An elusive evolutionary “missing link” bridging the bones of the mammalian middle ear with the reptilian jawbones is discovered in a fossil of an early squirrel-like mammal.

> One of the “knowns” in the evolutionary biology of mammals, including
> humans, is that the three little bones in their middle ear originated
> in the lower jaw of their reptilian predecessors. The link has been
> demonstrated in studies of developing mammalian embryos, and two of
> the three bones are found in the jaw of living reptiles…
>
> But finding fossils of the transitional middle ear, considered a
> classic example of gradual evolution in vertebrates, had until now
> eluded paleontologists.
>
> Scientists report in the current issue of the journal Nature the
> discovery in China of a 122 million-year-old fossil of a mammal the
> size of a small squirrel that lived in the shadow of the mighty
> Cretaceous dinosaurs…
>
> Its well-preserved skeleton, the scientists said, bore “the first
> unambiguous paleontological evidence” showing the close relationship
> between the lower jaw and the middle ear, the ring-shaped area just
> inside the ear drum. Two of the three bones associated with mammalian
> hearing, the malleus and the ectotympanic, had already detached from
> the lower jaw of the specimen, but they were held in place by an
> ossified cartilage.
>
> ...“In my mind I always had this dream, to complete the story of the
> middle-ear evolution,” Dr. Meng said. “When I first saw these
> specimens, I knew I had had this once-in-a-lifetime discovery.”

Read the full article | Print this article