Modern reptiles and amphibians are not sister taxa.
Historically, they have been confused and studied together because they are often found in similar habitats.
Linnaeus (1758), the father of biological nomenclature and classification, described them as "the worst and most horrible of animals," highlighting their cold bodies, dirty complexion, foul skin, grim faces, brooding gaze, foul smell, hoarse voice, squalid habitats, and horrible poison.
Egg: Shell-less, non-amniote egg, requiring water for reproduction.
Larval Stage: Often have a larval stage.
Skin: Moist skin plays a major role in gas exchange.
Habitat: Diverse mostly in humid habitats.
Keratinous Structures: Lack keratinous structures.
Egg: Shelled amniote egg, self-contained and independent of water.
Larval Stage: No larval stage.
Skin: Dry skin with little role in gas exchange.
Habitat: Often successful in dry habitats.
Skin: Covered in scales, often with complex structures.
Live on land and water (amphi = both, bios = life).
Reproduction often tied to water: aquatic larval life stage followed by metamorphosis. However, there are many exceptions, which will be discussed in later lectures.
Skin is moist and generally permeable, which is important for gas exchange but also makes them vulnerable to water loss.
Most species are tied to humid environments, with the greatest diversity in tropical forests.
Species inhabiting dry areas shelter in humid microhabitats and are often inactive for most of the year.
Three major groups:
Anura – frogs and toads – 7806 species
Caudata – salamanders and newts – 826 species
Gymnophiona – caecilians – 225 species
Limbless, burrowing amphibians.
Mostly small, a few species grow to > 100 cm.
Distribution: tropics, worldwide excluding Australia.
Fossorial or aquatic.
Live-bearing or egg-laying.
Feed on invertebrates.
Reduced or absent eyes.
Unique sensory tentacles.
Often pronounced parental care.
Hydrostatic "tube in a tube" movement, unique in vertebrates, which generates greater forward force than standard longitudinal muscles.
Fossoriality: constraint on head size.
Large muscle and posterior projection of the mandible ensure adequate bite force.
Maternal nutrition for offspring: Skin feeding in oviparous Boulengerula taitanus.
Parental care of oviparous Siphonops annulatus includes cloacal "milk" secretion that supplements skin feeding.
Limbed (usually), tailed amphibians.
Mostly small, some up to ~ 100 cm.
Terrestrial or aquatic, few arboreal.
Distribution: worldwide except Africa, Australia.
Family Plethodontidae – lungless salamanders – contains 67% of Caudata
* Lunglessness – more than 50% of caudates are functionally lungless, breathing through skin only.
* Paedomorphosis – retention of larval characters in adults – e.g. permanent aquatic life, gills; evolved multiple times.
Triturus cristatus – Great crested newt
Lissotriton vulgaris – Smooth newt
Lissotriton helveticus – Palmate newt
Smallest UK newt – to 9 cm.
Most common in north and west of UK.
Most common newt in montane and acid soil areas – including much of NW Wales.
Common in Bangor and on Anglesey (e.g., Treborth, Newborough Forest, throughout Snowdonia).
Male: black, enlarged feet; tail filament; Both sexes: pinkish unspotted throat
Small – to 10 cm
Most common in Midlands and eastern England
Rarer in northern and western hill and acid soil areas
Very uncommon in NW Wales – often confused with palmate newt. Only reliable records from NE Wales W. to Llandudno
Males: wavy crest, strongly spotted, feet not black, no tail filament. Both sexes: Throat yellow, clearly spotted
UK’s largest newt – to 18 cm
Most common in Midlands and eastern England
Rarer in northern and western hill and acid soil areas
Common on Anglesey (e.g., Newborough Forest), a few colonies along mainland coasts (Llanfairfechan, Pensychnant)
Males: high, jagged crest. Females: no crest. Rough, warty skin. Males: silver “flash” on tail
European Protected Species
Licence required to:
Disturb (including torchlight surveys!)
Handle
Habitats also protected
Hence: developers’ nemesis!
Delays could be avoided by taking ecology seriously from the start…
Tail-less amphibians with large heads, short bodies, well-developed limbs.
Worldwide distribution.
Extensive ecological and reproductive diversity.
88% of total amphibian diversity!
Note: “frogs” and “toads” are not a natural evolutionary subdivision!
“Frogs” (Ranidae), “Toads” (Bufonidae)
Arboreality, e.g. family Hylidae (tree frogs) – long fore- and hind limbs
Burrowing (short limbs & snout) – various families, evolved multiple times
Aquatic – long hind limbs, large webbed feet
Jumping vs hopping/walking – long muscular hind limbs vs short hind limbs
Toxic skin secretions +/-aposematic coloration
Dendrobatidae – C&S America
Mantella - Madagascar
Bufo marinus – cane toad
Key role of acoustic communication
Diversity of modes of reproduction, usually involving shift away from water
Marsupial frog (Flectonotus sp.) incubates eggs under the skin of the back; the female then deposits tadpoles in the water.
Foam nest-building frogs avoid the need to deposit eggs in water.
Rana temporaria – Common frog
Bufo bufo – Common toad
Epidalea calamita - Natterjack
Pelophylax lessonae – Pool Frog
Widespread throughout Britain and Ireland, to over 1000 metres elevation.
Remains common in gardens and the wider countryside.
Breeds January – March.
Eggs laid in clumps of spawn.
Dark ear patch / mask
Widespread throughout Britain, absent from Ireland.
Widespread in Europe and western Asia.
Declining severely in the UK and other parts of Europe.
Breeds Feb-March in UK, depending on region
Explosive breeder
Spawn laid in strings
Localised in Britain and SW Ireland
Found in heathlands and dune ponds; often breed in brackish water.
In severe decline
European Protected Species
light line along spine
UK populations were long believed to be introduced from C. Europe
Usually found in and around permanent pools – noisy!
The last population in East Anglia died out in the 1990s
Shortly thereafter, identified as having been native after all! (DNA, sound analysis)
Now being reintroduced from Sweden to Norfolk.