Dolphins are classic example of streamlining. The body is sleek and smooth. Above the upper jaw is a large mass of fat and oil containing tissue. The anterior appendages contain the skeletal remnants of five digits that form the flippers. The hind appendages are virtually absent and consist of a pair of small pelvic bones. The dorsal fin is formed from subcutaneous dermal tissue and is not movable by muscle action. The cardal or tail fin is also primary dermal in origin. The main thrust comes from vertical oscillation of the tail and flukes.
Dolphins are extremely and almost constantly vocal that is capable of generating sounds. Each sound comprises a broad range of frequencies including many in the ultrasonic range. The clicks are used as a form of sonar that enable the dolphin to defect obstacle other dolphins, fish or even tiny bits of matter in the water.
Dolphins can deliver an acoustic shock to kill small prey. Deeper in the respiratory system they can produce a high pitch whistle used to communicate a particular emotional state or denotes alarm or sexual excitement Copulation normally occurs during the spring months with the male-female pair exhibiting courtship for some time prior to the copulation. Gestation period in species is between 11 to 12 months, after which a single calf is produced. Delivery is normally tail first and after births the calf follows it mothers closely and sucking takes place. The dolphins two mammary gland opens into sacs either side of the anal opening, and the calf's breakfast into the sacs. The nipple is grasped between the upper jaw the tongue, muscular contractions by the mother literally squirt milk into the calf's mouth.