Most species live in the sea, some in rivers. Dolphins are able to guide to a humane self chosen death pdf very tight turns while swimming at high speeds. Some species are well adapted for diving to great depths.
Although cetaceans are widespread, most species prefer the colder waters of the Northern and Southern Hemispheres. This has drastically affected their anatomy to be able to do so. Calves are typically born in the fall and winter months, and females bear almost all the responsibility for raising them. Cetaceans have been depicted in various cultures worldwide. Most mysticetes prefer the food-rich colder waters of the Northern and Southern Hemispheres, migrating to the Equator to give birth. During this process, they are capable of fasting for several months, relying on their fat reserves. Their hearing is so well-adapted for both air and water that some blind specimens can survive.
Some species, such as sperm whales, are well adapted for diving to great depths. Cetacean bodies are generally similar to that of fish, which can be attributed to their lifestyle and the habitat conditions. They have a streamlined shape, and their forelimbs are flippers. Both the flipper and the fin are for stabilization and steering in the water. The male genitals and mammary glands of females are sunken into the body.
Males in these species developed external features absent in females that are advantageous in combat or display. The fluke is set horizontally on the body, unlike fish, which have vertical tails. The nostrils are located on top of the head above the eyes so that the rest of the body can remain submerged while surfacing for air. The back of the skull is significantly shortened and deformed. By shifting the nostrils to the top of the head, the nasal passages extend perpendicularly through the skull. The braincase is concentrated through the nasal passage to the front and is correspondingly higher, with individual cranial bones that overlap. Even the long tusk of the narwhal is a vice-formed tooth.
In many toothed whales, the depression in their skull is due to the formation of a large melon and multiple, asymmetric air bags. Other cetaceans have fused neck vertebrae and are unable to turn their head at all. In humans, these cells are thought to be involved in social conduct, emotions, judgment and theory of mind. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for cognitive tasks. In some whales, however, it is less than half that of humans: 0.
Blue Whale skeleton outside the Long Marine Laboratory of the University of California, Santa Cruz. Skeleton of a blue whale standing outside the Long Marine Laboratory of the University of California, Santa Cruz. Upper jaw of a sperm whale that has been weathered and yellowed. Weathered upper jaw of a sperm whale. This gives stability during swimming at the expense of mobility. The last two to three pairs of ribs are not connected and hang freely in the body wall. The stable lumbar and tail include the other vertebrae.
The front limbs are paddle-shaped with shortened arms and elongated finger bones, to support movement. They are connected by cartilage. The second and third fingers display a proliferation of the finger members, a so-called hyperphalangy. There are characteristics unique to cetaceans.