The Pleurodira are considered by many experts to be more primitive than the Cryptodira. Surprisingly, these turtles appear in the fossil record an entire period (about 50 million years) later than the cryptodirans: the earliest known pleurodiran fossils are Notoemys laticentralis and Platychelys oberndorfi from the Late Jurassic. The pleurodirans withdraw their necks laterally; that is, they bend the neck sideways to tuck the head under the rim of the shell. This has given rise to their common name: side-necked turtles. Two living families are included, Pelomedusidae and Chelidae, and the extinct family Araripemydidae. See Pleurodiran/cryptodiran turtles for a comparison of pleurodiran and cryptodiran turtles (modified from Romer, 1956 and Gaffney, 1975b).