Download or read book Cranial Ontogeny and Evolution of the Lambeosaurien Dinosaur Hypacrosaurus Stebingeri Ornithischia Hadrosauridae written by Kirsten Sara Brink and published by . This book was released on 2009 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ontogeny and Evolution of Lambeosaurine Dinosaurs Ornithischia written by David Christopher Evans and published by . This book was released on 2007 with total page 994 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lambeosaurinae is a Glade of hadrosaurid dinosaurs characterized by hypertrophied nasal passages housed within distinctive cranial crests. Large sample sizes, taxonomic diversity, and increasing resolution of their chronostratigraphic and paleoecological contexts make the group an ideal model Glade with which to test hypotheses related to Late Cretaceous dinosaur evolution. Anatomy and variation in the poorly known taxa Lambeosaurus magnicristalus and Hypacrosaurus altispinus are described in detail and both taxa are systematically revised. A complete digital endocranial cast derived from H. altispinus braincase reveals that the cerebral hemispheres are large and that the auditory system of lambeosaurines closely resembles those of other hadrosauroids. An abundance of juvenile specimens make lambeosaurines ideal subjects for comparative studies of growth and variation. The precise taxonomic identification of crestless juvenile specimens has proven difficult in the Dinosaur Park Formation (Campanian) of Alberta, Canada, where six closely related taxa are known. Discrete cranial characters are identified to distinguish lambeosaurine genera at early ontogenetic stages. Cranial ontogeny is compared among lambeosaurines with morphometric and qualitative approaches. Analyses of allometry confirm the general trends observed for Lambeosaurus and Corythosaurus in a larger subset of taxa that includes Hypacrosaurus. The first species-level phylogenetic analysis of Lambeosaurinae recovers completely resolved relationships within the Parasauolophini and Corythosaurim, and corroborates monophyly of the genera Lambeosaurus, Hypacrosaurus, and Parasaurolophus. The time-calibrated phylogeny and distribution of autapomoiphies allows for first order assessment of anagenesis in the clade. Previous hypotheses of anagenetic ancestor-descendant relationships can be rejected, although data does not reject the possibility that the biostratigraphic successions of Corythosaurus and Lambeosaurus species in the well-sampled Dinosaur Park Formation represent phyletic evolution within two independent, co-occuring dinosaur lineages. Hypotheses of sexual dimorphism in the cranial crests of Corythosaurus and Lambeosaurus are tested within a high-resolution biostratigraphic framework. Biostratigraphic succession of cranial morphotypes in both taxa is inconsistent with previously proposed sexual dimorphism, and, instead, indicates that the formation hosts a taxonomically diverse assemblage of lambeosaurines.

Download or read book A New Skull of Parasaurolophus Dinosauria Hadrosauridae from the Kirtland Formation of New Mexico and a Revision of the Genus written by Robert M. Sullivan and published by New Mexico Museum of Natural History and Science. This book was released on 1999 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Cranial Morphology of Prosaurolophus Ornithischia Hadrosauridae written by John R. Horner and published by . This book was released on 1992 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Evolution and Ontogeny of Hadrosaurs Dinosauria Ornithischia in the Judith River Formation late Cretaceous Campanian of Northcentral Montana written by Elizabeth Anne Freedman and published by . This book was released on 2015 with total page 477 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hadrosaurs, the "duck-billed" dinosaurs, were abundant members of Campanian (Late Cretaceous) communities in the Western Interior of North America, and are thus an ideal group for studying high-resolution evolutionary trends. This dissertation describes two new hadrosaurine taxa from the Judith River Formation exposed in Kennedy Coulee, northcentral Montana. The localities are stratigraphically equivalent to Unit 1 of the Oldman Formation, a time interval with no previously described hadrosaurine species. Phylogenetic and geometric morphometric analyses, combined with recalibrated radiometric dates, demonstrate that the new taxa form morphologic and stratigraphic intermediates within the lineages of Gryposaurus and Acristavus-Brachylophosaurus. The new genus of brachylophosaurin has a short posteriorly-oriented nasal crest hypothesized as an intermediate evolutionary state between the stratigraphically lower crestless Acristavus (lower Two Medicine Formation) and the stratigraphically higher Brachylophosaurus (middle Oldman Formation), with its wide posteriorly elongated crest. The nasal crest of Brachylophosaurus elongates posteriorly ontogenetically (as the individual grows). Histologic analysis demonstrates that the holotype of the new genus is relatively more mature than the largest Brachylophosaurus specimen, so its smaller crest size is not due to the ontogenetic status of the holotype. The new species of Gryposaurus is from a monodominant bonebed of at least ten individuals and three size classes: juvenile, subadult, and adult. The taphonomy of the bonebed is interpreted as a mass death assemblage deposited along a lake margin. The abundant postcranial bones are illustrated in a photographic atlas. In the new Gryposaurus species, the shape and position of the nasal crest is morphologically intermediate between the stratigraphically lower G. latidens (lower Two Medicine Formation) and the stratigraphically higher G. notabilis (lower Dinosaur Park Formation). In G. latidens, the nasal crest is low and anterodorsal to the posterior narial fenestra. The nasal crest becomes progressively higher and more posteriorly located in stratigraphically younger species. A similar trend occurs ontogenetically within specimens of the same species. Thus, in Gryposaurus and Acristavus-Brachylophosaurus lineages, directional trends in nasal crest morphology are observed both through ontogeny and between stratigraphically separated non-overlapping taxa, suggesting that the new taxa may be transitional members of anagenetic evolutionary lineages.