• A new specimen of the ornithischian dinosaur Hesperosaurus mjosi from the Upper Jurassic Morrison Formation of Montana, U.S.A., and implications for growth and size in Morrison stegosaurs

      Maidment, Susannah; Woodruff, DC; Horner, JR (Informa UK Limited, 2018-01-01)
      Stegosauria is a clade of ornithischian dinosaurs characterized by a bizarre array of dermal armor that extends from the neck to the end of the tail. Two genera of stegosaur are currently recognised from North America: the well-known Stegosaurus stenops and the much rarer Hesperosaurus mjosi. A new specimen of Hesperosaurus mjosi was discovered in some of the most northerly outcrops of the Upper Jurassic Morrison Formation near Livingston, Montana. The new specimen includes cranial, vertebral, and appendicular material as well as a dermal plate, and the excellent state of preservation of the palate reveals new anatomical information about this region in stegosaurs. Histological examination of the tibia indicates that the individual was not skeletally mature at time of death. Comparison with previously studied Stegosaurus and Hesperosaurus individuals indicates that Hesperosaurus mjosi may have been a smaller species than Stegosaurus stenops. Physiological processes scale with body mass, M, according to the relationship M0.75 in extant megaherbivores; thus, larger animals are better able to cope with more arid environments where forage is less abundant. Under this scenario, it is possible that Stegosaurus stenops and Hesperosaurus mjosi were environmentally partitioned, with the larger S. stenops occupying more arid environments. Analyses of the temporal overlap and latitudinal range of Morrison stegosaurs would allow this hypothesis to be investigated.
    • A new subfamily of fossorial colubroid snakes from the Western Ghats of peninsular India

      DEEPAK, V; Ruane, S; Gower, DJ (Informa UK Limited, 2019-01-18)
      We report molecular phylogenetic and dating analyses of snakes that include new mitochondrial and nuclear DNA sequence data for three species of the peninsular Indian endemic Xylophis. The results provide the first molecular genetic test of and support for the monophyly of Xylophis. Our phylogenetic results support the findings of a previous, taxonomically restricted phylogenomic analysis of ultraconserved nuclear sequences in recovering the fossorial Xylophis as the sister taxon of a clade comprising all three recognised extant genera of the molluscivoran and typically arboreal pareids. The split between Xylophis and ‘pareids’ is estimated to have occurred on a similar timescale to that between most (sub)families of extant snakes. Based on phylogenetic relationships, depth of molecular genetic and estimated temporal divergence, and on the external morphological and ecological distinctiveness of the two lineages, we classify Xylophis in a newly erected subfamily (Xylophiinae subfam. nov.) within Pareidae.