How Birds Lost Their Teeth
A bird’s beak is a remarkable thing. It can be dull or spectacularly colored, pointed or blunt, long or squat, thin or comically large. It can be used to tear flesh, probe flowers, or crack the toughest nuts. Birds aren’t the only animals with beaks, but they’re the only major group of animals in which a beak is the exclusive option. No modern birds have teeth. But why?
A new study, appearing in the current issue of Science, examines the evolution of the avian beak by going all the way back to modern birds’ ancestors: dinosaurs. All birds have a gene that deactivates the formation of teeth (yep, birds can grow teeth, we’ll get to that in a minute). The researchers, from the University of California, Riverside, found that this gene can be traced back to a common ancestor of all modern birds, which lived some 100 million years ago.
To solve this puzzle, the researchers used a recently created genome database that catalogues the genetic history of nearly all living bird orders—48 species in total. They were looking for two specific types of genes: one responsible for dentin, the substance that (mostly) makes up teeth, and another for the enamel that protects them. Upon finding these genes, researchers then located the mutations that deactivate them, and combed the fossil record to figure out when those mutations developed.
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