EnchantedLearning.com ALL ABOUT WHALES!

Whale Classification

Basilosaurus (or Zeuglodon), a primitive, extinct whale about 65 ft (20 m) long, from the late Eocene Epoch (50 million years ago).

THE ORIGIN OF WHALES

Fossil remains indicate that whales and other cetaceans (the whales, dolphins, and porpoises) evolved from hoofed land mammals (even-toed ungulates or artiodactyls, related to sheep, pigs, deer, camels, and cows). These animals returned to the sea about 50 million years ago, during the Eocene Epoch.

Going back to the oceans required many adaptations for living in the water, including a backwards and upwards shift of the nostrils, coverings for the nostrils, a streamlined shape, loss of the rear limbs, change of the forelimbs into flippers, addition of flukes for swimming, modification of senses for use in the water, loss of most hair, and addition of a layer of insulating blubber.

The Archaeoceti were the first primitive whales to appear. They had tiny heads and pointed snouts with teeth. Some (like Pakicetus and Protocetus) still had vestigial rear limbs (flippers) from their land roving days. Modern-day whales have larger heads and blunter snouts. By the late Pliocene Era (1.8 million years ago), modern forms of Cetaceans were swimming in the seas.

Although there are many gaps in the fossil record of whales, discoveries are frequently being made. In 1989, Philip Gingerich (University of Michigan, USA) found fossilized whale feet in an ancient Egyptian sea bed, the Zeuglodon Valley. Recently, scientists from the University of Roorkee in India and the University of Michigan found the oldest-known whale fossil, Himalayecetus subathuensis, in India.

CLASSIFICATION OF EXTINCT WHALES

Kingdom: Animalia (animals) Phylum: Chordata (having a spinal cord) Class: Mammalia (mammals) Order: Cetacea (aquatic mammals) Suborder: Archaeoceti (archaeocetes or zeuglodonts, extinct, primitive whales with teeth)

There are approximately 140 genera of extinct cetaceans. There are 40 genera of living cetaceans.

• Family Protocetidae (Eocene) - small (up to 10 feet (3 m) long and seal-like
  • Himalayecetus subathuensis - the oldest-known whale fossil, about 53.5 million years old. Its fossilized jawbone and teeth were found in the Simla Hills of northern India, in the foothills of the Himalayan mountains. This area was underwater (in the Tethys sea) during the Tertiary period (when India was an island off Asia). This whale may have spent some of its time on land.
  • Pakicetus inachus - This seal-like, toothed cetacean may have divided its time between the land and the shoreline, rivers, and estuaries.
    • The second-earliest-known whale, from the Early Eocene, about 50 million years ago.
    • It was about 6 feet (1.8 m) long.
    • Had small, vestigial rear flippers and a pointed tail (it had no flukes).
    • The nostrils were at the tip of the snout (like land animals, not modern-day cetaceans).
    • Fossils have been found in Pakistan, Asia.
  • Protocetus -
    • Middle-Eocene cetacean, it lived 8 million years after Pakicetus
    • It was about 8 feet (2.5 m) long.
    • It had a longer and more stream-lined body and its rear flippers were reduced in size.
    • The tail had developed flukes and the nostril were behind the eyes.
    • Fossils have been found in Africa and Asia.
• Family Dorudontidae (Eocene)
  • Dorudon atrox was an early whale, was about 20 feet (6 m) long. Its arms were small, flattened flippers. The rear limbs were only about 4 inches (10 cm) long. It had a long, pointed snout with many sharp, triangular teeth.
  • Zygorhiza - a long, serpent-like cetacean that may have spent some time on land (perhaps for breeding).
    • Late-Eocene.
    • It was up to 20 feet (6 m) long.
    • A long, serpent-like cetacean (no rear flippers) with the same head:body ratio as modern-day whales (1:6).
    • Fossils have been found on the Atlantic coast of North America.
• Family Basilosauridae (late Eocene) - larger, more whale-like cetaceans
  • Basilosaurus cetoides - (also known as Zeuglodon) snake-like cetaceans whose fossils were found in the 1830's.
    • Late-Eocene, about 40-35 million years ago.
    • It was up to 82 feet (25 m) long.
    • Reduced hind legs and pelvis; no rear flippers.
    • It had 44 teeth in its long jaws, like early placental mammals.
    • Fossils have been found on the Atlantic coast of North America.
• family Squalodontidae -
  • Prosqualodon - a 7.5 feet (2.3 m) long extinct, toothed whale that resembled a dolphin. It dates from the Oligocene to the early Miocene. It had complex teeth, more like the Archaeoceti than the Odontoceti (the toothed whales).
  • Squalodon - an extinct toothed whale from the Miocene and Pliocene. It had a long, pointed snout and serrated teeth in a skull 32 inches (80 cm) long. Named by Grateloup in 1840.
• family Eurhinodelphidae -
  • Eurhinodelphis - a 6.5 feet (2 m) long extinct, long-snouted porpoise with no teeth at the end of the snout. It dates from the mid to late Miocene. It had complex teeth, more like the Archaeoceti than the Odontoceti (the toothed whales).

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Whale Classification

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