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

Making Lizard Eggs

This is X-rated Making Dinosaur Eggs

Fossilized embryos still in the shells Closeup of developing embryo

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

Recovering the fossil seen in last slide Dinosaur eggs and reconstructed embryo

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 Living diapsid reptile: crocodile

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

Marine crocodiles of the Mesozoic

28 ft. alligator caught in Alabama lake Sarcosuchus imperator from the Cretaceous of Niger, 45 feet long

www.nationalgeographic.com/supercroc/

Jaw of Sarcosuchus in Cretaceous sandstone of Niger, Sahara Desert

Sereno’s team indicating the size of Sarcosuchus Paul Sereno and the reconstructed jaw of Sarcosuchus

Skull of a living 6 ft. long crocodile compared to Sarcosuchus

A short-necked Plesiosaur A Jurassic plesiosaur

A short-necked Plesiosaur

A Mosasaur eating a Cretaceous bird One species of mosasaur attacking another species

Ichthyosaurs looked like mammalian dolphins

An Ichthyosaur died giving birth A baby ichthyosaur hiding in a reef

The Flying Reptiles - Pterosaurs: did they have a high metabolism?

Pteranodon Cretaceous pterosaur with 45 ft wing span

Carnegie Museum, 2009 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. Field Work in Montana

Velociraptor was a very active predator Utahraptor waiting to ambush

Velociraptors hunted in packs

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)

Excavating bones at Dinosaur National Monument in Utah

A dinosaur mummy from Mongolia Dinosaur skin impression from North Dakota

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

Sauropods, Carnegie Museum, 2008

Sauropods, Carnegie Museum, 2008 Sauropods, Carnegie Museum, 2008

Sauropods, Carnegie Museum, 2008

Sauropods, Carnegie Museum, 2008 Looks like your diet is working! Apatosaurus out for a stroll

A modern view of sauropods

Sauropod trackways showing no evidence of tail dragging. Diplodocus - a gracile sauropod

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

A Cretaceous ornithopod

Crested hadrosaur or “duck-billed” ornithopod Duck-billed hadrosaur

Hadrosaur “styles” What were they for?

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

Triceratops from western USA 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).

Fossilized heart in an ornithopod. CAT scan shows it has 4 chambers.

The ornithopod Thescelosaurus LV RV

Theropods and Birds 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?

Tyrranosaurs, Carnegie Museum, 2009 Mechanical model of T. rex shatters a large bone

Compsognathus, a chicken-sized theropod

Archaeopteryx, the first bird. Its skeleton is nearly identical to Compsognathus Head of Archaeopteryx -- note the teeth

Yours truly with Archaeopteryx in Berlin, June 1998 Archaeopteryx carcass in a salty lagoon, 160 MY ago

Reconstruction of Archaeopteryx Feathered dinosaur from China, 2002

“Dave”, 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

Fossilized gastroliths in feathered dinosaur How similar are birds of prey to their theropod ancestors?

Chinese dromaeosaur, 1999 Chinese dromaeosaur skeleton with preserved feathers

Closeup of feathers on Chinese dromaeosaur

Complete skeleton of Chinese dromaeosaur with feathers, tail at the bottom. Tail of Chinese dromaeosaur showing bundles of bony ligaments for stiffening the tail, typical of theropods.

Actual fossil birds that are different from feathered dinos

Jurassic Blood-Sucking Fleas Discovered in China http://abcnews.go.com/blogs/technology/2012/03/jurassic-blood-sucking-fleas-discovered- in-northern-china/

A team of researchers has unearthed the fossilized remains of blood-sucking mini-beasts dating back at least 65 million years. They found them to be especially suited for sinking their teeth into dinosaurs. Nearly an inch long, the pesky, prehistoric critters were more than ten times the size of today’s average household flea.