Monday, February 14, 2005

4: Ear-splitting discovery rocks mammal identity - Triple bone structure arose independently in platypus and humans.

Care of Rachel Robson: - Ear-splitting discovery rocks mammal identity - Triple bone structure arose independently in platypus and humans.

This was published in Science. Why this is cool is a little tricky.

All modern mammals have one lower jaw bone and three bones in the middle ear. Reptiles have four bones in the jaw, and none in the ear. Since the mammalian ear bones are embyronically associated with the jaw, it is believed that they are homologous with the reptilian jaw bones, and one characteristic that shows common ancestry of the mammals is that transition (along with tooth characters, hair, mammary glands, homeothermy and various other skeletal novelties). Turns out, one fossil monotreme still had four jaw bones, and the ear bones evolved in the monotremes and the other mammals (therians) separately.

This demonstrates transitional forms, the ability to test evolutionary hypotheses, and relies on and demonstrates shared descent.