Tetrapod Lecture Flashcards
Tetrapods aka
“four foot”
Tetrapod show evolutionary transition
from life in water to land
Life on Land opportunities:
O2 more abundant (20x) in air than H2O
O2 more easily acquired in air than H2O
Variety of habitats on land (abundant shelter “vegetative structure” & food “invert.’s”)
Life on Land challenges:
air ~800x less dense than water @STP - no buoyancy / dealing w/ gravity new ways to support body required - girdles (modified) & limbs (evolved) to combat gravity on land - skeletal remodeling
life in the “Devonian” aka
the “age of fishes”
Devonian period began
> 400 mya
Devonian land masses & temperatures
- near the equator, swampy w/ FW, low elevation
- mild & consistent temperatures BUT many FW environments unstable (alternating wet & dry periods)
Early Tetrapod Origins Groups
Eusthenopteron, Panderichthys, Tiktaalik, Acanthostega
Eusthenopteron moves
along bottom of ocean w/ lobed fins
Eusthenopteron pectoral girdle attached to
skull (fish characteristic, not synap)
- t.f. no neck in fish
Eusthenopteron shows early origin of
limbs
Sarcopterygian (rhipidistian lineage) lobed fins homologous to
elements of tetrapod limb (arm) bones
Panderichthyes skull
depressed w/ eyes on top like early tetrapods
Panderichthyes lived
in shallow H2O (t.f. depressed skull)
Panderichthyes loss & reduction
loss: dorsal & anal fin
reduction: caudal fin
Panderichthyes girdle attached
still to skull (no neck)
- by bony gill coverings
Tiktaalik aka
“fishapod”
Tiktaalik lived
in late Devonian
Tiktaalik qualities (fish-like & tetrapod-like)
Fish-like: scales, gills, lateral line, & fins w/ rays (no digits)
Tetrapod-like: depressed skull, & shoulder, elbow, & wrist elements (mobile joints). Skull not attached to pectoral girdle, t.f. most basal “necked” vertebrate lineage
most compelling example to date of an animal close to the transition between water and land?
Tiktaalik
Acanthostega pectoral girdle
not attached to skull (had neck)
Acanthostega appendages
well-formed limbs (increase mobility)
Acanthostega fin rays on
tail
Acanthostega digits?
many digits (reduction & loss in modern tetrapods)
Acanthostega show homology in fish thru
stapes & hyomandibular????
Carboniferous radiation of tetrapods
- time of warm, moist, swampy environment w/ many insects on land & invertebrates in waters
- opportunity for tetrapods to invade habitats and diversify (adaptive radiation)
2 major lineages of tetrapods have extant representatives
Lissamphibia
Amniota
Temnospondyli =
extinct lineages + lissamphibia
Lissamphibia =
3 modern amphibian clades:
- Anura
- Caudata
- Gymnophiona
Temnospondyli monophyletic or paraphyletic?
monophyletic clade
Lissamphibia monophyletic or paraphyletic?
monophyletic clade
Anura monophyletic or paraphyletic?
monophyletic clade
Caudata monophyletic or paraphyletic?
monophyletic clade
Gymnophiona monophyletic or paraphyletic?
monophyletic clade
Lissamphibia synapomorphies
- naked moist skin w/ mucous & poison glands
- respiration in adults via lungs, gills, skin, or combo
- buccopharyngeal (+) pressure air pump (ribs don’t encircle viscera)
- no nails or claws
- bubble muscles elevate eyes & retract eyes into orbits
Caudata aka
salamanders
Caudata have limbs?
tail?
usually
always
Caudata diet
as larvae & adults: carnivorous
caudata condition
metamorphic (ancestral w/in lissamphibia)
- some paedomorphic (type of heterochrony) - (derived)
paedomorphic =
attains sexual maturity but retains larval characteristics (external gills, tail fin, aquatic habitat)
Caudata reproduction
most return to water to lay eggs (ancestral)
some w/ direct development in terrestrial environment
direct development
larval stage in egg & young hatch as miniatures of adults
Caudata fertilization
internal
- male drops spermatophore (packet of sperm) & female picks it up w/ cloaca
- complex courtship
Caudata extremes
tongue projection in prey capture
Caudata respiration
via lungs, gills, skin (usually a combo)
Largest Caudata family respiration
(Plethodontidae) & depend on respiration thru skin
Anura aka
“frogs”
Anura synapomorphies
- simplified skull (reduction & loss of bones)
- no teeth in mandible
- no tail in adult
Anura shared characteristics
- most w/ larval stage (tadpole)
- many w/ direct development
Anura tongue attached at
front of mouth and flips forward
Anura tongue evolution from caudata
independently evolved
Anuran ancestor
Triadobatrachus (extinct)
Triadobatrachus
frog-like but less specialized in jumping
Triadobatrachus had
small tail!!
Anuran skull morphology shows
similarities & indicate close relationship between outgrip & sister taxon to clade including all extant anurans
Anuran larvae diet?
adult diet?
herbivorous (larva = no true teeth)
carnivorous (adult = true teeth)
Anuran ventilatory mechanics
- air into lungs by using buccal (+) pressure pump
- air forced out of lungs via contraction of body musculature
Anuran calling
air forced from lungs to vocal sacs
anuran vocal sacs serve as
resonators to amplify sound during male mating calls
Anuran fertilization/reproduction
almost always external fertilization
male clasp females (amplexus) & fertilize eggs as they are laid
Among tetrapods, anurans show most bizarre
reproductive strategies
Gymnophiona (caecilian) aka
“caecilians”
Gymnophiona (caecilian) characteristics
- long, slender, legless
- fossorial w/ solid skull for burrowing (terrestrial forms)
Gymnophiona (caecilian) eyes
covered w/ skin & sometimes bone (reduction-derived)
Gymnophiona (caecilian) males have
intermittent organ
Gymnophiona (caecilian) fertilization (internal or external)
internal
Gymnophiona (caecilian) live
aquatic w/ larval stage
Gymnophiona (caecilian) lay eggs?
others?
some lay eggs in soil
others are viviparous & young get nutrients from walls of oviduct w/ specialized comb-like teeth
Gymnophiona (caecilian) development?
most have direct development
Gymnophiona (caecilian) unique organ
“tentacle”
- thought to be chemosensory
- bulbi muscles protract/retract tentacle
- lubricated by Harderian gland
Harderian gland homologous to
homolog in eye
