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Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the division Selachii [1] (or Selachimorpha) [2] and are the sister group to the Batoidea (rays and kin).
[9] [10] [11] Whale sharks have very large mouths and are filter feeders, which is a feeding mode that occurs in only two other sharks, the megamouth shark and the basking shark. They feed almost exclusively on plankton and small fishes, and do not pose any threat to humans.
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 556 described and 23 undescribed species in eight orders. The families and genera within the orders are listed in ...
Having the ability to keep their warmth helps them as predators as well. Another group of sharks, known as the mackerel sharks are able to warm their blood. These mackerel sharks retain their blood by using a heat exchange system called rete mirabile. The body temperature of mackerel sharks can be up to 10 o higher than the surrounding water. [10]
For instance, descendants of the first reptiles include modern reptiles, mammals and birds; the agnathans have given rise to the jawed vertebrates; the bony fishes have given rise to the land vertebrates; a group of amphibians, the labyrinthodonts, have given rise to the reptiles (traditionally including the mammal-like synapsids), which in ...
Batomorphs are flat-bodied, and, like sharks, are cartilaginous fish, meaning they have a boneless skeleton made of a tough, elastic cartilage. Most batomorphs have five ventral slot-like body openings called gill slits that lead from the gills , but the Hexatrygonidae have six. [ 4 ]
Why do sharks attack humans? According to the Shark Research Institute, there are over 400 plus species of shark around the world, which include great white sharks, tiger sharks and bull sharks.
Greenland sharks have also been found with remains of moose, polar bear, horse, and reindeer (in one case an entire reindeer body) in their stomachs. [13] [26] [22] The Greenland shark is known to be a scavenger and is attracted by the smell of rotting meat in the water. The sharks have frequently been observed gathering around fishing boats. [13]