The earliest archosaurs were rauisuchians, such as Scythosuchus and Tsylmosuchus, both of which have been found from Russia and date back to the Olenekian.[4]. But crocodilians have some features which are normally associated with a warm-blooded metabolism because they improve the animal's oxygen supply: So, why did natural selection favour the development of these features, which are very important for active warm-blooded creatures, but of little apparent use to cold-blooded aquatic ambush predators that spend the vast majority of their time floating in water or lying on river banks? A second species, P. langstoni, was originally the type species of the genus Lythrosuchus. Crocodylotarsi was defined as an apomorphy-based taxon based on the presence of a "crocodile-normal" ankle joint (considered to be the defining apomorphy of the clade). [9] Storicamente, molti arcosauriformi furono descritti come arcosauri, inclusi i proterosuchidi e gli eritrosuchidi, sulla base delle loro finestre antorbitali. The hip sockets faced sideways, but the knobs on the femurs were at right angles to the rest of the femur, which therefore pointed downwards. Archosauromorpha is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs rather than lepidosaurs. Mammals and birds have 4-chambered hearts, which completely separate the flows of oxygenated and de-oxygenated, If early archosaurs were completely cold-blooded and (as seems most likely). The ornithodirans differed from other archosaurs in other ways: they were lightly built and usually small, their necks were long and had an S-shaped curve, their skulls were much more lightly built, and many ornithodirans were completely bipedal. Aphanosauria is group of reptiles distantly related to dinosaurs. Phytosaurs are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. "Trucidocynodon riograndensis gen. nov. et sp. [14][17] Sereno and Arcucci incorporated archosaur features other than ankle types in their analyses, which resulted in a different tree than previous analyses. This "pillar-erect" arrangement appears to have evolved independently in various archosaur lineages, for example it was common in, The phytosaurs and crocodilians dominated the rivers and swamps and even invaded the seas (e.g., the, 4-chambered hearts. [18], The clades Crurotarsi and Ornithodira were first used together in 1990 by paleontologist Paul Sereno and A.B. [9] The earliest archosaurs had "primitive mesotarsal" ankles: the astragalus and calcaneum were fixed to the tibia and fibula by sutures and the joint bent about the contact between these bones and the foot. It includes two main clades: Pseudosuchia , which includes crocodilians and their extinct relatives, and Avemetatarsalia , which includes birds and their extinct relatives (such as non-avian dinosaurs and pterosaurs ). Archosauriformes is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Late Permian. Pseudosuchia was defined as all archosaurs more closely related to crocodiles, while Ornithosuchia was defined as all archosaurs more closely related to birds. Unlike Gauthier's tree, Benton and Clark's places Euparkeria outside Ornithosuchia and outside the crown group Archosauria altogether. One of the first studies of archosaur phylogeny was authored by French paleontologist Jacques Gauthier in 1986. [citation needed] Archosaur lifestyle [8] Gli arcosauri più primitivi erano forniti di mesotarsali primitivi: l'astragalo e il calcagno erano fissati alla tibia e al perone da suture, e l'articolazione mobile era presente solo tra queste ossa e il resto del piede. [35]. [citation needed]. It is generally agreed that birds have the most species of all terrestrial vertebrates. Both birds and alligators achieve unidirectional air flow through the presence of parabronchi, which are responsible for gas exchange. Archosauria as a term was first coined by American paleontologist Edward Drinker Cope in 1869, and included a wide range of taxa including dinosaurs, crocodilians, thecodonts, sauropterygians (which may be related to turtles), rhynchocephalians (a group that according to Cope included rhynchosaurs, which nowadays are considered to be more basal archosauromorphs, and tuataras, which are lepidosaurs), and anomodonts, which are now considered synapsids. However, a 2011 study argued that phytosaurs were not crown-archosaurs. Gli pseudosuchi apparvero nel Triassico inferiore, ed erano forniti di una caviglia dove l'astragalo era collegato alla tibia mediante una sutura. Because they are considered a "basal stock", thecodonts are paraphyletic, meaning that they form a group that does not include all descendants of its last common ancestor: in this case, the more derived crocodilians and birds are excluded from "Thecodontia" as it was formerly understood. "Rauisuchia" is currently considered an evolutionary grade, or even a wastebin taxon. The earliest avemetatarsalians, such as Teleocrater and Asilisaurus, retained "primitive mesotarsal" ankles. But crocodilians have some features which are normally associated with a warm-blooded metabolism because they improve the animal's oxygen supply: Historically there has been uncertainty as to why natural selection favored the development of these features, which are very important for active warm-blooded creatures, but of little apparent use to cold-blooded aquatic ambush predators that spend the vast majority of their time floating in water or lying on river banks?

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