Class Amphibia

Placoderms

Ostracoderms

Hagfish & Lampreys

Cartilaginous Fish Bony Fish

Lobe-Finned Fish

Ray-Finned Fish

Coelacanths

LungfishEarly Amphibian

(Ancestor of all Tetrapods)

Tetrapods● Animals with 4 limbs

○ Amphibians○ Reptiles○ Birds○ Mammals

● Evolved from lobe finned fish in the Devonian period (middle of the Paleozoic Era)

● The first tetrapods were amphibians

Transition from Sea to Land

Tiktaalik

● The first tetrapod to crawl out of the water to spend time on land

● Lobe-finned traits included fins, scales, & primitive jaws

● Tetrapod traits included a neck, wrists, & expanded ribs to accommodate lungs

Amphibians● Name derived from Greek words "amphi" & "bios" which

translates into "both kinds of life"

● Almost all amphibians begin life in freshwater and transition to land as they grow into adults via metamorphosis

● No scales, feathers or hair

● Heart with 3 chambers (2 atria & 1 ventricle)

● One cervical vertebra - can turn neck only slightly

● Exothermic - need a 4 chambered

heart to be endothermic

Frog Reproduction - Like Complete Metamorphosis

Salamander Reproduction - Like Incomplete Metamorphosis

Amphibian Adaptations for Land● Gills are usually lost by

adulthood

● Lungs function in adults, but they are small and inadequate

● Breathe through skin to compensate – cutaneous respiration

● Secrete mucus ○ Prevent dehydration○ Aids in respiration – Allows

a medium through which oxygen can pass through skin to blood vessels

Vertebrate Cutaneous Respiration

More Adaptations to live on land

● Skeleton undergoes several changes as larvae morph into adults

● Fins evolve into limbs

● Bony vertebral column grows more dense to support body underneath since air is not as buoyant as water

Evolution of Circulatory System

Fish Amphibian

Two chambers (1 atrium & 1 ventricle)

& a single circuit

Three chambers (2 atria & 1 ventricle)

& a dual circuit

Exothermic

Order Caudata● Salamanders

● "Cauda" is Latin for "tail"

● Front legs usually have 4 digits & the hind legs have 5 digits

● May be fully aquatic, amphibious, or fully terrestrial as adults

● Fully aquatic salamanders usually exhibit paedomorphosis

● Divided into two Families based on respiration

PaedomorphosisPaedomorphosis is the retention of juvenile characteristics in the adult stage of

the organism

AxolotlMudpuppy

Family Plethodontidae

● Lungless Salamanders

● Breathe through skin exclusively as adults

● Members tend to be tiny so they maximize their surface area to volume ratio - More O

2 can absorb

● Most lack aquatic larvae and hatch as miniature adults from eggs laid on land – must be very moist land!!

Family Salamandridae

● Lungs present

● True salamanders and newts

● Usually have rough skin (not as reliant on cutaneous respiration)

● Usually brightly colored with contrasting bands indicating poison

● Aquatic larval stage with external gills is common

Newt – Salamander With Rough Skin

Chinese Giant Salamander

● The largest amphibians on the earth today

● Can reach sizes up to 1.8 meters (6 ft) in length

● Folds in their skin increase their surface area allowing for more oxygen absorption to occur

Order Anura

● Anura means “no tail”

● Frogs and toads

● No tail in adult, but present in tadpole larval stage

● Long hind limbs, shortened body, and webbed feet characterize Anurans

● Considered to be the best jumpers of all vertebrates (up to 50 times their body length)

Frog Anatomy

Frog Anatomy

Toads vs. Frogs

● Most toads arose due to convergent adaptations to drier climates, not separate lineages

● Toads usually have thicker skin to conserve water in the drier habitats they normally occupy

● Toad lungs are better developed due to reduced cutaneous respiration

Anuran Mating

● Frogs & toads often return to their pond of origin to breed

● Males call out to females with a sound unique to each species

● Mate by amplexus. The male mounts the female, stimulates her to release eggs by squeezing her pelvis, and then externally fertilizes the eggs

Poison Dart Frogs

Order Apoda

● Caecilians

● Defining feature is a lack of legs – resemble worms or snakes

● More closely related to salamanders than to Anurans

● Live underground in tropical regions

● Least studied and understood amphibian

Order Apoda

● Caecilians have reduced eyes due to their subterranean lifestyle, but are not completely blind

● Many species undergo internal fertilization and have ovoviviparous births while others lay eggs underground in oviparous fashion

● Internal copulation may last 2 to 3 hours!

The End