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• 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