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

Ornithischians

Saurischians

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, 2008Looks 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

Triceratopsfrom

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 Archaeopteryxin 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.com/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.