Cetaceans is the taxonomic order that includes dolphins, porpoises and whales. They are all mammals and are subcategorized into two additional groups: baleen whales (Mysticeti), which filter food from the water, and toothed whales (Odontoceti), which prey on other animals. Within these two groups there are more than 80 different species of cetaceans, but they still share many common features in their behavior, physiology and anatomy.
All cetaceans exhibit similar surface behaviors including breaching, spy-hopping, porpoising, spouting and tail slapping. Additionally, all cetaceans live in family groups. Unfortunately, cetaceans occasionally strand themselves on beaches, either singly or en masse. According to the National Oceanic and Atmospheric Administration, stranding is a behavior that scientists do not understand; only about 20 species strand themselves and it happens more often with toothed species.
All cetaceans are aquatic, warm-blooded and give birth to live offspring, which are nursed by their mothers with milk. Cetaceans breathe air with lungs that exchange oxygen and carbon dioxide, and they use up and down biomechanical tail movements for swimming. They also all have excellent hearing and communicate with a variety of low- to high-pitched sounds, and have eyes with spherical lenses for optimal low-light vision.
Cetaceans have a higher concentration of myoglobin in their skeletal muscles, this allows them to stay underwater for long periods of time. Myoglobin attracts and bonds with oxygen more readily than hemoglobin, enabling them to submerge for 7 to 120 minutes depending on the species. Cetaceans are also virtually hairless, have tapered bodies with no visible neck, and a thick layer of insulating fat. They have blowholes situated on top of their heads, front flippers that evolved from forelimbs and vestigial hindlimbs.