ANATOMY

For millions of years cetaceans have managed to adapt to a totally aquatic existence. Although they have conserved innate mammal characteristics, like the presence of mammalian glands, the regulation of body temperature and their need to breathe oxygen from the air through their lungs, they have developed transformations that are more similar to fishes than they are to mammals. h1>

Due to the physical characteristics of water and to the gravity changes regarding the air, cetaceans have had to change their muscular and skeletal system in order to improve their fast swimming and deep dives.

• Stretching of the body in form of a torpedo
• Disappearance of hair and every cornea structure in the eyes (reduces water friction)
• Epidermis with fast cellular replacement and strong union of dermal and epidermal papilla
• Skeleton adapted for swimming
  • Long vertebral column
  • Flexible rib cage (great number of spare ribs)
  • Disappearance of hip bones (vestigial pelvic bones)
  • Transformation of legs into flippers
  • Skull lengthened to house structures related with acoustics (dolphins) and feeding (whales)

Digestion

The digestive system varies in its forms of nutritional functions. The misticetes have a beard that works like a filtering organ for planktons and small fishes, while the odontocetes have sharp and aligned teeth. The number of these depends on the species and in some cases may be absent. Their main function is to grip the food. In regard to the digestive tube, it is important to emphasize that in cetaceans there is a presence of a stomach divided into different compartments.

Thermoregulation and Osmoregulation

The greatest heat loss is produced in the water but this is counteracted by a naked skin with a thick layer of fat underneath it (blubber). On the other hand, heat excess is eliminated thanks to the special dispersal of the vascular system in the form of countercurrents of veins and arteries in specific zones like the flippers.

The kidneys of all aquatic mammalians present a characteristic referred to as lobular morphology that’s similar to a bunch of grapes. This increases the ability of liquid filtration and retention, and prevents the organism from excessive water loss.

Breathing

Another system that developed was the respiratory system which allows fast respiratory movements, long dives, sustains great pressures and reduces the derived problems from the high partial pressures of blood gases (ex: nitrogen N2). In cetaceans, the skull differs from the typical mammalians due to telescoping, which results in the positioning of the nasal cavities from the anterior part to the posterior dorsal part. The respiratory system begins in the nasal nostril or blowhole (double in misticetes and single in odontocetes) and ends in the lungs.