Reptiles Origin and Evolution History of Reptiles Reptiles

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 O 2 and CO 2

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 1/10 th 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