Amphibians   All Materials © Cmassengale  http://www.biologyjunction.com/amphibian_notes_bi.htm

Amphibian Evolution:

Arose from lobe-fined ancestor called CrossopterygiansLand plants & insects provided new food sourceHad primitive lungs & short, limb like fins for short periods on landAppeared during late DevonianIcthyostega early amphibian with 4 limbs, lungs, & a tail for swimming

Adaptations:

Four limbs with claws on digits (toes)Lungs instead of gillsBoth internal & external nares (nostrils)Three chambered heart (two atria & one ventricle)Double loop blood circulation to lungs & rest of body cells

Skin with keratin (protein) to prevent water lossNecks to more easily see & feedMost with smooth, moist skin to take in dissolved oxygenSome with oral glands to moisten food they eatWebbed toes without clawsEctothermic - body temperature changes with environmentShow dormancy or torpor (state of inactivity during unfavorable environmental conditions)Hibernate in winter and aestivate in summerAquatic larva called tadpole goes through metamorphosis to adultMetamorphosis controlled by hormone called thyroxine

Tadpole

External fertilization with amplexus (male clasps back of female as sperm & eggs deposited into water)Eggs coated with sticky, jelly like material so they attach to objects in water & do not float awayEggs hatch into tadpoles in about 12 days

Eggs

Males with vocal sacs to croak Digested system adapted to swallow prey whole Well developed muscular system

Classification:

Anura - frogs & toads Urodela - salamanders & newts Apoda - caecilians Trachystoma - sirens or mud eels

Anuran Characteristics:

Both terrestrial & freshwater species Tadpole with tail, gills, & two-chambered heart Adults without a tail, four limbs, & lungs Frog skin smooth & moist for cutaneous respiration, while toads is rough &

warty (poison glands)

Frog Toad

Long hind limbs for jumping Long, forked tongue hinged at front of mouth

Urodela Characteristics:

Includes salamanders & newts Have elongated bodies with a tail & four limbs  Smooth, moist skin for cutaneous respiration Less able to stay on dry land than anurans

Spotted Salamander

Size from a few centimeters long to 1.5 meters Nocturnal when live in drier areas Newts are aquatic species

Red Spotted Newt

Lay eggs in water or damp soil Some bear live young May or may not go through tadpole stage (some hatch & look like small adult)

Apodan Characteristics:

Includes caecilians Tropical, burrowing, worm like amphibians Legless

Small eyes & often blind Eat worms & other invertebrates Average length 30 centimeters, but can grow up to 1.3 meters internal fertilization Female bear live young

Caecilian

Trachystoma Characteristics:

Includes mud eels or sirens Known as "rough mouth" amphibians Found in eastern U.S. & southern Europe Have minute forelimbs & no hindlimbs

Mud Eel or Siren

External Frog Anatomy:

Live double life on land & water Powerful hind legs for jumping & swimming fold under body when at rest Bulging eyes to stay submerged but still see predators Blinking eyelids protect eyes from dust & dehydration Nictitating membranes clear to moisten eye & see underwater Internal nostrils or nares allow frog to breathe underwater Tympanic membranes or eardrums behind each eye transmit sound through bone

called columella to inner ear Eustachian tubes connect mouth & middle ear to equalize pressure

Males croak or make sound to attract females & ward off other males Have protective coloration from cells called chromatophores Granular glands secrete foul tasting or poisonous substance Mucus glands lubricate skin for oxygen to be dissolved & absorbed

Internal Frog Anatomy:Skeletal System

Nine spinal vertebrae (1 cervical in neck, 7 trunk, & 1 sacral supporting hind legs) Urostyle long, slim bone connecting sacral vertebrae & trunk No rib cage, but pectoral girdle forms shoulders & connects front legs Pelvic girdle connects to hind legs

Digestive System

Tongue sticky, forked, & hinged at front of mouth so can be extended out to catch insects

Can pull eyes inward to help swallow food Two, sharp, backward-pointing  vomerine teeth in roof of mouth help prevent prey from

escaping Maxillary teeth line the edge of the upper jaw Alimentary canal (mouth, esophagus, stomach, small & large intestines, and cloaca) is

where food is digested, absorbed & wastes eliminated Stomach makes gastric juices to break down food Pyloric sphincter muscle controls movement of food from stomach into first part of

small intestine called duodenum Liver makes bile to digest fats; stored in gall bladder Pancreas makes pancreatic juice to digest food in small intestine Ileum is coiled mid portion of small intestine Mesentery is a fanlike membrane holding the intestine in place Wastes collect in large intestine & then move into cloaca along with eggs, sperm, &

urine until they leave body through the anus

Circulatory System

Need more oxygen to burn increased amount of food needed to live on land 3 chambered heart (right atrium receives deoxygenated blood from body, left

atrium receives oxygenated blood from lungs, & ventricle pumps blood to lungs & rest of the body)

Double loop blood circulation (pulmonary from heart to lungs & systemic from heart to rest of body)

Conus arteriosus carries blood from ventricle to body cells

Respiratory System

Tadpoles use gills to breathe Adult frogs breathe through lungs & moist skin (cutaneous respiration) Glottis is the opening into throat & lungs

Excretory System

Carbon dioxide excreted through skin & lungs Kidneys filter blood & store urine in urinary bladder until leaves cloaca

Nervous System

Olfactory lobes at base of brain detect smells Cerebrum behind olfactory lobes controls muscles Optic lobes detect sight Cerebellum controls balance & coordination Medulla oblongata controls heart rate & breathing Cranial nerves connect brain & spinal cord, while spinal nerves branch off the spinal cord

to muscles & sensory receptors