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Modern Amphibians Part one Chapter 40 Amphibians • Origin and Evolution • Characteristics • Reproduction Adaptation to Land • Preadaptations - are adaptations in an ancestral group that allow a shift to new functions which are later favored by natural selection. Adaptation to Land Lobe-finned fishes had several preadaptations that allowed them to transition to life on land. • bone structure • pouches in digestive tracts for gas exchange • nostrils • higher metabolism • efficient hearts Adaptation to Land Characteristics of Early Amphibians Amphibians and lobe-finned fishes share many anatomical similarities, including: • similar skull • similar vertebral column • similar bone structure in fins and limbs • early amphibians had a large tail fin and lateral line canals Adaptation to Land Diversification of Amphibians • About 300 million years ago amphibians split into two main evolutionary lines. • One line included ancestors of reptiles, the other line included the ancestors of modern amphibians. Adaptation to Land Diversification of Amphibians Today there are about 4,500 species of amphibians belonging to three orders: • Anura - includes frogs and toads • Caudata - includes salamanders and newts • Gymnophiona - includes caecilians (legless tropical amphibians) Anura - includes frogs and toads Caudata - includes salamanders and newts Spotted Salamander Fire Bellied Newt Gymnophiona - includes caecilians (legless tropical amphibians) Modern Amphibians Modern amphibians share several key characteristics • Most change from an aquatic larval stage to a terrestrial adult form, in a transformation called metamorphosis. • Most have moist, thin skin with no scales. Modern Amphibians • Feet, if present, lack claws and often are webbed. • Most use gills, lungs, and skin in respiration. • Eggs lack multicellular membranes or shells, are usually laid in water, and are usually fertilized externally. Modern Amphibians Order Anura • Order includes frogs and toads. • Members may be fully aquatic, fully terrestrial, or amphibious American Toad Modern Amphibians: Order Anura • Most reproduce in water, laying eggs that hatch into swimming larvae called tadpoles. • Larvae are herbivores. Adults are carnivorous and will eat any animal they can capture. Modern Amphibians: Order Caudata • Includes salamanders (may also be called newts). • Members may be fully aquatic, fully terrestrial, or amphibious. • Many reproduce in water. Some reproduce on land, with no swimming larval stage. Modern Amphibians: Order Caudata • Larvae and adults are carnivorous. • Some have no lungs, and respire through their skin only. Modern Amphibians: Order Gymnophiona • Includes caecilians (legless amphibians that resemble small snakes). • Most are burrowing. They have small eyes beneath skin or bone, and are often blind. Modern Amphibians: Order Gymnophiona • All are carnivorous. • All are thought to have internal fertilization. • Some lay eggs which the female guards, others develop inside the female. Phylogenetic Diagram of Amphibians