Avemetatarsalia

Avemetatarsalians Temporal range: Middle Triassic–Present, 245–0 Ma PreЄ Є O S D C P T J K Pg N (possible Early Triassic record)
Clockwise from top-left: Tupuxuara leonardi (a pterosaur), Alamosaurus sanjuanensis, (a sauropod), Tsintaosaurus spinorhinus (an ornithopod), Daspletosaurus torosus (a tyrannosaur), Pentaceratops sternbergii (a ceratopsian), and Grus grus (an extant avian).
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Sauropsida
Clade:	Archosauria
Clade:	Avemetatarsalia Benton, 1999
Subgroups
†Aphanosauria †Scleromochlus Ornithodira Gauthier, 1986 †Pterosauromorpha Dinosauromorpha †Lagerpetidae Dinosauriformes †Marasuchus †Nyasasaurus †Saltopus †Silesauridae Dinosauria
Synonyms
Ornithosuchia Huene, 1908 Pan-Aves Gauthier, 2001

Avemetatarsalia (meaning "bird metatarsals") 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.^[1] It includes a similarly defined subgroup, Ornithodira. 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 crocodiles.

Members of this group include the Dinosauromorpha, Pterosauromorpha, the genus Scleromochlus, and Aphanosauria. Dinosauromorpha contains more basal forms, including Lagerpeton and Marasuchus, as well as more derived forms, including dinosaurs; birds, according to most modern scientists, belong to the latter as members of the theropods. Pterosauromorpha contains Pterosauria, which as far as is known were the first vertebrates capable of true flight. Aphanosaurs are a recently recognized group of carnivorous quadrupedal bird-line archosaurs only known from the Triassic.^[2]

Origin

Bird-line archosaurs appear in 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 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 the Triassic.^[3] The primitive traits found in the quadrupedal Teleocraters, shows that their last common ancestor had many crocodile-like features, and that the traits typical for the group evolved later.^[4]

Classification

Michael Benton originated the clade name Avemetatarsalia

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.^[5] In 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.^[6] It was thus a potentially larger group than the Ornithodira of Gauthier. In 1999 Michael Benton concluded that Scleromochlus was indeed outside of 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 the opinion that Ornithodira was not a useful concept, whereas Avemetatarsalia was.

In 2001, the same clade was given the name Pan-Aves (meaning "all [pan in Greek] birds" [aves in Latin]), 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 a variety of Triassic archosaurs, including Lagosuchus and Scleromochlus, to this group.^[7]

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 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 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.^[8] In fact, the name Ornithosuchia may be "illegal" under the PhyloCode because it does not include its eponymous taxon as part of its definition.^[8]

Cladogram after Nesbitt et al. (2017):^[2]

References

Sources

• Michael J. Benton (2004). "Origin and relationships of Dinosauria". In David B. Weishampel; Peter Dodson; Halszka Osmólska (Hrsg.). The Dinosauria. Berkeley: Zweite Auflage, University of California Press. pp. 7–19. ISBN 0-520-24209-2. 

Basal archosauriforms
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Subclass: Diapsida
Major clades Proterosuchidae Erythrosuchidae Proterochampsia Phytosauria Archosauria
Archosauriformes Archosauriformes Chasmatosuchus Fugusuchus Sarmatosuchus Proterosuchidae Archosaurus Proterosuchus Erythrosuchidae Chalishevia Erythrosuchus Garjainia Shansisuchus Uralosaurus Eucrocopoda Asperoris Dorosuchus Proterochampsia Euparkeriidae Euparkeria ?Halazhaisuchus ?Osmolskina Crurotarsi Phytosauria Archosauria Ornithodira Pseudosuchia
Proterochampsia Doswelliidae Ankylosuchus Archeopelta Doswellia Jaxtasuchus Tarjadia Vancleavea Proterochampsidae Cerritosaurus Proterochampsa Tropidosuchus Rhadinosuchinae Chanaresuchus Gualosuchus Rhadinosuchus Pseudochampsa
Phytosauria Basal phytosaurs Belodon Centemodon? Diandongosuchus Francosuchus? Mesorhinosuchus Phytosaurus? Parasuchidae Basal forms Arganarhinus Ebrachosuchus Paleorhinus Parasuchus Wannia Mystriosuchinae Angistorhinus Brachysuchus Protome Rutiodon Leptosuchomorpha Leptosuchus Pravusuchus Smilosuchus Mystriosuchini Angistorhinopsis Coburgosuchus Machaeroprosopus Mystriosuchus Nicrosaurus Redondasaurus
Related categories Archosaurs Crurotarsans

Avemetatarsalians (Dinosauromorpha and relatives)
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Clade: Archosauria Clade: Avemetatarsalia Dinosauromorpha Pterosauromorpha
Avemetatarsalia Avemetatarsalia †Scleromochlus †Aphanosauria Dongusuchus Spondylosoma Teleocrater Yarasuchus Ornithodira Dinosauromorpha see below †Pterosauromorpha see below
Dinosauromorpha †Lagerpetidae Dromomeron Lagerpeton Ixalerpeton Dinosauriformes Marasuchus Lagosuchus Saltopus Nyasasaurus? †Silesauridae Lewisuchus Asilisaurus Eucoelophysis Silesaurus Sacisaurus Diodorus Pisanosaurus? Pseudolagosuchus Lutungutali Ignotosaurus Agnosphitys? Technosaurus? Dinosauria (Dinosaurs) †Ornithischia see below Saurischia †Basal Alwalkeria Teyuwasu? Eusaurischia †Eoraptor †Sauropodomorpha see below Theropoda see below
†Pterosauromorpha Scleromochlidae Scleromochlus Pterosauria Eopterosauria Preondactylia Austriadactylus Preondactylus Eudimorphodontoidea Peteinosaurus Eudimorphodontidae Eudimorphodon Macronychoptera Dimorphodontia Dimorphodon Parapsicephalus Novialoidea Campylognathoides Breviquartossa Rhamphorhynchidae Pterodactylomorpha Sordes Allkaruen Monofenestrata
†Ornithischia Basal ornithischians Eocursor Fabrosaurus Heterodontosauridae Echinodon Fruitadens Tianyulong Heterodontosaurinae Lycorhinus Pegomastax Manidens Abrictosaurus Heterodontosaurus Genasauria Thyreophora Scutellosaurus Emausaurus Tatisaurus Scelidosauridae Scelidosaurus Eurypoda Ankylosauria Stegosauria Neornithischia Stormbergia Agilisaurus Hexinlusaurus Othnielosaurus Kulindadromeus Cerapoda Ornithopoda includes Iguanodontia Marginocephalia See Marginocephalia
†Sauropodomorpha Sauropodomorpha Pantydraco Thecodontosaurus Nambalia Efraasia Plateosauravus Ruehleia Buriolestes Guaibasauridae Guaibasaurus Saturnaliinae Saturnalia Chromogisaurus Plateosauria Sarahsaurus Plateosauridae Euskelosaurus Jaklapallisaurus Plateosaurus Unaysaurus Riojasauridae Eucnemesaurus Riojasaurus Massospondylidae Adeopapposaurus Coloradisaurus Glacialisaurus Leyesaurus Lufengosaurus Massospondylus Pradhania Anchisauria Anchisaurus Aardonyx Melanorosaurus Sefapanosaurus Leonerasaurus Lessemsaurus Antetonitrus Sauropoda
Theropoda Theropoda †Basal Eodromaeus Daemonosaurus †Herrerasauridae Caseosaurus Chindesaurus Herrerasaurus Sanjuansaurus Staurikosaurus Neotheropoda Liliensternus Tachiraptor Zupaysaurus †Coelophysoidea Dracoraptor Dolichosuchus Gojirasaurus? Lophostropheus Podokesaurus Sarcosaurus Tawa †Coelophysidae Coelophysis Camposaurus Panguraptor Procompsognathus Pterospondylus Segisaurus Lepidus †Dilophosauridae Dilophosaurus Dracovenator Averostra †Ceratosauria see Ceratosauria Tetanurae includes birds
Major clades underlined See also categories: Archosaurs Dinosaurs Pterosaurs Ornithodirans Cretaceous–Paleogene extinction event