Cetacean Evolution

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Cetacean Evolution

• When did whales evolove?
• First recognizable cetacean 50 mya
• From whom did whales evolve?
• Suborder Archaeoceti (first-whale)
• Up to 21m with reduced hindlimbs and strong
  snouts, long tail, short neck, reduced hindlimbs,
  paddle-shaped front limbs, and vertebrae that
  allowed up and down movement.
• adapted to life in shallow coastal fringes as
  well as open seas

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Cool Whale Evoluton Webpage

• http//www.indiana.edu/ensiweb/lessons/whalekiosk
  .html

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Precursor to Archaeoceti

• Terrestrial Mesonychid Condylarthra gave rise to
  archaeocetes
• Mesonychid- large-bodied creatures, some
  carnivorous, some herbivorous,
• Many of their fossils are found in sediments
  deposited in estuaries and therefore they may
  have been aquatic.
• Condylarthra- primitive ungulates (cows, hippos,
  etc.).

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Artiodactyls

• ORDER ARTIODACTYLA Means even-toed
• Suborder Suina
• Family Suidae pigs
• Family Hippopotamidae hippos
• Family Tayassuidae peccaries
• Suborder Tylopoda
• Family Camelidae camels and llamas
• Suborder Ruminantia
• Family Tragulidae chevrotains
• Family Moschidae musk deer
• Family Cervidae deer
• Family Giraffidae Giraffe and Okapi
• Family Antilocapridae pronghorn
• Family Bovidae cattle, goats, sheep, and
  antelope

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From Cows to Whales

• Cetaceans thus share common ancestry with
  Artiodactyla, that gave rise to modern ungulates
• Supported by the following evidence
• Blood composition
• Fetal blood sugar
• Chromosomes
• Insulin
• Uterine morphology
• Tooth enamel microstructure

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Where did whales evolve
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More Aquatic Meant

• A backwards shift of the external nostrils
• More streamlined form
• A dorsal fin
• A horizontal tail fluke
• Teeth became sharp uniform, typical of many
  present-day odontocetes
• Lost
• Long, mobile neck
• Functional hindlimbs
• Most of the pelvic girdle

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Mysticetes from Odontocetes

• Mid-Oligocene, some mysticetes lost their teeth
  for rows of baleen plates.
• Baleen is epidermal in origin, growing as fibres
  embedded in a softer matrix
• As the softer material is rubbed away by the
  tongue, the fibres become exposed
• Most present-day baleen whales still have teeth
  during the early stages of fetal development

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Other Adaptations

• Telescoping of the front of the skull occurred
  along with
• The development of acoustic scanning
• Echolocation may have been practiced by the
  earliest odontocetes, because their ear bones
  were isolated by fat bodies and air saces
  allowing directional hearing.
• Specialized Organs
• The mellon
• Nasal passages
• The spermaceti organ (in sperm whales)