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Sharks are the great scavengers of our oceans and as a species predate dinosaurs where the oldest fossils are believed 400 million years old, perhaps more. They are predators belonging to the class of Chondrichthyes'; that is: species having a skeleton comprising of cartilage. An amazing 370 different shark species exist today in tropical, temperate and cold-water regions of the world yet the majority are harmless to humans.

Sharks are vertebrates yet not much is known about species older than 150 million years because cartilage does not preserve well. This means a great deal of information is speculative at best. Most records are derived from teeth though which individual groups can be catalogued in a chronological order of evolution.

The first primitive fish began to appear in oceans between 500 450 million years ago but it was not until the early Palaeozoic era of 400 350 million years ago that oceans and seas began to fill with new species. Two main groupings were bony fish within which other subgroups derived, and the cartilaginous that evolved into what we know today as sharks, rays, chimaeras and skates. The earliest shark species discovered from fossilised remains was the Cladoselache with two dorsal fins and broad pectoral fins. Eyes were forward on their head with the mouth being towards the front of the head differing from the underslung and jawed mouth that characterizes sharks as we know them today.

New species began to appear from 350million to 300 million years ago where the main distinguishing features were an amazing array of teeth patterns as well as changes to dorsal and pectoral fins. Many of the fossilised remains discovered exhibited unusual extensions and appendages for which only speculation describes their form and purpose. By the Cretaceous ear most of the shark species we would recognise today were in existence but sharks were not the most dangerous predator the ichthyosaurs and plesiosaurs ruled the oceans and seas until approximately 60 million years ago when some form of catastrophe changed the world forever. Dinosaurs were decimated and the effect was not restricted to land however sharks survived to become the oceans most feared predators.

Around 50 million years ago one species continued to grow and evolved into the most feared predator of the seas. Fossilised remains of the megalodon boasted an unprecedented size and with teeth over six inches from base to tip. The overall size was estimated at somewhere between 50 to 100 feet with the overall shape resembling our great whites. Fortunately this species is thought to have become extinct approximately 30 25 million years ago!

Sharks today are an important part of the sea environment with the role as predator and scavengers, in other words: janitors' of the ocean. Attacks on humans occur but are generally a rare event. It is the terror and savagery of those attacks that do occur which perhaps lead to the misconception that incidence is far greater. Interestingly records reveal that death caused by bee sting is twice that of shark attack. We fear what cannot be seen and of course we are in a three dimensional environment from which the unseen monster lurks.

Sharks have been in our oceans and seas from the earliest period of life evolving on earth. Changes through evolution spanning 400 million years resulted in related species yet the true shark has remained a constant throughout time and it is likely they will survive humans as a species millions of years into the future.

Learn more about this author, Ian Loft.
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