Cetaceans Flashcards
Cetacean Evolution
Evolved early in the Eocene (53-45 mya).
Earliest stem cetaceans found in rocks of middle Eocene (c 50 mya)
First major radiation produced Archaeoceti, animals more specialised for marine life.
Mid to late Eocene fully marine forms emerged, by 42mya cetaceans around the globe.
Radiation co-incident with break up of Southern continental landmasses, and reorganisation of ocean circulation
Odontocete Evolution
Toothed whales and dolphins
Earliest known from N Atlantic region 32 mya, ecolocation early in evolution
Mysticete evolution
Baleen whales feed by filtration using baleen plates.
Earliest from Pacific region >28mya
Diversified in Miocene
Rise to largest whales in history
Cetacean body size
Range of sizes from small dolphin to blue whale
Small cetaceans <3m, 47 extant species
Intermediate, 3-10m, 31 extant species.
Large, >10m, 11 extant species
Much greater size diversity in the odontocetes
Mysticeti
Paired blow hole
Symmetrical skull
No development of a melon or sound focussing organ
Lack of ribs articulating with the sternum.
Large and have big migrations.
Females typically larger than males, and Sern species bigger than Nern
4 families, Right whales, pygmy right whales, grey whales, rorquals
Right whales, Balaenidae
Highly arched rostrum and longest baleen.
Disproportionately large head
Populations dramatically reduced
Live for more than 200 years
Surface skimming feeding
Pygmy right whales
Short head
Arched upper jaw and bowed lower lips
Dorsal fin
Baleen plates are long and yellowish
Grey whales
Short narrow heads
Slightly arched rostrum.
No dorsal fin, relatively short yellowish baleen.
Most coastal of baleen whales.
Rorquals
Most diverse group 7 species.
10m minke whale to 33m blue whale
Large slender body with short heads
Dorsal fin
Latitudinal migrations
Oceanic foragers with extensive ranges
Feeding in mysticetes
Filter system:
- Flow of water to bring food in
- Filter to collect food but let water out
- Means of removing food and transferring to gullet
Seek areas where food is concentrated
Swim open mouthed or engulf water.
Feeding cycle dependent on seasonal blooms of zooplankton and small fish.
Migration follows these patterns
Mysticete migration
Low lats in winter to high lats in summer.
Consume most food in spring to autumn.
Diverse prey, copepods to fish
Sperm whales
Spermaceti organ in the head, spermaceti oil, role in buoyancy.
Large body size, dive ability, brains and complex social structures
Through world ocean, males have larger ranges into poles.
F = 11m. M = 16m
Females res tricted to deep, tropical and warm temperate waters.
Large fish and squid are prey.
Heavily hunted
Beaked whales, Ziphuriidae
23 species 4 to 13m long
Beak length and prominence varies
Small pectoral fins can be folded for streamlining
Reduced teeth, only 1 or 2 pairs in lower jaw
Little-known, deep-water specialists, >200m feed on fish and squid
Plastic ingestion is a concern and sensitive to underwater noise.
Dolphins, Delphinidae
37 species, confused taxonomy.
Arose in Miocene 11-12 mya.
Typical morphology, spindle shape, 1 blowhole, telescope skull, left-skewed cranial asymmetry.
Echolocation.
Dolphin vary in the shape of their feeding apparatus.
All oceans, highest diversity in tropics, only orca go to ice edge.
Social, solid info on orca and bottlenose.
Cognitive abilities, brain:body 2nd to humans.
Monodontidae
Narwhale and beluga.
Emerged 10-14 mya.
Arctic specialists, narwhale restricted to Atlantic Arctic, Beluga have circumpolar distribution but absent in Atlantic.
Narwhal, in males the right tooth extended into tusk
Narwhal eat little in summer but in winter eat squid and fish. Restricted diet is a worry as polar fauna is changing with climate change.
Beluga eat range on verts and inverts of benthic and pelagic origin, beluga occupy coasts in winter and in offshore feeding grounds in summer.
80-100 years.
Polar bears and killer whales are main predators.
