1. Prepared by Dr. G. Sakunthala Dept. of Zoology
Amphibians
Prepared by
Dr. G. Sakunthala
Dept. of Zoology

2. 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

4. 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

5. Double loop blood circulation

6. 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

8. Classification: Anura - frogs & toads Urodela - salamanders & newts
Apoda - caecilians
Trachystoma - sirens or mud eels

9. 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

10. 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)

11. 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

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

13. 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

14. 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

15. 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)

17. 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

19. 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

20. 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

21. 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)

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

23. 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

24. 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

25. 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

26. 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

27. 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.

28. 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).

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

31. THANK YOU