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48-471: Avemetatarsalia (meaning "bird metatarsals ") is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians . The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs. Dinosaurs were the largest terrestrial animals for much of the Mesozoic Era , and one group of small feathered dinosaurs (Aves, i.e. birds) has survived up to

96-417: A doswelliid ). In 2023, Nesbitt et al . described Mambachiton as the earliest diverging avemetatarsalian, outside of the minimally inclusive clade containing aphanosaurs and ornithodirans. Preliminary analyses had considered Mambachiton to be a basal poposauroid (a clade of pseudosuchians ), though the later recognition of aphanosaurs as basal avemetatarsalians corrected this view. The results of

144-494: A branch-based clade, Pseudosuchia is the sister taxon of another branch-based clade, the Avemetatarsalia . Avemetatarsalians are bird-line archosaurs, including pterosaurs and dinosaurs (the latter including birds). A different definition was suggested by Benton and Clark, 1988: the node-based taxon including the last common ancestor of Rauisuchidae and aetosaurs and all of its descendants. Benton and Clark also named

192-570: A diverse array of lifestyles during the Jurassic and Cretaceous periods, although only a single subset of crocodylomorphs, the Crocodilia, survive to the present day. Living crocodilians include crocodiles , alligators , caimans , and gavialids . The name Pseudosuchia was originally given to a group of superficially crocodile-like prehistoric reptiles from the Triassic period, but fell out of use in

240-513: A group called Crocodylotarsi, which includes most taxa now considered pseudosuchians. In 1990, Paul Sereno erected the clade Crurotarsi to supplant Pseudosuchia. However, Sereno defined Crurotarsi as a node-based clade, relying on the inclusion of groups such as Phytosauria , Aetosauria, and Crocodylomorpha . It is not equivalent to Pseudosuchia, which by definition must include all crocodilian-line archosaurs. For many years, Pseudosuchia and Crurotarsi have been considered partial synonyms because

288-506: A major 2011 study of Triassic archosaur relations proposed that Rutiodon 's group, Phytosauria , was not closely related to other traditional "crurotarsans", at least compared to avemetatarsalians such as pterosaurs and dinosaurs . As a result, Crurotarsi could be a much broader clade than Pseudosuchia. Other recent studies support a more traditional phylogeny. Contrary to popular belief, crocodilians differ significantly from their ancestors and distant relatives, as Pseudosuchia contains

336-434: A membrane of skin, muscle, and other tissues stretching from the ankles to a dramatically lengthened fourth finger. Birds evolved flight much later. Their wings formed from elongated fingers and their arms, all covered with flight feathers . Avemetatarsalians were generally more lightly built than crocodile-line archosaurs . They had smaller heads and usually a complete lack of osteoderms . Bird-line archosaurs appear in

384-547: A new sock that incorporated a rubber silicone pad over the foot to provide protection to the top of the foot. Stress fractures are thought to account for 16% of injuries related to sports participation, and the metatarsals are the bones most often involved. These fractures are sometimes called march fractures , based on their traditional association with military recruits after long marches. The second and third metatarsals are fixed while walking, thus these metatarsals are common sites of injury. The fifth metatarsal may be fractured if

432-442: A shaft or body, a base ( proximally ), and a head ( distally ). The body is prismoid in form, tapers gradually from the tarsal to the phalangeal extremity, and is curved longitudinally, so as to be concave below, slightly convex above. The base or posterior extremity is wedge -shaped, articulating proximally with the tarsal bones, and by its sides with the contiguous metatarsal bones: its dorsal and plantar surfaces are rough for

480-407: A similar definition, Crocodylotarsi, was named in 1988, possibly as a replacement for Pseudosuchia. The name Pseudosuchia, meaning "false crocodiles", has been used for over a century, and traditionally included only non-crocodilians, but when defined as a clade, Pseudosuchia came to include the group Eusuchia ("true crocodiles") as well. Crocodylotarsi may have been named to remove confusion, but as

528-410: A staggering diversity of reptiles with many different lifestyles. Early pseudosuchians were successful in the Triassic period. They included giant, quadrupedal apex predators such as Saurosuchus , Prestosuchus , and Fasolasuchus . Ornithosuchids were large scavengers, while erpetosuchids and gracilisuchids were small, light-footed predators. A few groups acquired herbivorous diets, such as

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576-399: A stem-based clade, it is synonymous with Pseudosuchia. Because Pseudosuchia was named first, it has precedence. A third group, Crurotarsi , traditionally included the same archosaurs as Pseudosuchia, but as a node-based clade it is not synonymous. The scope of Crurotarsi has recently been changed by the phylogenetic placement of phytosaurs. In 2011, Sterling J. Nesbitt found phytosaurs to be

624-433: A variety of Triassic archosaurs, including Lagosuchus and Scleromochlus , to this group. In a 2005 review of archosaur classification, Phil Senter attempted to resolve this conflicting set of terminology by applying strict priority to names based on when and how they were first defined. Senter noted that Ornithosuchia, the earliest name used for the total group of archosaurs closer to birds than to crocodiles, should be

672-950: Is "undesirable" because it probably excludes the eponymous family Ornithosuchidae , and questioned the utility of using priority before the PhyloCode is implemented to govern it. In fact, the name Ornithosuchia may be "illegal" under the PhyloCode because it does not include its eponymous taxon as part of its definition. Cladogram after Nesbitt et al. (2017), with clade names from Cau (2018). Pseudosuchia (crocodile-line archosaurs) [REDACTED] † Aphanosauria [REDACTED] † Pterosauria [REDACTED] † Lagerpetidae [REDACTED] † Marasuchus [REDACTED] † Silesauridae [REDACTED] † Ornithischia [REDACTED] † Sauropodomorpha [REDACTED] Theropoda [REDACTED] Kammerer et al . (2020) and Ezcurra et al . (2020) supported an alternative hypothesis regarding

720-966: Is a cladogram modified from Nesbitt (2011) showing the new changes (bold terminal taxa are collapsed). † Proterosuchidae [REDACTED] † Erythrosuchus [REDACTED] † Vancleavea [REDACTED] † Proterochampsia [REDACTED] † Euparkeria [REDACTED] † Phytosauria [REDACTED] Avemetatarsalia (bird-lineage of archosaurs) [REDACTED] † Ornithosuchidae [REDACTED] † Gracilisuchus [REDACTED] † Turfanosuchus [REDACTED] † Revueltosaurus [REDACTED] † Aetosauria [REDACTED] † Ticinosuchus [REDACTED] † Poposauroidea [REDACTED] † Prestosuchus [REDACTED] † Saurosuchus [REDACTED] † Batrachotomus [REDACTED] † Fasolasuchus † Rauisuchidae [REDACTED] Crocodylomorpha [REDACTED] The following cladogram

768-583: Is one of the two primary "daughter" clades of the Archosauria . The skull is often massively built, especially in contrast to ornithodires ; the snout is narrow and tends to be elongated, the neck is short and strong, and the limb posture ranges from a typical reptilian sprawl to an erect stance like dinosaurs ' or mammals ', although achieving it a different way. The body is often protected by two or more rows of armored plates. Many crurotarsans reached lengths of three meters or more. Pseudosuchians appeared during

816-434: Is the "advanced mesotarsal" ankles, which are characterized by a large astragalus and a small calcaneum . This ankle orientation operated on a single hinge, allowing for better mobility. Probably as a result of this change, the common ancestor of the avemetatarsalians had an upright, bipedal posture, with their legs extending vertically, similar to that of mammals. Feathers and other filamentary structures are known across

864-483: The ichnogenus Prorotodactylus and were made by an unknown small quadrupedal animal, but footprints called Sphingopus , found from Early Anisian strata, show that moderately large bipedal dinosauromorphs had appeared by 246 Ma. The tracks show that the dinosaur lineage appeared soon after the Permian–Triassic extinction event . Their age suggests that the rise of dinosaurs was slow and drawn out across much of

912-491: The phylogenetic analyses of Nesbit et al . (2023) are shown in the cladogram below: Pseudosuchia [REDACTED] Mambachiton Aphanosauria [REDACTED] Lagerpetidae [REDACTED] Pterosauria [REDACTED] Lagosuchus [REDACTED] Dinosauria [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Metatarsal The five metatarsals are dorsal convex long bones consisting of

960-467: The "bird-line archosaurs" or Avemetatarsalia . Despite Pseudosuchia meaning "false crocodiles", the name is a misnomer as true crocodilians are now defined as a subset of the group. The clade Pseudosuchia is potentially equivalent to Crurotarsi even though the latter has a different, node-based definition: "all taxa the least inclusive clade containing Rutiodon carolinensis (Emmons, 1856), and Crocodylus niloticus (Laurenti, 1768)." However,

1008-473: The Triassic. The primitive traits found in the quadrupedal aphanosaur Teleocrater shows that the earliest avemetatarsalians had many pseudosuchian-like features, and that the traits typical for the group evolved later. In 1986, Jacques Gauthier defined the name Ornithosuchia (previously coined by Huene ) for a branch-based clade including all archosaurs more closely related to birds than to crocodiles. In

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1056-569: The archosaur family tree. This split corresponds to the subgroup Ornithodira ( Ancient Greek ὄρνις ( órnis , “bird”) + δειρή ( deirḗ , “throat”), defined as the last common ancestor of dinosaurs and pterosaurs, and all of its descendants. Until the discovery of aphanosaurs, Ornithodira and Avemetatarsalia were considered roughly equivalent concepts. Pterosauromorpha includes all avemetatarsalians closer to pterosaurs than to dinosaurs. True non-pterosaur pterosauromorphs have been historically difficult to determine. Small, insectivorous archosaurs of

1104-443: The attachment of ligaments . The head or distal extremity presents a convex articular surface, oblong from above downward, and extending farther backward below than above. Its sides are flattened, and on each is a depression, surmounted by a tubercle , for ligamentous attachment. Its plantar surface is grooved antero-posteriorly for the passage of the flexor tendons , and marked on either side by an articular eminence continuous with

1152-431: The avemetatarsalians, from the downy pycnofibers of pterosaurs, to quill-like structures present in ornithischian dinosaurs, such as Psittacosaurus and Tianyulong , to feathers in theropod dinosaurs and their descendants, birds. Two clades of avemetatarsalians, pterosaurs and birds, independently evolved flight. Pterosaurs are the earliest vertebrates known to have evolved powered flight. Their wings are formed by

1200-521: The birds, while the crocodilians continued with little change. Today, the crocodiles , alligators , and gharials are the surviving representatives of this lineage. The Mesozoic range of cranial disparity is higher than the Triassic one, suggesting crocodylomorphs attained a high degree of diversification compared to Triassic pseudosuchians. Pseudosuchia was defined as a stem-based clade in 1985. It includes crocodiles and all archosaurs more closely related to crocodiles than to birds. A second clade with

1248-504: The dominant terrestrial carnivores and herbivores. As the Mesozoic progressed, the Protosuchia gave rise to more typically crocodile-like forms. While dinosaurs were the dominant animals on land, the crocodiles flourished in rivers, swamps, and the oceans, with far greater diversity than they have today. With the end-Cretaceous extinction , the dinosaurs became extinct, with the exception of

1296-424: The extinction of all the pseudosuchians with the exception of Sphenosuchia and Crocodyliformes (both Crocodylomorpha ), the latter being the ancestors of modern-day crocodiles. A study published in 2010 postulates that there is significant evidence that volcanic eruptions changed the climate, causing a mass extinction that wiped out the dinosaurs' main competitors. This allowed the dinosaurs to succeed them as

1344-568: The family Lagerpetidae may potentially be examples, alongside the similar genus Scleromochlus . Dinosauromorpha , on the other hand, includes all avemetatarsalians closer to dinosaurs than to pterosaurs. Probable non-dinosaur dinosauromorphs include the diverse and widespread silesaurids , as well as more controversial and fragmentary taxa such as Marasuchus , Lagosuchus , Nyasasaurus , and Saltopus . Lagerpetids were also traditionally considered dinosauromorphs, though this has been more recently debated. The foundational characteristic

1392-415: The first row of phalanges at the metatarsophalangeal joints . Their bases also articulate with each other at the intermetatarsal joints The metatarsal bones are often broken by association football (soccer) players. These and other recent cases have been attributed to the lightweight design of modern football boots , which provide less protection to the foot. In 2010 some football players began testing

1440-744: The first to establish the name Pseudosuchia in a phylogenetic context, using it as a branch-based taxon for all archosaurs more closely related to crocodilians than to birds. This made the name Pseudosuchia somewhat ironic because true crocodiles (i.e. members of Crocodylia) were now included in the group. 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

1488-549: The foot is oversupinated during locomotion. Protection from injuries can be given by the use of safety footwear which can use built-in or removable metatarsal guards. Pseudosuchia Pseudosuchia (from Greek : ψεύδος (pseudos) , "false" and Greek : σούχος (souchos) , "crocodile") is one of two major divisions of Archosauria , including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs", in contrast to

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1536-579: The fossil record by the Anisian stage of the Middle Triassic about 245 million years ago, represented by the dinosauriform Asilisaurus . However, Early Triassic fossil footprints reported in 2010 from the Świętokrzyskie (Holy Cross) Mountains of Poland may belong to a more primitive dinosauromorph . If so, the origin of avemetatarsalians would be pushed back into the early Olenekian age, around 249 Ma. The oldest Polish footprints are classified in

1584-490: The heavily armored aetosaurs , and several were bipedal, such as Poposaurus and Postosuchus . The bizarre, ornithomimid -like shuvosaurids were both bipedal and herbivorous, with toothless beaks. Many of these Triassic pseudosuchian groups went extinct at or before the Triassic–Jurassic extinction event . However, one group, the crocodylomorphs , survived the major extinction. Crocodylomorphs themselves evolved

1632-528: The late Olenekian (early Triassic ); by the Ladinian (late Middle Triassic) they dominated the terrestrial carnivore niches. Their heyday was the Late Triassic, during which time their ranks included erect-limbed rauisuchians , herbivorous armored aetosaurs , the large predatory poposaurs , the small agile sphenosuchian crocodilians, and a few other assorted groups. The end-Triassic extinction caused

1680-399: The late 20th century, especially after the name Crurotarsi was established in 1990 to label the clade (evolutionary grouping) of archosaurs encompassing most reptiles previously identified as pseudosuchians. By this time, Pseudosuchia had also been defined as a clade , but it was not widely embraced until 2011. In 2011 paleontologist Sterling Nesbitt proposed that Crurotarsi, as it

1728-412: The latter clade encompasses all crocodilian-line archosaurs in most phylogenetic analyses. Sterling Nesbitt 's 2011 analysis places 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. Pseudosuchia

1776-512: The name "false crocodiles". In mid-20th century textbooks, like Alfred Sherwood Romer 's Vertebrate Paleontology and Edwin H. Colbert 's Evolution of the Vertebrates , Pseudosuchia constitutes one of the suborders of the now-abandoned order Thecodontia . Zittel's aetosaurs were placed in their own suborder, Aetosauria. Colbert considered small lightly built archosaurs, such as Ornithosuchus and Hesperosuchus — both of which were at

1824-425: The only avemetatarsalians to survive past the end of the Triassic, other groups flourished during the Triassic. The most basal (earliest-branching) and plesiomorphic ("primitive") known avemetatarsalians were the aphanosaurs . Aphanosaurs were rare, four-legged carnivores which were only properly distinguished as a group in 2017. The split between dinosaurs and pterosaurs occurred just after aphanosaurs branched off

1872-490: The opinion that Ornithodira was not a useful concept, whereas Avemetatarsalia was. In 2001, the same clade was given the name "Panaves" ( lit.   ' all birds ' , from Greek pan- + Latin aves ), coined by Jacques Gauthier. He defined it as the largest and most inclusive clade of archosaurs containing Aves (birds, anchored on Vultur gryphus ) but not Crocodylia (anchored on Crocodylus niloticus ). Gauthier referred Aves, all other Dinosauria, all Pterosauria, and

1920-775: The present day. Pterosaurs were the first flying vertebrates and persisted through the Mesozoic before dying out at the Cretaceous-Paleogene (K-Pg) extinction event . Both dinosaurs and pterosaurs appeared in the Triassic Period , shortly after avemetatarsalians as a whole. The name Avemetatarsalia was first established by British palaeontologist Michael Benton in 1999. An alternate name is Pan-Aves , or "all birds", in reference to its definition containing all animals, living or extinct, which are more closely related to birds than to crocodilians. Although dinosaurs and pterosaurs were

1968-438: The relationships of lagerpetids. They were interpreted as non-pterosaur pterosauromorphs. This phylogeny would shorten the morphological and chronological gap perceived between pterosaurs and other stem-birds, and explain the origin of this group. Bennett (2020) argued that Scleromochlus , a genus historically considered a relative of ornithodirans or even a basal pterosauromorph, was instead a non-archosaur archosauriform (possibly

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2016-511: The same year, Gauthier also coined and defined a slightly more restrictive node-based clade, Ornithodira, containing the last common ancestor of the dinosaurs and the pterosaurs and all of its descendants. Paul Sereno in 1991 gave a different definition of Ornithodira, one in which Scleromochlus was explicitly added. It was thus a potentially larger group than the Ornithodira of Gauthier. In 1999 Michael Benton concluded that Scleromochlus

2064-408: The sister taxon of Archosauria, and therefore not crocodile-line archosaurs. Because phytosaurs are included in the definition of Crurotarsi, crurotarsans are not solely crocodile-line archosaurs, but also bird-line archosaurs and phytosaurs. Under this phylogeny, Crurotarsi includes phytosaurs, crocodiles, pterosaurs, and dinosaurs, while Pseudosuchia still contains only crocodile-line archosaurs. Below

2112-405: The terminal articular surface. During growth, the growth plates are located distally on the metatarsals, except on the first metatarsal where it is located proximally. Yet it is quite common to have an accessory growth plate on the distal first metatarsal. The base of each metatarsal bone articulates with one or more of the tarsal bones at the tarsometatarsal joints , and the head with one of

2160-523: The time reconstructed as theropod dinosaur-like bipeds — to be typical pseudosuchians. These small forms were assumed to be the ancestors of all later archosaurs. The name Pseudosuchia became a wastebasket taxon into which all thecodonts that did not fit in the other three suborders could be placed. Even Sharovipteryx and Longisquama , two enigmatic Triassic reptiles that bear little resemblance to archosaurs, have been regarded as pseudosuchians. Gauthier and Padian (1985) and Gauthier (1986) became

2208-409: The valid name for that group, and have precedence over later names with identical definitions, such as Avemetatarsalia and Pan-Aves. While this has been followed by some researchers, others have either continued to use Avemetatarsalia or Ornithodira, or have followed Senter only reluctantly. Mike Taylor (2007) for example noted that, while Senter is correct in stating that Ornithosuchia has priority, this

2256-399: Was indeed outside Gauthier's original conception of Ornithodira, so he named a new branch-based clade for this purpose: Avemetatarsalia, named after the birds ( Aves ), the last surviving members of the clade, and the metatarsal ankle joint that was a typical character of the group. Avemetatarsalia was defined as all Avesuchia closer to Dinosauria than to Crocodylia . In 2005, Sereno stated

2304-568: Was then defined, must include not only crocodilian-line archosaurs, but all other archosaurs including birds, non-avian dinosaurs , and pterosaurs . The clade Pseudosuchia as originally defined could still be used to identify crocodilian-line archosaurs, and since many recent studies support Nesbitt's findings, Pseudosuchia is again commonly used. The name Pseudosuchia was coined by Karl Alfred von Zittel in 1887–1890 to include three taxa (two aetosaurs and Dyoplax ) that were superficially crocodilian-like, but were not actually crocodilian. Hence

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