Although sharks are generally identified as large predators, many species are in fact quite small. With more than 500 species of sharks in existence, a considerable range in sizes exists. The two largest fishes in the world are the plankton eating sharks – the whale shark (over 12 metres) is commonly found in warm tropical waters and the basking shark in cold temperate waters, including off Atlantic Canada. The largest predatory fish is the white shark, which can reach upwards of seven metres. Fossil remains of the megalodon, an extinct prehistoric shark, indicate that it may have been the largest shark in history, with a maximum length of 15 metres. The title of smallest shark is shared between the pygmy shark, the pygmy ribbontail cat shark, the dwarf lantern shark, and the Caribbean lantern shark. All four of these species are less than 20 cm in length.
Each species of shark has a unique colouration that it has adopted to best suit its natural environment. Although each species' colouration is unique, certain commonalities exist. Sharks' bodies are almost always dark on the dorsal or top side (e.g. gray, brown, dark green or blue) and white on the ventral or underside of the shark. This colour pattern makes sharks less visible to prey and predators from above and below.
Mouth and Teeth
The shark's main tool for defense, attack, feeding and even mating is the mouth and teeth. Mouth size, tooth shape and jaw morphology for each shark have adapted to the prey that is available.
In almost all sharks, the mouth is ventral (belly side) and pointing down. Only rarely are sharks' mouths located at the front, pointing forward (as in the whale shark). Jaw size varies considerably from species to species with some having spectacularly wide jaws, such as the basking shark (upper photo).
Shark teeth are modified and enlarged dermal denticles (see morphology). The teeth are arranged in rows, though only one or two rows are functional at a time. The rows slowly move forward like a conveyor belt system as the shark ages. Therefore, as shark teeth wear and fall out or break off, a new row moves forward to replace the damaged or absent teeth. This replacement happens every few weeks or months depending on the species. Shark teeth are also unique to each species, as they have evolved to be efficient at cutting, seizing or crushing prey.