Shark week is almost here!! I just love those shows - the earliest known sharks date back more than 420 million years.
Wow that's really old? Have sharks changed much in that time?
Well the term shark has been used for extinct members so yes, they have changed a bit.
Interesting... Sharks really scare me ever since I saw Jaws...
I'm scared of them too - but they are also so fascinating - especially the Megalodon that lived 23 to 2.6 million years ago.
Wow that's along time ago... is that the largest kind of shark? Hence the mega?
), the largest fish in the world, which reaches approximately in length. Sharks are found in all seas and are common to depths of . They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can be found in both seawater and freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.
Well-known species such
eugenedontidans.
Under this broader definition, the earliest known sharks date back to more than 420 million years ago. Acanthodians are often referred to as "spiny sharks"; though they are not part of Chondrichthyes proper, they are a paraphyletic assemblage leading to cartilaginous fish as a whole. Since then, sharks have diversified into over 500 species. They range in size from the small dwarf lanternshark ("Etmopterus perryi"), a deep sea species of only in length, to the whale shark ("Rhincodon typus"