BIO220H1 Lecture Notes - Lecture 25: Prototheria, Eutheria, Hyomandibula
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BIO220H1 Full Course Notes
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Looking at the basal sarcopterygia, there are a series of bones which articular with a dentary, eventually articulating with the skull. The tiktaalik"s jaw moves away from the jaw. The hyomandibula moves into the inner ear, this has evolved several times in the amphibian. Sound waves travel better and faster through solids, and the movement to the ear gives sound. The synapomorphy is the movement of three more bones into the inner ear the malleus and incus. Adding two more bones increases sound transfer efficiencies, mammals as a result can hear much higher frequency ranges than reptiles and amphibians. Because of these movements, mammal skulls are very much different from other jaws. There is a different jaw closing, which had huge ramifications for the evolution of predators in mammals. The most obvious indicator of mammals are the presence of hair.
