Search results
Results from the WOW.Com Content Network
The first shark-like chondrichthyans appeared in the oceans 400 million years ago, [1] developing into the crown group of sharks by the Early Jurassic. [2] Listed below are extant species of shark. Sharks are spread across 512 described and 23 undescribed species in eight orders. The families and genera within the orders are listed in ...
A great white shark at Isla Guadalupe, Mexico. The following outline is provided as an overview of and topical guide to sharks: Sharks (superorder Selachimorpha) are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 440 million years ago, before the time of the dinosaurs.
The use of sight probably varies with species and water conditions. The shark's field of vision can swap between monocular and stereoscopic at any time. [58] A micro-spectrophotometry study of 17 species of sharks found 10 had only rod photoreceptors and no cone cells in their retinas giving them good night vision while making them colorblind.
The blacktip reef shark is a species of requiem shark, family Carcharhinidae, easily identified by the prominent black tips on its fins. It is among the most abundant sharks inhabiting the tropical coral reefs of the Indian and Pacific Oceans, and prefers shallow, inshore waters. More selected pictures.
This species favors clear reef environments around oceanic islands, where it is often the most abundant shark species. A large species that grows to 3.7 m (12 ft), the Galapagos reef shark has a typical fusiform "reef shark" shape and is very difficult to distinguish from the dusky shark (C. obscurus) and the grey reef shark (C. amblyrhynchos).
Squaliformes. The Squaliformes / ˌskwɒlɪˈfɔːrmiːz / are an order of sharks that includes about 126 species in seven families. Members of the order have two dorsal fins, which usually possess spines, they usually have a sharp head, no anal fin or nictitating membrane, and five to seven gill slits. In most other respects, however, they are ...
The whale shark, the world's largest fish, is classified as Endangered. Binding legislation and harvest management strategies... are urgently needed to address the disproportionate impact of fisheries on cartilaginous fishes. – IUCN global study 2010 Threatened sharks are those vulnerable to endangerment (extinction) in the near future. The International Union for Conservation of Nature ...
Carcharhiniformes / kɑːrkəˈraɪnɪfɔːrmiːz /, the Requiem sharks, are the largest order of sharks, with over 270 species. They include a number of common types, such as catsharks, swellsharks, and requiem sharks. Members of this order are characterized by the presence of a nictitating membrane over the eye, two dorsal fins, an anal fin ...