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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.