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Chapter 41
Origin & Evolution of Reptiles
Section 41.1
History of Reptiles
• 350 million years old
• Reptiles arose from amphibians
• “Age of Reptiles” = Mesozoic era
• Reptile means “to crawl”
• Herpetology: study of reptiles & amphibians
Evolution of Dinosaurs
• Dinosaurs: group of extinct reptiles that
dominated life 235 mya
• Triassic dinosaurs: small, carnivorous
• Jurassic dinosaurs: large, carnivorous
• Cretaceous dinosaurs: large, herbivorous
Extinction of Dinosaurs
• 66 million years ago
1. Asteroid-impact hypothesis: huge
asteroid hit the earth, creating lots of
dust that reduced the amount of sunlight
causing massive climatic changes
2. Multiple-impact hypothesis: multiple
asteroid impacts
Success of Reptiles
• Only 4 orders of reptiles survived the
mass extinction
– Squamata, Chelonia, Crocodilia, &
• First totally terrestrial vertebrate
Amniotic Egg
• Egg that encases the embryo in a secure,
self-contained aquatic environment
Draw this picture!
Parts of the Egg
• Amnion: membrane enclosing the fluid where
the embryo floats
• Yolk sac: encloses the yolk (fat-rich food
• Allantois: stores wastes produced by embryo
• Chorion: protects the embryo
• Albumen: stores protein & water for embryo
Characteristics of Reptiles
Section 41.2
Watertight Skin
• Thick, dry skin with keratin:
– protein found in the outer surface cells
• Lipids & protein barrier
• Protects from water loss, infections, & injuries
Respiration & Excretion
• Efficient systems to help conserve water
– Little water loss in urine
• Lungs to breathe
Circulatory System
• Composed of two loops:
1. Pulmonary loop: deoxygenated blood
from heart to lungs, oxygenated blood
from lungs to heart
2. Systemic loop: oxygenated blood to
body, deoxygenated blood to heart
Heart Structure & Function
• Most have a 3 chambered heart:
– 2 atria & 1 ventricle (partially divided)
• Crocodiles have a 4 chambered heart:
– 2 atria & 2 ventricles
– Ventricle divided by septum tissue
• Reptiles can reroute blood flow away from
– Conserves energy
– Raises body temperature quickly
Crocodile Heart
• Large, several chambered lungs with
small sacs called alveoli
– Increases surface area for diffusion
• First vertebrae group to breath by
expanding & contracting their chest
– Air pressure gradient between outside and
the thoracic cavity
Nervous System
• Sight is very important thus big eyes
• Hearing is also important though snakes lack a
– Detect ground vibrations via jaw bones
• Jacobson’s organ: detects odor (smell), on roof
of mouth
• Heat sensitive pits below eyes of some snakes
• Definition: control of body temperature
• Ectotherm: warms body by absorbing heat
from the surroundings
– Fish, reptiles, amphibians
• Endotherm: generates heat from within
– Birds, mammals
Advantages & Limitations of
• Advantages:
– Slow metabolism
– Less food needed
• Limitations:
– Cannot live in cold climates (become dormant
in winter)
– No sustained exertion
Reproduction & Parental Care
1. Oviparity: egg surrounded by tough
protective shell, no parental care
2. Ovoviviparity: eggs stored within
female until just before hatching, limited
parental care
3. Viviparity: eggs stored with female and
receives nutrients from the placenta,
most parental care
Welcome to the world!
Modern Reptiles
Section 41.3
Order Chelonia
• Examples: turtles (water dwelling) &
tortoises (land dwelling)
• Body covered by a 2 part shell: carapace
(dorsal) & plastron (ventral)
• Vertebrae & ribs fused to carapace
– Cannot leave shell!
• Sharp beak with no teeth
• Lay eggs (oviparity)
Two parts of the shell
Some Ohio turtles on the next few slides…..
Eastern Box Turtle
Stinkpot Musk Turtle
Soft-shelled Turtle
Blanding’s Turtle
Spotted Turtle
Snapping Turtle
Painted Turtles
Tasha, Daisy, & Bowser – in the
Maroons’ house!
Order Crocodilia
• Examples: crocodiles & alligators
• Closest relatives to dinosaurs
• All are carnivores
– Eat turtles, fish, etc.
Order Squamata
• Examples: lizards & snakes
• Autotomy: the ability to detach a body
part often when a predatory is near
• Snakes swallow prey whole
– Detachable jaw
Types of Snakes
• Constrictors: wrap body around prey and
suffocate by increasing pressure
– Boas, pythons, anacondas
• Elapsid: inject venom through two small,
fixed fangs in front of mouth
– Cobras, coral snakes
• Vipers: inject venom through large,
mobile fangs in the front of mouth
– Rattlesnakes, copperheads, water moccasins
Order Rhynchoephalia
• Example: tuatara
• Meaning “spiny crest”
• Only two modern species
• Live in New Zealand
4 Order Note Cards
• Front Side:
– Name of order
– Picture (in color) of animal
• Back Side:
Example organisms
Where on Earth?/habitat
Unique characteristics
Feeding patterns
Reproductive behavior