Earth Sciences 2266F/G Lecture Notes - Lecture 7: Gill Slit, Branchial Arch, Agnatha
26 Jul 2016
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Lec 7: once biting occurs, you can eat larger prey; if it"s just suckers, only small prey and prey is limited. There were never huge jawless fish; fish only got really big once jaws started to evolve: many functions with the jaw. Gill arch hypothesis; behind the head are gill arches to support the gills. Theory is that the 1st three pairs of gill arches, when fused together, became the jaw structure. Mallatt: initial step to enlarge jaws were not for biting, was for breathing. Pre-adaptation: in evolution, a feature will initially evolve for one purpose but once that feature is more complex, it is used for a different purpose. Red ones form the jaw, and blue one forms the jaw support. In between every gill arch is a gill slit: where the original gill slits of chordates were. Between 3rd and 4th pair of gill arches, gill slit became the spiracle.
