Chapter 41ReptilesSection 1

Origin & Evolution of Reptiles

History of Reptiles• Fossils & comparative anatomy

suggest that reptiles arose from amphibians

• Earliest reptiles date 359-299 million years ago

• Many insects during this time period which served as food

History of Reptiles• Around 299 to 251 million years

ago- reptiles dominant land vertebrates

• Pangaea- super continent

• Interior of Pangaea was dry- suitable for reptiles- why?

• End of Permian Period (299 MYA)- mass extinction

History of Reptiles• Mesozoic era (251-66 MYA)- Age

of the Reptiles

• Nearly all large vertebrates were reptiles

Evolution of Dinosaurs• 235 MYA- dinosaurs- group of

extinct reptiles

• Evolved from thecodonts- extinct group of crocodile-like reptiles

• Evolution was affected by the break-up of Pangaea

• Climates changed- some died, some flourished

Thecodont

Triassic Dinosaurs• 235 MYA- oldest dinosaur fossils-

Triassic Period

• Successful because-

• 1. legs positioned under body provided support

• 2. well-adapted to dry conditions

• 3. Last mass extinction wiped out other animals

Triassic Dinosaurs• Evidence suggests asteroid

impacts contributed to mass extinction

• Canada, France, Ukraine, and Minnesota have evidence to support this theory

Jurassic & Cretaceous Dino• Jurassic- golden age of dinosaurs-

variety and abundance

• Sauropods- largest land animals of all time

• Theropods- powerful legs and short arms (T. Rex)

Dinosaur Diversity• Land dinosaurs

• Mesozoic reptiles- pterosaurs- evolved the ability to fly

• Ichthyosaurs & plesiosaurs- lived in the oceans- resembled bottle-nose dolphins

Ichthyosaurs

plesiosaurs

Extinction of Dinosaurs• Scientists still have many

questions, but they have some ideas and evidence as to why the dinosaurs are extinct

Asteroid Impact Hypothesis• Asteroid impact hypothesis-

suggests huge asteroid hit Earth and formed a crater on the Yucatan Peninsula in southern Mexico

Asteroid Impact Hypothesis

• Caused much dust that covered Earth and changed climate

• Sediments during Cretaceous time- high iridium- very rare metal (abundant in asteroids)

Multiple Impact Hypothesis• Proposes multiple asteroids hit Earth• Unfavorable environmental

conditions because of this event• Paleontologist- Gerta Keller-

provided evidence to support this hypothesis

Success of Reptiles• Order Chelonia- turtles & tortoises• Order Squamata- lizards & snakes• Order Crocodilia- alligators &

crocodiles• Order Rhynchocephalia- tuataras• Found on every continent except

Antarctica

Modern Reptiles• Turtles have changed very little in

structure

• Tuataras- lizard-like reptiles

• Snakes & lizards- majority of reptiles

• Crocodiles & alligators changed very little- decedents of thecodonts

Modern Reptiles• Crocodiles resemble birds

especially by looking at the structure of their heart (four-chambered)

• Crocodiles take care of young• Scientists suggest birds are direct

decedents of reptiles

Amniotic Egg• Amniotic egg- encase embryo in

a secure, self-contained aquatic environment

• More secure than jelly-like amphibian eggs

Amniotic Egg• Amnion- thin membrane enclosing

the fluid in which the embryo floats

• Yolk sac- encloses the yolk, fat-rich food supply for developing embryo

• Allantois- stores nitrogenous wastes produced by embryo

• Chorion- surrounds all other membranes and protects embryo

Amniotic Egg• First occurred in reptiles, but also

is found in birds and mammals

• Strong evidence suggests that reptiles, birds, and mammals evolved from a common ancestor

• The eggs of some reptiles & nearly all mammals lack shells & embryo develops in mother’s body

Water-tight skin• What type of skin do amphibians

have? Why do they have this type?

• Reptiles have thick, dry, scaly skin that prevents water loss

• Keratin- same protein that forms your fingernails & hair

• Lipids & proteins in the skin help make it water-tight

Respiration & Excretion• All reptiles have lungs for gas

exchange

• All reptiles have bodies adapted to conserve water

• Tissues for gas exchange located in body- kept moist

• Reptiles lose small amounts of water in urine (uric acid)

REVIEW!!!• Explain the importance of iridium found in

sediments from the end of the Cretaceous period.

• Summarize the two asteroid impact hypotheses.

• Describe three characteristics that contribute to the success of reptiles on land.