The Mesozoic Era is the second geologic era of the Phanerozoic Eon. The Mesozoic Era spans from 251 to 65.5 Million years ago and is divided into three geologic periods inlcuding the Triassic, Jurassic and Cretaceous. Mesozoic is derived from the Greek terms for "the middle" meso and animal zo (Borror, 1988, pp 58 & 111). The Mesozoic is best known for the appearance and diversification of the dinosaurs, swimming and flying reptiles. However, the Mesozoic also saw the appearance of mammals, birds, modern type primary producers in the oceans, flowers and social insects. The mass extinction that defines the end of the Mesozoic Era captures the publics attention because it resulted in the extinction of the non-avian dinosaurs.