Elasmobranchii

Elasmobranchii (rays and sharks) Fossil range: Late Silurian–Recent PreЄ Є O S D C P T J K Pg N [1]
Great white shark, Carcharodon carcharias
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii Bonaparte, 1838
Superorders
Batoidea (rays and skates) Selachimorpha (sharks)

Elasmobranchii (pronounced /ɛˌlæzmɵˈbræŋki.aɪ/) is the subclass of cartilaginous fish that includes skates, rays (batoidea), and sharks (selachii).

Evolution

Ostenoselache stenosoma fossil

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. Many surviving orders of elasmobranch date back to the Cretaceous, or earlier.^[2]

Description

Elasmobranchii is one of the two subclasses of cartilaginous fish in the class Chondrichthyes, the other being Holocephali (chimaeras). For features that distinguish Elasmobranchii from Holocephali, see those articles. This classification includes great white sharks and the extinct megalodon.

Members of the elasmobranchii subclass have no swim bladders, five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The eyes have a tapetum lucidum. The inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm. These fish are widely distributed in tropical and temperate waters.^[3]

References