Outline 17: Reptiles and Dinosaurs

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/2010/01/100127dinosaur-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-discoveredin-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.