Type of animal science: Classification
Fields of study: Anatomy, evolutionary science, physiology, systematics (taxonomy), zoology
Amphibians are cold-blooded animals with backbones. From an evolutionary standpoint, they link aquatic fish with terrestrial reptiles. Living forms include frogs and toads, salamanders, and caecilians.
The term "amphibian" is derived from the Greek word amphibios, which means "to live two lives." The majority of amphibians do this by spending the first part of their lives as aquatic, gill-breathing larvae and then transforming into terrestrial adults. The larval stage can be as short as a few weeks or as long as several years. Completion of the larval stage is triggered by hormonal events that initiate some dramatic developmental processes that are collectively termed metamorphosis. As adults, most amphibians seek out aquatic environments in which to deposit their eggs. These can range from fast-flowing mountain streams to ephemeral roadside ditches. Most male frogs have species-specific mating calls that serve both to attract females and to prevent interbreeding. Frogs have external fertilization, in which the male typically grasps the female and encourages her to deposit her eggs, which he promptly fertilizes. Normally, both parents abandon the eggs, but some variations of this pattern exist. In contrast, most salamanders have internal fertilization, accomplished after the male has performed a stereotypical species-specific courtship "dance," which culminates with the deposition of a packet of sperm cells that is called a spermatophore. The female squats on the spermatophore, transferring the spermatozoa to a specialized holding structure called a spermatheca. The spermatozoa can be used to fertilize her eggs up to several months after mating.
Adaptive radiation: rapid speciation that
occurs as the result of a particular group
being able to exploit a new resource
Convergence: a state that occurs when two forms that are not closely related evolve structures that appear similar
Disjunct: pertaining to the geographic distribution pattern in which two closely related groups are widely separated by areas that are devoid of either group
Metamorphosis: the complex developmental process of morphological change in which larval amphibians are transformed into adults
Neoteny: the retention of larval features by adults; this process has played a major role in the evolution of the amphibians
Phylogeny: the determination of the evolutionary history of a particular group of organisms
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