41-443: Pterosauromorpha (meaning "pterosaur-like forms") is one of the two basic divisions of Ornithodira that includes pterosaurs and all taxa that are closer to them than to dinosaurs and their close relatives (i.e. Dinosauromorpha ). In addition to pterosaurs, Pterosauromorpha also includes the basal clade Lagerpetidae and some other Late Triassic ornithodirans ( Maehary and Scleromochlus ). The name Pterosauromorpha
82-435: 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
123-475: A more recent common ancestor with it than with Alligator (originally Crocodilus ) mississippiensis (Daudin 1802) ( Suchia ) and Compsognathus longipes Wagner 1859 (Dinosauromorpha)". Lagerpetidae was traditionally considered the earliest diverging group of dinosauromorphs. This caused no other reptiles besides the true pterosaurs to be placed in Pterosauromorpha. The only notable exception
164-459: A non-archosaur archosauriform (possibly 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
205-514: A result of these being the bones most commonly preserved. Hip material is only known in Lagerpeton and Ixalerpeton , which share three adaptations of the ilium (upper blade of the hip). The supraacetabular crest, a ridge of bone which lies above the acetabulum (hip socket), is thickest above the middle portion of the acetabulum, rather than the front of it. However, it also extends further forwards than in most dinosauromorphs, snaking along
246-427: A small third one which was near the apex of the femoral head. However, lagerpetids lack the anterolateral tuber, instead having an emargination in the head just below where the tuber would normally be expected. The femoral head itself was notably hook-shaped when seen from the side. The distal portion of the femur (i.e. the portion near the knee) had a pair of condyles (knobs) on either side of the rear surface, as well as
287-498: A specimen from the Santa Rosa Formation attributed to Dromomeron sp., were able to get quite large (femoral length 150–220 mm (5.9–8.7 in)). Lagerpetid fossils are rare; the most common finds are bones of the hindlimbs, which possessed a number of unique features. As with most early avemetatarsalians, the most characteristic adaptations of lagerpetids occurred in their hip, leg and ankle bones, likely as
328-434: A study that used micro-CT scans , Ezcurra et al. (2020) have found additional similarities, including large semicircular canals within the bones of some lagerpetids that resemble that of pterosaurs. It is assumed that large semicircular canals are related to arboreal , aerial or other agile forms of terrestrial locomotion as well as rapid movements. The flocculus , the part of the brain that aids in transmitting information,
369-491: A third knob-like structure known as a crista tibiofibularis, which was present just above the lateral condyle . The crista tibiofibularis was uniquely enlarged in lagerpetids, and undergoes further evolution in Ixalerpeton and particularly Dromomeron . The tibia and fibula (shin bones) were long and thin, with the tibia longer than the femur and generally resembling the tibia of early theropod dinosaurs. The ankle
410-435: 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
451-964: 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
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#1732802370487492-465: 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 the present day. Pterosaurs were
533-610: Is a family of basal avemetatarsalians . Though traditionally considered the earliest-diverging dinosauromorphs (reptiles closer to dinosaurs than to pterosaurs), fossils described in 2020 suggest that lagerpetids may instead be pterosauromorphs (closer to pterosaurs). Lagerpetid fossils are known from the Triassic of San Juan ( Argentina) , Arizona ( USA ), Rio Grande do Sul ( Brazil ), Madagascar , New Mexico ( USA ), and Texas ( USA ). They were typically small, although some lagerpetids, like Dromomeron gigas and
574-434: 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
615-483: 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
656-519: 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] Lagerpetidae Lagerpetidae ( / ˌ l æ dʒ ər ˈ p ɛ t ɪ d iː / ; originally Lagerpetonidae )
697-481: 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
738-570: 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
779-578: The astragalus, one in front of the facet for the tibia, and the other behind it. The one in front is similar to a structure found in dinosauriform ankles known as the anterior ascending process, and it may be homologous with it. However, the posterior ascending process (the one behind the tibial facet) is entirely unique to lagerpetids. The rear of the astragalus lacks a horizontal groove, similar to Tropidosuchus , theropods, and ornithischians, but unlike most other archosauriforms. Like pterosaurs and dinosaurs (but unlike Marasuchus and most other archosaurs),
820-431: 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
861-438: The data matrices used in the study by Muller et al. (2018). Cladogram simplified after Cabreira et al ., 2016: Euparkeria Lagerpeton Ixalerpeton Dromomeron Marasuchus Pseudolagosuchus Lewisuchus Saltopus Dinosauria By contrast, Kammerer et al. (2020), Ezcurra et al. (2020) recovered Lagerpetidae as the sister clade to pterosaurs , based on newly-described fossils of
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#1732802370487902-484: The ear], which orients you in 3D space. The shape of those canals correlates with ecology and how you move your head — basically, are you agile or not? And a lot of things that have flight have semicircular canals with a really large and characteristic [shape] because you're flying, you're in a lot more 3D space. Kellner et al. (2022) described Maehary , a small ornithodiran from the Late Triassic of Brazil . It
943-409: The earliest pterosaurs were already capable flyers. First iteration of phylogenetic analysis produced by Kammerer et al. (2020) restored lagerpetids as a basal dinosauromorphs, which corresponds to the traditional point of view. But the second iteration, in which were added Scleromochlus, found Lagerpetidae as the most basal pterosauromorphs, and Scleromochlus as the sister taxon of pterosaurs. In
984-465: The facet on the calcaneum which receives the fibula is concave and there is no evidence of a pronounced rearward bump known as a calcaneal tuber. The lagerpetids were typically considered relatives of the dinosaurs , as a branch of the group Dinosauromorpha . The family was originally named Lagerpetonidae by Arcucci in 1986, though it was later renamed Lagerpetidae in a phylogenetic study by S. J. Nesbitt and colleagues in 2009. A clade of lagerpetids
1025-574: 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
1066-410: The femur (thigh bone) was slender and S-shaped. The femoral head was thin when seen from above, and its apex projected about 45 degrees between medially (inwards) and anteriorly (forwards). Most archosaurs had three tubera (bumps) on their flattened femoral head, one at the middle of the anterolateral (forwards/outwards) surface, another at the middle of the posteromedial (backwards/inwards) surface, and
1107-764: 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
1148-592: 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
1189-463: The length of the pubic peduncle (the area of the ilium which connects to the pubis ). The ilium's facet for the pubis opens downwards, a trait also acquired by ornithischian dinosaurs. The hip in general was wide, had a closed acetabulum (i.e. one with a bony inner wall), and had two sacral vertebrae, lacking many specializations of later dinosauromorphs, like dinosaurs. Like other early archosaurs (and archosaur relatives such as Euparkeria ),
1230-426: 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
1271-490: 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
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1312-399: 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
1353-518: 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
1394-409: 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
1435-466: Was a small reptile named Scleromochlus , whose placement within the clade itself remained controversial due the poor preservation of its otherwise complete remains . Different phylogenetic analyses found it as a basal pterosauromorph, a non- aphanosaurian , non- pterosaur basal avemetatarsalian, a basal dinosauromorph, or a basal archosauriform . This has resulted in a large gap between the fully aerial pterosaurs and their terrestrial ancestors, as
1476-414: Was also large in both pterosaurs and lagerpetids, though to a lesser extent. When Ezcurra et al. (2020) included Scleromochlus in their analysis, they found it to be the most basal pterosauromorph, sister to a clade including lagerpetids and pterosaurs. Baron (2021) conducted his own analysis, which confirmed the relationship between lagerpetids and pterosaurs. It has to do with the semicircular canals [in
1517-515: Was also recovered in the large phylogenetic analyses of early dinosaurs and other dinosauromorphs that were produced by Baron, Norman & Barrett (2017). More recently, Muller et al. (2018) carried out the most comprehensive study on lagerpetid phylogeny, which assembled all lagerpetid specimens, taxa and morphotypes known so far into three of the most recent data matrices on early dinosauromorph / archosaur evolution. Finally, Garcia et al. (2019) added an unnamed lagerpetid (a new morphotype ) to
1558-443: Was formed by two main bones: the astragalus (which contacts both the tibia and fibula), and the calcaneum (which only contacts the fibula). As with dinosauromorphs, the astragalus was twice as wide as the reduced calcaneum. In addition, the two bones were co-ossified (fused together), akin to the condition in pterosaurs and some early dinosaurs ( coelophysoids , for example). A pair of small, pyramid-shaped structures rise up out of
1599-399: 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
1640-606: Was interpreted as a basal pterosauromorph (along with lagerpetids). It is noteworthy that left maxilla of Maehary was previously considered to be a specimen of Faxinalipterus that was re-classified as a lagerpetid. Nesbitt et al. (2011) Lagerpetidae Dinosauriformes Pterosauria Ezcurra et al. (2020) Dinosauromorpha Lagerpetidae Pterosauria Kellner et al. (2022) Dinosauromorpha Maehary Lagerpetidae Pterosauria [REDACTED] [REDACTED] [REDACTED] Ornithodira Avemetatarsalia (meaning "bird metatarsals ")
1681-631: Was originally coined by Emil Kuhn-Schnyder and Hans Rieber (1986) for a reptilian subclass distinct from Archosauria which includes pterosaurs. In 1997, Kevin Padian classified Pterosauromorpha as a clade of archosaurs and proposed phylogenetic definition for this group: "Pterosauria and all ornithodiran archosaurs closer to them than to dinosaurs". Brian Andres and Kevin Padian redefined Pterosauromorpha as: "The clade consisting of Pterodactylus (originally Ornithocephalus ) antiquus (Sömmerring 1812) (Pterosauria) and all organisms or species that share