What is a bird?
bird (bûrd) n.
a.Any of the class Aves of warm-blooded, egg-laying, feathered vertebrates
with forelimbs modified to form wings.
b.Such an animal hunted as game.
c.Such an animal, especially a chicken or turkey, ud as food: put the bird
in the oven.
∙Bird Characteristics
o Two-legged (bipedal) vertebrates (animals with a backbone, includes mammals, amphibians, reptiles, and bony fishes).
o Distinguished from other vertebrates by the prence of feathers, a unique modification of the outer skin.
▪Feathers are dead structures that wear easily and must be replaced
regularly, but are esntial for both temperature regulation and flight.
o All birds have bills.
▪Bird bills can vary greatly in form and function from species to species, but they are always toothless and are covered with a horny sheath.
∙Bird Evolution
o Birds evolved from reptiles.
o Thomas H. Huxley: Birds are “merely glorified reptiles”.
▪Homology- Similarity in one or more body parts in different species;
attributable to descent from a common ancestor
∙Birds and reptiles both have
o Scales- Look at birds’ feet.
o Yolked, polar eggs
o Nucleated red blood cells. In mammals the red blood
毛蟹炒年糕cells lack nuclei.
o Occipital condyle- A single ball-and-socket device by
which the skull is articulated with the first neck
vertebra. Mammals have two of the.
o A single middle ear bone: the stapes. Mammals have
three.
o The lower jaws (mandibles) have five or six bones on
each side.
o Archaeopteryx lithographica- The Missing Link
▪Fossil found in Bavaria in 1861 dated at 135 to 155 mya
▪Clearly showed
∙Wing bones
∙Flight feathers
∙Pairs of feathers attached to each vertebra of the tail
▪Archaeopteryx was a crow-sized, bipedal “reptile” with a blunt snout and many small, reptilian teeth.
∙Feathers on both wings and tail
∙ A strong-ru nning terrestrial “bird” that could leap into trees,
jump among branches and make short flights.
书海拾贝
∙Capable of gliding, but not long sustained flight.
∙Had strong, curved claws, like tho of perching birds.
∙Could not launch from the ground becau it lacked the
principal muscles that lift the wing rapidly in the recovery
stroke.
∙Vanes were asymmetrical, like that of strong fliers.
▪Immenly important for the theory of evolution.
∙Found only two years after Darwin published Origin of Species (1859)
o Evolution of Feathers
▪Derived from scales of some kind
▪Not exactly sure what advantage(s) promoted the evolution of feathers ∙One scenario
o Slightly elongated and then frayed scales on the trailing
edges of the forelimbs possibly enhanced either
primitive gliding or parachuting.
o As gliding abilities improved and steering requirements
incread, so did the elaboration of feathers on the
wings and the tail.
∙ A cond scenario
动植物分类
o Scales became more feather like as temperature
regulation devices, particularly as heat shields, that
enabled the organism to be more active in hot, sunny
environments
o Modern lizards that live in hot, sunny climates tend to
have large scales that reduce heat loads.
o Featherlike fraying of a scale’s edges would increa its
flexibility and effectiveness as a heat shield during the
day and insulation at night
o Reptilian Ancestors of Birds
▪No doubt birds evolved from Mesozoic reptiles, but which reptiles?
▪Thecodonts or Theropods
▪Thecodont Theory
∙Thecodonts were lightly built reptiles in the early Mesozoic era that gave ri to pterosaurs and crocodiles. Some (eg.
Longisquama) had elongated scales, that em like a natural
precursor to feathers.
∙Fourteen shared, derived characters unite birds and crocodilian thecodonts.
∙But there is a 90 million year gap between crocodilian
thecodonts and Archaeopteryx.
∙Protoavis, a fossil found in western Texas, dating 75 million
years before Archaeopteryx, may be a link, but its poor
condition makes classification very difficult.
▪Theropod theory
∙Theropod dinosaurs evolved from thecodonts, and lived
simultaneously with Archaeopteryx.
∙Both share 23 of 42 specialized skeletal features of the hand,
vertebrae, humerus and ulna, pectoral arch, hindlimb and pelvis.
∙Juvenile dinosaurs and birds both have growth plates with a
unique cellular structure in their leg bones.
o Evolution of Avian Flight- The Debate
▪Arboreal Theory vs. Cursorial Theory
∙Arboreal Theory
o Evolution of flight started with the parachuting and
gliding from elevated perches.
o The extensions of the bones of the forelimb enhanced
by elongated (flight) feathers enabled the ancestors of
Archaeopteryx to parachute and glide between trees.
o The favored theory for many years.
∙Cursorial Theory
o Forelimbs first elongated becau they heightened
leaping ability in a small bipedal theropod dinosaurs
that ran and jumped to catch incts in its jaws.
Extension of forelimbs would help to control and
extend its leaps.
o Elongation of the arms and tail would enhance
maneuverability and higher velocities of running and
互联网接入jumping.
o Us adaptive steps bad on trajectory ballistics, rather
than the aerodynamics of true flight. Flight would be a
logical extension of the first small jumps by this little
dinosaur.
o Protowings, incread arboreal habits and gliding
would be the next logical steps.
∙Bird Adaptations
花羡人间四丁目o Birds are feathered flying machines.
▪Skeleton is strengthened and reinforced through fusion of bones of the hands, head, pelvis and feet.
期望薪资怎么填最好▪Uncinate process overlap other ribs and so strengthen the walls of
the thorax.
▪The furcula (wishbone) compress and rebounds like a spring in
rhythm to the beat of the wings.
▪Wings are modified forelimbs, who sole (almost) purpo is flight.
▪Fud hand bones support and maneuver the flight feathers.
▪Arboreal (tree-dwelling) birds have feet that tightly grip branches.
▪An enlarged, keeled sternum hous and anchors the large breast muscles that empower wings.
▪The pygostyle, made of fud tail vertebrae, supporsta nd controls the tail feathers, which are ud for breaking and steering.
o Bird physiology accommodates the extreme metabolic demands of flight and temperature regulation.
▪Red fibers of avian flight muscles have an extraordinary capacity for sustained worka nd can also produce heat by shivering.
▪Birds maintain high body temps (40︒ to 44︒C) over a wide range of ambient temps.
▪Circulatory and respiratory systems
∙Four-chambered heart and efficient, flow-through lungs, which deliver fuel and remove both waste and heat produced by
metabolic activities.
o Reproduction
▪Large, richly provisioned external eggs, the most elaborate
reproductive cells of any animal.
▪Requires dedicated parental care.
▪Most birds form monogamous pairs, though many engage in additional xual liaisons.
o Large well, developed brains 6 to 11 times larger than that of similarly sized reptiles
▪Bird brains and primate brains exhibit functional lateralization, with left hemispheric dominance associated with learning and innovation in
美容神器
vocal repertoires.
o Highly developed neural systems and acute ns mediate feats of communication and navigation.
怎样生儿子▪Birds (esp. song birds) have the greatest sound-producing capabilities of all vertebrates.
▪Birds can navigate using patterns of the Earth’s magnetism, celestial cues, and perhaps polarized light.
▪Birds can e into the near-ultraviolet and can hear infrasounds-sounds below the range of human hearing.
