Sperm Whales' Amazing Adaptations
by AMNH on
Fifty-five million years ago, a group of hoofed mammals began a slow move from shore to sea, in time evolving a set of extraordinary features to thrive in their new environment.
Today’s whales share many anatomical traits with other mammals, but the unique adaptations of species such as Physeter macrocephalus, the sperm whale, illustrate how organisms can transform over time as they carve out their place on the planet. (A number of exhibits within the Whales: Giants of the Deep exhibition feature these large whales.)
The sperm whale's sleek shape is well-suited for deep diving, this species' specialty. Sperm whales can dive over 6,500 feet, remaining under water for more than an hour.
Unlike fish, which swim by moving their tails side to side, whales and dolphins move their flukes up and down. Sperm whale flukes are the largest, relative to body size, of any whale.
The sperm whale's flippers, or pectoral fins, help the animal maneuver through water. They also share bone structure with the human arm and hand.
In fact, the bones of cetacean flippers are the same kinds of bones as in the human arm, with an upper arm bone, two forearm bones, and hand, wrist, and finger bones. In whales, fingers are elongated and may have additional bones. The joint between upper arm and forearm is immobile, creating an effective paddle.
Among sperm whales' (and other toothed whales') most amazing adaptations is echolocation, the use of sound to locate objects based on their echoes−and a way of navigating the world that is also used by some land mammals, including bats. The whales use this ability to, among other things, hunt successfully for deepwater prey, such as giant squid.
To create sound, the whale pushes air through one of its nasal passages to a pair of flaps that vibrate to create sound. The sound passes through the spermaceti organ (rendered in blue, top of the skull), bounces off an air sac, and is redirected to the whale's "melon" organ (rendered in yellow). Called "junk" by whalers, this organ contains fatty tissue that transmits sound, focusing the pulses in the process and allowing sperm whales to direct, or aim, sound waves.
At the crux of the whale's jaw, the lozenge-shaped yellow portion (shown above, right) is the "acoustic fat pad." As echoes bounce back toward the sperm whale, they are received by this deposit of fat in the back of the whale's long, thin jaw. The sound is then transmitted through the ear bones.
A version of this story appears in the Spring 2013 issue of Rotunda, the Member magazine.
Whales: Giants of the Deep was developed and presented by the Museum of New Zealand Te Papa Tongarewa. This exhibition was made possible through the support of the New Zealand Government.
The American Museum of Natural History gratefully acknowledges the Richard and Karen LeFrak Exhibition and Education Fund.
Generous support for Whales: Giants of the Deep has been provided by the Eileen P. Bernard Exhibition Fund.