Zoology: Birds Lecture 1

Non-avian dinosaurs (in class Reptilia)

•Rise of giant reptiles ~200 MYA

•Pterosaurs dominated the skies; largest had a 40 foot wing span

•Ichthyosaurs, pleisosaurs & marine crocodiles dominated the oceans at this time

•A wide variety of species roamed the land.

Dinosaurs are commonly classified into two orders based on what their hip structure looks like

-Order Saurischia: the "lizard hips"

-Order Ornithischia: the "bird hips"

Order Saurischia: "lizard hips"

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Traditionally includes:

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Carnivorous, bipedal theropods, e.g. Allosaurus, T-rex

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Herbivorous, quadrupedal sauropods, e.g. Branchiosaurus

Order Ornithischia: "bird hips"

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Traditionally includes

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Herbivorous dinosaurs including the duck-billed dinosaurs, Stegasaurus, Triceratops

Which group of dinosaurs contained the ancestor of modern birds?

There is strong evidence that Theropoda (the raptors) is the clade from which modern birds are descended.

Theropods

clade of carnivorous dinosaurs that contains the ancestor of all modern birds

Flying, bird-relative dinosaurs

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~150 million years ago

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Archaeopteryx represents one of several extinct lineages with characteristics of both non-avian reptiles & birds

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Used feathers to glide. Did not fly via flapping.

Traits of modern birds + theropod dinosaurs

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Birds & other theropods share a furcula (wish bone), long S-shaped neck, & lunate wrist bone that allows twisting.

The furcula of a bird is much more robust than that of a dinosaur.

There were 2 main hypotheses for how bird flight evolved, Cursorial hypothesis

Cursorial hypothesis

("ground up")

Prediction: flapping

muscles evolved along

with gliding adaptations

There were 2 main hypotheses for how bird flight evolved, Arboreal hypothesis

Arboreal hypothesis ("trees down")

prediction: flapping muscles evolved after gliding adaptations

Which flight hypothesis is best supported by the fossil record?

Arboreal hypothesis is the best supported by the fossil record. Early bird-like reptiles like Archaeopteryx could glide but they lacked the musculature to produce substantial upward thrust (they were weak flappers)

Where are birds, taxonomically?

•phylum Chordata

-superclass Tetrapoda

•class Aves - birds

Class Aves

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All extant birds are taxonomically placed in class Aves

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Found on every continent, including Antarctica

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Most can fly, although some are flightless

Some characteristics shared by modern birds:

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Feathers

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Forelimbs are wings & hind limbs are scaled legs with clawed toes

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Many skeletal adaptations for flight

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Keratinized beak with no teeth

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They are all endothermic

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4-chambered heart

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Amniotic egg with a calcified shell

Functions of feathers:

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Insulation/warmth

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Smooth the surface & streamline the contour of the body; making flight more efficient

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Can mechanically brace against objects (woodpeckers)

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Enable lift in flight

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Camouflage

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Sexual selection

Contour feathers (outer)

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Non-flight contour feathers - cover the outside of the bird, optimize airflow

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Flight feathers - contour feathers extending beyond the body & used in flight (stiff, some asymmetrical)

down feathers

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Down (under the contour feathers in mature birds)

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Down feathers: fine, soft feathers located under & between contour feathers

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Important for insulation!!!

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Young birds are covered in down feathers before developing adult plumage

Feathers

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Feathers are keratinous outgrowths from specialized areas of skin called papillae

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Evolved from reptilian scales

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While growing, feather has a blood supply; when fully grown, blood supply is cut off

Feather anatomy

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The quill emerges from skin follicle

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The shaft bears numerous barbs from which branch tiny overlapping filamentous barbules

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Up to several hundred barbs are arranged to form a flat, webbed surface, called the 'vane'.

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Barbules from two neighboring barbs overlap and zip together with tiny hooks

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When separated, they are zipped back together by the action of preening

Preening

involves the bird using its beak to hook breaks in contour feathers back together or to brush away foreign matter

uropygial gland

Birds water-proof feathers by taking oil on their beak from the uropygial gland & applying over feathers

molting

Feathers can be replaced individually as needed or all at once, a process called _______

diapsid

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Bird skulls are ______, like most other reptiles' skulls

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Lighter & mostly fused into on piece

sclerotic rings

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Birds have _______ that support the eyes

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ancestral structures present in some dinosaurs

quadrate

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Birds skulls even have ______ bones that attach the mandible to the upper part of the skull, just as in non-avian reptiles

flight adaptations of birds

Tetrapod forelimbs adapted as wings

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Flight requires a light, but rigid skeleton

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2 main kinds of flight adaptations:

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those reducing body weight

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those enabling powerful wing movement

Major modifications that lighten the load

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Most have either hollow bones or bones with air spaces

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Loss of functional forelimb claws

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Loss of heavy tail, jaws & teeth

Major modifications that increase rigidity & strength:

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Reduction in number of digits

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Bone Fusion

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metacarpals & most of carpals ("hands")

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Pelvis

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Sternum

Uncinate processes

projections from rib bones; rib-cage reinforcement

cervical vertebrae

Rigid vertebral column; most vertebrae fused (except the cervical vertebrae)

Pygostyle

_____ is the last few vertebrae, which are fused & support tail feathers

Pectoral muscles

______ _______ are the largest & support bird during flight, providing the down stroke of the wing

Supracoracoideus muscles

______ _______ raise the wing during flight

Types of flying

Gliding, soaring, dynamic soaring, flapping flight

Gliding

_____ is several strong wing strokes & then coast; saves energy

Soaring

_____ is flight where a bird rises on thermal currents & glides down down until carried back up by another thermal current

Dynamic soaring

____ ____ is flight that requires continuous winds to lift bird; common in seabirds soaring above waves

Flapping flight

_____ _____ requires continuous flapping of wings to keep the bird airborne

Class Aves: Feeding

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Endothermic: heat derived from internal processes

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Maintain a homeostatic body temperature around 105°F

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High metabolic rate & must feed often

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Beaks of birds adapted to specialized food habits

Class Aves: digestion

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In herbivorous birds, food is stored in a crop which leads to a two-part stomach:

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proventriculus secretes gastric juice

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muscular gizzard grinds food (sometimes with stones!)

Class Aves: Excretion

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Paired kidneys; nephrons filter blood & remove metabolic wastes

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Like reptiles, birds conserve water by excreting nitrogenous waste as uric acid (white, paste-like)

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passed to cloaca & combined with feces; birds have no bladder

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Seabirds consume large amounts of salt with food

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Remove excess salt through special glands located above the eye

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Salt excreted via nostrils

Class Aves: Respiration

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One-way flow of air. Most efficient of any vertebrate.

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Have lungs with tube-like parabronchi & air sacs for excess fresh air

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During inhalation, 75% of fresh air enters air sacs & 25% enters lungs

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During exhalation, depleted air flows out of lungs & fresh air in sacs enters the lungs

Class Aves: Circulation

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4- chambered heart with two circulatory circuits (pulmonary & systemic)

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No mixing of oxygenated in deoxygenated blood.

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Independent evolutionary origin of this from mammals

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Fast heartbeat in some, such as the hummingbird

Class Aves: Nervous system

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Brain is ~10X larger than the brain of a similar sized reptile

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Large optic lobe (vision), cerebrum (behavior, singing, navigation, mating) & cerebellum (interprets visual cues, coordinates muscles)

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Cerebellum is much larger than in reptiles (flight)

tetrachromatic

4 types of cone cells in the eye

monocular vision

Most birds have _____ ______, with eyes on the sides of their heads (prey species)

binocular vision

Some have _____ ______, with eyes at the front of the head (predatory species)

3 part ear:

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External ear with sound- conducting canal that runs to eardrum

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Middle ear with rod-like, vibration-transmitting columella

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Inner ear where the cochlea (hearing organ) is located