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General Biology for Nonmajors Lecture Notes Part 4 - 4.0ed the course!

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Biological Science
BSC 1005
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Introduction to the Ornithischia – Bird-hip Dinosaurs: Chapter 3 • Useful questions students in class e-mailed to Dr. Erickson (and his answers) o How have people tested the rates for uranium to lead breakdown? Using lava flow rates at deep sea ridges and uranium/lead dates of lava away from ridges o What were the gastroliths (rocks) that the dinosaurs ingested for? They aided digestion – most reptiles can’t chew, and the rocks churn around in a muscular crop prior to entering the stomach and do the same job as our molars. (Crocodiles do this, too.) • Part 1: Plated Dummies and Walking Tanks o First dinosaurs had three fingers. o All of the dinosaurs that fall in these categories are on the left side of the cladogram diagram (found at the back of the unit textbook). o Today, we will start looking at the Ornithischia – the bird-hipped dinosaurs. These constitute about half of all dinosaurs and are composed solely of herbivores. o All Ornithischians can be identified by –  Bird-shaped hip bones (pubis pointed backward)  Beaks to crop plants  Nut-cracking jaw joint (Don’t need to remember this for test.) o The first dinosaurs appeared in the Middle Triassic Period about 225 million years ago. o Like all early dinosaurs, the first ones were small (30-100 pounds) and bipedal. o NOTALL DINOSAURS WERE GIANT. o All dinosaurs in each group on the tree started off small (with a small ancestor) and evolved to become bigger. o North America’s smallest-discovered dinosaur – Fruitadens haagarorum o These earliest dinosaurs had simple, leaf-shaped teeth that did not occlude (come into contact with another top of the opposite jaw) and thus presumably ate succulent plants, like many lizards today with similar dentitions. o Amajor group of ornithischians were the Thyreophora – shield-bearers or armored dinosaurs. o The diagnostic characteristics of the Thyreophora were armor, also known as “osteoderms,” like that on the backs of alligators.  Early forms like Scuttelosaurus were small and still bipedal.  Later forms of Thyreophorans wre big, more heavily armored, and quadrapedal. • These include the Stegosaurs (plated lizards) and theAnkylosaurs (the dinosaur tanks) • Note – all of these dinosaurs were limited in what they could eat because of their teeth and lack of ability to perform gastrolith (rock) ingestion. o The Plated-Lizards or Stegosaurs were characterized by –  Plates and spikes along or beside the backbone o Stegosaurs are the most commonly known members of this group.  The Great Stegosaurus Plate Debate • For over a century, it has been debated how the plates of Stegosaurus were arranged, how many there were, and what they did. • Theories of orientation ran the gamut of possibilities o Early renditions following Marsh’s description of the animal in 1891 showed a single upright row and eight tail spikes (the animal actually had four). o But it was found that there were too many plates to do this – line them all along the back, that is. o Several other renditions developed  Plates in pairs  Plates on sides of body  Plates all over, on their sides, and many more spikes  All plates paired and in upright rows  Alternating, upright plates  Paired, flat, outward plates  Variable movement of plates o Finally, in the 1980s, Stephen Czerkas thought he had discovered what the plates had really looked like.  Some early finds showed they were staggered, which had somehow been ignored.  Single rows would have made the row longer than the tail; attachment fibers show they were only attached as bases. o Arecent, very rare find shows that plates were actually all staggered, and there were probably a few more than 17 plates – case closed! o More madness – what were the plates for?  Upright for defense?  Against body for defense?  Flappable for scaring away allosaurs – no way!  Camouflage against a backdrop – no!  Thermoregulators – plates up for sun, down for cold, or if permanently up, the body was turned to orient with sun in the morning and turned parallel in the afternoon.  Staggered for heat dissipation in the wind 
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