Ontogenetic evolution of bone structurein Late Cretaceous Plesiosauria from New Zealand

摘要: Abstract Histological observations of homologous bones (vertebrae, ribs, humerus, phalanges) among conspecific juvenileand adult Upper Cretaceous plesiosaurs from New Zealand (elasmosaurs and pliosaurs) demonstrates a unique “ontogenetic trajectory” skeletal histogenesis in these animals. While juveniles demonstrate “pachyosteosclerotic” condition the skeleton, adults have very light “osteoporotic-like” bone structure. Until now, one or other histological specializations was known aquatic tetrapods, adapted along contrasting pathways to this environment, either by ballasting (pachyosteosclerosis; e.g. sirenians) lightening (osteoporotic-like adaptation: modern cetaceans) skeleton. The successive occurrence constrasting conditions during ontogenesis single organism had never been reported, as far we know, but could well be an ontogenetic characteristic Plesiosaurs sensu lato . significance findings are discussed various phylogenetical, functional paleoecological contexts. trajectory plesiosaur skeleton is interpreted within general framework developmental heterochrony. Specifically, it suggests that juvenile kept conservative (plesiomorphic) ecology for sauropterygians, poorly mobile, lagoon shore dwellers while, contrast, would shift towards much more active locomotory behaviors open sea.