Crossword clues for tetrapod
The Collaborative International Dictionary
Tetrapod \Tet"ra*pod\, n. [Gr. ? fourfooted; te`tra- (see Tetra-) + ?, ?, foot.] (Zo["o]l.) An insect characterized by having but four perfect legs, as certain of the butterflies.
Douglas Harper's Etymology Dictionary
a. Having four limbs or feet n. 1 Any vertebrate with four limbs. 2 Any vertebrate (such as birds or snakes) that have evolved from early tetrapods; especially all members of the superclass ''Tetrapoda'' 3 Concrete structures with 'arms' used to arrest wave energy along the shore in sea defence projects.
n. a vertebrate animal having four feet or legs or leglike appendages
The superclass Tetrapoda ( Ancient Greek τετραπόδηs tetrapodēs, "four-footed"), or the tetrapods , comprises the first four-limbed vertebrates and their descendants, including the living and extinct amphibians, birds, mammals, reptiles and some ancient, exclusively aquatic creatures such as the Acanthostega. Tetrapods evolved from the lobe-finned fishes around 390 million years ago in the middle Devonian Period, with modern tetrapod groups having appeared by the late Devonian, 367.5 million years ago. The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear, and are areas of active research and debate among palaeontologists at present.
While most species today are terrestrial, the first tetrapods were fully aquatic. Amphibians today generally remain semiaquatic, living the first stage of their lives as fish-like tadpoles. Amniotes evolved about 340 million years ago (crown amniotes 318 mya), and their descendants drove most amphibians to extinction. One population of amniotes diverged into lizards, dinosaurs, birds and their relatives, while another diverged into mammals and their extinct relatives. Several groups of tetrapods, such as the caecilians, snakes, cetaceans, sirenians, and moas have lost some or all of their limbs. In addition, many tetrapods have returned to partially aquatic or fully aquatic lives throughout the history of the group (modern examples of fully aquatic tetrapods include cetaceans and sirenians). The first returns to an aquatic lifestyle may have occurred as early as the Carboniferous Period, whereas other returns occurred as recently as the Cenozoic, as in cetaceans, pinnipeds, and several modern amphibians.
The change from a body plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known. It is also becoming increasingly well-understood as a result of more transitional fossil finds and improved phylogenetic analysis.
In coastal engineering, a tetrapod is a tetrahedral concrete structure used as armour unit on breakwaters. A tetrapod's shape is designed to dissipate the force of incoming waves by allowing water to flow around rather than against it, and to reduce displacement by allowing a random distribution of tetrapods to interlock.
Earlier barrier material used in breakwaters, such as boulders and conventional concrete blocks, tended to become dislodged over time by the force of the ocean constantly crashing against them. Tetrapods and similar structures are often numbered so any displacement that occurs can be monitored from photographs.
The unit was originally developed in 1950 by Laboratoire Dauphinois d'Hydraulique (now ARTELIA) in Grenoble, France. They are no longer protected by a patent, and are widely used all over the world, produced by many contractors.
The tetrapod inspired many similar concrete structures for use in breakwaters, including the Modified Cube (U.S., 1959), the Stabit (U.K., 1961), the Akmon (Netherlands, 1962), the Dolos (South Africa, 1963), the Stabilopod (Romania, 1969), the Seabee (Australia, 1978), the Accropode (France, 1981), the Hollow Cube (Germany, 1991), the A-jack (U.S., 1998), and the Xbloc (Netherlands, 2001), among others. In Japan, the word tetrapod is often used as a generic name for wave-dissipating blocks including other types and shapes.
Tetrapods and concrete have become a Japanese institution in modern times. Their manufacture and dispersal create jobs for Japanese citizens and contracts for construction companies. It is estimated that nearly 50 percent of Japan's 35,000 kilometer coastline has been covered or somehow altered by Tetrapods and other forms of concrete. Because of the proliferation of Tetrapods, tourists to the Hawaii-like island of Okinawa often find it difficult to find pristine beaches and unaltered shoreline, especially in the southern half of the island.
Usage examples of "tetrapod".
All the new animals were built on the ancient tetrapod body plan, inherited from the first wheezing fish to have crawled out of the mud.
When the wind was right, she could hear large amphibians roaring on the banks of rivers, and the little tetrapods peeped or trilled in their courting seasons, but most of the noise here came from wind, water, and foliage.
In particular they sought lobe-finned fish of the type that presumably were ancestral to us and all other walking creatures, known as tetrapods.
Dr Narlikar neared the place where, with the Municipal Corporation's permission, he had arranged for a single, symbolic tetrapod to be placed upon the sea‑.
Why, little by little, did the vision of full‑sized concrete tetrapods marching over sea walk, four‑legged conquerors triumphing over the sea, capture him as surely as it had the gleaming doctor?
I tell you, my friend: you and I and our tetrapods: from the very oceans we shall bring forth soil!
Dinosaurs, whales, birds, humans, even fish—all are tetrapods, which clearly suggests they come from a single common ancestor.
Ninomiya is on a bluff in the middle of a town, and the beach below it is a narrow strip of sand chockablock with giant concrete tetrapods, looking like vastly magnified skeletons of plankton and intended to keep waves from washing up onto the busy coastal highway that runs between the beach and the station.