Transcript Modern Amphibians

Modern Amphibians
Part one
Chapter 40 Amphibians
• Origin and Evolution
• Characteristics
• Reproduction
Adaptation to Land
• Preadaptations - are adaptations in an
ancestral group that allow a shift to new
functions which are later favored by
natural selection.
Adaptation to Land
Lobe-finned fishes had several
preadaptations that allowed them
to transition to life on land.
• bone structure
• pouches in digestive tracts for
gas exchange
• nostrils
• higher metabolism
• efficient hearts
Adaptation to Land
Characteristics of Early Amphibians
Amphibians and lobe-finned fishes share many anatomical
similarities, including:
• similar skull
• similar vertebral column
• similar bone structure in fins and limbs
• early amphibians had a large tail fin and lateral line
canals
Adaptation to Land
Diversification of Amphibians
• About 300 million years ago amphibians
split into two main evolutionary lines.
• One line included ancestors of reptiles, the
other line included the ancestors of
modern amphibians.
Adaptation to Land
Diversification of Amphibians
Today there are about 4,500 species of
amphibians belonging to three orders:
• Anura - includes frogs and toads
• Caudata - includes salamanders and newts
• Gymnophiona - includes caecilians (legless
tropical amphibians)
Anura - includes frogs and toads
Caudata - includes salamanders
and newts
Spotted Salamander
Fire Bellied Newt
Gymnophiona - includes caecilians
(legless tropical amphibians)
Modern Amphibians
Modern amphibians share several key
characteristics
• Most change from an aquatic larval
stage to a terrestrial adult form, in a
transformation called metamorphosis.
• Most have moist, thin skin with no
scales.
Modern Amphibians
• Feet, if present, lack claws and often are
webbed.
• Most use gills, lungs, and skin in respiration.
• Eggs lack multicellular membranes or shells,
are usually laid in water, and are usually
fertilized externally.
Modern Amphibians
Order Anura
• Order includes
frogs and toads.
• Members may be
fully aquatic, fully
terrestrial, or
amphibious
American Toad
Modern Amphibians:
Order Anura
• Most reproduce
in water, laying
eggs that hatch
into swimming
larvae called
tadpoles.
• Larvae are
herbivores.
Adults are
carnivorous and
will eat any
animal they can
capture.
Modern Amphibians:
Order Caudata
• Includes salamanders
(may also be called
newts).
• Members may be fully
aquatic, fully
terrestrial, or
amphibious.
• Many reproduce in
water. Some
reproduce on land,
with no swimming
larval stage.
Modern Amphibians:
Order Caudata
• Larvae and adults
are carnivorous.
• Some have no
lungs, and respire
through their skin
only.
Modern Amphibians:
Order Gymnophiona
• Includes caecilians (legless amphibians
that resemble small snakes).
• Most are burrowing. They have small
eyes beneath skin or bone, and are often
blind.
Modern Amphibians:
Order Gymnophiona
• All are carnivorous.
• All are thought to have internal fertilization.
• Some lay eggs which the female guards,
others develop inside the female.
Phylogenetic Diagram of
Amphibians