L03-04chondrichthys11COLOR

L03-04chondrichthys11COLOR - PRIMITIVE FISHES (cont)...

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PRIMITIVE FISHES (cont…)
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InfraPhylum Vertebrata SuperClass Agnatha SuperClass Gnathostomata- Jawed fishes Class Placodermi - plate-skinned (extinct) Class Acanthodii - spiny sharks (extinct) Class Chondrichthyes - sharks, skates, rays Class Sarcopterygii - lobed fin fishes Class Actinopterygii - ray-finned fishes
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Class Chondrichthyes, Cartilaginous fishes Subclass Elasmobranchii, shark-like Subclass Holocephali, chimaeras Outline A. Evolution of elasmobranchs B. Elasmobranch basic characteristics C. Elasmobranch basic adaptive patterns
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Evolution of Elasmobranchs Class Chondrichthyes Subclass Elasmobranchii InfraClass: Cladoselachimorpha - extinct InfraClass: Euselachii Order Hybodontiformes - extinct 13 Orders of modern elasmobranchs
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1) Arose in early Devonian (400 mya) – but already well- developed forms (cartilage doesn’t fossilize well) 2) Modern forms in place by early Cretaceous (144 mya) 3) Three major radiations: 1 st - InfraClass: Cladoselachimorpha (extinct) InfraClass : Euselachii 2 nd - Hybodonts (extinct) 3 rd - Modern elasmobranchs Evolution of Elasmobranchs
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1st elasmobranch radiation: Mid Paleozoic (450mya) Cladoselachid sharks (example: Cladoselache ) Cladodont (branched tooth): all had a three-cusped tooth
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Cladoselache 1. Terminal mouth 2. Fins broad-based and stiff, long radial elements 3. No anal fin 4. Caudal fin is homocercal 5. Body supported by notochord only 6. Often spines in front of dorsal, pectoral, pelvics Cladoselachid features
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Pelagic predators on placoderms, acanthodians and bony fishes. Ate by engulfing or slashing May have swam in sinusoidal way Cladoselache
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2nd elasmobranch radiation: Euselachii: Hybodonts Early Mesozoic (250 mya) Front teeth grasping Back teeth crushing Hybodont = humpback tooth
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Hybodus 1. Terminal mouth 2. Fins flexible and mobile 3. Anal fin 4. Caudal fin heterocercal 5. Body supported by notochord w/ neural arches 6. Spines on dorsal fin Hybodont features
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Hybodus Palaeospinax, an ancestor of modern sharks
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Hybodus Symmorium Stethacanthus Fossil
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3rd elasmobranch radiation: coming of the modern sharks Mid-Mesozoic (200 mya) 1. Jaws: ventral mouth with protrusible upper jaw 2. Dentition: tooth replacement system 3. Fins: ceratotrichia supporting the fins 4. Vertebrae: calcified vertebrae instead of notochord Improved feeding and locomotion. Parallel changes were occurring in bony fishes.
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Ventral mouth protrusible jaw 3 fused basal elements - radials Flexible, horny rays- ceratotrichia Calcified vertebral centra Notochord with neural arches Terminal mouth Spines on D fin Multiple basal elements with cartilage supports Fig. 11.17
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Modern sharks: rows of replacement teeth Ancient shark Helicoprion : Spiral tooth replacement
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Class Chondrichthyes: Cartilaginous fishes Subclass Elasmobranchii - sharks, rays - 13 Orders Subclass Holocephali - ratfish, chimaera -1 living Order
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1. Cartilaginous skeleton 2. Usually 5 gill slits, not covered by an operculum 3. Spiracles to intake water 4. Paired ventral nostrils 5. Subterminal mouth
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This note was uploaded on 01/10/2012 for the course EEMB 106 taught by Professor Staff during the Spring '08 term at UCSB.

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L03-04chondrichthys11COLOR - PRIMITIVE FISHES (cont)...

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