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Are sharks mammals?
Fish.

Sharks are cartilaginous fish, not mammals. But sharks are viviparous animals, that is, fertilized eggs hatch in the mother, and the mother gives birth to larvae. But it is different from ordinary oviparous animals, such as crocodiles, and viviparous animals, such as whales, which have placenta and umbilical cord.

Sharks belong to cartilaginous fish, a subclass of vertebrates, and live in the ocean. A few species enter fresh water, which is a group of medium and large marine fish with fast swimming speed. The endoskeleton of sharks is completely composed of cartilage, which is often calcified, but there is no real bone tissue. The exoskeleton is not developed or degenerated. The body is often covered with skin teeth (thin-walled scales), with various teeth and hard muscles, but the membranous bone never exists and the skull is seamless.

The upper forehead is composed of palatal cartilage and the lower forehead is composed of Mayer cartilage. The body is long spindle-shaped. Lateral branchial fissure, normal pectoral fin, not healing with anterior snout; Dorsal position of the north fin; Crooked tail type.