Amphibians Chapter 40 Origins Evolution of Amphibians Section

Amphibians Chapter 40

Origins & Evolution of Amphibians Section 40. 1

Adaptation to land • Amphibian means “double life” • Came out of the water to escape predation & competition for food – Need a strong bony endoskeleton to deal with force of gravity

Characteristics of early amphibians • Oldest amphibian fossil is 370 myo • Evolved from lobe-finned fish – Four limbs homologous to pectoral & pelvic fins of fish – Similar skull & vertebrae • some had gills and lungs • More toes than modern amphibians

Modern amphibians • Metamorphosis • Moist, thin skin with no scales • Feet lacking claws & often webbed • Use skin, gills, & lungs to breathe • Eggs lack membrane or shells • Eggs laid in water • Fertilization externally

Diversification of amphibians • Two main evolutionary lines 1. Modern amphibians 2. Ancestor of reptiles • 4, 500 species in 3 orders 1. Order Anura 2. Order Caudata 3. Order Gymnophiona

Order Anura • Meaning “tail-less” • Examples: frogs & toads – “toad” = rough, bumpy skin – “frog” = smooth, moist skin • Adaptations for jumping • Tadpole: swimming larvae • Carnivores

Order Caudata • Example: salamanders & newts • Elongated bodies with moist skin and long tails • Live in moist places • Carnivores

Order Gymnophiona • • Example: caecilian Legless & resemble small snakes Very small eyes, often blind Carnivores • Video

3 Order Note Cards! • Front Side = Order name & picture • Back Side = Anura Caudata Gymnophiona – example organisms – Location of animal on Earth – Habitat/environment – Adaptations for life/ key characteristics – Fun fact!

Characteristics of Amphibians Section 40. 2

External covering • Skin = respiration & protection • Mucous glands: supply lubricant to keep skin moist & poison for protection *Video - The Waxy Monkey Frog Poison dart frogs

Internal anatomy • Strong bony skeleton – Needed for life on land (larger animals) – Pectoral & pelvic girdles help support • More developed internal anatomy – Closer to humans! – video

Male internal anatomy a. Large intestine. b. Small intestine. 1. Lung lobes. 2. Heart. 3. Liver lobes. 4. Gall bladder. 5. Stomach. 6. Small intestine. 7. Testis. 8. Fat body. 9. Urinary bladder.

Female internal anatomy 1. Liver lobes. 2. Heart. 3. Ovary with eggs. 4. Gall bladder. 5. Small intestine. 6. Stomach. 7. Oviduct.

Heart & circulatory system • Two separate loops 1. Pulmonary circulation: blood from heart to lungs & back to heart 2. Systemic circulation: blood from heart to muscles & organs then back to the heart

Three chambered heart 1. Right atrium: where (deoxygenated) blood leaves to go to the lungs 2. Left atrium: where oxygenated blood enters from the lungs 3. Ventricle: main pumping chamber 1. 2. 3.

Respiration • Larvae respire via gills and skin • Adults respire via lungs and skin – Pulmonary respiration: through lungs – Cutaneous respiration: through skin

Digestive system • All adults are carnivores • Mouth esophagus stomach liver Gallbladder sm. Intestine lg. intestine cloaca vent • New terms: – Pyloric sphincter – Duodenum – Ileum – Mesentery

Excretory system • Two kidneys that filter nitrogenous wastes from the blood • Urine flow: – Kidneys urinary ducts urinary bladder cloaca

Nervous system • Brain: – – – Olfactory lobes Cerebrum Optic lobes Cerebellum Medulla oblongada • Nerves – 10 pair cranial nerves – Spinal cord – Spinal nerves

Sense organs • Sight: light travels through nictitating membrane (transparent movable membrane covering the eyes) eye • Sound: travels through tympanic membrane (eardrum) columella (small bone) inner ear (embedded in skull)

Reproduction of Amphibians Section 40. 3

Reproductive System • Males: sperm cells develop in testes and leave thru cloaca • Females: eggs produced in ovaries – Eggs enlarge and burst thru ovary into body cavity – Coated with jelly-like material in oviducts before leaving thru cloaca

Life Cycle • Eggs hatch into tadpoles a few days after fertilization • As the tadpole grows, it slowly changes from an aquatic larvae to a swimming adult • Legs grow from body • Tail and gills disappear • Mouth develops teeth and jaws • Lungs become functional • Thyroxine – hormone produced by thyroid gland to stimulate metamorphosis

Life cycle

Courtship & fertilization • Males croak to females in spring • Amplexus: male embrace of female during mating – Once female releases eggs, male releases sperm direct external fertilization video

Metamorphosis • Tadpole frog

Parental care • Males often remain with eggs for protection • Example: Darwin’s frog puts eggs in his vocal sac where they hatch, go through metamorphosis, and emerge in the adults form video

gol Goliath Frog Mudpuppy