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Fish to Tetrapod Transition (Tiktaalik - 'fishopod' (Large weight…
Fish to Tetrapod Transition
Tiktaalik - 'fishopod'
Fish on verge of becoming tetrapod
Large weight-bearing limb
attached to rigid shoulder
Large, distinct radius & ulna
(forearm)
Large humerus
(upper arm)
Wrists rotate & flex
supports weight / walks
Beginnings of
short discrete neck
Ribs = broad & overlapping
Eyes spaced closely on skull
Tiktaalik
= crucial link between fish and tetrapods
Tetrapodomorphs
Lived in the water
Did not have fins with true digits
Not true tetrapods
e.g. Tiktaalik, Panderichthys
Could not support self on land
Fossils found in tidal estuary rocks
True tetrapods
Had fins with true digits
Capable of moving on land
Oldest Fossil Tetrapods
Greenland
Icthyostega
7 digits on each hand and foot
Longer neck
More rigid ribcage
More robust limbs
bigger muscles / robust girdle
More derived, more terrestrial
Acanthostega
Most primitive tetrapod?
8 digits on each hand & foot
Lived in water, capable of venturing onto land
Inhabited land-water interface
Modern Tetrapods
baseline 5 digits
Why Venture onto Land?
STORIES
∴ hard to test
Habitat Loss
(Classic View)
Arid climate with lakes drying up
in Devonian
Driven by envmtal change
Move btwn drying pools
Predation
Escape predators i.e. large arthopods
Protection - lay eggs on land
Thermoregulation
bask in warmth of sun
What we can say
Features allowed it - ventured onto land because they could
Tetrapods Diversify into Carboniferous
Become more suited to land
became dominant
developed many ecologies
Pederpes
More terrestrial animal
Looks less fishy
Only 5 digits
Metatarsal & metacarpal bones
clearly distinguished
Muscle attachment
to support & control digits
Metacarpal - palm of hand
Metatarsal - foot
Growing diversity in size & ecologies
Fish-Tetrapod Transition
Gradual transition / morphological change
Changes in skull / neck / rib / limb anatomy
Devonian
Tetrapods = primitive & experimentation with digits
Some lobe-finned fishes evolved features well-suited to life on land
i.e. fleshy lobed fins, lungs
Carboniferous
Diverse sizes and ecologies developed
Rapid evolution
Tetrapods became more fine-tuned to land