Amphibians Flashcards
What set the stage for the invasion of land?
Evolution or lung like sacs in response to the inadequacy of gills in oxygen poor waters
What did the evolution of lung like sacs allow
Allowed them to breathe in air and leave the water temporarily
What was the first lineage to evolve jointed limbs?
Sarcopterygii - lobe finned fish
In what ways do lobe finned fish differ from ray finned?
The fins are attached on a fleshy, lobe like scaly stalk extending from the body
Pectoral and pelvic fins resemble tetrapods limbs
Teeth covered with enamel
How are lungfish specially adapted
Have lungs and gills, can burrow in mud when ponds dry up surviving for months inactive breathing air
Believed to have given rise to the tetrapods
What is the prototetrapod?
A descendant of lungfish
What fossil represents an intermediate between a finned fish and limbed tetrapod?
Devonian fossil found on Ellesmere Island
- pectoral girdle seperate from skull
- fins separated from opercular bones
What is the advantage of separating the pectoral girdle from the skull?
Feeding
- greater mobility of skull, greater feeding
- snout and jaws become elongated
- improved articulation of the jaw and expansion of primary palate
Why did lobe fins evolve into limbs? (Advantages of terrestrial land)
- adaption to temporary and shallow pools
- foraging above water surface (insects, plants)
- juvenile dispersal movements
- escape from predatory fish
- new semi-terrestrial foraging niches available
What happened because of the movement to terrestrial life
- smell, airborne now, olfactory organs had to adapt
- reproduction, can no longer do spray fertilisation
- adapted to breath air through skin and lungs, so circulatory system needed to adapt
- implications for sound conduction because of pectoral girdle divorcing from skull
What skeletal changes occurred due to terrestrialisation?
- undulatory locomotion
- suspension of vertebral column
- regionalisation of vertebral column
- organisation of amphibian vertebrae
- suspension of internal organs
- reorganisation of the skull
How did amphibians deal with water loss through evaporation?
Producing concentrated urine in kidneys
What is the buccal pump?
The method of extracting oxygen from the air
- opens mouth, closes opercula,
- depresses buccal floor, increasing the volume
- air enters, closes its mouth, then depresses the buccal cavity
- air is forced into the lungs
- positive pressure system
- elastic recoil of the lungs forced air out the operculum
What is the problem with fish form vertebrae?
There is no support so sags on land when there is no buoyancy
What did terrestrial animals evolve in their vertebrae?
Zygapophyses
Regions of vertebra that fix against the preceding vertebra to form a stop, stopping it from bending downwards
What’s the acanthostega
A stem tetrapod of late Devonian
Shows precursor of our limbs, with humorous, radius and ulna, and 8 digits
Weak developments of zygapophyses
Little differentiation between regions of vertebral column
What is icthyostega
A stem tetrapod of late Devonian
Has distinct zygapophyses, vertebral column is supported
Differentiation of regions: abdominal region has large ribs
Reduction in size of tail
Robust limbs
7 digits now
What are extant amphibians (lissamphibia) early ancestors and what were they like
Temnospondyls
Scary, superficially crocodile like
Survived until 130mya, lissamphibia diverged from them in early Triassic
What is amphibians 2 stage life cycle?
- Usually a free-living aquatic development stage
2. Usually a terrestrial juvenile/adult stage
What are the 3 divisions of lissamphibia?
Urodela - salamanders and newts
Anura - frogs and toads
Gymnophiona - caecilian (limbless amphibians)
What are amphibians teeth like
Pedicellate
Has a crown and a pedicel, as the crown wears, it breaks off and is replaced by a new one
What is amphibians skin like?
Moist, permeable, poison glands
2 types of skin gland:
- mucous gland maintains moist skin for respiration
- granular glands produce toxic secretions
What is different about amphibian hearing to other tetrapods?
They have the basilar papilla, but also have a larger 2nd amphibian papilla, set to a lower frequency
What is the bone complex in the amphibian ear?
Operculum-columella complex
What is the supporting structure called in amphibians?
Choroidal hyaline cartilage
What are the 2 types of rod cells in amphibians
Red rods (rhodopsin) - green wavelength Green rods (unique to amphibians) - blue wavelength
What are the 2 types of cones in amphibians eyes?
Single cones - yellow wavelength
Double cones - 2 singles fused together, one rhodopsin one yellow
What are the 3 colour pigment cells in amphibians?
- melanophores - Black, brown reddish
- iridophores - reflect light
- xanthophores - yellow orange or red
Basic features of urodela?
- undulate swimming
- paedomorphosis (adult resembles child)
- 400 species
Basic features of Anura?
- 3750 species
- an = without, uro =tail
- enlarged hind legs
- fast powerful hind limb muscles
- very large nerves to limb muscles
What is the lethal does for a 68kg person of poison dart frog toxin?
100ug, 2 grains of salt!
10x more potent than pufferfish toxin
Basic features or gymnophiona?
- legless, either burrowing or aquatic
- dermal scales
- internal fertilisation
- nests or viviparous
Why are amphibian eggs different?
- must be laid in water to avoid desiccation
- egg stores large amounts of yolk so embryo can be advanced stage of development before hatching
Features of amphibian reproduction
- external or internal
- water or land
- larvae of miniature adults initially
- parental care, often male, can be attached to adults, mouth or stomach brooders
Are the larvae of different species adapted to the environment they grow up in?
Yes,
Eg. Salamanders that spawn in fast moving streams are more streamline, ones that spawn in oxygen poorer waters have bigger gills
