BISC 316 Lecture Notes - Lecture 14: Shoulder Girdle, Monotreme, Thoracic Cavity
11 Dec 2016
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Document Summary
Mammals evolved from the reptilian lineage of synapsida. Order therapside had basic feature of mammals: carboniferous. Therapsids had a marginal existence until the cenozoic. First mammals appear at the end of the triassic. Skull and jaw: reduction in number of bones, skull extended. Mammals are not radically different from therapsids. Features distinguishing mammals from reptiles: jaw articulation with skull, dentary to squamosal, middle ear bones, hyomandibular moves into middle ear and becomes stapes. Incus, malleus, stapes: tympanic bone, surrounds and protects the middle and inner ear, 2 occipital condyls, dyson vacuum analgy (moves in all directions, we are like old vacuum cleaners. Specializations to acquire and process food: post-cranial features, marked distinction among types of vertebrae, legs are rotated in and under the body, rotation of knee and elbow, soft anatomy. Poor fossil record (since they do not fossilize readily: hair present at some stage in life cycle. Some aquatic forms only have a few still bristles.
