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Lecture 9

BISC 316 Lecture Notes - Lecture 9: West Indian Ocean Coelacanth, Holostei, Teleost

Biological Sciences
Course Code
BISC 316
Tammy Mc Mullan

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4 clades of gnathostomes present
1. Placoderms
2. Acanthodii
3. Chondrichthyes
4. Osteichthyes
4. Class Osteichthyes (bony fish)
Subclass Actinopterygii (ray finned fish)
Infraclass Chondrostei (sturgeons, paddlefish)
Infraclass Neopterygii
Series Holostei (gars, bowfins)
Series Teleostei salo, trout, od…
Subclass Sarcopterygii (fleshy finned fish)
Order Dipnoi (lungfish)
Order Crosspoterygii (lobe-finned fish)
Characteristics of Osteichthyes
1. Bony skeleton
2. Dermal bones; teeth attached to bones of jaw
3. Fish scales
Cosmoid scales
i. bone, dentine, enamel
ganoid scale bone enamel
elasmoid scale
i. bone, very thin layer of enamel
4. internal support for fins
no fleshy base; fin rays come directly from side of body
i. appendage comes out from body and rays come from the appendage
5. hyostylic jaw suspension (most)
dipnoi autostylic
crossopterygii amphistylic
6. caudal fin
primitive forms hypercercal
most homocercal
7. diverticulum
lung or gas bladder
Subclass Actinopterygii
3 major groups
1. Infraclass Chondrostei
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Sturgeon, paddlefish
2. Series Holostei gars, bowfins
3. Series Teleostei salmon, herring, cod, guppies
1. Infraclass Chondrostei
Sturgeon, paddlefish
Early forms abundant in Devonian to Permian
Modern forms lack ossification of skeleton
Hypercercal tail
Thick ganoid scales
Gas bladder
Number of fin rays is greater than the number of radial bones
2. Series Holostei
Gars, bowfins
Very abundant in Triassic
Slightly hypocercal tail
Decrease in bony armour
o Light ganoid scales; modern forms remnant only around head
Number of fin rays equals the number of radials
Gas bladder
3. Series Teleostei
Salmon, herring, cod, guppies
Evolved later; most abundant in Cretaceous
Homocercal tail
Gas bladder well developed
Thin elasmoid scales
Many dermal bones complex skul
Fins tucked close to body to reduce drag
Hyostylic jaw suspension
7-8 bones in upper and lower jaw
o Pre-maxilla and maxilla
Trends in Actinopterygii
Reduction in amount of bone
Simplification of scales
Improvement in feeding mechanisms
Hypercercal homocercal tail
Number of fin ray > number of radials number of fin ray = number of radials
Increased flexibility and movement of fins
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Subclass Sarcopterygii
Order Dipnoi
o Modern forms
o Unconstructed notochord
o Decrease in ossification
o Autostylic jaw suspension
o Homocercal tail
o Lungs w/ diverticulum (not as efficient as in mammals)
o Has to come to top of water to gulp air, push air back with pharynx/buccal
cavity and then burp it out
o Aestivation (hot monthes, stay in mud with low metabolic rate until rainy season (6
months to four years)
Order Crossopterygii (lobe finned fish)
o Devonian to present
o Early forms
o Lobe fins with fin raysin lower part; internal skeleton in fin
o Cosmoid scales
o Autostylic jaw suspension
o Notochord unconstructed
o Modern forms
o Cosmoid scales
o Amphistylic jaw suspension
o Latimeria chalumnae or Coelacanth; 1938 first capture
o Devonian to Permian (Chondrostei)
o Large number of fin rays compared to radials
o Hypercercal tail
o Thick heavy ganoid scales
o Triassic to Cretaceous (holostei)
o Fewer rays
o Symmetrical tail
o Reduction in scale size
o Cretaceous to modern (teleostei)
o Homocercal tail
o Thin elasmoid scales
o Many feeding adaptations
o Sarcopterygii flesh-fined forms gave rise to tetrapods
Life in Water
o Locomotion in water provides
o Access to a variety of habitats
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