Non-archosaur reptiles[edit]
The two living non-archosaurian reptile taxa, testudines (turtles) and lepidosaurians (lizards and tuataras), along with choristoderes (semi-aquatic archosauromorphs that would die out in the early Miocene), survived across the K–Pg boundary.[24] Over 80% of Cretaceous turtle species passed through the K–Pg boundary. Additionally, all six turtle families in existence at the end of the Cretaceous survived into the Paleogene and are represented by living species.[65] Living lepidosaurs include the tuataras (the only living rhynchocephalians) and the squamates. The rhynchocephalians were a widespread and relatively successful group of lepidosaurians during the early Mesozoic, but began to decline by the mid-Cretaceous. They are represented today by a single genus located exclusively in New Zealand.[66]
The order Squamata, which is represented today by lizards, including snakes and amphisbaenians (worm lizards), radiated into various ecological niches during the Jurassicand was successful throughout the Cretaceous. They survived through the K–Pg boundary and are currently the most successful and diverse group of living reptiles with more than 6,000 extant species. No known family of terrestrial squamates became extinct at the boundary, and fossil evidence indicates they did not suffer any significant decline in numbers. Their small size, adaptable metabolism, and ability to move to more favorable habitats were key factors in their survivability during the late Cretaceous and early Paleocene.[24][65] Giant non-archosaurian aquatic reptiles such as mosasaurs and plesiosaurs, which were the top marine predators of their time, became extinct by the end of the Cretaceous.[67][68] The ichthyosaurs had already disappeared before the mass extinction occurred.
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