Osteichthyes Flashcards
Which group are Osteichthyes + Chondrichthyes in?
Gnathostomes
What are actinopterygii?
What are sarcopterygia?
Ray-finned fish
Lobe-finned fish
What are the features of osteichthyes?
> swim bladder/lung
mobile fins
reduced gill arches (3-4) + a gill cover (operculum)
bony skeleton
What is the lung used for in ray-finned fish?
Buoyancy
- can move at low speeds + stay afloat
What is Polypterus?
The most primitive living member of the ray-finned fish
What does the presence of lungs in Polypterus suggest about the evolution of lungs?
Can breathe air
(warm, stagnant water has little O2)
Lungs originally evolved to help aquatic fish cope w/ low O2 water
- NOT for life on land
Lung later modified into swim bladder (buoyancy device)
What are the fins like in Sarcopterygian fish?
Mobile fin base
- allows them to move the pectoral + pelvic fins
What is a mobile fin made of?
A series of bony structs sporting a flexible membrane
How can bony fish use their fins for propulsion?
Fold + unfold their fins
= changes their shape
What is special about the fins in Polypterus?
Mobile fin bases (+ lungs) allow them to crawl up onto land
Describe the respiratory system in bony fish
3 pairs of gills covered by a movable operculum
(lost in amniotes but retained in amphibians)
Advanced pumping mechanism - can effectively oxygenate blood while still
What is bone made of in bony fish?
Mixture of collagen (protein) + calcium phosphate (mineral)
Describe the mineralisation process
1st mineralised = external head plates + scales
Then deeper tissues are mineralised e.g. vertebrae, cartridges of fin skeleton + fin rays
Outside in
What enables bony fish to perform complex movements?
Complex joints + rigid support structures
What are the features of ray-finned fish/teleosts?
> swim bladder
loss of electroreception
reduced armour
mobile snouts
Why are the Coelacanths special?
> Retain electroreceptors
Have internal fertilisation & give birth to live young
Muscular, limb-like fin base that’s v mobile - has a shoulder joint
Living fossils
What is special about lungfish?
Obligate air breathers
What does ‘amphibian’ mean?
‘dual-life’
What is special about amphibians?
Bridge gap between aquatic + terrestrial
- water needed for reproductive cycle
- hunt for prey on land
What features do Panederichthyes have?
Loss of midline fins
Eyes on top of head
Flattened head
What does the flattened head & eyes on top of head of Panderichthyes imply?
Typical of bottom dwelling fish
- implies our ancestors were bottom-feeders
What features do Tiktaalik have?
Well developed limb bones
Reduced fin rays
= functionally between a limb + a fin
What features do Acanthastega have?
8 fingers + toes
Elongated limbs (weak wrist so can’t support weight on land)
Retains tail
Retains gill arches
What were limbs + digits originally evolved for?
Walking underwater
- reduces chance of disturbing + altering prey
- easier than swimming against strong currents
When did tetrapods move onto land?
After the end-Devonian mass extinction
What features did terrestrial tetrapods have?
Eyes on side
Powerful legs
5 strong toes
