Birds, turtles and other toothless vertebrates have remnants of tooth genes

As stated in a previous post, the toothless baleen whales and the enamelless pygmy sperm whales retain remnants of genes that encode proteins important for developing the enamel crowns of teeth. However, these have become inactivated through deleterious mutations. There are other vertebrate species that lack teeth or enamel, and theory suggests that they descended from ancestors with enamel-crowned teeth. This predicts that these species may also have enamel pseudogenes.

Some examples of toothless/enamelless species include the toothless anteaters, pangolins, turtles, and birds

and the enamelless armadillos, sloths and aardvarks.

Several studies have demonstrated that several enamel genes in these species have become pseudogenes. For example, Meredith et al. [1] showed that the enamelin (ENAM) gene was repeatedly deactivated in the mammalian species listed above:

frameshift

This figure shows comparisons of toothless/enamelless species with their toothed relatives. Colored regions indicated deleterious mutations. A shows the inactivation of ENAM in the aardvark (Orycteropus); B displays a shared mutation in pangolins (Manis); C in baleen whales and pygmy sperm whales; D indicates shared mutations in sloths (Bradypus, Choloepus) and anteaters (Myrmecophaga, Tamandua, Cyclopes), and separately in armadillos (Dasypus, Tolypeutes, Chaetophractus, Euphractus).

Springer’s lab later demonstrated that two enamel genes in addition to ENAM, ameloblastin (AMBN) and amelogenin (AMEL) were lost in several of these mammals, as well as two turtles and five birds. Of particular interest, all three genes have shared mutations in the birds, indicating enamel genes were lost in the last avian ancestor.

1471-2148-13-20-1

Phylogeny showing distribution of shared and unique mutations in enamel genes across various vertebrates. B = AMBN; E = ENAM; A = AMEL.

This work provides further evidence that all of these species descended from ancestors with enamel-capped teeth, which they subsequently lost during their evolution.

Questions for Creationists

Why would God create toothless and enamelless animals with nonfunctional remnants of enamel genes? Birds and turtles have beaks without teeth, so why would they have these nonfunctional pseudogenes? Why would God create anteaters, sloths, pangolins, armadillos and birds to have shared inactivating mutations, respectively, in these genes? Do you think it’s possible that these animals could have descended from toothed ancestors? What sort of evidence might you expect in support of this hypothesis?

References

1. Meredith, R. W., Gatesy, J., Murphy, W. J., Ryder, O. A., & Springer, M. S. (2009). Molecular decay of the tooth gene enamelin (ENAM) mirrors the loss of enamel in the fossil record of placental mammals. PLoS genetics5(9), e1000634.

2. Meredith, R. W., Gatesy, J., & Springer, M. S. (2013). Molecular decay of enamel matrix protein genes in turtles and other edentulous amniotes. BMC evolutionary biology13(1), 20.

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4 thoughts on “Birds, turtles and other toothless vertebrates have remnants of tooth genes

  1. Pingback: Transitional Fossils #22 through #24: Before the turtle had a shell | Evolution For Skeptics

  2. Pingback: Ontogeny recapitulates phylogeny: Fetal sloth teeth point to evolutionary history – Evolution For Skeptics

  3. Pingback: Transitional Fossils: How dinosaurs gave rise to birds – Evolution For Skeptics

  4. Pingback: Molecular Phylogenetics: DNA points to reptilian ancestry of birds – Evolution For Skeptics

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