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

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