Think - Pair - Share: How do you turn an Artiodactyl into a Cetacean?

The fossil record on whale evolution

• I. General Characteristics
• II. Suborder Mysticeti
• III. Suborder Odontoceti

Order Cetacea

I. General Characteristics

1. Morphology
   1. Fusiform-shaped body
   2. Large body size
   3. Virtually hairless
   4. Blubber
   5. No sebaceous glands
   6. Tails flattened dorso-ventrally into flukes
   7. Forelimbs are modified into flippers
   8. Vestigial hindlimbs
   9. Dorsal fin in most species
   10. Skull
       1. Unusually long rostrum
       2. Nares have migrated back
       3. Bones of skull are telescoped
   11. Specialized muscles to control blow hole
   12. Neck is short and cervical vertebrae are often fused

2. Sensory abilities
   1. Large brains
   2. Use auditory communication
   3. Some species can echolocate
   4. Dolphins (best studied) can see just as well above or below the surface of the water

3. Diving and swimming
   1. Respiratory/circulatory adaptations permitting prolonged submersion
      1. Extra capillaries in the lungs
      2. Use 3 times as much of the oxygen from a breath of air as do terrestrial mammals
      3. Can force almost all air out of the lungs when exhaling
      4. Twice as high a concentration of red blood cells
      5. 2-9 times as much myoglobin in muscle tissue
      6. Heart rate drops to half its normal rate during long dives
      7. During dives, blood is redistributed
      8. High tolerance to lactic acid
      9. High tolerance to carbon dioxide
   2. Can tolerate very high pressures associated with deep dives
      1. Usual mammalian response to increased pressures
      2. Cetacean adaptations to deep diving
   3. Very fast swimmers
      1. Drag, turbulent flow, laminar flow
      2. Adaptations

         1) Lack of hair except for a few vibrissae
         2) Few external appendages/protuberances
         3) Parabolic body form

II. Suborder Mysticeti

1. General characteristics
   1. Largest animals ever known (living or fossil)
   2. Mostly plankton feeders
   3. Populations have been driven near extinction by hunting

2. Foraging adaptations
   1. Lack teeth as adults
   2. Have plates of baleen
      baleen in a humpback whale
      1. Horny epithelial material in longitudinal strands
         another view of baleen
         Close-up view
      2. 130-400 plates
      3. Telescoped maxilla extends infraorbitally
   3. Methods of feeding
      1. Skimming (eg, right whales)
         video clip of right whale skimming
      2. Gulp-feeding (eg, rorquals: blue whale, humpback whales)
         
         Gulp-feeding in humpback whales is a cooperative behavior:
         • Vocalizations to herd schools of fish
         • Make Bubble nets encircle fish
         • Whales lunge upward through the school of fish and consume them
         • National Geographic crittercam view
      3. Bottom-ploughing (eg, grey whale)

4. Migrations
   Humpback whale
   Gray whale

III. Suborder Odontoceti

1. General characteristics
   1. Most diverse suborder of Cetaceans
   2. Asymmetry of cranial bones
   3. Telescoped maxilla extends supraorbitally

2. Foraging
   1. Many of them are carnivorous
   2. Many more teeth than the typical pattern, OR lost all (or all but one) teeth
   3. Teeth are homodont and cone-shaped

3. Respiratory canal and food passages are completely separated by specializations in the glottis and larynx

4. Sensory systems
   1. Echolocation
      dolphin sonar demonstration
      acoustic impedence demo
      1. Production of clicks
      2. Focusing of clicks through melon
         dolphin dissection showing melon
      3. Reception by the lower jaw
      4. Some sound reception by the teeth? May help with localization of sound
      5. Reception by the middle ear
   2. Prey stunning with high frequency sound?

5. Interesting examples
   1. Sperm whale
   2. Narwal
      cranium
   3. family Delphinidae
      spotted dolphin
      dusky dolphin
   4. family Platanistidae
      Ganges River dolphin
      Amazon river dolphin