- Related Topics:
- Gymnophiona
- salamander
- lepospondyl
- Temnospondyli
- lissamphibian
amphibian
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What is an amphibian?
Amphibians are vertebrates that can live in both aquatic and terrestrial habitats, a trait reflected in their name, which means "living a double life".
There are roughly 8,100 amphibian species, including frogs and toads (Anura), newts and salamanders (Caudata), and caecilians (Gymnophiona).
Amphibians breathe through their moist skin and depend on cutaneous respiration. While amphibian larvae use gills and tail fins for gas exchange, adult amphibians use simple saclike lungs.
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Where do amphibians live?
Amphibians are widespread, inhabiting diverse environments worldwide, even north of the Arctic Circle in Eurasia, but are absent in Antarctica, remote oceanic islands, and extremely dry deserts. Frogs and toads thrive in humid tropical environments, while salamanders are abundant in cool, moist, montane forests of the Northern Hemisphere. Caecilians are spottily distributed throughout the wet tropics of Africa, America, and Asia.
However, habitat destruction has severely impacted amphibian distribution and abundance, with populations of many frog species declining since the 1980s. Factors such as acid rain, global warming, ozone depletion, and the chytrid fungus contribute to these reductions.
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How do amphibians differ from reptiles?
Amphibians and reptiles are both cold-blooded vertebrates, but they have key differences. Amphibians, like salamanders, need moist environments and have smooth, moist skin without scales. Reptiles, on the other hand, have dry, scaly skin and can live in drier, hotter environments. Amphibian eggs lack shells and must be laid in moist places, often underwater, while reptile eggs have shells and are laid in nests, typically in sand. Reptiles were the first truly terrestrial vertebrates, having developed a skin relatively impermeable to water. Amphibians depend on aquatic respiration to a degree that varies with species.
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What is metamorphosis in amphibians?
Amphibian metamorphosis is a significant transformation from a larval stage to an adult form, involving considerable changes in physiology, biochemistry, structure, and behavior. This process is under hormonal control and often marks a shift from an aquatic to a terrestrial or semiaquatic life.
In anurans (frogs and toads), metamorphosis involves radical skeletal changes as tadpoles transition to their adult form. Limbs complete development, the tail shrinks, skin thickens, and lungs develop as gills disappear. The digestive system adapts, eyes enlarge, and eyelids appear. Thyroid hormones play a crucial role in this process, influencing various tissues differently. For instance, thyroxine causes the tail muscles to degenerate while stimulating limb development.
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Why are amphibians important for the environment?
Amphibians play a crucial role in the environment as they are an integral part of local food webs. Mosquito eggs and larvae serve as a food source for fishes, turtles, other insects, and amphibians, while flying adults are preyed upon by bats, birds, and spiders. Additionally, amphibians, especially anurans, are economically useful in reducing the number of insects that destroy crops or transmit diseases.
However, habitat destruction has severely impacted numerous amphibian species, leading to population declines. A parasitic fungus, the amphibian chytrid, is a major cause of frog die-offs in parts of Australia, Central America, North America, and Europe.
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What are some threats facing amphibians today?
Amphibians face several threats today, with human activities being the primary driver. Habitat loss and degradation from agriculture, logging, and infrastructure development endanger many species. Pollution, including chemical pollutants and endocrine disruptors, also poses a significant risk, especially to aquatic species like amphibians.
A major threat is the spread of amphibian chytridiomycosis, a fungal disease that has led to severe population declines and extinctions in frog species worldwide. Climate change also contributes to the decline, with global warming impacting sensitive groups. These factors, combined with unsustainable hunting and disease, threaten amphibian biodiversity globally.
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News •
amphibian, (class Amphibia), any member of the group of vertebrate animals characterized by their ability to exploit both aquatic and terrestrial habitats. The name amphibian, derived from the Greek amphibios meaning “living a double life,” reflects this dual life strategy—though some species are permanent land dwellers, while other species have a completely aquatic mode of existence.
Approximately 8,100 species of living amphibians are known. First appearing about 340 million years ago during the Middle Mississippian Epoch, they were one of the earliest groups to diverge from ancestral fish-tetrapod stock during the evolution of animals from strictly aquatic forms to terrestrial types. Today amphibians are represented by frogs and toads (order Anura), newts and salamanders (order Caudata), and caecilians (order Gymnophiona). These three orders of living amphibians are thought to derive from a single radiation of ancient amphibians, and although strikingly different in body form, they are probably the closest relatives to one another. As a group, the three orders make up subclass Lissamphibia. Neither the lissamphibians nor any of the extinct groups of amphibians were the ancestors of the group of tetrapods that gave rise to reptiles. Though some aspects of the biology and anatomy of the various amphibian groups might demonstrate features possessed by reptilian ancestors, amphibians are not the intermediate step in the evolution of reptiles from fishes.
Modern amphibians are united by several unique traits. They typically have a moist skin and rely heavily on cutaneous (skin-surface) respiration. They possess a double-channeled hearing system, green rods in their retinas to discriminate hues, and pedicellate (two-part) teeth. Some of these traits may have also existed in extinct groups.
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Members of the three extant orders differ markedly in their structural appearance. Frogs and toads are tailless and somewhat squat with long, powerful hind limbs modified for leaping. In contrast, caecilians are limbless, wormlike, and highly adapted for a burrowing existence. Salamanders and newts have tails and two pairs of limbs of roughly the same size; however, they are somewhat less specialized in body form than the other two orders.
Many amphibians are obligate breeders in standing water. Eggs are laid in water, and the developing larvae are essentially free-living embryos; they must find their own food, escape predators, and perform other life functions while they continue to develop. As the larvae complete their embryonic development, they adopt an adult body plan that allows them to leave aquatic habitats for terrestrial ones. Even though this metamorphosis from aquatic to terrestrial life occurs in members of all three amphibian groups, there are many variants, and some taxa bear their young alive. Indeed, the roughly 8,100 living species of amphibians display more evolutionary experiments in reproductive mode than any other vertebrate group. Some taxa have aquatic eggs and larvae, whereas others embed their eggs in the skin on the back of the female; these eggs hatch as tadpoles or miniature frogs. In other groups, the young develop within the oviduct, with the embryos feeding on the wall of the oviduct. In some species, eggs develop within the female’s stomach.
