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Order Cetacea Characteristics:

• All completely aquatic – many marine, some freshwater • Fusiform body = cigar-shaped • Lack sebaceous glands • (nearly) hairless • Thick insulation; blubber • Forelimbs = flippers; tail forms flukes • No clavicle; no external digits/claws • No mucous membrane = no sense of smell • No outer visible ears • No vocal chords – but still emit high-frequency sound (?)

o Air exhaled across air sacs in nasal passage, producing clicks?

o Melon (oil-filled frontal sac) may help direct clicks forward o Sound waves bounce off higher-density objects back to inner

ear • Modified skull

o Shifting external nares to top and back o Premaxillary & maxillary bones cover roof of skull

• Reduced differentiation of vertebrae; high neural spines; compressed cervical vertebrae

• “pinhole camera” type of eye o Good for depth of field, but not fine adjustment

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Suborder Odontoceti (Odontocetes = toothed whales, dolphins, porpoises)

• Many, homodont teeth • Well developed brains • Echolocation

• Toothed whales emit a variety of sounds ranging around 280,000 Hz • Baleen whales emit a variety of sounds ranging around 20,000 Hz (human

range, reach volume of 8 decibels, carry hundreds of km underwater

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Family Delphinidae (dolphins, orca whales)

• Cone-shaped teeth • Off shore/deeper waters • Curved or hooked dorsal fin

Family Phocoenidae (porpoises)

• Spade-shaped teeth • Near shore/shallower waters,

including estuaries • Triangular dorsal fin

Family Physeteridae (sperm whales)

• 1,100+ m deep for 1.5 to 2 hrs! • Mollusk & fish feeders

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Family Platanistidae (river dolphins)

• Amazon River, Ganges River

Suborder Mysticeti (Mysticetes = baleen whales) • Lack teeth • Baleen plates extending from palate (100-400 each side of

mouth); sieves

• No echolocation; but ultrasonic sounds (navigation,

communication) • Historically high mortality rates due to whaling

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Family Balaenidae (right whale, bowhead whale)

• Long, finely fringed baleen plate • Plankton feeders, skim surface or

swim through

Family Balaenopteridae (blue whale, finback whale, humpback

whale)

• Throat grooves elongate • Shorter, triangular, coarser comb

structure to plates • Krill & fish feeders

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humpback migration Family Eschrichtiidae (gray whale)

• Bottom feeder? (abrasions) • Scoop/filter food material from

bottom • Long migration (Siberia, Korea,

Alaska, down to Gulf of CA)

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Diving Adaptations of Mammals (namely deep divers) 1) Breathing

• Often exhale before dive (reduces buoyancy & risk of decompression sickness)

• Low lung capacity relative to non-diving mammals • Collapse of thorax results in collapse of alveoli; pushes air

into non-collapsible trachea (reduces decompression sickness – maintain pressure)

2) Circulation

• Bradycardia (drop in heart rate) • Vasoconstriction of peripheral blood vessels (maintain blood

flow to brain) • Increased blood volume relative to body size • Increased hemoglobin / oxygen carrying capacity • Increased myoglobin oxygen carrying capacity; more oxygen

in muscle 3) Metabolism related

• Muscles function under anaerobic conditions (20+ min) • Lactic acid tolerance

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Low Frequency Active (LFA) Sonar

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http://www.nrdc.org/wildlife/marine/sonar.asp