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Chapter 41 Reptiles. Section 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.

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Chapter 41 reptiles

Chapter 41Reptiles

Section 1

Origin & Evolution of Reptiles

History 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 reptiles1
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 reptiles2
History of Reptiles

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

  • Nearly all large vertebrates were reptiles

Evolution of dinosaurs
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

Triassic dinosaurs
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 dinosaurs1
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 & 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
Dinosaur Diversity

  • Land dinosaurs

  • Mesozoic reptiles- pterosaurs- evolved the ability to fly

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



Extinction of dinosaurs
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

  • Asteroid impact hypothesis- suggests huge asteroid hit Earth and formed a crater on the Yucatan Peninsula in southern Mexico

Asteroid impact hypothesis1
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
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
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
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 reptiles1
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

  • Amniotic egg- encase embryo in a secure, self-contained aquatic environment

  • More secure than jelly-like amphibian eggs

Amniotic egg1
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 egg2
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
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
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)


  • 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.