Brief Summary: The Evolution Of Sharks

“The shark is the apex predator in the sea. Sharks have moulded evolution for 450 million years. All fish species that are prey to the sharks have had their behaviour, their speed, their camouflage, their defense mechanisms moulded by the shark.” – Paul Watson. Sharks are cartilaginous fish with pair fins and nares, two chambered hearts and jaws. These characteristics are unique to the class, chondrichthyes. Ray, skates, and chimaeras are members of this class and sharks closest relatives.

Shark fossil aren’t like dinosaur fossils, because sharks skeletons are made of cartilage (a connective tissue) they don’t fossilize well at all. However shark teeth and scales (called dermal denticles) do fossilize well and those fossils teach us up the
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The cladoselache was a 4-foot long shark with a mouth on the front of its head. Most prehistoric sharks mouths’ were in the same location but modern sharks have mouths at the bottom of their heads. Sharks today have dermal denticles that the cladoselache lacked. Dermal denticles provide protection and that is why over time sharks have developed them. Male sharks today have claspers that are used to mate with females; the cladoselache lacked those too. Ctenacanths are another type of shark that were around at about the same time as the cladoselache. Ctenacanths continued development for over a million years. These sharks are identified by their fin spines that are long and cylindrical with comb like ridges. The oceans after the mass extinctions had less fish and lots of open ecological niches. The stethacanthus evolved from these conditions. This shark lived in warm shallow seas and was 2 feet in length. The males had flat topped dorsal fins and enlarged scale on the top of their heads either for courtship purposes or offering protection. In the Carboniferous period many sharks underwent a very large adaptive radiation, which created the golden age of sharks approximately 250 million years

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