terça-feira, setembro 21, 2010
Pele de estegossauro do Jurássico
Saiu um interessante artigo sobre preservação de pele num estegossauro Hesperasaurus mjosi dos Estados Unidos, assinado por Nicolai Christiansen e Emanuel Tschopp.
O primeiro foi preparador de fósseis no Museu da Lourinhã e mais tarde foi meu orientando de mestrado pela Universidade Marie et Pierre et Marie Currie (Paris VI). O segundo é actual estudante de doutoramento sob minha orientação na Universidade Nova de Lisboa.
Dinosaur skin impressions are rare in the Upper Jurassic Morrison Formation, but different sites on the Howe Ranch in Wyoming (USA), comprising specimens from diplodocid, camarasaurid, allosaurid and stegosaurian dinosaurs, have proven to be a treasure-trove for these soft-tissue remains. Here we describe stegosaurian skin impressions from North America for the first time, as well as the first case of preservation of an impression of the integument that covered the dorsal plates of stegosaurian dinosaurs in life. Both have been found closely associated with bones of a specimen of the stegosaurianHesperosaurus mjosi Carpenter, Miles and Cloward 2001. The scales of the skin impression of H. mjosi are very similar in shape and arrangement to those of Gigantspinosaurus sichuanensis Ouyang 1992, the only other stegosaurian dinosaur from which skin impressions have been described. Both taxa show a ground pattern of small polygonal scales, which in some places is interrupted by larger oval tubercles surrounded by the small scales, resulting in rosette-like structures. The respective phylogenetic positions of G.sichuanensis as a basal stegosaurian and H. mjosi as a derived form suggest that most stegosaurians had very similar skin structures, which also match the most common textures known in dinosaurs. The integumentary impression from the dorsal plate brings new data to the long-lasting debate concerning the function of dorsal plates in stegosaurian dinosaurs. Unlike usual dinosaur skin impressions, the integument covering the dorsal plates does not show any scale-like texture. It is smooth with long and parallel, shallow grooves, a structure that is interpreted as representing a keratinous covering of the plates. The presence of such a keratinous covering has affects on all the existing theories concerning the function of stegosaurian plates, including defense, thermoregulation, and display, but does not permit to rule out any of them.
Christiansen, N., & Tschopp, E. (2010). Exceptional stegosaur integument impressions from the Upper Jurassic Morrison Formation of Wyoming Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0026-0