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Most (if not all) archosaurs are oviparous. Birds and crocodilians lay hard-shelled eggs, as did extinct dinosaurs, and crocodylomorphs. Hard-shelled eggs are present in both dinosaurs and crocodilians, which has been used as an explanation for the absence of viviparity or ovoviviparity in archosaurs. [38]
Archosaurus (meaning "ruling lizard") is an extinct genus of carnivorous proterosuchid archosauriform reptile. [1] Its fossils are dated to the latest Permian of Russia and Poland , it is one of the earliest known archosauriforms.
Avemetatarsalia (meaning "bird metatarsals") is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians. [2] The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs.
Extinct archosaurs include non-avian dinosaurs, pterosaurs, and extinct relatives of crocodilians. Modern paleontologists define Archosauria as a crown group that includes the most recent common ancestor of living birds and crocodilians, and all of its descendants.
The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. [1] Birds are categorized as a biological class, Aves. For more than a century, the small theropod dinosaur Archaeopteryx lithographica from the Late Jurassic period was considered to have been the earliest bird.
Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles encompassing archosaurs and some of their close relatives. It was defined by Jacques Gauthier (1994) as the clade stemming from the last common ancestor of Proterosuchidae and Archosauria. [3]
Two names were proposed for crocodile-line archosaurs before Crurotarsi was erected. The first, Pseudosuchia, was established as a stem-based clade in 1985. [5] It includes crocodiles and all archosaurs more closely related to crocodiles than to birds. The second, Crocodylotarsi, was named in 1988, possibly as a replacement for Pseudosuchia. [6]
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 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.