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The parade of the Craniates
Part 1
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Major synapomorphies of the Craniates
Developmental Neural crest Neurogenic placodes Nervous System Above Braincase (skeletal) Complex sense organs Cranial nerves Tripartite brain Endocrine system is complex Gut Muscularization Regionalization Differentiated organs Cardiovascular Gills Heart Hemoglobin
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Craniate phylogeny and diversity of living species Fig. 3.1
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Agnathans Jawless Include: Ostracoderms Hagfishes and lampreys
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Ostracoderms Extinct “Armored” – bony dermis
Middle Ordovician (maybe Cambrian) Most lacked paired fins Length 2-3cm to 2-2.5m Heterocercal tail
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Ostracoderms
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Hagfish and Lampreys Hagfish Lamprey Marine Scavengers Anadromous
Buccal funnel Parasitic Historically conservative anatomy (Carboniferous)
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Gnathostomes Paleozoic Placoderms Chondrichthyans Teleostomes
Ostracoderms Paleozoic Placoderms Chondrichthyans Teleostomes Acanthoidians Ostichthyans jaws
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Placoderms Devonian (~400mya) Paired p. and p. fins
Jointed, bony shields
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Chondrichthyes Cartilaginous skeleton Bones in scales and teeth
Elasmobranchs (sharks, skates, rays, sawfishes) Naked gill slits (cf. bony fish operculum) spiracle Heterocercal tail morphology Holocephalans (Chimaeras (ratfish)) Scales reduced to absent Upper jaw continuous with braincase Fleshy operculum Bony plates instead of teeth
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Squaliformes - sharks Lateral gill slits
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Rajiformes – skates, rays, sawfishes
Ventral gill slits
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Holocephalans Upper jaw connected to braincase
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Acanthodians and Osteichthyans
Extinct Hollow spines in paired fins Bony armor
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Osteichthyans The extant bony fish Bony skeleton Airsac
Paired appendages (fins) Actinopterygii – ray-finned fishes Basal actinopterygians (sturgeons, paddlefishes, Polypterus) Neopterygians (gars, bowfins, teleost fishes) Sarcopterygii – lobe-finned fishes Actinistians – coelacanths Rhipidistians – lungfishes
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Basal Actinopterygians
Neopterygii Ganoid scale
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Neopterygians Teleosts (23,000 species) Bowfin Gar
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Sarcopterygians Tetrapods Lungfishes (Rhipidistians)
Coelocanths (Actinistians)
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The parade of the craniates
Part 2
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Tetrapoda
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