In some species of salamanders, hindlimbs are reduced or absent, but all caecilians are secondarily limbless. An important characteristic of extant amphibians is a moist, permeable skin that is achieved via mucus glands. Most water is taken in across the skin rather than by drinking.
The skin is also one of three respiratory surfaces used by amphibians. The other two are the lungs and the buccal mouth cavity. Air is taken first into the mouth through the nostrils, and then pushed by positive pressure into the lungs by elevating the throat and closing the nostrils.
All extant adult amphibians are carnivorous, and some terrestrial amphibians have a sticky tongue used to capture prey. Amphibians also have multiple small teeth at the edge of the jaws. In salamanders and caecilians, teeth are present in both jaws, sometimes in multiple rows.
In frogs and toads, teeth are seen only in the upper jaw. Additional teeth, called vomerine teeth , may be found in the roof of the mouth. Amphibian teeth are pedicellate , which means that the root and crown are calcified, separated by a zone of noncalcified tissue. Amphibians have image-forming eyes and color vision. Ears are best developed in frogs and toads, which vocalize to communicate.
Frogs use separate regions of the inner ear for detecting higher and lower sounds: the papilla amphibiorum , which is sensitive to frequencies below 10, hertz and unique to amphibians, and the papilla basilaris , which is sensitive to higher frequencies, including mating calls, transmitted from the eardrum through the stapes bone. The only male amphibians that possess copulatory structures are the caecilians, so fertilization among salamanders typically involves an elaborate and often prolonged courtship.
Such a courtship allows the successful transfer of sperm from male to female via a spermatophore. Development in many of the most highly-evolved salamanders, which are fully terrestrial, occurs during a prolonged egg stage, with the eggs guarded by the mother. During this time, the gilled larval stage is found only within the egg capsule, with the gills being resorbed, and metamorphosis being completed, before hatching.
Hatchlings resemble tiny adults. Frogs : The Australian green tree frog is a nocturnal predator that lives in the canopies of trees near a water source. Frogs are amphibians that belong to the order Anura.
Anurans are among the most diverse groups of vertebrates, with approximately 5, species occurring on all of the continents except Antarctica. Anurans have a body plan that is more specialized for movement. Adult frogs use their hind limbs to jump on land. Frogs have a number of modifications that allow them to avoid predators, including skin that acts as camouflage.
Many species of frogs and salamanders also release defensive chemicals that are poisonous to predators from glands in the skin. Frog metamorphosis : A juvenile frog metamorphoses into a frog. Here, the frog has started to develop limbs, but its tadpole tail is still evident. Frog eggs are fertilized externally.
As with other amphibians, frogs generally lay their eggs in moist environments. This is required as eggs lack a shell and will dehydrate quickly in dry environments. Frogs demonstrate a great diversity of parental behaviors: some species lay many eggs and exhibit little parental care; other species carry eggs and tadpoles on their hind legs or backs. The life cycle of frogs, as with other amphibians, consists of two distinct stages: 1 the larval stage followed by 2 metamorphosis to an adult stage.
The larval stage of a frog, the tadpole, is often a filter-feeding herbivore. The birds Class Aves are tetrapods in which the two front limbs are wings Fig. The mammals Class Mammalia are warm-blooded and possess hair, among other characteristics Fig. It should be noted that scientists now consider birds to be a type of reptile Fig.
Even though all tetrapods share a common ancestry, there is great diversity in their morphology and physiology, thus the study of tetrapods has been divided into several disciplines. The study of amphibians and reptiles is known as herpetology. The study of birds is called ornithology. The study of mammals is known as mammalogy.
Organisms within the subphylum Vertebrata, which includes the tetrapods, are an amazingly diverse group, currently living in almost every habitat on Earth. Vertebrates possess an internal skeleton, or endoskeleton, with a backbone made of vertebrae and cartilage. Within the subphylum Vertebrata there are seven classes of organisms and approximately 52, species Fig. However, prior to million years ago, the only vertebrates that existed were the fishes, including the jawless fish Class Agnatha , the sharks and rays Class Chondrichthyes , and the bony fishes Class Osteichthyes.
Ancient fishes were a very diverse group, but they had been constrained to marine habitats. At that time plants, molluscs, and arthropods dominated terrestrial habitats, though they were primarily centered on coastlines and areas with an abundance of water. Around to million years ago, a significant evolutionary step took place that initiated a radiation of species into terrestrial habitats. The fins of some lobe-finned fishes evolved into the limbs of tetrapods. Figure 5.
Adaptive radiation is a process in which organisms diversify rapidly into many new forms. Adaptive radiations particularly occur when new environmental resources arise, providing new habitats and food sources. When tetrapods first evolved, the land represented a new environment with an abundance of plant and insect food resources that were not being exploited by the relatively large land animals. However, life on land presented a number of challenges for aquatic organisms.
Air is much less dense than water, so organisms that live on land had to develop structural systems to support their weight and allow for movement. For example, the evolution of jointed limbs allowed tetrapods to walk by transmitting muscle energy against their endo-skeleton to the ground. Another challenge on land is the threat of desiccation, or drying out, from water loss. Land-based organisms developed much thicker skin compared with fish as a way to prevent water loss.
Other sensory organs also had to work in air rather than water. The lateral line and electric organs of bony fish no longer worked, so ears, nasal passages, and focusing eyes developed. A common misconception is that lungs developed in early tetrapods. However, lungs that were used for respiration had already developed in some bony fishes from their swim bladders.
The lungfish Fig. Tetrapods did develop pumping mechanisms to bring air in and out of the body cavity. Tetrapods evolved from fish ancestors and diversified on dry land or in freshwater habitats. Some of these terrestrial reptiles including birds and mammals then independently evolved adaptations that allowed them to survive in ocean conditions. There are no extant marine amphibians.
Examples of marine tetrapods include sea turtles, shorebirds, penguins, whales, and seals. Most marine tetrapods retain some connection to dry land.
Sea turtles and penguins must return to shore to build nests and lay eggs just as their non-marine ancestors did. All marine tetrapods have to surface for air to breathe. Amphibians are a group of tetrapod vertebrate animals with moist, scaleless skin, all sharing a common evolutionary ancestry.
Examples of amphibians include frogs, toads, salamanders, and newts Fig. Amphibians are a diverse group of animals that includes almost 7, species and that are adapted to live in a wide variety of environments. All amphibians are aquatic animals to some degree. Most amphibian species live in freshwater or moist terrestrial environments but not marine environments.
Although there are no marine amphibians alive today, some species of frogs can tolerant brackish water. Some species, like desert toads, have adapted to arid conditions but still require aquatic habitats to breed. Amphibians were the earliest tetrapods to evolve. Modern amphibians can be classified into three major groups: legless caecilians, salamanders, and frogs. Measure ad performance. Select basic ads. Create a personalised ads profile.
Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products. List of Partners vendors. Share Flipboard Email. Bob Strauss. Science Writer. Updated August 15, Featured Video. Cite this Article Format. Strauss, Bob. Prehistoric Amphibian Pictures and Profiles. Learn About the Different Dinosaur Periods.
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