Characters and Anatomy

Stethacanthus (Used with permission from Todd Marshall)	Scalloped Hammerhead Shark (Sphyrna lewini) (Used with permission from George Burgess)

Chondrichthyans are gnathostomes (= jawed fishes), and, as such, share a number of characters with other jawed vertebrates (i.e. bony fishes, amphibians, reptiles and mammals). These include jaws and paired appendages with internal skeletal support (in the form of pelvic and pectoral fins). Chondrichthyans are also the first vertebrates to possess true teeth. Throughout the evolutionary history of chondrichthyans, these characters have undergone a great deal of independent adaptive change. This has greatly complicated attempts to resolve the relationships of chondichthyan groups, as many specimens exhibit bizarre combinations of advanced and primitive characters (i.e. advanced tooth structure with primitive fins).

There are two broadly accepted synapomorphies (i.e. characters unique to a group) that define chondrichthyes as a monophyletic clade. These are

1. The presence of a unique type of calcified cartilage called "tesserae"

2. Modification of the pelvic fins in males to generate "claspers" (specialized sperm transfer organs)

Chain Dogfish (Scyliorhinus retifer) (Used with permision from George Burgess)

• Major subgroups
• Fossil forms
• Modern forms
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Author: Andrew Gillis
Last updated: 15 November 2004
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