Transcript Reptiles history

Reptiles
Origin and Evolution
History of Reptiles
• Reptiles arose from
amphibians
• Earliest fossils 359 m.y.a
• Small, four – legged
vertebrates w/small teeth
Pangaea
• Drier climate
• Mass extinction during
Paleozoic era
• Diversified to fill niches left by
extinct species
• Mesozoic era “Age of Reptiles”
Evolution of Dinosaurs
• 235 m.y.a dinosaurs dominated the earth
• Evolved from thecodonts
– Extinct group of crocodile – like reptiles
• Pangaea separated climates changed
dinosaurs became extinct, while new species
flourished
Evolution of Dinosaurs (Triassic)
• Oldest known fossils
• Small carnivorous dinosaurs replaced
thecodonts
• Successful because
– Legs directly under body
• Good support, more agile, fast runners
– Well adapted for dry conditions
– Mass extinction of thecodonts and large
amphibians reduce competition
Extinction of Dinosaurs
• Asteroid Impact Hypothesis
• Multiple Impact Hypothesis
Success of Reptiles
• Four modern orders of reptiles
– Chelonia (turtles and tortoises)
– Squamata (lizards and snakes)
– Crocodilia (crocodiles, alligators, caimans)
– Rhynchocephalia (tuataras)
Success of Reptiles
• Watertight skin
– Keratin
• Respiration
– Lungs
• Excretion
– Uric acid requires little water
• Amniotic Egg
Amniotic Egg
• Reptiles considered the first terrestrial
vertebrate
• Amniotic egg
– First evolved in reptiles but also found in
mammals and birds
– Protection from physical damage
– Limits evaporation of water
– Diffusion of O2 and CO2
Internal Structure of Amniotic Egg
• 4 specialized membranes
– Amnion
• Thin membrane encloses the fluid where embryo floats
– Yolk sac
• Encloses the yolk, fat – rich food supply for embryo
– Allantois
• Stores wastes produced by embryo
– Chorion
• Surrounds all other membranes
• Albumen
– Protein and water for embryo
Body Systems of Reptiles
• Circulatory System
– Two loops
– Heart structure and function
• Two atria and a single ventricle (except crocodiles)
• Divert blood from lungs when inactive
– Conserves energy
– May help raise body temp
• Respiratory system
– Lungs are large
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Divided into chambers (alveoli)
Increases surface area
Filled by expanding rib cage
Snakes right lung enlarged, left obsolete
• Nervous system
– Brain
– Sight detect light
– Hearing
• Tympanum (eardrum) and columella
• Snakes lack tympanum (low frequency sounds) transmitted
to the bones of the jaw
– Jacobson’s organ
• Roof of mouth in reptiles (crocodiles and most turtles)
• Sensitive to odors
– Pit Vipers
Thermoregulation
• Vertebrates regulate body heat in two ways
– Ectotherm
• Warms the body from the environment
– Endotherm
• Generates heat as needed to warm body
• Behavior
• Require little energy and 1/10th food as
endotherms same size
Reproduction and Parental Care
• 3 patterns among reptiles
– Differences based on how long the eggs remain
within the female and how nutrition is provided to
them
Reproduction
• Oviparity
• Deposits egg in environment
• Ovoviviparity
• May be laid shortly before hatching or hatch inside
female
• Viviparity
• Shell does not form around egg and young are retained
within female