Episode 172 – Toothed Whales

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The world’s most famous marine mammals come in two varieties. This episode, we discuss the diversity and evolutionary history of the more diverse of the two: Toothed Whales.

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Whales with Teeth

Whales evolved from terrestrial ancestors during the Eocene, and quickly gave rise to a diversity of aquatic species. During the Oligocene, these early whales gave rise to two prominent groups: baleen whales (Mysticetes) and toothed whales (Odontocetes). Today, toothed whales include over 70 species of dolphins, porpoises, beluga whales, narwhals, beaked whales, and sperm whales.

A sample of modern toothed whale diversity.
Top: Sperm whale. Image by Gabriel Barathieu, CC BY-SA 2.0
Middle left: Orca. Image by Robert Pittman
Middle right: Common bottlenose dolphin. Image from NASA
Bottom left: Beluga. Image from premier.gov.ru, CC BY 4.0
Bottom left: Amazon river dolphin. Image by Oceancetaceen, CC BY-SA 2.0 DE

Unlike their baleen cousins, toothed whales typically have teeth. These teeth are usually simple, peg-like structures, although some species have evolved specialized tooth shapes. Toothed whales also tend to be much smaller on average than baleen whales, with most species being dolphin- or porpoise-sized, although there are notable exceptions. Toothed whales are also famous for their ability to echolocate, made possible by specialized structures in their skulls.

Some toothed whales go all out with the teeth.
Left: Skull of a strap-toothed whale. Image by Nkansahrexford, CC BY 4.0
Right: Skull of a narwhal. Image by Pcornill, CC BY-SA 4.0

During the Oligocene, over 20 million years ago, the oceans were home to a number of extinct families of early toothed whales or close cousins. These included Simocetidae, Squalodontidae, and Xenorophidae, for example. More familiar families appeared later on, with many well-known toothed whales from the Miocene and later.

Ancient toothed whales came in many fascinating forms.
Top left: Squalodon, the “shark-toothed” whales. Image by Nobu Tamura, CC BY 3.0
Bottom left: Odobenocetops, the “walrus whale.” Image by Nobu Tamura, CC BY 3.0
Right: Semirostrum, an ancient porpoise with a weirdly long lower jaw. Image by Nobu Tamura, CC BY-SA 4.0

Many fossil toothed whales looked and probably lived a lot like modern dolphins and porpoises. There are exceptions, however, such as the impressive macroraptorial sperm whales of the Miocene, the bizarre Odobenocetops which had walrus-like tusks, and a surprising variety of long-snouted species related to modern river dolphins.

The skulls of two ancient macroraptorial sperm whales, specialized for hunting large prey.
Top: Acrophyseter. Image by Olivier Lambert, CC BY-SA 3.0
Bottom: Livyatan. Image by Ghedoghedo, CC BY-SA 4.0

Dive Deeper

Macroraptorial sperm whales
Oligocene dolphin with tusk-like teeth

The awkward record of fossil whales (technical, open access)
The shape of cetacean skulls through deep time (technical, open access)
The origins of the killer whale ecomorph (technical, open access)
Macroraptorial sperm whales from the Miocene of Peru (technical, open access)

Encyclopedia of Marine Mammals (paywall)

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