Earth Sciences 2266F/G Lecture Notes - Lecture 25: Mandible, Squamosal Bone, Occipital Condyle
26 Jul 2016
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Document Summary
Most of the features evolved from cynodonts later appear in mammals. Review: zygomatic arch, coronoid process (strong muscles to control lower jaw) Reduction in lumbar ribs, double occipital condyle. Double occipital condyle is clear to see in humans. In dinosaur head, there is a single knob; so advanced synapsids are quite diff from advanced diapsids. In cynodont, started off with 3 bone pieces: dentary, angular, articular that probably came from the 3 gill arches in fishes. Angular and articular bones become reduced until they were tiny pieces in cynodonts. These 2 bones got sucked into the ear canal and became true ear bones later in evolution. Single dentary bone in lower jaw didn"t happen until true mammals. Angular and articular become further reduced in cynodonts b/c development of 2nd jaw joint. Orig jaw joint is the articular-quadrate jaw joint, in the back of the skull, seen in reptiles.
