Why Did the Chicken Loose Its Teeth?

This news article describes an interesting finding--a mutant chicken growing teeth. The particular mutation is lethal to the developing chicken embryo, but it lives long enough to begin developing teeth.

"They don't make a molar," explains development biologist John Fallon, who oversaw Harris's work. "What they make is this conical, saber-shaped structure that is clearly a tooth. The other animal that has a tooth like that is an alligator."

Previous efforts to produce teeth in chickens had relied on introducing genetic information from mice, resulting in chickens growing mammalian molars. But a chicken's underlying ability to grow teeth derives from a common ancestor with alligators--archosaurs--that is more recent than the one linking birds and mammals. Nevertheless, the underlying genetic mechanism that produces teeth in mice, alligators and mutant chickens remains the same.

I think this little historical bit is also interesting:

In the early 19th century, Saint-Hillaire observed that developing parrots have tiny bumps on their beaks that resemble teeth, something he ascribed to modern animals deriving from more basic primitive forms. But due to his developing battles with Georges Cuvier over evolution, the finding was forgotten until Harris, a graduate student, re-discovered it nearly 200 years later.

The details will need to be teased out, but it appears that birds do not make teeth, not because the deveopmental pathways do not exist, but because the regulation of those pathways has been altered in a manner that prevents tooth development.

(via Pharyngula.)