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Birds and several crocodyliform lineages were the only archosaurs to survive the K-Pg extinction, rediversifying in the subsequent Cenozoic era. Birds in particular have become among the most species-rich groups of terrestrial vertebrates in the present day.
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.
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.
Phylogenetic definitions of Pseudosuchia include "Crocodiles and all archosaurs closer to crocodiles than to birds" (Gauthier and Padian), "Extant crocodiles and all extinct archosaurs that are closer to crocodiles than they are to birds" (Gauthier, 1986), and more recently "the most inclusive clade within Archosauria that includes Crocodylia ...
Archosauria includes crocodilians, birds, and all descendants of their common ancestor. Extinct archosaurs include aetosaurs, rauisuchids (both members of the crocodilian branch), pterosaurs, and non-avian dinosaurs (both members of the avian branch). [6]
An alternate theory to the dinosaurian origin of birds, espoused by a few scientists, notably Larry Martin and Alan Feduccia, states that birds (including maniraptoran "dinosaurs") evolved from early archosaurs like Longisquama. [11] This theory is contested by most other paleontologists and experts in feather development and evolution. [12]
The Fish and Wildlife Service just delisted 21 species from the Endangered Species Act due to extinction.
They argue that the digits of birds number I-II-III, just as those of theropod dinosaurs do, by the conserved phalangeal formula. The phalangeal count for archosaurs is 2-3-4-5-3; many archosaur lineages have a reduced number of digits, but have the same phalangeal formula in the digits that remain. In other words, paleontologists assert that ...