Chapter 40Amphibians

Section 1

Origin and Evolution of Amphibians

Amphibians• Greek word meaning “double” and

“life”

• Many amphibians spend part of their life in water and part on land

Adaptation to Land• Most likely evolved from lobe-finned

fishes

• Pre-adaptations- adaptations in an ancestral group that allow a shift to new functions which are later favored by natural selection

Adaptation to Land• Lobe-finned fish ancestral

amphibians- appendages to walk• Had modified pouches in their

digestive tract that evolved into lungs• Had nostrils to help aid in breathing

on land

Characteristics of Early Amphibians

• Amphibians and lobe-finned fishes share many similarities: skull & vertebral column

• Sarcopterygian- extinct lobe-finned fish that is thought to be closely related to amphibians

Sarcopterygian

Diversification of Amphibians

• 4,500 species belonging to three orders

• Anura- frogs and toads

• Caudata- salamanders

• Gymnophiona- caecilians- legless tropical amphibians

Modern Amphibians• Most change from aquatic larval

stage to a terrestrial adult form- metamorphosis

• Most have moist, thin skin with no scales

• Feet, if present, lack claws and often are webbed

Modern Amphibians• Most use gills, lungs, and skin

respiration

• Eggs lack multi-cellular membranes or shells. They are usually laid in water or in moist places and are usually fertilized externally

Order Anura• Frogs & toads• World-wide, except in polar climates

and a few oceanic islands• Either spend part of or entire live in

water• Toad- rough, bumpy skin• Frog- smooth, moist skin

Order Anura• Body adapted for jumping (long

muscular legs)

• Adult anurans are carnivores

• Have a sticky tongue to help capture food

• Return to water to reproduce

• Tadpoles- fertilized eggs hatch into swimming, tailed larva

Poison Dart Frog

Gray Tree Frog

Bull Frog

Leopard Frog

Cane Toad

American Toad

Order Caudata• Salamanders- elongated bodies,

long tails, and moist skin

• Smallest are only a few centimeters long, largest are over 4.5 feet

• Aquatic and terrestrial species

• Carnivores

Order Caudata• Most live in North America and

Central America

• Some are lungless and breathe through their skin

• Some reproduce in water, while others lay eggs on land

Order Caudata• Water reproduction- larval stage

• Land reproduction- no larval stage

• Internal fertilization

• Some terrestrial species stay with eggs until hatched

Spring Salamander

Dusky Salamander

Red-Spotted Newt

Spotted Salamander

Order Gymnophiona• Caecilian- legless amphibian-

resembles snakes

• Found in tropical areas of Asia, Africa, and South America

• 12 inches to 4.5 feet

• Often are blind because their eyes are found under skin and bone

Order Gymnophiona• Rarely seen- little is known

• Some burrow and some are aquatic

• Have teeth- eat worms and other invertebrates

Order Gymnophiona• Internal fertilization

• Some species lay eggs & some are born live

• Young use their jaws and teeth to scrape secretions “uterine milk” from the walls of the female’s reproduction tract

Sagalla Caecilian

Purple Caecilian

REVIEW!!!• Name some characteristics that

are common to modern amphibians.

• Compare and contrast the three living orders of amphibians.