassic Period, 230-225 million years ago, in what is now Kyrgyzstan...
have been regarded as pseudosuchians.
Under the cladistic system, Gauthier
Jacques Gauthier
Jacques Armand Gauthier is a vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology....
and Padian
Kevin Padian
Kevin Padian is a Professor of Integrative Biology at the University of California, Berkeley, Curator of Paleontology, University of California Museum of Paleontology and President of the National Center for Science Education. Padian's area of interest is in vertebrate evolution, especially the...
(1985) and Gauthier (1986) became the first to establish this name in a phylogenetic context, using it as a monophyletic stem-based taxon for crocodile-ancestors and their descendants. This made the name Pseudosuchia somewhat ironic, because true crocodiles are now included. Phylogenetic definitions of Pseudosuchia include "Crocodiles and all archosaurs closer to crocodiles than to birds" (Gauthier and Padian), "Extant crocodiles and all extinct archosaurs that are closer to crocodiles than they are to birds" (Gauthier 1986), and more recently "the most inclusive clade within Archosauria that includes Crocodylia but not Aves" (Senter 2005). As a stem-based taxon, Pseudosuchia is the sister taxon of another stem group, the Avemetatarsalia
Avemetatarsalia
Avemetatarsalia is a clade name established by British palaeontologist Michael Benton in 1999 for all crown group archosaurs that are closer to birds than to crocodiles. It includes a similarly defined subgroup, Ornithodira...
. Avemetatarsalians are bird-line archosaurs, including pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s, non-avian 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...
s, and all modern birds.
A different definition was suggested by Benton
Michael J. Benton
Michael J. Benton is a British paleontologist, a Fellow of the Royal Society of Edinburgh, and professor of vertebrate palaeontology in the Department of Earth Sciences at the University of Bristol....
and Clark, 1988: the node-based taxon including the Rauisuchidae
Rauisuchidae
Rauisuchidae is a group of large predatory Triassic archosaurs, and constitute advanced representatives of the larger group Rauisuchia. There is some disagreement over which genera should be included in the Prestosuchidae, which in Rauisuchidae, and which in the Poposauridae, and indeed whether...
and the aetosaur
Aetosaur
Aetosaurs are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae...
s. However, relations between those two groups and other archosaurs are controversial, and so this clade may be invalid (or include living crocodiles).
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...
rejects the term Pseudosuchia, and it is not often applied by him; his Crurotarsi
Crurotarsi
The Crurotarsi are a group of archosauriformes, represented today by the crocodiles,...
is more often used instead (another partial synonym is Benton and Clark's Crocodylotarsi). Crurotarsi, however, is defined as a node-based taxon, relying on the inclusion of groups such as Phytosauria, Aetosauria, and Crocodylomorpha
Crocodylomorpha
The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were...
. Pseudosuchia and Crurotarsi have been considered partial synonyms because the latter clade encompasses all crocodile-line archosaurs in most phylogenetic analyses. However, some analyses such as Nesbitt (2011) place one crurotarsan group, Phytosauria, outside Pseudosuchia. Since the definition of Crurotarsi relies on phytosaurs, their placement outside Pseudosuchia (and thus Archosauria) means that the clade Crurotarsi includes both pseudosuchians and avemetatarsalians.
External links
- Taxon Search - Pseudosuchia
- Re: Even more last papers for 2005 and follow up posts, on the Dinosaur Mailing List archives, for comments critical of applying "Pseudosuchia" in a cladistic context.