Saturday, March 26, 2011
In chapter 10 of Shubin's book, he describes the evolutionary advantages of the inner ear bones and how they affect balance as well as the creation of the mallus, incus, and stapes, or the inner ear bones. Earlier in the book (in chapter five), he had explained the evolution of certain structures including the jaw and ear bones from gill arch 1. Explain a possible way that the creation of the inner ear bones could come to be as well as their comparative location on our ancestors.
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The mammalian inner ear has three tiny bones known as ossicles. They consist of the malleus (hammer), the stapes (stirrup), and the incus (anvil). These three bones work together to transport sound to the tympanic membrane or eardrum. As Shubin stated, these three bones have been shown to come from the mandible/gill area of fish. A new finding by Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh shows the “middle man” between mammals and fish as far as hearing design goes. He found the very small Yanoconodon allini in the Yan Mountains of China. Although it is just a mere 5 inches long, its significance from an evolutionary standpoint is huge. Just as Tiktaalik was the “bridge” organism between water and land species, the Yanoconodon allini connects reptiles to humans. The organism shows a separation between the jawbones and the inner-ear bones, but it is incomplete. In fact, the organism displays almost the same layout as mammal embryos do today before the ear bones and cartilage precursors of the jaw separate during gestation.
ReplyDeleteBefore these organisms, the bones were attached to the mandible or cheek/jaw bone. But over time the bones began to be seen more towards the back of the jaw and eventually into the ear. This could be a big selective advantage because the increase in hearing ability could be the difference between an organism being eaten because it did not hear a predator come up from behind and possibly surviving and reproducing. If it was able to survive and reproduce more, then its offspring would be more likely to have the same selective advantage which would eventually lead to the evolution of a new species.
http://www.scientificamerican.com/article.cfm?id=fossil-reveals-ear-evolution-in-action
Matt Micucci (coochqbk@sbcglobal.net)