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 fromridgeso 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 yearsago. o Like all early dinosaurs, the first ones were small (30-100 pounds) and bipedal. o NOT ALL 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 A major 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 the Ankylosaurs (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 backboneo 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 possibilitieso 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 plateso 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 A recent, 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 inthe afternoon. Staggered for heat dissipation in the wind Sexual (attraction) or same species (threats) – paleo answer to anything strange. Good answer to just about anything. Very likely theory. o Some of these theories are not testable, and we may never know the real answer. o Studies of the outsides and insides of plates show that they were highly vascularized and delicate and probably were not resistant to bites and were vulnerable to injury. o One study of airflow over heated models showed the staggered arrangement was ideal for dissipating heat – but why hadn’t any other stegosaurs figured this out? That is why this theory is unlikely; it doesn’t make sense that only one species would determine something. o Lizards today use similar structures solely for display, not for defense or heat dissipation. o Stegosaurus was the “supermodel” for stupidity. From endocasts (sediments that filled the brain cavities of dinosaurs or from filing hollowed skulls with latex), we know the size of some dinosaur brains. Two ton Stegosaurs had 2.5 to 2.9 ounce brains. Our human brains are 3 to3.5 pounds. Their olfactory blubs were relatively large, suggesting a good sense of smell, but their very small cerebrum suggests they were dimwits. The saying “dumb as a dinosaur” comes primarily from this animal’s neuroanatomy. Note – Stegosaur brains are often said to be the size of a walnut, but they were actually a little bigger than that. o It was noted that along the spinal column of the Stegosaurus that the neural canal was expanded in the hip region. Why?- It was theorized that this housed a second brain, one to control the back of the animal, since clearly the front one had its hands full. o Problems with this theory No animals have an “extra brain.” All reptiles and legged vertebrates (people) have expansions in the hip where the nerves to the legs exit the spinal column. Some animals, such as birds, also have additional expansion in this region, where fat and sugar is stored. o Why all of these crazy theories about functions? Why couldn’t people make better, more accurate guesses? Because paleontology has a history founded solely in geology. Biological training in anatomy, physiology, and animal behavior has not been part of the curriculum for people who are finding dinosaurs. o Ankylosaurs: the dinosaur tanks
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