15: Amphibians Flashcards by Rebecca Crummett

When did amphibians split into two main evolutionary lines?

300mya

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What are the two main evolutionary lines of amphibians?

Ancestors of reptiles

Ancestors of modern amphibians

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How many species of amphibian are there?

Around 6000

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What is their water/land relationship?

Adapted for life on land, but still depended on water

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Why move onto land?

Competition/predation with other aquatic species
More food sources- metamorphosis, so exploit different niches
Can get back into the water under arid conditions

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Amphibian fossil record

None found from before early Jurassic- gap in fossil record

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Why is the fossil record so bad?

Burrowing species
Lived in fertile environments
Had a reduced skeleton
Had soft, delicate bodies

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What happened in the Triassic?

Lots of environmental change
Huge rise in CO2 concentration at the end of Triassic
Deserts expanded their range
No recorded glacial activity
These could have impacted the potential for fossilisation

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What were Stereospondyl?

A group of extinct amphibians

Eg. Mastodontosaurus, Peltobatrachus

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Features of Stereosponyli compared to other tetrapods

More simplified backbones and weak vertebrae-
couldn’t support own body weight, could only crawl on land
Appeared in Late Permian

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When were amphibian ancestors from?

The Permian

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Two theories of the ancestry of modern amphibians

Single phylogenetic group due to similarities in soft tissue and physiology
Frogs and amniotes evolved from different groups of fishes than those that gave rise to salamanders

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Tooth similarities between frogs, salamanders and caecilians

All have pedicellate teeth- base of tooth is separated from crown by fibrous tissue that is softer than dentine or enamel

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Importance of pedicellate teeth

Unique, probably only evolved once

Suggests that extant amphibians are monophyletic

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Characteristics of modern amphibians

Bony skeleton
2 types of skin glands
Ectothermal
Ribs do not encircle body
Pedicellate teeth
Fat bodies
Green rods in eyes
Presence of operculum

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Name for all extant amphibians

Lissamphibia

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Shared characteristics with tetrapods

Fenestration of skull
Loss of posterior skull bones
10 cranial nerves

Amphibian heart features

3 chambered hearts

Incomplete separation of the ventricles

Examples of salamanders

Great Crested Newt, Britains largest and most endangered newt species
Giant salamander

Salamander’s ties to water

Aquatic larvae
Metamorphosis to terrestrial adults
Some are entirely aquatic
So not separate from water

Ancestry of salamanders

Possibly from Triassic

Don’t see transition fossils due to Romer’s Gap (Cretaceous)

Common characteristics of salamanders

500 species
Limbs at a right angle (sprawling gait)
Aquatic and burrowing limbs
Carnivorous- worms, arthropods, molluscs
Have gilled larvae

Characteristics of salamander skulls

Loss of primitive bones at the back of the skull
Large orbits
Pedicellate teeth
Lower jaw consists of Meckel’s cartilage
No bony connection between pterygoid and maxilla

Characteristics of salamander skeleton

Single sacral vertebrae
Short ribs
Extensive tail
Loss of dermal bone on the shoulder girdle
Small pubis

What are axolotyls?

They can metamorphose under certain conditions into salamander-type things Gills become lungs Look very prehistoric Don't live long after transformation

How do salamanders capture prey?

Use tongue prehension Very sticky tongue Rapid projection/retraction Modify speed and angle of attack based on prey size

What are Caecilians?

Amphibians that totally lack girdles and limbs Weird slimy snake things Eg. blue caecilian

How many Caecilian fossils are there?

Only 3 well preserved enough to be named

How many species of Caecilian are there?

160

Caecilian characteristics

``` Elongated body Small scales Limbless Burrow Internal fertilisation Aquatic larvae Eat worms and small invertebrates ```

What is skin feeding?

Parents grow bits of skin very high in nutrients | Babies eat this

Jurassic frogs

Look a lot like modern frogs

What is Prosalirus bitis?

The oldest known frog (Jurassic) Known from post cranial skeleton Bones indicate that it was capable of jumping

What is Vieraella?

Nearly complete frog fossil From the Lower Jurassic 10 vertebrae Fused tibia and fibula

What are Shomronella?

Cretaceous tadpoles | Fossil record of tadpoles is quite good

Extant Anuran (frogs) features

``` Aquatic reproduction Tailed larvae form with gills No tails in adult, lungs Specialised for jumping If frogs go, so will everything else ```

How many species of Anuran are there?

4840

Frog anatomy

``` Large orbits Pedicellate teeth No ribs Loss of scales No hyoid bone Fused ulna and radius and tibula and fibula- to prevent breaking when jumping ```

Why do snakes need lots of venom to kill frogs?

They have low metabolic rates

How do some frogs fly?

Glide using webbed hands and skin flaps