Lust - a steam room, as a rule, a flat limb adapted for the movement of an animal in water and characteristic (as opposed to fish fins ) for secondary water (i.e., originating from land ancestors, whose ancestors, in turn, once also lived in water) vertebrates animals .
Content
Anatomy and origin
up to six phalanges.
Flippers are flat, skinned, more or less wide blades , webbed or not.
Outwardly, they are similar to the paired fins of fish, but the skeleton structure indicates the origin of land animals from the extremities. All elements of the skeleton are flattened and are in the same plane [1] . The bones of the proximal parts (shoulder and thigh, forearm and lower leg) are enlarged and shortened, and the bones of the distal part (hand and foot), on the contrary, are elongated [2] . For flippers, hyperphalangism is characteristic (an increased number of phalanges in each finger), hyperdactyly (an increased number of fingers) is also found (in particular, in ichthyosaurs) [3]
Fins of flippers, as a rule, lack claws [1] . The exceptions are pinnipeds; some species of manatees also have nails on flippers.
Despite external similarity, flippers in different groups of animals developed independently [3] and are an example of convergent evolution [1] .
Owners
Flippers are found in a variety of animals, both living and extinct.
Among modern animals, flippers are penguins , cetaceans , pinnipeds ( eared and real seals , as well as walruses ), sea turtles and sirens . Among the extinct holders of flippers can be noted various groups of reptiles - for example, plesiosaurs , mosasaurs , ichthyosaurs , placodons and metriorinchs .
In sea turtles, pinnipeds, placodons, plesiosaurs and metriorinhs, there are two pairs of flippers. In modern cetaceans, sirens and penguins, a pair of flippers is the same - the front one.
Functions
In some animals, flippers are the main organ of translational motion . As a rule, this applies to animals that, at least occasionally, go to dry land — for example, sea turtles or pinnipeds. Lastov at the same time usually four.
In other animals with flippers, a powerful tail serves primarily for movement. In such cases, the flippers usually perform the function of motion control — they play the role of rudders of depth and rotation. In this case, the back pair of flippers is often lost, and only the front pair is retained. Such a structure is more characteristic of animals that have completely lost the ability to land, such as cetaceans, sirens [3] . However, the extinct ancestors of those and others standing more close to their terrestrial predecessors had four limbs used for swimming at certain stages [1] [4] .
In some cases, flippers have a streamlined shape and are very effective hydrofoils, functionally similar to conventional “air” wings. Sometimes the shape of the flippers is less streamlined, and irregularities may remain on them; An example is the semi-aquatic turtle flippers.
Notes
- ↑ 1 2 3 4 Great Soviet Encyclopedia. - Moscow: Soviet Encyclopedia.
- ↑ Biology. Modern illustrated encyclopedia / Ch. ed. A. P. Gorkin. - Moscow: Rosmen, 2006.
- ↑ 1 2 3 Biological encyclopedic dictionary / Ch. ed. M.S. Gilyarov. - 2nd ed., Corrected .. - Moscow: Soviet Encyclopedia, 1986.
- ↑ The first whales with legs determined the style of swimming of all whales (September 16, 2008). The appeal date is November 29, 2012.