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Unlike traditional scales, sharks have placid scales, known as denticles. Denticles are V-shaped and are made of layers of dentine and a surface of enamel. [24] Riblets are sockets in the shark's skin which hold the denticles. [22] These denticles on the skin allow for the shark to move quietly, swiftly, and almost effortlessly.
Shark skeletons are very different from those of bony fish and terrestrial vertebrates. Sharks and other cartilaginous fish (skates and rays) have skeletons made of cartilage and connective tissue. Cartilage is flexible and durable, yet is about half the normal density of bone. This reduces the skeleton's weight, saving energy. [29]
A shark tooth contains resistant calcium phosphate materials. [7] The most ancient types of shark-like fish date back to 450 million years ago, during the Late Ordovician period, and are mostly known by their fossilized teeth and dermal denticles. [5]
However, sharks continuously produce new teeth throughout their lives [3] [4] [5] via a drastically different mechanism. Shark teeth form from modified scales near the tongue and move outward on the jaw in rows until they are eventually dislodged. [6] Their scales, called dermal denticles, and teeth are homologous organs. [7]
The bonnethead (Sphyrna tiburo), also called a bonnet shark or shovelhead, [3] is a small member of the hammerhead shark genus Sphyrna, and part of the family Sphyrnidae.It is an abundant species in the littoral zone of the North Atlantic and the Gulf of Mexico, is the only shark species known to display sexual dimorphism in the morphology of the head, and is the only shark species known to be ...
The bodies of the eugeneodontids were entirely coated in shark-like dermal denticles, to enough of an extent that it obscures the anatomy of the underlying skeleton. [6] These denticles consisted of two morphologies; single, leaf-shaped scales called lepidomoria, and compound scales with multiple crowns termed polydontode scales.
The frilled shark eats a diet of cephalopods, Nudibranchs, smaller sharks, and bony fish; [2] 60 percent of the diet is composed of squid varieties, such as the Chiroteuthis, the Histioteuthis, and the Onychoteuthis, the Sthenoteuthis and the Todarodes; [17] and other sharks, as indicated by the stomach contents of a 1.6 m (5.2 ft)–long ...
Physical characteristics of sharks – shark skeleton, respiration and skin Dermal denticle – small outgrowths which cover the skin of sharks; Ampullae of Lorenzini – sensing organ that helps sharks and fish to sense electric fields; Electroreception – the biological ability to perceive electrical impulses (see also Ampullae of Lorenzini)