Lec 8 Primitive bony Flashcards
What are Actinopterygians
bony or ray-finned fishes
bony” because, of all the major groups of living fishes, they are, for the most part, the only taxon that has retained the ability to ossify the skeleton. Although they are exceptions like sturgeons and paddle fishes that are largely cartilaginous fishes.
What are they called ray finned?
fins are fully rayed from the base as shown.
Lobed fins
Fins mounted on pectoral lobes
ganoid scale structure
Primitively all actinopterygians share a three-layered scale
outer lamellar layer of an enamel-like substance called ganoine, acentral layer of dentine filled with vascular canals
deep or innermost layer of spongy bone
Ganoid scales shape
rhomboid in shape and arranged in sloping diagonal rows along the side of the body
Ganoid scales are found in what kind of fishes?
More primitive fishes
Most ancient lineage of fishes that has survived?
bichirs and reedfish
Polypteridae, bichirs characteristics
Have lungs, so can inhabit lox oxygen places
Chondrostei are known as
sturgeons and paddlefishes
Acipenseridae: sturgeons
What are the characteristics?
anadromous and freshwater
five rows of bony scutets (ganoid scales), an inferior mouth without teeth, 4 barels, large swimbladder
Polyodontidae: paddlefish characteristics
paddle-like snout, naked body (no scales), few ganoid scales on caudal peduncle, gill rakers are extremely,
Sister group of paddlefish are
sturgeons, they hace similar asymmetircal caudal fin
Difference between the American and Chinese Paddlefish?
American is a filter feeder, has lower jaw that drops and expand out like funnel.
Chinese paddlefish is a fish eater. Has long flatten, bony snout.
Ginglymodi, aka gars characteristics, origin, and distribution
Heavily armored fishes found in shallow, weedy areas in fresh water.
Distribution is primarily USA East side.
Gars’ snout and jaw structure.
Upper and lower jaws are elongate and armed with rows of strong sharp teeth Highly voracious carnivores.
Gars’ tail structure
dorsal and anal fins are set back on the body and caudal fin is heterocercal.
Opisthocoelous
Present in gars. They have vertebrae that is convex anteriorly and concave posteriorly.
Amphicoelous
Vetebrae of most fishes that are concae on both ends.
What family is the bowfin from?
Amiidae
How are bowfins similar to derived teleosts?
they have single layered cycloid scales that lacks a gnoine.
What’s the bowfin tail like?
caudal fin is abbreviated hetrocercal.
What are sturgeons and paddlefishes’ tails like?
Strongly asymmetrical tails.
How are teleosts characterized by having what kind of tails?
Symmetrical or homocercal tails.
What is the earliest known teleost?
Pholidophoriforms, that originated in the late Triassic and early Jurassic times
Pholidophoriform characteristics?
Large teeth, tail was symmetircal, scales had a thin layer of ganoine
When did the teleost first appeared?
Appeared in the mid Triassic deposits, about 200 MYBP.
What is the teleosts’ feeding mechanisms?
Upper Jaw mobility
What did the evolution of greater upper jaw mobility lead to?
It opened up many feeding possibilities, and increase potential of mouth parts. This lead to successful exploitation of food resources that were unavailable to Actinopterygian.
How does the fin change through actinopterygian evolution?
The change of the caudal fin would change from strongly asymmetrical, heterocercal, to abbreviated heterocercal, to less symmetrical, homocercal.
Heterocercal shape, which fishes?
asymmetrical, present in sturgeons and paddlefishes
abbreviate heterocercal shape, which type of fishes?
moderately asymmetrical, in gars and the bowfin
homocercal shape
less symmetrical, in teleosts
heterocercal function.
used to provide lift. Something a thick scaled, armored, primitive actinopterygian requires to get off the bottom
How do fins vary with fishes with heterocercal tail?
Position and shape of the fins depends on shape of caudal fin. So there’s functional constraints that leads to limited maneuverability.
How does the homocercal and heterocercal tails operate differently?
Homocercal tails has a vertical axic rotation. So the fish moves directly forward.
Heterocercal tail has upward and forward rotation on the rear end. Somersault effect is counteracted by large horizontally inserted pectoral fins that serves as planing devices.
What are the advantages of having a homocercal tail?
- increased efficiency in horizontal swimming
- increased versatility for the fins, since they are free from the constraint of planing devices. The fins moved from low horizontal insertion to vertical insertion high on the body
What evolutionary changes had to take in order for the homocercal tail to appear?
- Loss of heavy bony armor and heavy scalation, it would no longer require a body plan that provides lift
- led to the evolution of the swimbladder, so lungs acted as a hydrostatic organ
