The oldest modern sharks are known from the Early Jurassic. However, the term "shark" has also been used to refer to all extinct members of Chondrichthyes with a shark-like morphology, such as hybodonts and xenacanths. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the rays. Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Clockwise from top left: spiny dogfish, Australian angelshark, whale shark, great white shark, horn shark, frilled shark, scalloped hammerhead and Japanese sawshark representing the orders Squaliformes, Squatiniformes, Orectolobiformes, Lamniformes, Heterodontiformes, Hexanchiformes, Carcharhiniformes and Pristiophoriformes respectively.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |