Convergence; ear drums (Introduction)

by David Turell , Wednesday, April 22, 2015, 15:29 (3295 days ago) @ David Turell

Another example of how an IM might work following built-in patterns. Ear drums in mammals developed from the lower jaw while in snakes and birds from the upper jaw:-"The evolution of the eardrum and the middle ear is what has allowed mammals, reptiles, and birds to hear through the air. Their eardrums all look similar, are formed when the ear canal reaches the first pharyngeal pouch, and function similarly. However the fossil record shows that the middle ears in these two lineages are fundamentally different, with two of the bones that make up the mammalian middle ear—the hammer and the anvil—being homologous with parts of diapsid jawbones—the articular and quadrate. In both lineages, these bones connect at what is called the primary jaw joint.-"Although scientists have suspected that the eardrum—and thus hearing—developed independently in mammals and diapsids, no hard evidence has been found in the fossil record because the eardrum is never fossilized. To overcome this difficulty, the research team and their collaborators turned to evolutionary developmental biology—or "evo-devo." They noted that in mammals, the eardrum attaches to the tympanic ring—a bone derived from the lower jaw, but that in diapsids it attaches to the quadrate—an upper jawbone. Hypothesizing that eardrum evolution was related to these different jawbones, they performed a series of experiments that manipulated lower jaw development in mice and chickens."-
 Read more at: http://phys.org/news/2015-04-mom-eardrums-evolution-fossil.html#jCp