Section 3: Most amphibians begin life as aquatic organisms and then live on land as adults. K What I Know W What I Want to Find Out L What I Learned
Essential Questions What were the kinds of adaptations that were important as animals moved to the land? What are the characteristics of amphibians? What are the differences between the orders of amphibians?
Vocabulary Review metamorphosis New cloaca nictitating membrane tympanic membrane ectotherm
Evolution of Tetrapods The move to land Tetrapods are four-legged vertebrates that first appeared on Earth 360 million years ago. Several physical challenges in the move from water to land Differences between the environments included buoyancy, oxygen concentration, temperature, and transmission of sound/vibrations.
Evolution of Tetrapods Terrestrial habitats While there were many challenges to adapting to life on land, there were also many available habitats for animals. A diversity of biomes support animal life with the appropriate adaptations.
Characteristics of Most amphibians begin life as aquatic organisms, but live on land as adults. Modern amphibians include frogs, toads, salamanders, newts, and legless caecilians. Generally characterized by having four legs, moist skin with no scales, gas exchange through the skin, lungs, and a double-loop circulatory system.
Characteristics of Feeding and digestion Most frog larvae are herbivores, whereas salamander larvae are carnivores. As adults, their diets are similar as both groups become predators. The digestive system of an amphibian is very similar to that of a fish. The intestines end in a chamber called the cloaca, which receives wastes and reproductive cells before they leave the body.
Characteristics of Excretion filter wastes from the blood through their kidneys, and excrete either ammonia or urea as the waste product. Ammonia is excreted by amphibians that live in the water.
Characteristics of Respiration and circulation As larvae, most amphibians exchange gases through their skin and gills. As adults, most breathe through lungs, their thin, moist skin, and cavities in the mouth. have a double-loop circulatory system: oxygen-poor blood is pumped from the heart to the skin and lungs to pick up oxygen, then returned to the heart where it is pumped out to the body.
Characteristics of The brain and senses use sight to locate and capture prey that fly at high speeds and to escape predators. Frogs have nictitating membranes, clear eyelids that protect the eye. Frogs use their tympanic membrane, or eardrum, to hear high-pitched sounds and to amplify sounds from the vocal cords. are ectotherms that obtain their body heat from the external environment.
Characteristics of Reproduction and development In most amphibians, fertilization is external and the shell-less eggs must be laid and fertilized in water. Tadpoles hatch from the egg and undergo metamorphosis from a fishlike animal to an air-breathing one.
Amphibian Diversity Scientists classify modern amphibians into three orders. Order Anura includes frogs and toads. Order Caudata includes salamanders and newts. Order Gymnophiona includes caecilians.
Amphibian Diversity Frogs and toads Lack tails and have long legs, enabling them to jump Frogs have moist, smooth skin, and generally live closer to water than toads. Toads have kidney-bean-shaped glands in the back of their heads that release poison to deter predation.
Amphibian Diversity Salamanders and Newts Long, slim bodies with necks and tails. Newts are generally aquatic throughout their lives, while salamanders live on land, under logs or leaf litter.
Amphibian Diversity Caecilians Legless and wormlike, nearly blind Burrow in soil and eat worms and other invertebrates Found in the tropical forests of South America, Africa, and Asia
Evolution of Many scientists think that early tetrapods are closely related to a group of now-extinct lobe-finned fishes. Early tetrapods branched out to produce amphibians, reptiles, birds, and mammals.
Ecology of Local factors Many amphibian populations are declining. Can be due to habitat destruction, introduction of exotic species Global factors Various global factors may be causing decline as well Changes in temperature and rainfall can make amphibians more susceptible to disease.
Review Essential Questions What were the kinds of adaptations that were important as animals moved to the land? What are the characteristics of amphibians? What are the differences between the orders of amphibians? Vocabulary cloaca nictitating membrane tympanic membrane ectotherm