19 - Cetacea

19 - Cetacea

1. morphology

   • highly TELESCOPED skull structure 
   • posterior bones of cranium COMPRESSED and OVERLAPPING
   • anterior bones elongated and overlap posteriors
   • posterior displacement of nares to TOP of skull
   • tympanic bones NOT braced against skull (partly insulated from the rest of the cranium by surrounding FAT BODIES)
   • THERMOREGULATION
   • nearly hairless
   • LOW surface area-to-volume ratio
   • subcutaneous blubber for insulation and heat retention 
   • COUNTERCURRENT exchange 
   • diving adaptations (100-200 meter depths)
   • many ribs lack CONNECTION to sternum, collapsible and elastic lungs
   • bronchioles BRACED by CARTILAGE RINGS
   • gas exchange > terrestrial mammals
   • oxygen efficiency: 12% cetacean, 4% terrestrial mammals
   • erythrocytes: 2x more
   • myoglobin: 2-9x more
   • tolerate high lactic acid, CO2
   • apnea: 3-70 minutes
   • bradycardia, reduced peripheral circulation
   • sub-dermal "springs" in tailstock store and release elastic energy for swimming 
   • drag reduced on body surfaces 
   • compliant spongy layer in outer skin dampens pressure and turbulence 
   • LARGER BODY MASS increases speed
   • recorded speeds of 36 kph (dolphins) to 55 kph (killer whale)
   • also favors THERMOREGULATION

2. paleontology

   • EOCENE cetaceans from coastal Tethys Sea
   • transitional forms from terrestrial to aquatic
   • hippos considered sister group to ancestral cetaceans
   • double-pulley ASTRALAGUS bone in ankle common bond
   • PAKICETUS = the earliest known whale in early EOCENE
   • RHODOCETUS from MID-EOCENE
   • transition to FILTER FEEDING corresponds to opening of circum-Antarctic currents
   • explosion in marine plankton productivity

3. economics & conservation

   • whaling dates back thousands of years 
   • land-based: slower species in coastal waters driven onto land
   • by 16th and 17th centuries, Europe and North America begin commercial trade with large ships 
   • high economic value of MEAT, OIL, BALEEN
   • significant declines began
   • technology improved efficiency, hastened declines (harpoon guns, steam-driven ships by 1860s)
   • floating factory ships, stern slipways by 1925
   • right whales so named for ease of hunting, lots of oil and meat so it is economically valuable 
   • FIRST SPECIES (right whale) to be overexploited, 2 endangered
   • GRAY WHALES extirpated from Atlantic in 1700s, eastern Pacific population protected and growing 
   • Beluga = threatened 
   • California harbor porpoise, finless porpoise = endangered
   • 2006: Chinese river dolphin = first cetacean to go extinct sincce 1950s
   • Establishment of International Whaling Commission in 1946
   • governs the conduct of whaling throughout the world 
   • limits numbers, size of whales which may be taken 
   • COMPLETE PROTECTION of certain species 
   • designate specified areas as whale sanctuaries 
   • prescribe seasons and areas for whaling
   • prohibit capture of suckling calves and females with calves
   • require CATCH reports, other statistical and biological records
   • encourages, co-ordinates and funds whale research
   • promotes humane killing operations 
   • moratorium in 1985, but thousands still killed for "research" 
   • Japan, Russia, Norway, Iceland, Finland 
   • Institute of Cetacean Research for "Research Goals and Results"

4. suborders & families

   • Mysticeti
     • GRAZING near surface: right whales swim through swarms of plankton
     • lunge feeding: RORQUALS
     • furrows on throat for expansion
     • during contraction of pouch, water and food pass through baleen plates 
     • mandible braced by frontomandibular stay apparatus
     • bubble netting = a form of lunge feeding 
     • sediment feeding: gray whales 
     • plow head through mud at bottom
     • scoop or suck up sediments
     • filter out marine organisms
     • "moustache/whale"; baleen whales
     • TWO external narial openings (blowholes) on top of head
     • do NOT echolocate 
     • distributed worldwide marine
     • teeth VESTIGIAL in embryos and ABSENT in adults 
     • baleen of CORNIFIED EPITHELIUM in place of teeth
   • Odonteceti
     • DENTITION and ECHOLOCATION
     • VARIABLE tooth number, usually HOMODONT
     • active pursuit of prey, requres agility and speed 
     • echolocation sounds likely produced in NASAL sacs
     • focused by oil-filled melon in forehead, sent out 
     • return echoes pass through oil-filled LOWER JAW to bullae, isolated from skull bones by tissue
     • "tooth/whale"; toothed whales
     • generally smaller than mysticetes
     • skyll BILATERALLY asymmetrical
     • single external narial opening on top of head (left)
     • teeth present, from 2-260 in different species
     • use ECHOLOCATION 
     • nasal sacs and fatty melon
     • foraging and orientation
     • distributed worldwide marine, some species riverine

5. characteristics

   • whales, dolphins, porpoises, narwhal 
   • besides SIRENIANS, only mammals to be ENTIRELY aquatic (never leaving water)
   • some are the LARGEST vertebrates (30m blue whale)
   • loudest VOICES of all mammals
   • dive deeper, exposed to higher pressures than ANY other mammal
   • longest MIGRATIONS of any mammals (18,000km in gray whales) 
   • Fusiform
   • NO external ears
   • teats enclosed within slits next to urogenital opening
   • testes remain ABDOMINAL 
   • hindlimbs ABSENT 
   • vestigal pelvic girdle present but not attached to vertebral column
   • forelimbs (flippers) paddle-shaped but limb elements not visible externally (STABILIZERS, not thrust generators)
   • digits long, with additional phalanges 
   • tail (fluke) flattened DORSOVENTRALLY 
   • caudal undulations provide THRUST through medium
   • simple postcranial skeleton 
   • mostly vertebrae; cervical COMPRESSED chevron bones on anterior caudal vertebrae; high neural spines
   • has CLAVICLE