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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.
Small spikes (enlarged versions of the dermal denticles commonly covering shark skin) covered this crest, and the ratfish's head as well. [8] The crest may have played a role in mating rituals, aided in clamping to the belly of larger marine animals, or been used to frighten potential predators.
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, the most commonly found fossil shark teeth are from the Cenozoic era (the last 66 million years).
He discovered that shark skin denticles are structured in a characteristic diamond-repeating micro-pattern with millions of small ribs [3] at the micrometer scale. His mathematical model for the texture of a substance that would deter microorganisms from settling corresponds to the width-to-height ratio of shark denticle riblets.
The dermal denticles of a lemon shark, viewed through a scanning electron microscope. Unlike bony fish, sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body. This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy. [33]
[34] [35] [36] Shark teeth are embedded in the gums rather than directly affixed to the jaw as in some fish. [37] Shark teeth form within the jaw move outward in rows until they are eventually dislodged in a manner similar to a conveyor belt. [38] Their scales, called dermal denticles, and teeth are homologous organs. [39]
As such, according to Zangerl's account, Troll reconstructs Listracanthus as resembling a tremendous, fiercely bristled frill shark. [3] However, other authors have noted that Listracanthus -like denticles have been found associated with the remains of Menaspiformes like Deltoptychius (which do not have eel-like bodies), and have suggested that ...
Keeled scales of a colubrid snake (banded water snake; Nerodia fasciata). In zoology, a scale (Ancient Greek: λεπίς, romanized: lepís; Latin: squāma) is a small rigid plate that grows out of an animal's skin to provide protection.