Amphibians Flashcards
Summary
Three groups of Lissamphibians
Anura
Urodela
Gymnophiona
Summary
Lissamphibia –
modern amphibians; most still have reliance on water for reproduction
Summary
The origin of the tetrapods in the
Devonian period, pre-adapted for life on land
What is an amphibian
1. A tetrapod gnathostome Excludes the Actinistia (coelacanths) and the Dipnoi (lungfish) Tetrapoda AGr tetra = “four” + pous = “foot” All vertebrates whose ancestors had four limbs and digits 2 lineages Lissamphibia (today) Amniota (next week)
What is an amphibian
- A tetrapod gnathostome
Excludes the Actinistia (coelacanths) and the Dipnoi (lungfish)
- Tetrapoda
All vertebrates whose ancestors had four limbs and digits
2 lineages
Lissamphibia [focus this deck]
Amniota
Preadaptation for life on land
5 points
- Lungs developed before moving onto land
outgrowths of the gut, for buoyancy and/or oxygen supply (ambient oxygen was half modern amount in the Devonian)
- The choanae
Bony fish have 2 pairs of nostrils: water flows in through the forward pair, over the olfactory tissue and out through the second pair
Tetrapods have one pair, plus internal choanae which allow them to breath in through the nose
- Adaptations for shallow water
Flattened body and skull; paired lobed fins adapted for movement rather than anal fin
- Fins develop a bend at the elbow and knee
- Modified skull and jaw to grab food on land
Fish need to expand buccal cavity to create pressure difference
Tetrapods
3 points
- Earliest tetrapods were wholly aquatic, probably in brackish water
- The Late Devonian extinction (c. 370 Mya) killed off all fish-like tetrapods and left only those adapted to terrestrial existence
Some later returned to aquatic lifestyle - Later adaptation
Placement of eyes on head: heads become tall and narrow again
Head and neck mobility: fish lack necks
Fused sacrum: connects pelvis and hindlimbs
Loss of gills, tail fins, lateral lines
Labyrinthodonts
- Ancestral to all extant land-living vertebrates
- Name (“maze-tooth”) refers to infolding of dentine and enamel
- Heavily armoured skulls and complex vertebrae
Ichthyostegalia
Reptiliomorpha
Temnospondyli
Lepospondyli [one of these 2 ancestor of modern amphibians]
“Amphibia” included
all extinct and modern amphibians
Lissamphibia includes
just modern day frogs, salamanders, and caecilians
Modern Amphibians
Lissamphibia
3 points
- Anura: frogs and toads
- Urodela: salamanders and newts
- Gymnophiona: caecilians
Most of the differences between these groups are down to different modes of locomotion
Modern Amphibians
Lissamphibia
Common ancestor probably possessed:
6 points
- Pedicellate teeth (have a crown and base/pedicel of dentine)
- Operculum-plectrum complex to transmit sounds to the inner ear
- Skin with mucous cells (keep skin moist) and granular cells (produce poison)
- A two-channel sensory area in the inner ear to pick up high and low frequencies
- Ability to elevate eyes with levator bulbi muscles
- Fat bodies located near gonads
Body Plan
3 points
- Evolved from a salamander-like body plan
- Skin has cornified layer but is permeable to water
Moulted in one piece
Gas exchange takes place through skin
Mucous glands keep skin moist
Granular glands secreted distasteful or poisonous substances - Hollow bones
Respiration
3 points
- Lungs are simple compared to amniotes
Large alveoli, few internal walls
Less efficient: oxygen diffuses slowly
Use buccal pumping rather than ribs to ventilate
- Cuticular respiration
Requires water layer
More efficient at lower temperatures (oxygen concentration goes up)
- Larvae have external gills
Circulation
2 points
- Two-chambered heart in larvae (like a fish)
Only pumps deoxygenated blood
- Three chambered heart in adult
One ventricle, two atria
Some mixing of oxygenated and deoxygenated blood
Digestion
4 points
- All living species are carnivorous
Few morphological specialisations
- Most catch prey with sticky tongue
- Inertial feeding to assist with swallowing, plus eyeballs
- Large liver stores glycogen, also possess fat bodies near kidneys
Excretion
2 points
- Kidneys are dorsal; filter blood with high pressure system
- Excrete urea due to need to conserve water
Some tree frogs excrete uric acid (can be even drier)
Larvae excrete ammonia
Nervous system
2 points
- Brain is equal parts cerebrum, midbrain, and cerebellum
2. Pineal body controls hibernation and aestivation
Senses
3 points
- The operculum-plectrum complex is responsible for transmitting both vibration and sound
- Papillae amphibiorum and papillae basilaris detect sound at different frequencies
- Larval amphibians retain lateral line
Reproduction
- Usually requires fresh water
Some tropical frogs have direct development (tadpoles do not emerge from eggs)
- Frogs use external fertilisation
Male grasps female (amplexus) - Salamanders and caecilians use internal fertilisation
Male salamanders produce a spermatophore; the female takes it up
male caecilian uses an intromittent organ
- Metamorphosis regulated by thyroxine and prolactin
Anura
Frogs and toads
3 points
- Urostyle formed of fused vertebrae
9 presacral vertebrae
Long, forward-sloping ilium in pelvis
Lower jaw without teeth
Frontoparietal bone between eyes
- Earliest fossil is early Triassic (250 Mya)
- No biological difference between frogs and toads
Urodela
Salamanders
5 points
- Slender bodies with blunt snouts
Short limbs projecting at right angles, digit and/or limb reduction
Tail in both adult and larval forms
- Earliest fossil is Middle Jurassic (c. 170 Mya)
- Reduction of toes, amphiumas have reduced legs, sirens have no hind limbs
- Extreme self-defence
- Caudal autotomy & puncturing ribs
Gymnophiona
Caecilians
7 points
- Eyes only detect light dark,
- have a pair of tentacles between eyes and nostrils
- Adaptations to burrowing lifestyle
Completely lack limbs, tails may be absent
Skin has ring-shaped folds as
well as scales containing calcite
Strong skull with pointed snout
- Most are viviparous, giving birth to well-developed offspring
- One egg-laying species feeds its own skin to newly-hatched young
- Live in wet, tropical regions
Eat soil-dwelling invertebrates, particularly worms - One aquatic family has an eel-like fin
