BI256 Study Guide - Dermis, Bird Anatomy, Palaeognathae

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9 Sep 2014
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Birds
Phylum: Chordata
Class: Aves
Subclass; Archaeornithes
Subclass: Neornithes
Living Birds: Divided into two groups (Super Orders)
1. Paleognathae (old jaw)
Large, flightless ostrich like birds and kiwis
Flat sternum, poorly developed pectoral muscles
2. Neognathae (new jaw)
All other birds, nearly all of which are flying
Keeled sternum, to which powerful flight muscles are attached
Evolution
Birds and Reptiles share many similarities. Are birds more closely related to
crocodilians or the dinosaurs?
Poor fossil record (improving)
Archaeopteryx: mainly theropod features; feathers link to birds
Dromeosaurs, a group of theropods that includes Velociraptor, share many
characters with birds. i.e. fused clavicles and lunate wrist bones. Recently
described dromeosaur-like theropods fossils with feathers! Feathers may have
been useful for controlling glides or jumps from trees or in social displays.
Uniformity in Structure
Forelimbs are modified as wings, although not all are capable of flight
Hindlimbs are adapted for walking, swimming or perching
All birds have horny, keratinized beaks
All birds lay eggs
Characteristics:
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1. Body usually spindle-shaped, with four divisions; Head, neck, trunk, and tail;
neck elongate and S-shaped
2. Forelimbs modified as wings; hindlimbs adapted for perching, walking, or
swimming; foot with four toes (2 or 3 toes in some)
3. Epidermal covered of feathers and leg scales; thin integument of epidermis and
dermis; no sweat glands; oil or preen gland at base of tail; pinna of ear
rudimentary
4. Fully ossified skeleton with air cavities; skull bones fused with one occipital
condyle; skull diapsid; each jaw covered with a keratinized sheath, forming a
beak; no teeth; ribs with strengthening processes, tattaching ribs with one
another; tail not elongate, reduced to pygostyle; sternum usually well developed
with keel; single bone in middle ear
5. Nervous system well developed, with 12 pairs of cranial nerves and brain with
large cerebellum and optic lobes.
6. Circulatory system of four-chambered heart with two atria and two ventricles;
separate pulmonary and systemic circuits; nucleated red blood cells
7. Endothermic
8. Respiration by slightly expansible lungs (parabronchi), with thin air sacs among
the visceral organs and skeleton; syrinx (voice box) near junction of trachea and
bronchi
9. Excretory system of metanephric kidney; ureters open into cloaca; no bladder;
semisolid urine; uric acid main nitrogenous waste
10. Sexes separate; testes paired, with the vas deferens opening into the cloaca;
females with functional left ovary and oviduct only; copulatory organ (penis)
in ducks.
11. Fertilization internal; amniotic eggs with much yolk and hard calcareous
shells; incubation external; young active at hatching (precocial) or helpless and
naked (altricial); sex determination by chromosomes (female heterogametic)
Adaptations Necessary for Flight
Wings
oPresent for lift and propulsion
Respiratory system
oMust meet high oxygen demands and cool the body
Bones
oMust provide a light but rigid airframe
Digestion and Circulation
oMust meet high-energy demands of flight
Nervous system
oMust have superb sensory systems for high-velocity flight
Feathers
Contour Feathers (typical body and flight feathers)
Lightweight but very strong, covering and streamlining the body
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Composed of
oHollow Quill : emerging from a skin follicle
oShaft: continuation of the quill that supports the barbs
oBarbs: arranged in a closely parallel fashion, and spread diagonally
outward from both sides of the central shaft to form a flat, expansive and
webbed surface  the vane
oBarbules: link adjacent barbs by overlapping hooks. If they become
dethatched they can be easily re-hooked by preening (running beak
parallel to barbs)
Filoplume Feathers (Sensory)
Fine hair-like, degenerate feathers with a weak shaft and a tuft of short barbs
Not exposed above contours
Numerous nerve endings at the base (communicating information about the
position and movement of contour feathers)
Down Feathers (warmth)
Soft tufts hidden beneath contour feathers (soft because barbules lack hooks)
Location is dependent on life style and stage of development
oNumerous on breast and abdomen of water birds (warmth)
oCover entire body of some juvenile birds
Origin and Development of Feathers
Homologous to reptile scales
Develop from an epidermal elevation overlying a nourished, blood supplied
dermal core
Rather than flattening they role into a cylinder and sink into the follicle form
which they grow
Pigments are added during growth, then (1) shafts and barbs keratinize for
strength & (2) protective sheath splits open
Molting (highly ordered process)
Fully grown feathers are dead structures
Except in penguins, molting is a gradual process (no bare spots)
Flight and tail feathers are lost in pairs (one on each side) to maintain balance
In some species replacement is continuous and flight is unimpaired
In many water birds primary feathers are molted all at once and they are
temporarily grounded
Most molt once a year, usually in late summer after nesting season
Skeleton
Light but strong
Pneumatized bones
oNo tissues in the marrow cavity of long bones
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