GLGY 307 Lecture Notes - Lecture 19: Ankle, Mesozoic, Acanthostega
26 Dec 2017
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Oldest chordate pikaia: 5 cm long, cephalocordate, similar to modern lancelet, differ by having a pair of small antennae at head, tapering tail probably used for swimming. Conodonts: first occurrence in stratigraphic record in upper cambrian, composed of calcium phosphate (apatite) w/ trace of organic matter, color varies with heat, can be used to estimate sediment depth of burial. Silurian agnatha marine habitat: jamoythyus silurain agnathan, approx 18 cm. Agnatha jawless vertebrates: lasanius one of oldest members of agnathan group. Early ordovician agnathans: sacabambaspis headshield 20 protective plates (20cm) Late ordovician agnathans: astaspis oldest american vertebrates (15cm) Modern rays similar way of life of lanarkia. Placoderms: devonian placoderms were remarkable active dwellers either in oceanic water mass or proximity of sea floor, arthrodires: formidable predators of large dimensions (up to 9m, antiarchs: mud-grubbers just like ostracoderm ancestors. Devonian fish: fossil record shows there were present ancestors of important fish groups today, sharks (skeleton not bony, bony fish (most other fish)
