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
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