Evolutionary Biology Lecture 22

Amphibians = rough draft for terrestrial. Reptiles solve problems with living on land, dominate for 250MY. Reptiles solve terrestrial problems 1) Have new leg arrangement – helps move heavy bodies, run efficiently 2) Lungs & heart improve in efficiency – complete takeover of O2 intake by lungs, increased delivery of O2 to tissues. 3) Watertight eggs – protects embryos from drying out 4) Dry, watertight skin – prevents the body from drying out itself Four defining reptile traits 1) Amniotic eggs 2) Dry Skin 3) Thoracic Breathing 4) Improved Kidneys Humans share all of these traits Amniotes – reptiles are first group, birds and mammals also. a. Amniotic Eggs – has food source  yolk, watertight shell, four internal membranes that allow for gas exchange and waste removal from developing baby. Eggs allow for an independent life support system, eliminate need for water with gestation & embryo development. b. Internal fertilization – eggs make external impossible; sperm can’t penetrate the egg. Sperm placed inside female, fertilizes egg before membranes fully form. After fertilization, reptiles and birds have external gestation. Mammals have internal gestation  lost hard shell & yolk. Reptile Skin – dry, watertight skin. Layer of keratin rich scales that prevent water loss. Same material in human nails & hair, also found in bird feathers. Not homologous. Scales; skin is unavailable for gas exchange. Thoracic Breathing – Reptiles have to exchange gas entirely through lungs. Increased lung capacity to facilitate  allows for thoracic breathing. Increases O2 intake, O2 intake is only limited by size of lungs which can be inflated and deflated, much larger. More surface area. Humans breathe this way. a. Glottal Breathing – amphibians, lungs are pair of thin walled sacs, connected to mouth through glottis. Lungs inflated by filling mouth with air, swallowing air into lungs. O2 intake limited by size of mouth. Improved Kidneys – allows for excretion of concentrated urine, can get rid of waste without heavy water loss. Maintain as much fluid as possible while getting rid of wastes, water conservation is critical Ectotherms – body temperature changes with environmental temperature. can’t control with internal metabolism, can control by going in and out of the sun. Endothermic – maintain body temperature using internal metabolism, not dependent on outside environment Amniotes are characterized by the number of openings in the skull bone behind the eye. Jaw muscles – anchored to these holes behind eye opening, form strong bonds that allow reptiles to bite prey with more power than amphibians. Much stronger bite. Number of openings is important. All amniotes evolved from either synapsids or Diapsids. Synapsids – have 1 opening. Extinct, ancestral to group. Mammals are considered synapsids. a. Pelycosaurs – early dominant synapsid, 50MY. Gradually replaced amphibians. Long steak knife type teeth to kill and eat animals of their own size, jaws and anchor muscles are important. b. Therapsids – evolved around 250MYA, end of Pelycosaurs dominant period. Very reptilian, some evidence of fur and were endothermic. Dominant for 20MY, diverging away from early groups. More active than other groups, could survive winter. Dinosaurs arose around 230MYA, therapsids died out, couldn’t compete with dinosaurs. Exception: mammals survived! We are survivors of this lineage. Diapsids – have 2 openings. Birds evolved from here, all reptiles onward. Dominate earth around 230MYA. Monophyletic group includes all modern reptiles & extinct dinosaurs. a. Archosaurs – turtles  birds. Largest animals so far. First to walk on 2 legs BIPEDAL. Can see rows of bony plates  similar to modern crocodiles. 1. Dinosaurs – evolved from early archosaurs. Improved on early archosaur body plan. Had legs that point directly downward  allows for greater speed & agility when running. Dominant for 150MY. Died out suddenly due to large asteroid  dust cooled earth that a. limited photosynthesis & b. cold enough that ectotherms couldn’t survive the stress. 4 Extant Groups of Reptiles Lepidosaurs – Diapsids that are not archosaurs (Tuataras & Squamates) 1) Tuataras – very rare. Widespread in Mesozoic. 2 remaining species. 2) Lizards & Snakes (Squamates) – carnivorous species. Important improvements to heads and jaws  more strength and mobility. Paired copulatory organs in males  2 penises. a. Lizards – insectivorous, some herbivorous. Walk on 4 limbs b. Snakes – limbless  evolved many times, snakes most extreme. All carnivorous. Unhinge jaw to eat large objects, can stretch around things. Can produce venom to inject into prey. 3) Turtles & Tortoises – aquatic, terrestrial. Individuals are not monophyletic, group together is. All have lost teeth, have sharp beak to crush and grind food. Protect body with hard shell. Can pull head into shell, vertebrae and ribs are fused to top of shell  cannot run out of shell. a. Marine turtles – must return to land to lay eggs 4) Crocodilians – evolved alongside dinosaurs. Only living archosaurs (except birds). Outgroup to extinct dinosaurs. Large, primarily aquatic predators. Made up of crocodiles, alligators, caimens, and gavials. All carnivorous, hunt by stealth and ambush prey. Have eyes and nostrils on top of snout, can see and breathe while almost entirely submerged in water. Large mouths with lots of sharp teeth. Strong neck muscles  use to twist and thrash while killing prey. a. Parental care – remind us of birds. Fairly intense parental care. Build nests, spend time caring for young. Theropods – small group of dinosaurs that evolved feathers. Gave rise to new lifestyle perfected in birds. All have bipedal stance, hollow bones, swiveling wrist bones for flight, 3 fingered hands & feet and backward pointing pelvis. Descendants include Archaeopteryx. Show direct path from dinosaur the birds. Birds – last reptile group to evolve, share many traits with crocodilians & dinosaurs. Most diverse group of terrestrial vertebrates. Have asymmetrical feathers. Share: scales on feet & legs. Lay amniotic eggs. Lack: teeth, have a vestigial tail. Four traits birds share 1) Feathers– lift for flight, provide heat. Flexible, maintain strength due to good structure, secondary braches hook together to form smooth surface. Thick central quills to support flying surface. Stabilize flying bird. Also have under layer called Down – small, not as strong, keep birds insulated. Maintaining internal temperature allows birds to survive in diverse habitats. Feathers are easily replaced if damaged. 2) Flight Skeletons – bones are thin & hollow, not heavy. Fused together to have rigid skeleton  sturdy frame to anchor muscles for flight to, allows for a lot of force. Large breast muscles from wing to Keel (prominent, large bone, allows muscles to connect to) allow for powerful flight. huge muscles needed because flight consumes a lot of oxygen & energy. 3) Lung Design – more O2 intake than any other species, gain O2 quickly. Needed for flight. Very different from other vertebrate lungs to maximize efficiency of O2 intake, energy requirement is much higher. 4) Endotherm – maintain body temperature regardless of outside. Higher than most mammals. Allows metabolism to proceed quickly, provides ATP necessary for rapid muscle movement for flight  leads to a lot of heat loss  down feathers keep warm by insulation. Morphology – predictive of lifestyle, look at feet & beaks. Ducks  webbed feet, filter beak. Bird evolution – Large flightless birds  water fowl  owls, swifts, parrots, woodpeckers. Passeriformes (Song birds) – most successful group, very diverse.