Earth Sciences 2266F/G Lecture Notes - Lecture 10: Osteolepiformes, Sarcopterygii, Shoulder Girdle

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Lec 10
Osteo = bone, ichthyes = fish
Very diverse; can adapt to salt water, fresh water, shallow water, deeper water, and even under
Arctic ice below 0°C
Actinopterygii are the ray-finned fish – the ones we eat
Sarcopterygii are lobe-finned; they have a big lobe and have a lot of meat on them, along with
strong bones inside of them
These eventually evolved into amphibians and reptiles, and then to us
Within this group, some of them have lungs
Both these groups started in the late Silurian, but radiated in the Devonian
Sarcopterygians evolved to be quite big and were the top predators
Lungfish: 3 species still living today
Coelacanths hide in deeper waters and people thought they were extinct before
Just 1 genus living today
Osteolepiformes are represented by only fossils, no living species today
Very strong lobes can allow them to crawl out of water
Some people think lungfish are most related to us, some think it’s lobe-finned, some think it’s
ray; we are still not entirely sure
- We think that Osteolepiformes are most closely related to land-dwelling animals
Eusthenopteron
Shoulder girdle links fin to body
In a Sarcopterygian, linkage is one big bone at the root of the fin
Where their fin starts there is one bone, and then eventually there were more bones to develop
into a flapper-like structure
Other fish have smaller bones in their fin that aren’t strong enough to prop up the fish onto land
So this type of fish is not directly related to land tetrapods
Second important structure is the lung
Today there are 3 genera of Dipnoi: Neoceratodus, Protopterus, and Lepidosiren
Most of modern lungfish experienced a deterioration in their bone structure; their skull
ossification was reduced and bones became cartilaginous again
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