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Earliest amphibians. The earliest are the labyrinthodonts, which included Icthyostega and Acanthostega . During the Carboniferous a couple of major lineages of labyrinthodonts arose: the Temnospondyls and the Anthracosaurs. Anthracosauria and Temnospondyls.

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Earliest amphibians

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Earliest amphibians

  • The earliest are the labyrinthodonts, which included Icthyostega and Acanthostega.

  • During the Carboniferous a couple of major lineages of labyrinthodonts arose: the Temnospondyls and the Anthracosaurs.


Anthracosauria and Temnospondyls

  • The Anthracosauria and the Temnospndyls were both diverse groups and many were very large being several meters long.

  • They looked a bit like large, sprawling reptiles with scaly skin and big heads.


Seymouria: an Anthracosaur

http://www.prism.gatech.edu/

~gh19/b1510/tetra.gif

Poterogyrinus an Anthracosaur

http://upload.wikimedia.org/wikipedia/

commons/thumb/2/2c

/Proterogyrinus_DB.jpg/260px-Proterogyrinus_DB.jpg


A small carboniferous temnospondyl and a scorpion

http://www.hmnh.org/galleries/permocarboniferous/temnospondyl.gif

Eryops: a temnospondyl http://comenius.susqu.

edu/bi/202/

animals/DEUTEROSTOMES/

vertebrata/eryops.jpg


Anthracosauria and Temnospondyls

  • Both groups left modern descendants behind.

  • The Anthracosauria gave rise to the amniotes in the late Carboniferous, but the rest of the group became extinct in the Permian.

  • There were diverse temnospondyl groups during the Carboniferous and Permian periods, but except for one lineage (the Lissamphibia: the modern amphibians) became extinct by the end of the Triassic.


Lissamphibia

  • The Lissamphibia includes all three modern groups of amphibians. All three have smooth skin, hence their name (“Liss” means smooth.).

  • The oldest fossil salamanders date to the Jurassic (about 145 mya).

  • The oldest true frog fossils date to 190mya, but froglike vertebrates are known from 200 mya.

  • Caecilian fossils are scarce but the oldest known are from 195 mya. These had well-developed eyes and small functional limbs (unlike modern forms).


Callobatrachus sanyanensis: fossil frog from Lower Cretaceous.

http://images.google.com/imgres?imgurl=http://www.fossilmuseum.net/Fossil-Pictures/

Frogs/Callobatrachus/Callobatrachus-sanyanensis1024.jpg&imgrefurl=

http://www.fossilmuseum.net/Fossil-Pictures/Frogs/Callobatrachus/

Callobatrachus-sanyanensisb.htm&usg=__mJ8yZDNglWYiMrS7kPPE3NHV794=&h=

768&w=1024&sz=146&

hl=en&start=6&um=1&tbnid=I7dMno_ZrUhMuM:&tbnh=113&tbnw=150&prev=/

images%3Fq%3Dfossil%2Bfrog%2B%2Bimages%26hl%3Den%26sa%3DG%26um%3D1


Lissamphibia

  • The evolutionary relationships between the three modern groups of the Lissamphibia are not clear and a lack of fossils has hindered an understanding of their relatedness and evolutionary origins.


Class Lissamphibia

  • The amphibians are represented by about 4800 hundred species divided into three orders.

  • Urodela “tailed ones”: salamanders

  • Anura: “tailless ones” frogs, toads.

  • Gymnophiona (“naked snake”; previously Apoda “legless ones”) caecilians.


Eastern Mud salamander

http://fwie.fw.vt.edu/VHS/amphibians/salamanders/eastern-mud-salamander/

Eastern_Mud_Salamander_Pseudotriton_mlr.jpg


http://upload.wikimedia.org/

wikipedia/commons/6/66/

Caecilian_wynaad1.jpg

Caecilian

http://www.gregboettcher.com/as/science/classification/images/caecilian.jpg


Red-eyed Tree frog

http://www.frogsite.org/pic/Redeyed_Tree_Frog.jpg


Amphibian skin

  • Amphibians lack scales and are characterized by a moist permeable skin.

  • This limits the environments in which they typically can live as they are constrained by the threat of water loss.

  • Typically they inhabit wet or damp habitats where the humidity is high (e.g., ponds. forest floors in leaf litter).


Amphibian skin

  • Many anurans and salamanders absorb moisture from the soil or other substrates through their skin.

  • A number of anurans have a specialized region of skin on the ventral surface around the pelvis (the “seat patch” or “pelvic patch”) that is highly permeable to water and allows water to flow rapidly into a dehydrated animal.

  • In dehydrated Giant Toads (Bufomarinus) the pelvic skin is 6X as permeable to water as skin from the pectoral region.


Mucous gland and poison glands

  • Amphibian skin often contains mucous glands and granular (poison) glands.

  • Mucous glands continuously produce mucopolysaccharides, which help keep the skin moist and able to function in gas exchange when the animal is out of water. The mucus may also have anti-predator benefits as it makes the animal slippery and difficult to grip.


Poison glands

  • Granular glands in many amphibians produce noxious and sometimes toxic secretions.

  • These glands are often grouped together and give the skin a textured appearance. The warts and parotid glands of toads and the dorsolateral ridges of Rana frogs are good examples.


Poison glands

  • Toxin-secreting granular glands are widespread in anurans, but also occur in some salamanders and caecilians.

  • Toxins include vasoconstrictors, hemolytic substances, neurotoxins and hallucinogens. Their effects range from localized irritation to hypothermia, convulsions, and paralysis.


Poison glands

  • Newts of the genus Taricha produce a neurotoxin that is present in high concentrations and a single individual produces enough toxin to kill 25,000 mice.

  • The salamander Bolitoglossa rostrata produces skin secretions that may paralyze and sometimes kill garter snakes that attempt to eat them.


Poison dart frogs

  • Several genera of brightly colored Neotropical frogs (Dendrobates, Phyllobates, and Epipedobates) produce highly toxic steroidal alkaloids in their skin.

  • The alkaloids affect both the muscular and nervous systems causing muscles to remain contracted and blocking nerve transmissions, which can result in cardiac arrest and death.


Green and Black Poison Dart Frog

http://www.shoarns.com/frog.jpg


Poison dart frogs

  • These frogs are very small (rarely more than 2” long), but just one frog produces enough toxin to kill several people.

  • Several tribes of Colombian Indians use the toxins of Phyllobates frogs to tip the darts for their blowguns.

  • The toxin is extracted by impaling the frogs on sticks and holding them over a fire, which causes the toxin to seep out so it can be collected.

  • The tips of darts are then dipped in the poison, allowed to dry and used to kill birds and small mammals.


Medical applications of skin secretions

  • There have been a variety of investigations into the medical benefits of various amphibian skin secretions.

  • For example a powerful painkiller called epibatidine (200X more powerful than morphine) has been isolated from a poison dart frog.


Medical applications of skin secretions

  • In addition, a bacteria-killing antibiotic peptide called magainin has been isolated from the skin of the African clawed frog.

  • This and similar peptides are released to the skin when it is injured and kills a wide range of bacteria as well as parasites, fungi and certain viruses.

  • Unlike most antibiotics, which disable important bacterial enzymes, these peptides disrupt bacterial membranes punching holes trough them so the contents leak out.


Gas exchange

  • The moist skin is used extensively for gas exchange and some salamanders and one species of caecilian have lost their lungs over evolutionary time and depend exclusively on gas exchange across the skin and oral cavity.

  • To enhance gas exchange the skin in many species (e.g. hellbenders) is highly folded and heavily vascularized.


Eastern Hellbender

http://fwie.fw.vt.edu/VHS/amphibians/salamanders/eastern-hellbender/hellbender-

MikePinder.jpg


Gas exchange

  • Gas exchange also takes place via lungs and gills (in larvae).

  • Amphibians use a force pump mechanism to get air into their lungs. Air enters the oral cavity through the nostrils, the nostrils close and the floor of the mouth is raised forcing air into the lungs and prevented from escaping by a sphincter muscle.

  • Some frogs and toads can repeatedly use this mechanism to inflate their lungs greatly and make themselves appear large and less attractive to a predator.


Gills

  • Larval amphibians breathe using external gills. In anuran tadpoles the gills are concealed behind a flap of tissue and water flows through the mouth across the gills and out of a spiracle.

  • When anuran tadpoles metamorphose into adults the gills are reabsorbed.


Gills

  • In larval salamanders and caecilians the gills are exposed and project from the sides of the head.

  • Most species lose their gills when they mature but some retain them into adulthood (neotony). For example, the aquatic salamanders Necturus and Crytobranchus possess both gills and lungs. These species usually air breathe only when oxygen levels in the water are low or when recovering from strenuous activity.


Larval Tiger Salamander

http://www.axolotl.org/images/tiger/tiger_larva.jpg


Feeding

  • All adult amphibians are carnivorous and amphibians eat anything they can catch and swallow.

  • Because amphibians generally swallow their prey whole, head size limits prey size.

  • Frogs of the genera Lepidobatrachus and Ceratophrys which mainly eat other frogs have enormous heads relative to their body size.


Amazon Horned Frog

http://www.itsnature.org/wp-content/uploads/2008/02/amazon-horned-frog.jpg


Feeding

  • Most amphibians have small, identical teeth (homodnont dentition), which are found on both the palate and jaw.

  • The function of the teeth is to grasp and hold prey not to chew it.


Tongue protrusion

  • Most amphibians possess a sticky tongue and many can rapidly evert it to catch prey.

  • In salamanders of the genus Hydromantes the tongue can be extended 80% of the body length (about 6cm). A ballistic mechanism is used to fire the tongue out and it is retracted by a series of muscles.

  • When the tongue is everted the whole tongue skeleton leaves the mouth. Hydromantes is the only vertebrate that is known to shoot a part of its skeleton as a missile.


Hydromantes salamander shooting its tongue to catch a housefly

http://autodax.net/tngphoto.jpg


Tongue protrusion

  • In some anurans, such as Rana and Bufo, the tongue is very protrusible.

  • It is attached to the front of the mouth and flipped out using muscular action so that the rear upper surface of the retracted tongue becomes the front lower surface of the extended tongue.

  • Caecilans have rudimentary tongues that cannot be everted.


http://www.ourclassweb.com/projects/webquest_frogs_tongue.jpg


Reproduction

  • The word amphibian means “two lives” and is a reference to the fact that frogs go through metamorphosis from a tadpole stage.

  • In most anurans fertilization is external. The male grips the female and fertilizes the soft eggs as the female sheds them from her body.


Reproduction

  • Amphibian eggs do not have a hard shell and dry out quickly if not kept in a moist environment.

  • Many species lay their eggs directly in water or on the undersides of leaves over water so the larvae fall in when they hatch.

  • Others show more parental care and brood eggs in (depending on the species) the mouth, stomach or pressed into soft skin on their backs.


Reproduction

  • Eggs in frogs develop into tadpoles that have a fishlike tail and external gills.

  • As the tadpole develops, often very quickly in a race against time to escape a pool before it dries up, limbs develop, the tail shortens by reabsorption and the gills are lost as the tadpole metamorphoses into a miniature frog.


Salamander reproduction

  • Unlike frogs most salamanders (>90%) use internal fertilization.

  • An intromittent organ is not used. Instead males produce packets of sperm called spermatophores.

  • Depending on the group of salamander, males may insert the spermatophore into the female or the female may pick it up with her cloaca and then use the sperm to fertilize eggs as they pass out of her body.


Salamander spermatophores

http://www.wildlife.state.nh.us/Wildlife/Nongame/salamanders/

salamander_images/spermatophore2-Marchand.jpg


Reproduction

  • Unlike frogs the young of most terrestrial salamanders develop from eggs into a larva that looks like a smaller version of the adult, but which has gills, which are lost at metamorphosis.

  • The most terrestrial salamanders, the lungless plethodontids, have evolved young that hatch from the egg as miniature versions of the adult and there is no aquatic larval stage.


Reproduction

  • Other salamanders lay their eggs in water. Eggs may be laid singly or in clumps.

  • These eggs develop into larvae that are miniature versions of the adults, but they have external gills.

  • In terrestrial species larvae transform into a juvenile stage called an eft and when sexually mature these return to water to breed.


Caecilian reproduction

  • In caecilians fertilization is internal (males possess an intromittent organ) and they employ a variety of developmental strategies.

  • Some species are oviparous with aquatic larvae, others are oviparous, but the young develop directly into terrestrial young. In many cases, the mother will brood the eggs until they hatch.


Many caecilians lay their eggs in the mud near water,

but some caecilians brood their eggs in burrows.


Caecilian reproduction

  • However, the majority of caecilians are viviparous (about 75%) and matrotrophic (young obtain nutrition from the mother).

  • Newborn caecilians are 30-60% of the length of their mother and a litter may include 9 or 10 babies, so mother’s clearly invest heavily in their offspring.


Caecilian with young

http://www.abdn.ac.uk/~nhi708/

classify/animalia/chordata/amphibia/

apoda/caecilian.jpg


Caecilian reproduction

  • Egg yolk provides the initial nourishment for viviparous young, but further growth comes from feeding directly on the mother.

  • Viviparous forms have teeth (shed after birth), which they use to scrape the epithelial lining of the oviduct to obtain nutrition. The epithelium secretes a thick, creamy substance that has been called uterine milk that the young consume along with epithelial tissue.


Caecilian reproduction

  • A Kenyan species of caecilian Boulengerulataitana feeds its young in a different, but similar way.

  • These young are born relatively undeveloped and feed by peeling off layers of their mother’s skin, which contains lipid-filled vesicles.


Courtship and mate selection in amphibians

  • A variety of courtship activities occur in amphibians.

  • In anurans most breeding occurs at night and males call to attract females.

  • Females assess male quality on the basis of the calls (e.g. larger males have deeper calls) and choose the highest quality males.


http://www.arkive.org/media/5A/5A3F66F4-5FA6-4C81-9B92-0D29A942F58D/

Presentation.Large/photo.jpg


Courtship and mate selection

  • Calling is energetically expensive and only the healthiest males can call for long periods.

  • Lower quality males unable to attract a female to themselves may adopt other tactics such as gathering around calling males and attempting to intercept females attracted by the caller.


Courtship and mate selection

  • Many salamanders defend territories and those that can control high quality territories (usually the larger males) attract the most mates.

  • Females are also attracted to the fecal smell of male salamanders that have consumed high quality diets.


Order Urodela

  • There are about 550 species of salamanders. They have an elongate body and long tail and most live on land.

  • Salamanders are almost entirely confined to the Northern Hemisphere with only a few species occurring in northern South America.


Order Urodela

  • The greatest diversity of salamanders occurs in North and Central America and more species of salamander occur in Tennessee than in Europe and Asia combined.


Order Urodela

  • Salamanders have an elongate body and long tail and most live on land.

  • Apart from a few completely aquatic species, salamanders have four functional limbs and use a walk that combines the lateral bending of fish with leg movements.

  • Because the legs project to the sides (instead of being under the body as in e.g. reptiles) salamanders sprawl and the belly often rubs against the substrate.

  • This form of movement is probably similar to that used by the earliest tetrapods.


Order Urodela

  • Most salamanders are <15cm long, but some aquatic forms are bigger, the largest being the Japanese Giant Salamander (1.5 meters long).


Japanese Giant Salamander

http://farm3.static.flickr.com/2387/2368605286_95f46c45c4.jpg


Paedomorphosis

  • Paedomorphosis is widespread among salamanders and in a number of families only paedomphic forms occur.

  • These animals retain as adults larval characteristics.

  • These can include a lack of eyelids, a lateral line system, larval tooth and bone patterns and, in some instances, external gills.


Paedomorphosis

  • Paedomorphic forms include the widespread hellbenders and mudpuppies, which occur in North American streams and rivers.


Cave dwelling salamanders

  • Several groups have salamanders have become specialized for living in caves.

  • Forms that live in cave mouths tend to retain fully metamorphosed adults, but species adapted to the darkest parts of caves are paedomrophic.


Cave dwelling salamanders

  • The most specialized cave dwellers include the Texas Blind salamander and the European Olm.

  • These are both white, blind and possess external gills and flattened snouts that help them reach food under stones.


Texas Blind Salamander

http://pubs.usgs.gov/circ/circ1293/images/Figure8_large.jpg


Order Anura

  • The frogs and toads are by far the largest group of amphibians with more than 4000 described species.


Order Anura

  • Anurans have a large worldwide distribution despite being tied to water for reproduction, having a moist permeable skin and being ectothermic, which means they cannot occupy polar or sub-polar environments.

  • They are specialized for jumping and as adults lack a tail.


Specializations for jumping

  • The hind legs are very enlarged and elongated.

  • The vertebral column is short and the vertebrae are braced by zygapophyses that limit lateral bending.

  • The pelvis is solidly attached to the vertebral column and it has been greatly modified and strengthened.

  • The ilium has been elongated and the rearmost vertebrae have been fused into a solid rod called the urostyle.

  • Together the pelvis and urostyle make the bottom half of the body very stiff.

  • A flexible pectoral girdle and strong forelimbs provide cushioning on landing.


http://www.k-state.edu/organismic/images/frog_skeleton.jpg


Order Anura

  • Anurans have inflexible bodies and unlike salamanders, which swim in the same manner as fish, they swim using simultaneous thrusts of the hind legs.

  • There is dispute about whether the anuran body form evolved because its mode of swimming is more effective or because the large hind limbs allowed anurans to occupy the boundary between land and water and escape into either if threatened.


Order Anura

  • Anurans differ in the relative dimensions of their limbs and these differences relate to their ecological specializations.

  • Most anurans given the common name frog are long legged and move by jumping. Shorter-legged terrestrial anurans are usually called toads and they move by making short hops.


Order Anura

  • Toads move around a lot looking for prey. This makes them conspicuous, but being short legged they cannot flee predators easily. Most instead rely on defensive chemicals produced by their skin for protection.

  • Frogs with their long legs are usually sit-and-wait predators and flee predators by leaping away. Most of them are not protected by toxins.


Leaping Frog

http://www.funfacts.com.au/

images/leaping-frog1.JPG

Woodhouse Toad

http://geoinfo.nmt.edu/staff/wilks/interests/

toads/images/Woodhouse%

27s-Toad-01.jpg


Arboreal frogs

  • There are many species of frogs specialized for climbing in trees and shrubs.

  • These are usually slim and long legged with large heads and eyes.

  • Some of the most specialized arboreal species are called tree frogs and possess specially modified toe pads that allow them to adhere to surfaces.


Common Tree Frog

http://www.naturephoto-cz.com/photos/others/common-tree-frog-9282.jpg


Tree frog toe pads

  • The toe pads of tree frogs have an epidermal layer made up of many projecting papillae separated by small gaps.

  • Mucus glands secrete a viscous fluid that forms a thin layer between the pad and the surface being gripped and a combination of surface tension and viscosity holds the frog in place.

  • These pads allow the frogs to adhere to vertical and even beyond vertical surfaces.


White-lipped Tree frog: note toe pads

http://dic.academic.ru/pictures/enwiki/87/White_lipped_tree_frog_cairns_jan_8_2006.jpg


http://greenerloudoun.files.wordpress.com/2009/01/

frog20hanging20on20for20dear20life.jpg


Order Gymnophiona (Apoda)

  • The caecilians of which there are about 150 species have evolved a legless state and are specialized for burrowing.

  • They look superficially like earthworms.

  • Caecilians are distributed worldwide and most are tropical forest species that burrow in moist forest soil.


Order Gymnophiona (Apoda)

  • The eyes have been greatly reduced in size (fossil forms had much larger eyes) and most species are blind as adults with the eyes being covered by a layer of skin (and in some cases bone).


Yellow-striped Caecilian

http://www.ecologyasia.com/images-a-j/caecilian-head_0007.jpg


Order Gymnophiona (Apoda)

  • The superficial resemblance to earthworms is due in part to the regular skin folds (annuli) that encircle the body.

  • The main annuli overlie vertebrae and myotomal septa and reflect the underlying segmentation of the body.

  • Many caecilians have dermal scales in pockets of the annuli, so caecilians are the only living amphibians with scales.


Caecilian: note prominent annuli.

http://static.howstuffworks.com/gif/caecilian2.jpg


Order Gymnophiona (Apoda)

  • Caecilians feed on worms and other invertebrates that they find burrowing underground.

  • They are probably helped to find their food by another unique feature of the group, protrusible tentacles, which are located either side of the snout between the eye and nostril.

  • The tentacles probably transport chemicals to the vomeronasal organ on the roof of the mouth.


Disappearing Amphibians

  • In the early 1990’s it became apparent that amphibian populations worldwide were in rapid decline.

  • Subsequent review suggested that at least 9 and perhaps as many as 122 species had become extinct since 1980 and that population declines were ongoing.


Disappearing Amphibians

  • Localized causes of declines that have been identified include:

    • microclimate changes due to logging, which results in less forest humid environments that suit amphibians.

    • mining which often employs toxic chemicals that amphibians are especially sensitive to.

    • Habitat destruction by cattle around breeding ponds: young anurans e.g. become trapped in hoofprints


Disappearing Amphibians

  • On a global level however there are a number of factors that appear to be associated with amphibian declines. These include

    • Global warming

    • Acid rain

    • UV radiation

    • Disease


Global warming

  • Amphibian populations at high altitudes are declining faster than those elsewhere.

  • As temperatures rise amphibians adapted to cooler environments are pushed higher and higher up mountains until they run out of habitat.

  • Studies in Queensland, Australia indicate that a 1ºC increase in average temperature will diminish the core available habitat for high altitude species by 65%. An increase of 3.5ºC would eliminate the habitat of half of these species.


Acid rain

  • In the Northern Hemisphere acid precipitation as a result of industrial pollution has affected the pH of water amphibians breed in.

  • Embryos of many species are killed at pH 5 or below.

  • Sub-lethal effects also occur. For example, spotted salamanders reared in acidic water are less coordinated and grow more slowly because they are less effective at catching prey.


UV radiation

  • Thinning of the ozone layer has resulted in higher levels of UV rays reaching the Earth’s surface.

  • There is debate about how important the effects of UV radiation are but UV-B radiation does kill amphibian eggs and embryos.

  • For example only 50-60% of the eggs of Cascade frogs in Oregon exposed to ambient sunlight hatched, but 70-85% of those protected by a UV-B filter hatched.


UV radiation

  • Factors such as water turbidity and variation in different species of amphibians sensitivity to UV damage as well as variation in the ability of different species to repair UV damage complicate an analysis of UV effects.

  • As a result, certain species and breeding sites appear to be unaffected by UV radiation effects.


Disease

  • Most recently there has been increased focus on the role of disease in amphibian declines.

  • In particular, attention has focused on iridoviruses and chytrid fungi.

  • Iridoviruses infect a variety of salamanders, but there appears to be a long evolutionary relationship between hosts and pathogens and it now appears that the viruses may cause local population fluctuations but not extinctions.


Disease

  • There is much more concern about the danger of chytrid fungi.

  • This fungus has been identified as responsible for the disappearance of amphibian populations from the Americas to Australia and New Zealand.


Disease

  • The fungus in the form of motile zoospores in water penetrates the skin and causes a disease called chytridiomycosis.

  • The fungus forms a reproductive body called a zoosporangium and this interferes with respiration and control of water flow and kills adult frogs.


Disease

  • Infected tadpoles appear to survive, but grow slower than uninfected individuals.

  • The fungus appears to have originated in African Clawed frogs, which are resistant to it.

  • African clawed frogs have been used extensively worldwide in lab work and many escaped or were released into the wild bringing the fungus with them.


Disease

  • Waves of chytridiomycosis infection have spread along mountain chains in Central America, South America and Australia and the effects on local populations are often devastating.

  • It is likely that vulnerability to fungal infections is increased because of the effects of stress on immune systems. Thus, pollution, UV radiation and acid rain may be making amphibians more susceptible than they would otherwise be.


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