Cnemial crest on the tibia (protruding part of the top surface of the shinbone) arcs anterolaterally (curves to the front and the outer side) Iggulden, Hal; Iggulden, Conn (2007). "Dinosaurs". The Dangerous Book for Boys. New York: HarperCollins. pp.30–34. ISBN 978-0061243585. Concave articular surface for the fibula of the calcaneum (the top surface of the calcaneum, where it touches the fibula, has a hollow profile) Based on fossil evidence from dinosaurs such as Oryctodromeus, some ornithischian species seem to have led a partially fossorial (burrowing) lifestyle. [174] Many modern birds are arboreal (tree climbing), and this was also true of many Mesozoic birds, especially the enantiornithines. [175] While some early bird-like species may have already been arboreal as well (including dromaeosaurids) such as Microraptor [176]) most non-avialan dinosaurs seem to have relied on land-based locomotion. A good understanding of how dinosaurs moved on the ground is key to models of dinosaur behavior; the science of biomechanics, pioneered by Robert McNeill Alexander, has provided significant insight in this area. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have investigated how fast dinosaurs could run, [136] whether diplodocids could create sonic booms via whip-like tail snapping, [177] and whether sauropods could float. [178] Communication Robert Plot" (PDF). Learning more. Oxford: Oxford University Museum of Natural History. 2006. Archived from the original (PDF) on October 1, 2006 . Retrieved November 14, 2019.

Dinosaurs were primitively bipedal: their probable ancestors were small bipedal Archosaurs. The date of the early dinosaur genus Eoraptor at 231.4 million years ago is important. Eoraptor probably resembles the common ancestor of all dinosaurs; [16] its traits suggest that the first dinosaurs were small, bipedal predators. [17] The discovery of primitive, pre-dinosaur, [18] types in Middle Triassic strata supports this view. Analysis of their fossils suggests that the animals were indeed small, bipedal predators. Paul, Gregory S. 2000. The Scientific American book of dinosaurs. New York: St. Martin's Press. ISBN 0-312-26226-4 Langer, Max C.; Ferigolo, Jorge (January 1, 2013). "The Late Triassic dinosauromorph Sacisaurus agudoensis (Caturrita Formation; Rio Grande do Sul, Brazil): anatomy and affinities". Geological Society, London, Special Publications. 379 (1): 353–392. Bibcode: 2013GSLSP.379..353L. doi: 10.1144/SP379.16. ISSN 0305-8719. S2CID 131414332. Paul, Gregory S. (2002). Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Baltimore; London: Johns Hopkins University Press. ISBN 978-0-8018-6763-7. LCCN 2001000242. OCLC 1088130487. .

Dinosaur discoveries

The book combines hard facts with interesting and intriguing feature spreads detailing dinosaur lifestyle, behavior, families, and habitat, from how life on earth began and how animals evolved to the catastrophic events that brought about the end of the dinosaurs.

Evolution of dinosaurs Dinosaur features [ change | change source ] Labeled diagram of a typical archosaur skull, the skull of Dromaeosaurus Nesbitt, Sterling J.; Irmis, Randall B.; Parker, William G. (2007). "A critical re-evaluation of the Late Triassic dinosaur taxa of North America". Journal of Systematic Palaeontology. Milton Park, Oxfordshire: Taylor & Francis on behalf of the Natural History Museum, London. 5 (2): 209–243. doi: 10.1017/S1477201907002040. ISSN 1477-2019. S2CID 28782207. When dinosaurs appeared, they were not the dominant terrestrial animals. The terrestrial habitats were occupied by various types of archosauromorphs and therapsids, like cynodonts and rhynchosaurs. Their main competitors were the pseudosuchians, such as aetosaurs, ornithosuchids and rauisuchians, which were more successful than the dinosaurs. [118] Most of these other animals became extinct in the Triassic, in one of two events. First, at about 215million years ago, a variety of basal archosauromorphs, including the protorosaurs, became extinct. This was followed by the Triassic–Jurassic extinction event (about 201million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, phytosaurs, and rauisuchians. Rhynchosaurs and dicynodonts survived (at least in some areas) at least as late as early –mid Norian and late Norian or earliest Rhaetian stages, respectively, [119] [120] and the exact date of their extinction is uncertain. These losses left behind a land fauna of crocodylomorphs, dinosaurs, mammals, pterosaurians, and turtles. [10] The first few lines of early dinosaurs diversified through the Carnian and Norian stages of the Triassic, possibly by occupying the niches of the groups that became extinct. [12] Also notably, there was a heightened rate of extinction during the Carnian pluvial event. [121] Evolution and paleobiogeography The supercontinent Pangaea in the early Mesozoic (around 200 million years ago) Nesbitt, Sterling J. (2011). "The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades". Bulletin of the American Museum of Natural History. New York: American Museum of Natural History. 2011 (352): 1–292. doi: 10.1206/352.1. hdl: 2246/6112. ISSN 0003-0090. S2CID 83493714. Archived from the original on February 29, 2016 . Retrieved October 16, 2019. Research by Matthew G. Baron, David B. Norman, and Paul M. Barrett in 2017 suggested a radical revision of dinosaurian systematics. Phylogenetic analysis by Baron et al. recovered the Ornithischia as being closer to the Theropoda than the Sauropodomorpha, as opposed to the traditional union of theropods with sauropodomorphs. This would cause sauropods and kin to fall outside traditional dinosaurs, so they re-defined Dinosauria as the last common ancestor of Triceratops horridus, Passer domesticus and Diplodocus carnegii, and all of its descendants, to ensure that sauropods and kin remain included as dinosaurs. They also resurrected the clade Ornithoscelida to refer to the group containing Ornithischia and Theropoda. [15] [16] General description Triceratops skeleton, Natural History Museum of Los Angeles CountyDinosaurs were, at the start, small and bipedal: they walked on their hind legs. They laid eggs in nests, and included both carnivores and herbivores. We now know that birds are their living descendents, and more about that later. Glut, Donald F. (1997). Dinosaurs: The Encyclopedia. Foreword by Michael K. Brett-Surman. Jefferson, NC: McFarland & Company. ISBN 978-0-89950-917-4. LCCN 95047668. OCLC 33665881. Tanner, Lawrence H.; Spielmann, Justin A.; Lucas, Spencer G., eds. (2013). "The Triassic System: New Developments in Stratigraphy and Paleontology". Bulletin of the New Mexico Museum of Natural History and Science. New Mexico Museum of Natural History and Science Bulletin. Albuquerque, NM: New Mexico Museum of Natural History and Science. 61. ISSN 1524-4156. OCLC 852432407 . Retrieved October 21, 2019. Using one of the above definitions, dinosaurs can be generally described as archosaurs with hind limbs held erect beneath the body. [17] Other prehistoric animals, including pterosaurs, mosasaurs, ichthyosaurs, plesiosaurs, and Dimetrodon, while often popularly conceived of as dinosaurs, are not taxonomically classified as dinosaurs. [18] Pterosaurs are distantly related to dinosaurs, being members of the clade Ornithodira. The other groups mentioned are, like dinosaurs and pterosaurs, members of Sauropsida (the reptile and bird clade), except Dimetrodon (which is a synapsid). None of them had the erect hind limb posture characteristic of true dinosaurs. [19]