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