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| shell skinned; name given to first fishes |
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| armor, made of dermal bone (not preformed by cartilage) |
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| first record of bone in fossils, protection from predators |
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| internal, made of cartilage |
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| lack paired fins, weak swimmers |
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| small, none longer than 15cm |
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| first use of bone; for protection, not support, used as auxillary supply of calcium?; filter feeding to exploit common and abundant food: plankton and suspended organic matter |
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| limitations of ostracoderms:habitat |
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| restricted to benthos; weak swimmers due to heavy armor; weight and inflexibility |
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| limitations of ostracoderms: food |
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| no jaws, restricted to plankton, suspended organics, slow growth |
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| 100 mill yrs evolution: Ordovician (460 mya) through Silurian, Devonian |
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| 2 classes: Pteraspidomorphi and Cephalaspidomorphi |
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| Order Arandaspidiformes; Order Pteraspidiformes; Order Thelodontiformes |
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| Order Anaspidiformes; Order Galeaspidiformes; Order Cephalaspidiformes; Order Petromyzontiformes |
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| lampreys as order of class Cephalaspidomorphi? |
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| in rich devonian fossil record of group, reconstruction of cranial nerves possible. suggests close relationship to extant lamprey;first appearence of ossified endoskeleton;sister taxon to superclass gnathostomata(not part of agnatha) |
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