The largest chelonian is a marine turtle, the great leatherback sea turtle, which can reach a shell length of 200 cm (80 inches) and can reach a weight of over 900 kg (2,000 lb, or 1 short ton). Turtles vary widely in size, although marine turtles tend to be relatively big animals. It did lack the ability to pull its head into its shell (and it had a long neck), and had a long, spiked tail ending in a club, implying an ancestry occupying a similar niche to the ankylosaurs (though, presumably, only parallel evolution). The earliest known modern turtle is proganochelys, though this species already had many advanced turtle traits, and thus probably had many millions of years of preceding "turtle" evolution and species in its ancestry. They are also closer to lizards than they are to archosaurormophs, including placodonts. Indeed turtles are related to other reptiles without temporal openings. The closest pareiasaur to turtles appears to be a rarely-studied form, Stephanospondylus. Future analyses may show the turtles to be relatives of the placodonts.Ī new phylogenetic analysis agrees with prior analyses nesting turtles with pareiasaurs within the much larger clade, Lepidosauromorpha. Re-analysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa broadly enough for constructing the cladogram. All molecular studies have strongly upheld this new phylogeny, though some place turtles closer to Archosauria. More recent phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. However, it was recently suggested that the anapsid-like turtle skull may be due to reversion rather than to anapsid descent. Most anapsids became extinct in the late Permian period, except procolophonoids and possibly the precursors of the testudines (turtles). All anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygomatic arch). It was believed that they are the only surviving branch of the ancient clade Anapsida, which includes groups such as procolophonoids, millerettids, protorothyrids and pareiasaurs. The first turtles are believed to have existed in the Mesozoic, around 200 million years ago.
Like birds, turtles are able to detect the Earth's magnetic field with magnetosensors, which allow them to migrate. Some species of turtles are highly endangered. The Order Testudines includes both extant (living) and extinct species, the earliest turtles being known from the early Triassic Period, making turtles one of the oldest reptile groups, and a much more ancient group than the lizards and snakes. Turtles are reptiles of the order Testudines (all living turtles belong to the crown group Chelonia), most of whose body is shielded by a special bony or cartilagenous shell developed from their ribs. Gradita e darà luogo ad una immediata rettifica.įor other uses, see Turtle (disambiguation). Le risposte grammaticali sono infatti improntateĪd un criterio di praticità e pragmaticità più che ad una completezzaĮd esaustività che finirebbe per frastornare, per l'eccesso di informazioneįornita, il nostro utente. Questi annunci e delle eventuali affermazioni o promesse che inĪccetta di tenerci indenni da qualsiasi tipoĭi responsabilità per l'uso - ed eventuali conseguenze di esso -ĭegli esercizi e delle informazioni linguistiche e grammaticaliĬontenute sul siti.
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