Amphibians

1. Amphibians Presenters Kencho Galey SamdrupRinzin TsheringPhuntsho

2. Amphibians are a group of animals that include modern-day frogs and toads, caecilians, and newts and salamanders. These animals' ancestors were the first to venture out from the water and adapt to life on land. Amphibian larvea are often aquatic and go through a complex metamorphosis process as they grow to adulthood. They have moist skin and do not have scales, feathers or hair. • The life cycles of amphibians reflects their evolutionary history of bridging land and water. Most amphibians lay their eggs in freshwater. A few species tolerate brackish water and some species lay their eggs on land. Extraordinarily, some species even carry their eggs inside their body. Although life cycles of amphibians vary from species to species, they all share the following three basic stages of development: egg, larva, adult.

3. Amphibian eggs do not have a hardened shells which means amphibians are not amniotes like reptiles, birds, and mammals. Instead, amphibian eggs consist of a gelatinous envelope that must remain moist to survive. Eggs hatch to release tiny larvae which later undergo a metamorphosis into the adult form. • Many amphibians can absorb oxygen directly into their bloodstream through their skin and are also able to expell carbon dioxide waste back into the air. The skin of amphibians lacks scales and hair. It is smooth and sometimes moist, making it quite permeable to gases and water. • This permeability is thought to make amphibians particularly vulnerable to toxins in air and water such as herbicides, pesticides, and pollutants. Amphibians have been sharp decline throughout many areas worldwide. This is thought to be an early warning sign of a troubled environment.

4. Amphibians are divided into three groups which include newts and salamanders, frogs and toads, and caecilians. • Newts and salamanders are slender-bodied amphibians that have a long tail and four legs. Newts spend most of their life on land and return to water to breed. Salamanders, in contrast, spend their entire lives in water. • Frogs and toads belong to the largest of the three groups of amphibians. Adult frogs and toads have four legs but do not have tails. • Caecilians are the least-known group of amphibians. Caecilians have no limbs and only a very short tail. They have a superficial resemblance to snakes, worms, or eels but are not closely related to any of these animals.

5. General characterstics The living amphibians have very different body forms but the members of the various orders share the following characteristics: • A bone endoskeleton with varying numbers of vertebrae; ribs present in some, absent or fused to vertebrae in others. None possess an exoskeleton and the notochord (a rod of tissue) does not persist in adults. • A smooth, thin, porous skin containing both mucus glands and poison glands. • Four limbs (tetrapod) which may vary in size with the forelimbs of some being much smaller than the hindlimbs; some are legless. Limbs have varying numbers of digits and webbed feet are often present; no true nails or claws. • The mouth is usually large with small teeth in upper or both jaws; two nostrils open into the anterior part of the mouth cavity.

6. Respiration is accomplished either separately or in combination by lungs, skin, and gills; some larval types possess external gills and these may persist throughout life. • A three-chambered heart consisting of two atria and one ventricle. • Body temperature regulation is ectothermic (cold-blooded) in nature. That is, the body is heated from without rather than from within (endothermic). • Separate sexes (dioecious) with internal fertilization via spermatophore (a sperm packet on a stalk) in salamanders and caecilians, but external fertilization in frogs and toads. Larvae develop in water or very moist environments and undergo complete metamorphosis. Amphibians are the only vertebrates to undergo complete metamorphosis. • Pity the poor amphibian for they know not biologically what they are. They begin life as a legless animal with gills and tail like a fish and end up a with four legs and lungs like a reptile. Yet clearly they are neither fish nor reptile. They are amphibians, the only vertebrates that lead a double life.

7. Difference between amphibians and fish • Fish and amphibians are different because fish must live in water to survive. Amphibians, however, are born in water but live on land and in the water. • A major difference between the two is that amphibians breathe using gills or spiracles when they are young and develop lungs as they grow: fish rely on gills for their entire lives. • Amphibians undergo metamorphosis as they grown from young to adult, but fish do not undergo this radical change. Read more. • Amphibians have eyelids and ears; fish do not. • Amphibians are capable of vocalisations; as far as we know, fish are not. • Amphibians have moist skin, whilst fish have scales.

8. Ancester of amphibians • The first amphibians evolved from lobe-finned fishes approximately 370 million years ago during the Devonian Period. Early amphibians included creatures such as Diplocaulus, Ophiderpeton, Adelospondylus, Diplocaulus, and Pelodosotis. The world of those early amphibians was quite different than it is today. • The Crossopterygians, a group of primative lobe-finned fish are believed to be the ancestors of amphibians. Which is similar to lung fish. Amphibians originated from from a tetrapod. Early tetrapods were like fish but may have had limbs to move on the bottom of marshes. In later fossils, the limbs were found further below to lift the animal off the ground. Eventually, amphibians arose the ability to breath through the air as well as water.

9. Adaptions in water • streamlined body shape for swimming - no movement of head is beneficial during swimming - easier to swim through water. • thin and moist skin allows for gaseous exchange (cutaneous respiration) - allows for water exchange (osmosis). • long, powerful,legs with 5 toes ble to jump great distances, and change direction quickly - webbed toes aid in swimming. • Their eyes is positioned on top of head - it gives the them a wide angled visual field; allows them to remain in water with only part of head exposed lower. • eyelid transparent - able to see under water. • large and bulging - aid in swallowing; - detect movement and velocity of an object

10. a flat disk-like tympanic membrane around their ear that streamlines the body, prevents water from entering ear canal. • very large and broad mouth able to catch and eat large prey. • Their tongue is attached at front of mouth - enables it to be flicked out quickly long and sticky - prey sticks to it when caught.