Transcript File
Biology 11 Phylum Chordata Subphylum Vertebrata Class Aves: The Birds Aves Objectives • General characteristics • Archeopteryx • Body systems: reproduction, circulatory, respiratory and nervous Bird Evolution • A lot of fossil evidence indicates the evolution of birds from reptiles; particularly from the dinosaur group that gave rise to the raptors • Recent evidence from China discovered by Canadians from the Royal Terrell Museum in Alberta has provided convincing evidence Archeopteryx – Earliest known bird (140 mya) – Reptilian characteristics – bony teeth, tail, claws – Bird characteristics – feathers, bones (light) Archeopteryx Characteristics of Birds 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Head, trunk, tail Bones – lightweight Air sacs Teeth – none Wings, 2 legs Endothermic Heart – four chambers Feathers Amniotic egg Uric acid excretion Class Aves The Birds • Evolved in the late Mesozoic, not from the flying dinosaurs (pterydactlys) Body Systems and Advances 1. Endothermic • Ability to maintain a constant body temp. regardless of external conditions • Has a high energy cost Class Aves 2. Reproduction •Both sexes typically only use the left gonad •Both sexes have a cloaca: a reproductive compartment •A “cloacal kiss” occurs very quickly, in some cases in less than 1 sec! •Sperm is stored by the female for 1-52 weeks! Class Aves 2. Reproduction Continued: • Still had amniotic egg but had to incubate it (embryo is also an endotherm) • This required pre-natal nesting behavior • Egg has calcified shell (for sitting on!) • Young born immature: need for post-natal behavior and learning – bigger cerebrum Avian Egg • Amnion: surrounds only the embryo, inner layer of cells secretes amniotic fluid in which the embryo floats • Chorion: surrounds all embryonic structures & serves as a protective membrane • Allantois (or allantoic sac): works together with chorion to in respiration and excretion; important in storage of nitrogenous wastes (uric acid) Chick Development Class Aves 3. Flight • Gained all the same advantages of the insects • Also has a very high metabolic cost • Evolved feathers from modified scales for flight (and insulation) Basic Form of Wings • Elliptical Wings – maneuver in forest habitats (sharp turns) • High Speed Wings – long flying migrations • Soaring Wings – broad wings for soaring Feather Structure • Follicle – sac in skin from which feather grows • Rachis (rA-ks) – central cylinder running length of feather; solid • Quill – part of rachis beneath skin, hollow • Barbs – branch off rachis, make up soft flexible part of feather • Barbules – small lateral projections that link barbs together • Vane – several barbs together Preening – care of feathers Molting – shedding of feathers Class Aves 4. Nervous system • Very well developed senses especially sight as required for flight • Brain continues to develop greater cephalization especially in the cerebrum due to need for extensive pre and post natal care of young • Behavior also involves territoriality and mate selection Class Aves 5. Circulatory System • High energy demand of endothermic behavior and flight requires maximum oxidation of blood • Birds evolved a complete 4 chamber heart – a true double pump • Complete separation of oxygenated and deoxygenated blood • Spleen – removes old red blood cells Class Aves 6. Respiratory System • Have 7 or 9 (depending on species) air sacs imbedded into bones in wings/legs & cranium as well as much more efficient lungs • Some species do not have cervical air sacs • Syrinx is the avian larynx and is used as its voice box Birds require two round of inspiration/expiration to complete a full cycle of air movement Classification of Birds Type Examples Feet Adaptations Beak Adaptation Flightless Penguins, Ostriches Running Varies Water birds Ducks, Geese, Swans Webbed Broad, flat for filtering or long, pointed for fishing Perching birds Sparrows, Robins, Cardinals Toes for clinging Short, thick for eating seeds or long for probing for fish Birds of prey Hawks, Eagles, Owls Talons Hooked for tearing flesh