SUPER CLASS PISCES
are a primitive and highly successful group of fish with a
skeleton consisting entirely of cartilage, and having open
gill slits. Most are marine predators, with well developed
teeth. Some species are protected by hard scales on
Chondrichthyes, retaining over 950 different species, is composed
of two sub classes, Elasmobranchii (sharks, rays and skates)
and Holocephali (the chimeras, such as rat fish and elephant
Order Selachii (sharks) first appeared in the Silurian Geological
period somewhere between 430 and 395 million years ago.
During the Devonian geological period 395 to 345 million years
ago they expanded rapidly and probably became
the dominant predator in the sea.
box for more information on geological time.
do not know the exact number of species or genera that have
existed, because of the incomplete nature of their preservation.
Many times the assignment of a genera or species was biased
on isolated teeth or scales, and as new specimens become available
their classifications are periodically being reassigned.
box for links to other sites about sharks.