The Arizona lizard, Arizonasaurus (1947)

Phylum : Chordata
Class : Reptilia
Order : Paracrocodylomorpha
Suborder : Poposauroidea
Family : Ctenosauriscidae
Genus : Arizonasaurus
Species : A. babbitti

  • Middle Triassic (240 Ma)
  • 7 m long and 220 kg (size)
  • North America (map)

Until 2000, the poorly understood Arizonasaurus languished in the back pages of paleontological history. Then, the discovery of a near-complete skeleton in 2002 revealed that this archosaur had a sailed back, like its distant relative of the Permian period, Dimetrodon. The anatomy of Arizonasaurus has led to speculation that birds and crocodiles split off from the archosaur family tree earlier than once thought, toward the middle rather than the end of the Triassic period. As for the purpose of this reptile’s sail, it probably served both as a temperature-regulation device and a sexually selected characteristic (meaning males with bigger sails had the opportunity to mate with more females).