Two new gaps appear in the mammilian fossil record ...

marco_polo

... is what Ken Ham would say, as another tired old creationist argument is blown apart by science.

A team of American and Chinese Paleontologists have discovered a long sought after specimen of a mammal fossil showing a transitional middle ear, the strongly suggests that the middle ear evolved at least twice in mammals, seperatley in both the monotreme and marsupial-placental groups.

The 125 million year old specimen has been named Liaoconodon hui (after where it was found ).

http://www.sciencedaily.com/releases/2011/04/110413132949.htm

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The transition from reptiles to mammals has long been an open question, although studies of developing embryos have linked reptilian bones of the lower jaw joint to mammalian middle ear bones. Previously discovered fossils have filled in parts of the mammalian middle-ear puzzle. An early mammal, Morganucodon that dates to about 200 million years ago, has bones more akin to a reptilian jaw joint but with a reduction in these bones, which functioned for both hearing and chewing. Other fossils described within the last decade have expanded information about early mammals -- finding, for example, that ossified cartilage still connected to the groove was common on the lower jaws of early mammals. But these fossils did not include the bones of the middle ear.

The new fossil described this week, Liaoconodon hui, fills the gap in knowledge between the basal, early mammaliaforms like Morganucodon, where the middle ear bones are part of the mandible and the definitive middle ear of living and fossil mammals. Liaoconodon hui is a medium-sized mammal for the Mesozioc (35.7 cm long from nose to tip of tail, or about 14 inches) and dates from 125 to 122 million years. It is named in part for the bountiful fossil beds in Liaoning, China, where it was found. The species name, hui, honors paleontologist Yaoming Hu who graduated from the American Museum of Natural History-supported doctoral program and recently passed away. The fossil is particularly complete, and its skull was prepared from both dorsal and ventral sides, allowing Meng and colleagues to see that the incus and malleus have detached from the lower jaw to form part of the middle ear. These bones remain linked to the jaw by the ossified Meckel's cartilage that rests in the groove on the lower jaw. The team hypothesizes that in this early mammal, the ear drum was stabilized with the ossified cartilage as a supporting structure.