Phylum: Chordata

Class: Amphibia

Order GymnophionaOrder AnuraOrder Caudata

Class AmphibiaDerives from Greek:

The Greek prefix amphi- means "both" or "double" The Greek word bios means "life.“

Amphibian = “double life”

Class: Amphibia – means

Subclass Labyrithodontia (extinct)

Order Anthracosauria (extinct)

Subclass Lepospondyli (extinct)

Subclass Lissamphibia (living amphibians)

Order Gymnophiona (aka Apoda, Caecilians)

Infraclass Batrachia

Order Anura (frogs and toads)

Order Urodela (Caudata) (salamanders, newts, sirens, etc.)

From Romer

From Conant and Collins

From Linzey 2001

Most have 4 limbs, except Caecilians (limbless) and Sirens (forelimbs only)

Many have webbed feet

Typically the glandular skin is smooth, moist, and lacks scales

-Caecilians have concealed dermal scales

Class: Amphibia

Lesser Siren Caecillian Red-eyed Tree frog

Rough Spotted Newt

Wood frog

Caecilians

Movement onto Land

Life began in the water, animals are made of mostly water, and all cellular functions occur in water.Invasion onto land required modification of almost every system in the vertebrate body. The Amphibian is an example of this terrestrial transition.

Amphibian OriginsThough actual origins are uncertain, it is clear that there was plenty of selective pressure for amphibians to emerge onto land

-the Devonian was a period of tremendous climatic fluctuation

-Wet and dry spells – dry spells would have set up intense competition in aquatic habitats

-Would favor an ability to move from one pond to another

-Oxygen poor waters would favor air-breathing

Amphibian Origins

-Also, at this time, there was a tremendous radiation of arthropods into the terrestrial environment

-Centipedes, millipedes, spiders, insects, etc. = food!

-This would create an open niche in a relatively low-competition terrestrial environment

Accommodations to be considered when moving to

land

Oxygen contentOxygen diffuses more readily in air then water

Development of lungs

SupportProvides little support against gravity

Requires the development of strong skeleton and limbs to get around

Accommodations to be considered when moving to land

 

Development of limbs required only a few minor modifications

-elongation of proximal elements into long-bones of limbs

-Proliferation of more distal elements into bones of feet

-Elaboration of pectoral and pelvic girdles (for anchoring the limbs)

Accommodations to be considered when moving to

landTemperature regulation

Air fluctuates in temperature more then water

Requires behavioral and physiological strategies to protect themselves from thermal extremes

Homeothermy—regulated constant body temperature

birds and mammals

Habitat diversityDiverse biomes to live in and adjust to

Characteristics of Class: Amphibia—on both sides

4,200 speciesRequire a metamorphosis from water to land during developmentSkin is thin and requires moistureEctothermic—body temperature varies with outside changing temperature (cold blooded)

Body PlanBilateral symmetrySkeleton mostly bonySmall teethSegmentation-head normally distinct from bodyFour limbs (except caecilians) Webbed feet

no nails or claws, 4-5 digits

SkinMade of Keratin, a tough protein that protects against abrasions and water lossMoist Two layers—epidermis and dermisWith many glands

Serous glands secrete poison; effectiveness varies from species to speciesMucous glands waterproof the skin

Pigment cells—Chromatophores

RespirationAir is forced into the lungs with mouth muscles [positive pressure]Air can be diffused through skin and the inside of the mouthThe majority of carbon dioxide is released through the skinSound is created by forcing air over vocal cords and a large pair of sacs in the floor of the mouth

-Gas exchange occurs through lungs, gills, and/or the skin

-Some salamanders have no lungs (secondarily lost)

Respiration

Eastern Red-backed Salamander – no lungs

Larval tiger salamander showing gills

Adult mudpuppy showing gills

CirculationClosed systemOrigin of the Systemic and Pulmonary Circuits3 chambered heart

2 atria 1 ventricleSpiral valve helps separate the flows of oxygenated vs unoxygenated blood

NutritionCarnivores feeding on insects, spiders, worms slugs, snails, millipedesProtrusive tongue is attached at the front of the mouth

DigestionComplete digestion with both intracellular and extra-cellular digestion

ExcretionPair of mesonephric kidneysUrea main nitrogenous waste

Nervous SystemTen pair of cranial nervesSenses

Smell—olfactory epitheliumHearing--ear

One advance associated with a more terrestrial existence is the refinement of the ear

-the amphibian ear, unlike that of fishes, consists of three components

-Inner ear, middle ear, outer ear

-There is increased sensitivity to accommodate airborne sounds

Hearing

ReproductionSexual with both “internal” and external fertilizationIn the spring, males vocally attract females to mate withEggs are laid in large masses and can be anchored to vegetation, simply float in water, or laid under logs in moist ground

Packet of sperm may be left on vegetation and then inserted by the female herselfMale may force eggs to be evacuated from the female as he discharges his sperm over the eggs —amplexus

Reproduction

Amphibian eggs are very vulnerable to desiccation.

Hence, amphibians are reproductively constrained to exist in moist environments.

Frog eggs Toad eggs Salamander eggs

Spermatophores

DevelopmentEggs hatch into aquatic larva having external gills and tailMetamorphosis

ReproductionAustralian Marsupial frog (A)

(use pouch on dorsum)Surinam Frog Surinam (B)

(babies in skin on dorsum)Poison Dart frog (C)

(carries tadpoles from forest floor to canopy)

Darwin’s frog (D)(babies mature in vocal pouch)

Gastric Brooding frog (keeps young in stomach!)

Environmental Interaction

Require a somewhat cool environmentMost amphibians hibernate during winter months in soft mud of the bottoms of pools and streamsSome can tolerate freezing temperatures by making a type of antifreeze by accumulating glucose and glycerol in body fluids

Environmental Interaction

Are both predators and prey to others, for protection amphibians have developed

Poison glandsUrinate on predatorStrong legs for leaping awayBiting at predatorsInflate lungs to avoid being swallowedCamouflage

Importance of Amphibians

To Ecosystem – Pest control, food for other animalsTo humans – Food, genetic researchThey are “nature’s indicator”

YikesWorldwide, populations of frogs have been decreasing and experiencing mutations. No one knows the cause for sure!!!!

Pollution, acid rain, ozone depletion, pesticides/chemicals, introduction of non-native predators are just a few ideas

Order Gymnophiona -caecilians (aka

Apoda)Limbless (“naked snake”)160 speciesTropical forests of South America, Africa, and South East AsiaMost species totally blindBurrow or aquaticCarnivores

Order Caudatasalamanders, newts,

sirens“having a tail”360 speciesFound in all North America, tropical areas of Central and northern south AmericaCarnivorous both as larva and adultRange from about 2” in length (Patch-nosed Salamander) to over 5’ in length (Japanese Giant Salamander)

Order Anurafrogs and toads

“without tail”3,400 speciesCarnivores and herbivoresFound in temperate and tropical regions throughout the world except New Zealand