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Unformatted text preview: TOPIC 21 THEROPODA- DINOSAURS IN TIME AND SPACE Dinosaurs first appeared 228 million years ago and became extinct 65 million years ago. Their reign on Earth was 163 million years, by any measure a considerable span of time that was cut short by a global catastrophe. The dinosaurs' reign spanned all three periods of the Mesozoic Era; the last portion of the Triassic (245-208 million years ago), and the entire Jurassic (208-144 million years ago) and, Cretaceous (144-66.4 million years ago). Dinosaurs inhabited all continents, although their record is sparse in Australia and Antarctica. More than three hundred species of dinosaurs have been described. In recent years, new discoveries have increased, especially in remote areas of the world. A new genus is being described every six weeks. - INTRODUCTION Characteristics of the Theropods (web) This group of dinosaurs exhibits a wide variety of adaptive features making them efficient predators, including: sharp, large, serrated, recurved teeth for slicing, claws on all fingers and toes, largest brain (relative to body size) among dinosaurs, bipedal, strong hind limbs, long hands generally with three main fingers (4th and 5th reduced) and three main toes (1st and 5th reduced), elongated zygopophyses (processes of the neural arch of vertebrae) on the vertebrae near the end of the tail, hollow bones (important adaptation), as in birds, and a stiffened tail toward the end that acts as a body balance. Geologic Range and Geographic Distribution Late Triassic-Late Cretaceous - TYPES OF THEROPODS Ceratosauria (web) The Ceratosauria (named after Ceratosaurus) and the Tetanurae (tetanus - stiff; uro - tail) are the two major descendant groups within the Theropoda. Ceratosaurs are primitive theropods, but younger than the rare basal theropods not dealt with herein. The group is not very diverse, but is characterized by several important derived features, including: fusion of ilium, pubis, and ischium in adults (web) to form a strong support between the hind limbs and the vertebral column, neck vertebrae with two pairs of pleurocoels (side cavities) (web), a flaring of the lower end of the fibula, bone fusion in the ankles and feet, an S-shaped neck inherited from archosaurian ancestors, and a gap between premaxillary and maxillary bones of the skull for placement of a large tooth fitted to the dentary bone (in Coelophysis and Dilophosaurus, but lacking in Ceratosaurus). Ceratosaurs exhibit a great deal of sexual dimorphism. Females often have longer skulls and necks and more robust, thicker limbs than in male forms. Crests of thin bone only occur on some adults, presumably functioning in display, probably by males. Ceratosaurs were fast bipedal runners with a narrow gait. Most are restricted to the Late Triassic and Jurassic, and are known from North America, Europe, Africa, and possibly South America....
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This note was uploaded on 04/13/2008 for the course GLY 1102 taught by Professor Ciesielski during the Spring '08 term at University of Florida.
- Spring '08