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BIO211H5 (55)


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Jessica Hawthorn

Ammonoids -some species make excellent index fossils- widespread -cephalopods ex. Squid, octopus, nautilus Heterostracans  Name means “different shell”- bony armour Extinct by end of Devonian Toward front= anterior Back= posterior Dorsal= up Down= ventral Lateral view= side Midline= medial Away midline= lateral Ventral view= upside down Dorsal view= on back Anaspids  Name means “no shields” (some had thin, elongated scales) Thelodonts Depressed (top to bottom) and compressed (side to side) forms Stomach-like chamber in the gut filled with petrified mud- first stomach? Osteostracans • “Cephalic fields” clearly seen; connected to inner ear- sensing vibrations? Electic organs? Expansions of ear canals? Evolution of jaws Popular theory: jaw derived from gill arches Placoderms -jaws present -No true teeth -craniothoracic joint= open/ raise cranium up, increased gape - most primitive jawed vertebrates Filled many ecological niches Dunkleosteus was largest predator Viviparity- live birth -Materpiscis Chondrichthyans  Claspers in males- allowed internal fertilization Acanthodians Apparent trend: decreasing spiny-ness Ancestoral to sharks? Ancestoral to bony fishes? Bony Fish Dermoskeleton (scales) and endoskeleton (bony internal skeleton) Ganoid scales made of ganoine Cosmoid made of cosmine Both are primitive, modern scales are called cycloid Opercle- bony gill cover Sarcopterygii – “lobe-finned” fishes, related to us Actinopterygians Fins supported by bony or horny rays made from keratin Previously thought to have become extinct in Cretaceous- lack of researchers, change in range, habitat shift? Lungfishes are durophagous- eat shell fish Sarcopterygians  Modern South American and African lungfishes can aestivate – dormant state; buries self, s
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