Elasmobranchii

Elasmobranchii  is a subclass of the Chondrichthyes or cartilaginous fish. It includes the modern sharks and the rays and skates.

 Evolution 
Fossilised shark teeth are known from the early Devonian, around 400 million years ago. During the following Carboniferous period, the sharks underwent a period of diversification, with many new forms evolving. Many of these became extinct during the Permian, but the remaining sharks underwent a second burst of adaptive radiation during the Jurassic, around which time the skates and rays first appeared.

Taxonomy
Subclass Elasmobranchii
†Plesioselachus
†Order Squatinactiformes
†Order Protacrodontiformes
†Infraclass Cladoselachimorpha
†Order Cladoselachiformes
†Infraclass Xenacanthimorpha
†Order Xenacanthiformes
Infraclass Euselachii (sharks and rays)
†Order Ctenacanthiformes
†Division Hybodonta
†Order Hybodontiformes
Division Neoselachii
Subdivision Selachii (Selachimorpha) (modern sharks)
Superorder Galeomorphi
Order Heterodontiformes (bullhead sharks)
Order Orectolobiformes (carpet sharks)
Order Lamniformes (mackerel sharks)
Order Carcharhiniformes (ground sharks)
Superorder Squalomorphi
Order Hexanchiformes (frilled and cow sharks)
Order Squaliformes (dogfish sharks)
†Order Protospinaciformes
Order Squatiniformes (angel sharks)
Order Pristiophoriformes (sawsharks)
Subdivision Batoidea (rays)
Order Torpediniformes (electric rays)
Order Pristiformes (sawfishes)
Order Rajiformes (skates and relatives)
Order Myliobatiformes (stingrays and relatives)

References

Category:Cartilaginous fish