Outline 17: Reptiles and Dinosaurs Evolution of Reptiles • The first reptiles appeared in the Mississippian. • They evolved from amphibians, which first appeared in the Devonian. • The evolutionary jump was the invention of the amniote egg. The Amniote Egg • Requires internal fertilization, unlike amphibians. • Has a hard, but porous shell. • Can be laid on dry land. Skips the tadpole stage of amphibians. • Has a complex series of membranes and a very large yolk. Amphibian Egg: No Shell Frog eggs in a Morgantown pond Typical amniote egg with an embryonic reptile. Crocodiles hatching from their amniote eggs Dinosaur Eggs Fossilized embryos still in the shells Searching for sauropod dinosaur eggs in Patagonia A single egg laying on an outcrop Dinosaur developing in the egg Researcher working on a nest of sauropod dinosaur eggs Mother and hatchlings in Patagonia sometime in the Cretaceous The fate of many hatchlings Dinosaur parent died while sitting on nest with eggs Major Reptile Groups • Anapsids - the stem reptiles, turtles are the only living group. • Synapsids - the mammal-like reptiles. Mammals evolved from synapsids. • Diapsids - all modern reptiles except for turtles. Dinosaurs evolved from diapsids. Pennsylvanian anapsid or stem reptile Living anapsid reptile: snapping turtle Living diapsid reptile: iguana Permian synapsid reptiles: Dimetrodon Triassic synapsid reptiles: Therapsids or mammal-like reptiles The Mesozoic: The Age of Reptiles A Nile crocodile. Notice the unspecialized reptilian teeth. Fossil Crocodile from the Jurassic 28 ft. alligator caught in Alabama lake A short-necked Plesiosaur A Jurassic plesiosaur A Mosasaur eating a Cretaceous bird Ichthyosaurs looked like mammalian dolphins An Ichthyosaur died giving birth The Flying Reptiles - Pterosaurs: did they have a high metabolism? Pteranodon Evolution of Dinosaurs • First appeared in late Triassic, 220 MY ago. • Evolved from thecodont archosaurs (crocodiles are closest living relatives). • Thecodont ancestor was bipedal and carnivorous. • First dinosaurs were bipedal and carnivorous. A Triassic thecodont avoiding a synapsid reptile Archosaurs Archosaurs Evolution of Dinosaurs • Later dinosaurs that walked on 4 legs were secondarily quadrapedal. • Herbivorous dinosaurs evolved from carnivorous dinosaurs. 2 Major Groups of Dinosaurs • Saurischians - theropods and sauropods • Ornithischians - a variety of herbivores – Ornithopods – Pachycephalosaurs – Stegosaurs – Ankylosaurs – Ceratopsians Dinosaurs are popular with the public Jack Horner, Montana State Univ. Dr. Alan Grant, Jurassic Park Velociraptor was a very active predator Utahraptor waiting to ambush The prey’s view of a pack of Allosaurus Dinosaur classification Saurischians Ornithischians Dinosaur hips differ between the two major groups Saurischian hip structure (theropod) Saurischian hip structure (sauropod) Ornithiscian hip structure (stegosaur) A dinosaur mummy from Mongolia Coelophysis, a late Triassic theropod Dinosaur Paleobiology • Herbivorous dinosaurs - sauropods, the largest animals ever on land, had very small heads. How were they able to eat enough? Gizzards • In contrast, ornithischians had massive grinding teeth. Apatosaurus or Brontosaurus, the classic sauropod Apatosaurus out for a stroll A modern view of sauropods Sauropods, Carnegie Museum, 2008 Sauropods, Carnegie Museum, 2008 Sauropods, Carnegie Museum, 2008 Sauropod femur of a Titanosaurus found in Argentina in 2014. Sauropod trackways showing no evidence of tail dragging. Sauropods eating a coniferous forest The massive digestive system of a sauropod, note the large gizzard Inside of sauropod gizzard, note the gastroliths for grinding food Sauropod gastroliths Plant Debris Iguanodon, an ornithopod Duck-billed hadrosaur Crested hadrosaur or “duck-billed” ornithopod Hadrosaur (ornithopod) grinding teeth Skull of a pachycephalosaur Head butting by pachycephalosaurs Stegosaurus Stegosaurus at the Carnegie Stegosaurus Ankylosaurus Protoceratops from Mongolia Triceratops at the Smithsonian Institution Dinosaur Paleobiology • Posture - all dinosaurs had erect limbs, like mammals and unlike living reptiles. • Complex behaviors - moved in herds, hunted in packs, had breeding grounds like birds. Sauropod trackways show evidence of herd behavior. Theropod tracks in Utah Warm-Blooded Dinosaurs? Evidence • Erect posture, particularly bipedal • Bone histology - extensive vascular canals for production of red blood cells • Structure of the heart - probably had 4 chambers like birds and mammals, rather than 3 chambers like reptiles. • Birds evolved from theropods • Evidence of feathers in some dinosaurs Abundant vascular canals in dinosaur bone support the warm-blooded theory Thin section of dinosaur bone www.bio.fsu.edu/erickson/histological_analysis.php A four-chambered heart. A three-chambered heart has only one ventricle (pump). Theropods and Birds Jurassic Park 3D https://www.youtube.com/watch?v=5y4PTsFI2v8 Tyrannosaurus rex, the Cretaceous theropod everyone loves to hate Modern view of a T.rex Sue Henderson, founder of the T. rex named “Sue” Sue Henderson, founder of the T. rex named “Sue” It’s my bone, I found it. Tyrannosaurus Sue on display in the Chicago Field Museum What makes it a girl? Stan Sue Tyrranosaurs, Carnegie Museum, 2009 Compsognathus, a chicken-sized theropod Archaeopteryx, the first bird. Its skeleton is nearly identical to Compsognathus Head of Archaeopteryx -- note the teeth Combination of bird and theropod features Archaeopteryx carcass in a salty lagoon, 160 MY ago Reconstruction of Archaeopteryx Feathered dinosaur from China, 2002 Microraptor,a feathered dinosaur preserved in volcanic ash from China Birds evolved from feathered theropods Sinosauropteryx with colored fuzzy feathers based on preserved melanosomes http://news.nationalgeographic.c om/news/2010/01/100127- dinosaur-feathers-colors-nature/ Feathered dinosaur from China, 1998 Reconstruction of feathered dinosaur, Caudipteryx Fossilized gastroliths in feathered dinosaur Actual fossil birds that are different from feathered dinos.