15: Amphibians Flashcards
When did amphibians split into two main evolutionary lines?
300mya
What are the two main evolutionary lines of amphibians?
Ancestors of reptiles
Ancestors of modern amphibians
How many species of amphibian are there?
Around 6000
What is their water/land relationship?
Adapted for life on land, but still depended on water
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
Amphibian fossil record
None found from before early Jurassic- gap in fossil record
Why is the fossil record so bad?
Burrowing species
Lived in fertile environments
Had a reduced skeleton
Had soft, delicate bodies
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
What were Stereospondyl?
A group of extinct amphibians
Eg. Mastodontosaurus, Peltobatrachus
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
When were amphibian ancestors from?
The Permian
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
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
Importance of pedicellate teeth
Unique, probably only evolved once
Suggests that extant amphibians are monophyletic
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
Name for all extant amphibians
Lissamphibia
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
