L02_JawlessfishHO11

L02_JawlessfishHO11 - EEMB 106 Lecture 2 Origin of Fishes 1...

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EEMB 106 – Lecture 2 – Origin of Fishes 1 Origin of fishes A. From what? B. When? C. How? D. Where? A. From What? Probably from invertebrate chordate ancestors Phylum Chordata 1. Notochord -flexible dorsal rod for support. Present at some stage in all chordates (usually in embryonic development). Present in adults of many fishes: sharks, rays, sturgeons. 2. Dorsal, hollow nerve chord 3. Pharyngeal gill slits - present in embryos of all chordates Subphylum Urochordata: tunicates Subphylum Cephalochordata: lancelets Subphylum Craniata Infraphylum Vertebrata B. When? 1) chordates date from early to mid Cambrian (600 mya) – Pikaia , Burgess shale 2) first good vertebrate fossils – Late Cambrian/Ordovician (500 mya) 3) BUT first bones were of external armor, characteristic of early jawless fishes 4) so, vertebrates probably originated during the early Cambrian explosion (600 mya) Because they already had specialized tissue types, true bone, and a muscular feeding pump C. How? Neoteny = retention of larval features into the adult stage Stages: 1) Ancestors (tunicates?) had: a) sessile adult stage b) free swimming larval stage for dispersal 2) Larval stage became more active; more vertebrate-like 3) Eventually, larvae capable of reproduction evolved: neoteny
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EEMB 106 – Lecture 2 – Origin of Fishes 2 D. Where?
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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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L02_JawlessfishHO11 - EEMB 106 Lecture 2 Origin of Fishes 1...

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