Amphibians

Amphibian Evolution: Arose from lobe-fined ancestor called Crossopterygians Land plants & insects provided new food source Had primitive lungs & short, limb like fins for short periods on land Appeared during late Devonian Icthyostega early amphibian with 4 limbs, lungs, & a tail for swimming

Icthyostega Well developed limbs (*showed adaptations for life on land but probably spent most of their time in water) Large tail fin Lateral line canals on head Large sharp teeth, indicating a diet of fish

Icthyostega

Adaptations: Metamorphosis Moist, thin skin with no scales (the structure of amphibian skin indicates the habitats in which they can survive) Most use gills, lungs, and skin in respiration Feet, if present, lack claws and are often webbed Both internal & external nares (nostrils) Three chambered heart (two atria & one ventricle) Double loop blood circulation to lungs & rest of body cells Eggs lack multicellular membranes or shells. They are usually laid in water or in moist places and are usually fertilized externally

Double loop blood circulation

Adaptations: cont… Skin with keratin (protein) to prevent water loss Necks to more easily see & feed Most with smooth, moist skin to take in dissolved oxygen Some with oral glands to moisten food they eat Webbed toes without claws Ectothermic - body temperature changes with environment Show dormancy or torpor (state of inactivity during unfavorable environmental conditions) Hibernate in winter and aestivate in summer Aquatic larva called tadpole goes through metamorphosis to adult Metamorphosis controlled by hormone called thyroxine

Adaptations: cont… 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 away Eggs hatch into tadpoles in about 12 days. 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) Long hind limbs for jumping Long, forked tongue hinged at front of mouth

Anuran Characteristics:

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

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

Urodela Characteristics:

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

Apodan Characteristics:

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

Trachystoma Characteristics:

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

External Frog Anatomy: 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

External Frog Anatomy:

Internal Frog Anatomy: Skeletal System (adaptation for life on land) Rigid spine to bear weight of body 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 A fused lower forelimb (radio-ulna) and a hind limb (tibiofibula)

Internal Frog Anatomy: 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, pharynx, esophagus, stomach, small & large intestines, and cloaca) is where food is digested, absorbed & wastes eliminated Stomach makes gastric juices to break down food

Internal Frog Anatomy: 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 or vent

Internal Frog Anatomy: 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

Internal Frog Anatomy: Circulatory System cont… Sinus venosus – deoxygenated blood enters first Right atrium – deoxygenated blood from the sinus venosus enters Ventricle – deoxygenated and oxygenated blood enters the ventricle Conus Arteriosus – both kinds of bood is expelled into this chamber Lungs – deoxygenated blood leaves the conus arteriosus and travels to the lungs Left atrium – oxygenated blood from the lungs enters the left atrium Ventricle - oxygenated and deoxygenated blood is forced into the ventricle, then to the conus arteriosus where it is sent separate ways Body – oxygenated blood leaves the conus arteriosus and travels to the body

Circulatory System

Internal Frog Anatomy: Respiratory System Tadpoles use gills to breathe Adult frogs breathe through lungs & moist skin (cutaneous respiration) Glottis is the opening into throat & lungs

Respiratory System Positive-pressure Breathing See figure 42 – 9, pg 826 The floor of the mouth drops and the nostrils open (air rushes in) The floor of the mouth is raised and the nostrils close ( air is pushed into the lungs)

Internal Frog Anatomy: Excretory System Carbon dioxide excreted through skin & lungs Kidneys filter blood & store urine in urinary bladder until leaves cloaca

Internal Frog Anatomy: Nervous System Olfactory lobes at base of brain detect smells Cerebrum behind olfactory lobes controls muscles (voluntary activities of the body) Optic lobes detect sight Cerebellum controls balance & coordination Medulla oblongata controls heart rate & breathing Cranial nerves connect brain & spinal cord, Spinal nerves branch off the spinal cord to muscles & sensory receptors Tympanic membrane and columella detect vibrations in the air

Life cycle of a frog including metamorphosis Mating embrace (amplexus); male’s sperm fertilizes female’s eggs externally Eggs hatch and the tadpole is released Tadpole metamorphosis (stimulated by the hormone thyroxine) Metamorphosis: First lives off yolk stored in its body Gradually grows larger and develops three pairs of gills

Life cycle of a frog including metamorphosis Metamorphosis cont… 3. Tadpole’s mouth opens, allowing it to feed 4. Legs grow from the body, and the tail and gills disappear 5. The mouth broadens, developing teeth and jaws 6. The lungs become functional 7. A small adult frog emerges from the water onto dry land

Parental care in Amphibians Some species of poison dart frog lay eggs on the forest floor and protect them, guarding the eggs from predation and keeping them moist. The frog will urinate on them if they become too dry. After hatching, a parent (the gender depends upon the species) will move them, on its back, to a water-holding bromeliad. The parent then feeds them by laying unfertilized eggs in the bromeliad until the young have metamorphosed The females of some species sit on their eggs to keep them moist

Poison Dart Frog

Parental care in Amphibians Other frogs carry the eggs and tadpoles on their hind legs or back (e.g. the midwife toads, Alytes spp.). Some frogs even protect their offspring inside their own bodies. The male Australian Pouched frog (Assa darlingtoni) has pouches along its side in which the tadpoles reside until metamorphosis.

Parental care in Amphibians The female Gastric-brooding frog (genus Rheobatrachus) from Australia, now probably extinct, swallows its tadpoles, which then develop in the stomach. To do this, the Gastric-brooding Frog must stop secreting stomach acid and suppress peristalsis (contractions of the stomach).

Parental care in Amphibians Darwin’s frog(Rhinoderma darwinii) from Chile puts the tadpoles in its vocal sac for development.