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ZOO 2090
Fred Laberge

Lecture 1 ZOO*2090 September 9, 2013 Origin of Chordates Homology and analogy - homologous characters share a common ancestry/derived from the same ancestral structure (ex. human hands, bird wings, dolphin flippers) - evidence: linked in fossil records, come from the same embryonic precursor, phylogenetic comparison - analogous characters are those have the same function but not necessarily the same ancestry o they may be homologous but not necessarily ex. insect wings and bird wings Adaptation - adaptation is an evolutionary process > adjustment to a new mode of life or environment o genetic variation o selection o it is also often used to refer to the product of evolution - exaptation is the structure or function that was useful in one way before but is now used from another purpose - form and function is often correlated and usually function precedes form - when form precedes function  exaptation Chordates and relatives - Phylum Chordata: o Subphylum Urochordata o Subphylum Vertebrata Cephalochordata Urochordata Vertebrata Echinodermata - Phylum Echinodermata - Phylum Hemichordata - Together the three phyla make up Deuterostomia with Protostomia as the outgroup - protochortdates are NOT a clade Characters of chordates - notochord – some stage in their life o promotes or organizes embryonic development of nearby structures o keeps the body straight and prevents collapse during axial muscle contraction o in most adults, it disappears or becomes highly modified - a dorsal, hollow nerve cord giving ride to the central nervous system o major nerve cord is hollow and runs ventral
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