Tuesday, September 29, 2009

Come Together … Right Now … Over Teeth

I dare say that all paleontologists, including myself, drool over papers like this one recently published in PLoS Genetics, because, as the authors write, it “provides manifest evidence for the predictive power of Darwin’s theory."

Instead of looking at the genes behind new or modified existing traits, the authors looked at the genes for traits that have disappeared. Most lost or vanishing traits that come to mind are comprised of soft tissues that do not preserve well in the fossil record (e.g. cave fish eyes), but thanks to the steadfast properties of enamel, tooth loss and enamel loss can be examined both genetically and in the fossil record. That means the evolutionary scenarios for the evolution of enamel loss and tooth loss can be rendered in much higher resolution, if you will, than those for soft tissue traits.

Tubulidentata (aardvarks), Pholidota (pangolins), Cetacea (whales, porpoises, and dolphins), and Xenarthra (armadillos, sloths and anteaters) are four groups of mammals with toothless and/or enamelless taxa. They also have pretty decent fossil records, especially when it comes to teeth. What’s more, mutations in known mammalian genes (e.g. enamelin’s gene ENAM) that are involved in enamel formation are known to – wait for it – cause defects in enamel.

This is a perfect opportunity to bring fossils and DNA together.

Do these mammals in question show degeneration, like a pseudogene, at ENAM? Yes, various kinds.

Do the nature of those changes support the phylogenetic hypotheses made by comparative anatomy and the fossil record? Yes, mostly (e.g. enamel may have been lost independently in different armadillo lineages).

See for yourself here:

Molecular Decay of the Tooth Gene Enamelin (ENAM) Mirrors the Loss of Enamel in

the Fossil Record of Placental Mammals

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