BISC 316 Study Guide - Final Guide: Buccal Pumping, Passerine, Caudipteryx
10 Dec 2012
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Document Summary
Homology between crossopterygian and isthyostegid limbs not due to direct evolution of limbs, but to a common pattern of development. Fin to limb: formation of stylopod and zeugopod (sarcopterygion, form of autopod region (wrists, fingers, determination of number of bones/digits (sarcopterygion, loss of fin rays (tetrapods) Tetrapods late activation of hox d 12. Sarcopterygion fish shape some characteristics with early tetrapods. Earlier tetrapods are more fish like than once thought. Some environment with fluctuating water levels, decreasing oxygen supply. Limbs evolved from fins with axial skeleton. Fin rays allowed the fins to be flexible. Selective pressure that favored limbs: exploit unoccupied habitats. Shallow water, more abundant prey, less predators: explot abundant food in shallow water, escape unfavorable environment. Leaves a drying out pond: avoidance of predators in shallow water, improve locomotion; anchor points as body undulates forward, improve locomotion; strut to prevent body from tipping on side. First skeletal evidence of tetrapods appear in early devonian.
