14: Tetrapods Flashcards
When does fossil evidence suggest the first tetrapods made the transition to land?
Devonian
What did tetrapods arise from?
Sarcopterygian lobefin fish
Evidence for the evolution of lobe fin fish to amphibians
Arrangement of skull bones
Amphibian limb can be derived form fin structure
Labyrinthodont tooth structure
Opening in nostrils inside mouth
What are labyrinthodont teeth?
Have ridges on the outside, folded structure
What was Eusthenopteron?
An aquatic lobe-finned fish
From Late Devonian
Internal nostrils
What was Panderichthyes?
Late Devonian incomplete fossil
Lacks anal and dorsal fins
Tetrapod-like features: tail, shoulders
Tetrapod-unlike features: front fins
What do most fish/amphibian differences relate to?
Locomotion- either on water or on land
Also breathing and feeding
Skull differences in land vs water
Smaller temporal and opercular bones in tetrapods
Due to otic capsules under skull getting smaller in tetrapods
Braincase is flatter
Features of Ichthyostega
Primitive-
Opercular bones suggest gills still present
Skull bones homologous to fish
Fish-like fin rays in tail
Notochord in tetrapods
Notochord is replaced by bone
No longer runs into the brain case = flexible skull
Advantages of a flexible skull
Bones that support gill arches redeployed for tongue support + muscles
On land, can’t use water to support food so need muscles
Unique grasping and manipulating tongue
What is a neck?
No bones which join the shoulder to the girdle
Skull not attached to shoulder girdle = neck
What lead to the evolution of lungs?
Fluctuations in rainfall, leading to the drying up of bodies of water
Water temperatures increased, O2 levels decreased
Gills are less useful when there’s less O2
Problems with air breathing
Lose water through evaporation via moist respiratory surfaces
So lungs are invaginated and folded
Use a tidal flow system- air in and out the same set of tubes
Not as efficient as unidirectional through-flow system (fish gills)
Add pumps to improve efficiency
Changes to shoulder girdle
In fish, the shoulder girdle is integral to the skull
Produces streamlined shape
The hip isn’t attached
In tetrapods, the shoulder girdle consists of an enlarged scapulocaracoid and clavicle
The hip is attached
