earliest amphibians the earliest are the labyrinthodonts, which included icthyostega and...

Earliest amphibiansEarliest amphibians

The earliest are the labyrinthodonts, which The earliest are the labyrinthodonts, which included included IcthyostegaIcthyostega and and AcanthostegaAcanthostega. .

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

AnthracosauriaAnthracosauria and and TemnospondylsTemnospondyls

The The AnthracosauriaAnthracosauria and the and the Temnospondyls were both diverse groups Temnospondyls were both diverse groups and many were very large being several and many were very large being several meters long. meters long.

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

Poterogyrinus an Anthracosaurhttp://upload.wikimedia.org/wikipedia/commons/thumb/2/2c/Proterogyrinus_DB.jpg/260px-Proterogyrinus_DB.jpg

Seymouria: an Anthracosaurhttp://www.prism.gatech.edu/~gh19/b1510/tetra.gif

A small carboniferous temnospondyl and a scorpionhttp://www.hmnh.org/galleries/permocarboniferous/temnospondyl.gif

Eryops: a temnospondyl http://comenius.susqu.edu/bi/202/animals/DEUTEROSTOMES/vertebrata/eryops.jpg

AnthracosauriaAnthracosauria and and TemnospondylsTemnospondyls

Both groups left modern descendants behind. Both groups left modern descendants behind. The Anthracosauria gave rise to the amniotes in The Anthracosauria gave rise to the amniotes in

the late Carboniferous, but the rest of the group the late Carboniferous, but the rest of the group became extinct in the Permian.became extinct in the Permian.

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

LissamphibiaLissamphibia

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

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

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

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

LissamphibiaLissamphibia

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

Class Class LissamphibiaLissamphibia

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

Urodela “tailed ones”: salamandersUrodela “tailed ones”: salamanders Anura: “tailless ones” frogs, toads.Anura: “tailless ones” frogs, toads. Gymnophiona (“naked snake”; previously Gymnophiona (“naked snake”; previously

Apoda “legless ones”) caecilians.Apoda “legless ones”) caecilians.

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

Eastern Mud salamander

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

http://upload.wikimedia.org/wikipedia/commons/6/66/Caecilian_wynaad1.jpg

Red-eyed Tree froghttp://www.frogsite.org/pic/Redeyed_Tree_Frog.jpg

Amphibian skinAmphibian skin

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

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

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

Amphibian skinAmphibian skin

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

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

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

Mucous gland and poison glandsMucous gland and poison glands

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

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

Poison glandsPoison glands

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

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


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

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


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

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

Poison dart frogsPoison dart frogs

Several genera of brightly colored Neotropical Several genera of brightly colored Neotropical frogs (frogs (DendrobatesDendrobates, , PhyllobatesPhyllobates, and , and EpipedobatesEpipedobates) produce highly toxic steroidal ) produce highly toxic steroidal alkaloids in their skin. alkaloids in their skin.

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

Green and Black Poison Dart Frog http://www.shoarns.com/frog.jpg

Poison dart frogsPoison dart frogs These frogs are very small (rarely more than 2” long), These frogs are very small (rarely more than 2” long),

but just one frog produces enough toxin to kill several but just one frog produces enough toxin to kill several people. people.

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

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

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

Medical applications of skin Medical applications of skin secretionssecretions

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

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

Medical applications of skin Medical applications of skin secretionssecretions

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

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

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

Gas exchangeGas exchange

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

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

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

MikePinder.jpg

Gas exchangeGas exchange Gas exchange also takes place via lungs and gills (in Gas exchange also takes place via lungs and gills (in

larvae).larvae).

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

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

GillsGills

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

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

GillsGills

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

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

Larval Tiger Salamanderhttp://www.axolotl.org/images/tiger/tiger_larva.jpg

FeedingFeeding

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

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

Frogs of the genera Frogs of the genera LepidobatrachusLepidobatrachus and and CeratophrysCeratophrys which mainly eat other frogs have which mainly eat other frogs have enormous heads relative to their body size. enormous heads relative to their body size.

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

FeedingFeeding

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

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

Tongue protrusionTongue protrusion

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

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

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

In some anurans, such as In some anurans, such as RanaRana and and BufoBufo, , the tongue is very protrusible. the tongue is very protrusible.

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

Caecilans have rudimentary tongues that Caecilans have rudimentary tongues that cannot be everted.cannot be everted.

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

Bullfrog feeding clipBullfrog feeding clip

http://www.youtube.com/watch?http://www.youtube.com/watch?v=wXqK5QulbJ8&feature=results_video&pv=wXqK5QulbJ8&feature=results_video&playnext=1&list=PLF0F6BFDE4C37D6F7 laynext=1&list=PLF0F6BFDE4C37D6F7

ReproductionReproduction

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

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


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

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

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

Figure 25.04


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

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

Figure 25.26

Salamander reproductionSalamander reproduction

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

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

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

Salamander spermatophoreshttp://www.wildlife.state.nh.us/Wildlife/Nongame/salamanders/salamander_images/spermatophore2-Marchand.jpg


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

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


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

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

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

Figure 25.08

Caecilian reproductionCaecilian reproduction

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

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

Figure 25.05

Many caecilians lay their eggs in the mud near water, but some caecilians brood their eggs in burrows.


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

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

Caecilian with younghttp://www.abdn.ac.uk/~nhi708/classify/animalia/chordata/amphibia/apoda/caecilian.jpg


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

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


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

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

Courtship and mate selection in Courtship and mate selection in amphibiansamphibians

A variety of courtship activities occur in A variety of courtship activities occur in amphibians.amphibians.

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

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

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

Courtship and mate selectionCourtship and mate selection

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

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

Courtship and mate selectionCourtship and mate selection

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

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

Order UrodelaOrder Urodela

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

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


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

Order UrodelaOrder Urodela Salamanders have an elongate body and long tail and Salamanders have an elongate body and long tail and

most live on land. most live on land.

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

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

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


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

Japanese Giant Salamanderhttp://farm3.static.flickr.com/2387/2368605286_95f46c45c4.jpg

PaedomorphosisPaedomorphosis

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

These animals retain as adults larval These animals retain as adults larval characteristics.characteristics.

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

PaedomorphosisPaedomorphosis

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

Cave dwelling salamandersCave dwelling salamanders

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

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

Cave dwelling salamandersCave dwelling salamanders

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

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

Texas Blind Salamanderhttp://pubs.usgs.gov/circ/circ1293/images/Figure8_large.jpg

Order AnuraOrder Anura

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


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

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

Specializations for jumpingSpecializations for jumping

The hind legs are very enlarged and elongated.The hind legs are very enlarged and elongated. The vertebral column is short and the vertebrae are The vertebral column is short and the vertebrae are

braced by zygapophyses that limit lateral bending.braced by zygapophyses that limit lateral bending. The pelvis is solidly attached to the vertebral column and it The pelvis is solidly attached to the vertebral column and it

has been greatly modified and strengthened.has been greatly modified and strengthened. The ilium has been elongated and the rearmost vertebrae The ilium has been elongated and the rearmost vertebrae

have been fused into a solid rod called the urostyle.have been fused into a solid rod called the urostyle. Together the pelvis and urostyle make the bottom half of Together the pelvis and urostyle make the bottom half of

the body very stiff.the body very stiff. A flexible pectoral girdle and strong forelimbs provide A flexible pectoral girdle and strong forelimbs provide

cushioning on landing. cushioning on landing.

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

Order Anura Order Anura

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

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


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

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


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

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

Woodhouse Toadhttp://geoinfo.nmt.edu/staff/wilks/interests/toads/images/Woodhouse%27s-Toad-01.jpg

Leaping Froghttp://www.funfacts.com.au/images/leaping-frog1.JPG

Arboreal frogsArboreal frogs

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

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

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

Common Tree Froghttp://www.naturephoto-cz.com/photos/others/common-tree-frog-9282.jpg

Tree frog toe padsTree frog toe pads The toe pads of tree frogs have an epidermal The toe pads of tree frogs have an epidermal

layer made up of many projecting papillae layer made up of many projecting papillae separated by small gaps.separated by small gaps.

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

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

White-lipped Tree frog: note toe padshttp://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)Order Gymnophiona (Apoda)

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

They look superficially like earthworms. They look superficially like earthworms.

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

Order Gymnophiona (Apoda)Order Gymnophiona (Apoda)

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

Yellow-striped Caecilianhttp://www.ecologyasia.com/images-a-j/caecilian-head_0007.jpg

Order Gymnophiona (Apoda)Order Gymnophiona (Apoda) The superficial resemblance to earthworms is The superficial resemblance to earthworms is

due in part to the regular skin folds (annuli) that due in part to the regular skin folds (annuli) that encircle the body.encircle the body.

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

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

Caecilian: note prominent annuli.http://static.howstuffworks.com/gif/caecilian2.jpg

Order Gymnophiona (Apoda)Order Gymnophiona (Apoda) Caecilians feed on worms and other Caecilians feed on worms and other

invertebrates that they find burrowing invertebrates that they find burrowing underground.underground.

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

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

Disappearing AmphibiansDisappearing Amphibians

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

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


Localized causes of declines that have Localized causes of declines that have been identified include:been identified include: microclimate changes due to logging, which microclimate changes due to logging, which

results in less forest humid environments that results in less forest humid environments that suit amphibians. suit amphibians.

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

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


On a global level however there are a On a global level however there are a number of factors that appear to be number of factors that appear to be associated with amphibian declines. associated with amphibian declines. These includeThese include Global warmingGlobal warming Acid rainAcid rain UV radiationUV radiation DiseaseDisease

Global warmingGlobal warming

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

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

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

Acid rainAcid rain In the Northern Hemisphere acid precipitation as In the Northern Hemisphere acid precipitation as

a result of industrial pollution has affected the pH a result of industrial pollution has affected the pH of water amphibians breed in.of water amphibians breed in.

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

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

UV radiationUV radiation

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

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

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

UV radiationUV radiation

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

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

DiseaseDisease Most recently there has been increased focus on Most recently there has been increased focus on

the role of disease in amphibian declines.the role of disease in amphibian declines.

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

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

DiseaseDisease

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

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

DiseaseDisease

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

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

DiseaseDisease

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

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

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

DiseaseDisease

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

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

earliest amphibians the earliest are the labyrinthodonts, which included icthyostega and...

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