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A dragonfly in its final moult, undergoing metamorphosis, it begins transforming from its nymph form to an adult. Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. [1]
Amphibians are ectothermic, anamniotic, four-limbed vertebrate animals that constitute the class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all tetrapods excluding the amniotes (tetrapods with an amniotic membrane , such as modern reptiles , birds and mammals ).
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. [1] Tetrapods (under the apomorphy-based definition used on this page) are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals.
Modern amphibians, which evolved from earlier groups, are generally semiaquatic; the first stages of their lives are as waterborne eggs and fish-like larvae known as tadpoles, and later undergo metamorphosis to grow limbs and become partly terrestrial and partly aquatic.
The life cycle is completed when they metamorphose into adults. A few species deposit eggs on land or bypass the tadpole stage. A few species deposit eggs on land or bypass the tadpole stage. Adult frogs generally have a carnivorous diet consisting of small invertebrates , but omnivorous species exist and a few feed on plant matter.
Semiaquatic animals include: Vertebrates. Amphibious fish; also several types of normally fully aquatic fish such as the grunion and plainfin midshipman that spawn in the intertidal zone; Some amphibians such as newts and salamanders, and some frogs such as fire-bellied toads and wood frogs.
While the early amniotes resembled their amphibian ancestors in many respects, a key difference was the lack of an otic notch at the back margin of the skull roof. In their ancestors, this notch held a spiracle, an unnecessary structure in an animal without an aquatic larval stage. [25]
The best known representatives of taxa that exhibit some kind of the ontogenetic niche shift are fish (e.g. migration of so-called diadromous fish between saltwater and freshwater for purpose of breeding [2]), insects (e.g. metamorphosis between different life stages; such as larva, pupa and imago [2]) and amphibians (e.g. metamorphosis from ...