reptiles chapter 41. origin & evolution of reptiles section 41.1
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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 ago1. 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, &
Rhynchocephalia
• First totally terrestrial vertebrate
Parts of the Egg
• Amnion: membrane enclosing the fluid where the embryo floats
• Yolk sac: encloses the yolk (fat-rich food supply)
• Allantois: stores wastes produced by embryo
• Chorion: protects the embryo• Albumen: stores protein & water for
embryo
Watertight Skin
• Thick, dry skin with keratin: – protein found in the outer surface cells
• Lipids & protein barrier• Protects from water loss, infections,
& injuries
Excretion
• Efficient systems to help conserve water– Little water loss in urine
• Lungs to breathe out CO2
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 lungs – Conserves energy– Raises body temperature quickly
Respiration
• 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 tympanum – Detect ground vibrations via jaw bones
• Jacobson’s organ: detects odor (smell), on roof of mouth
• Heat sensitive pits below eyes of some snakes
Thermoregulation
• 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 Ectothermy
• 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
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)
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