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modern reptile

early tetrapod. modern reptile.

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modern reptile

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  1. early tetrapod modern reptile

  2. Modern Lepidosaurs (Reptiles) In Comparison to Synapsids/mammals: Jaw joint bones (articular and quadrate, + some others) shown in green. Note how close the squamosal (upper jaw) and dentary (lower jaw) are to the quadrate and articular (respectively) of the jaw joint. In mammals, the dentary and squamosal replace the articular and squamosal as the jaw joint bones, freeing the ancestral joint bones to become incorporated into the middle ear hearing mechanism. Likewise, note position of angular (develops reflected lamina in synapsids and becomes ectotympanic bone of modern mammals). [angular = ectotympanic; articular = malleus; quadrate = incus; columella = stapes]

  3. Modern Birds: green = quadrate and articular of jaw joint. Although birds are highly derived reptiles, they retain the same basic jaw joint anatomy as in the lizard (previous slide).

  4. From: Rowe, T. (1996) Coevolution of the Mammalian Middle Ear and Neocortex. Science 273:651-654.

  5. Ontogeny recapitulates phylogeny in mammal jaw/brain development. In other words, embryonic development of an opossum jaw/brain passes through stages very similar to the evolution of the mammalian jaw/brain. Brain expansion seems to account for the transition of jaw elements to association with the otic (ear) region of the skull! From: Rowe, T. (1996) Coevolution of the Mammalian Middle Ear and Neocortex. Science 273:651-654.

  6. DEVELOPMENT modern mammal EVOLUTION time early therapsid

  7. MEDIAL VIEW LATERAL VIEW EVOLUTION OF THE LOWER JAW, JAW JOINT AND MIDDLE EAR IN SYNAPSIDS

  8. TIME EVOLUTION OF THE JAW JOINT BONES AND MIDDLE EAR OSSICLES IN SYNAPSIDS angular

  9. Evolution of the Masseter Muscle in Synapsids/Mammals: just one of the things that happened that helped to re-orient forces on the jaws so that jaw-joint reaction forces were reduced, allowing jaw-joint bones to become smaller and smaller to increase sensitivity to airborne sound waves, including higher frequency sounds.

  10. Evolution of the Masseter Muscle in Synapsids/Mammals seen in Transverse Section Through the Jaw-Closing (Adductor) Muscles

  11. EVOLUTION OF THE SECONDARY PALATE IN MAMMALS

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