Definition of mesosaur in US English:


(also mesosaurus)


  • An extinct small aquatic reptile of the early Permian period, with an elongated body, flattened tail, and a long, narrow snout with numerous pointed teeth.

    Genus Mesosaurus, order Mesosauria, subclass Anapsida

    • ‘At the same time as the mesosaurs were flourishing in this newly formed inland sea, a major period of mountain building began in the south, due to the Andean-style collision of the Palaeo-Pacific plate under the African plate.’
    • ‘Mesosaur fossils appear suddenly in the fossil record, and disappear equally suddenly, and their fossils show no sign of evolution during their existence.’
    • ‘Only mesosaurs and araeoscelidians demonstrate more lightly built limbs than protorothyridids.’
    • ‘Mesosaur remains are abundant at several sites in this formation, where they occur preserved in centimetre-thick beds and displaying various degrees of skeletal disarticulation.’
    • ‘The most basal anapsids, the mesosaurs, are oldest known fully aquatic reptiles.’


1950s: modern Latin, from Greek mesos ‘middle’ + sauros ‘lizard’.