These bird relatives lost their teeth 70-80 million years ago and subsequently developed beaks, but Harris and his team believe their study results prove that the potential to form teeth still exists in birds, especially during their earliest stages of growth.
"The main point is that within an embryonic bird in which development is shifted, teeth start to form," Harris said. "Thus, the genes and process are still there with the capability to be initiated."
The researchers studied 14- to 16-day-old chicken embryos with a natural genetic mutation that supports tooth growth. These so-called "talpid2 mutant chickens" express a chemical called catenin that initiates tooth growth signals. Harris and his team exposed the mutant chickens to a virus that increases catenin levels.
The chickens then grew conical-shaped, alligator-type teeth.
Harris, a scientist at the Max-Planck Institute for Developmental Biology in Germany, said that "alligators and birds shared a common ancestor(s) — the archosaurs."
Dinosaurs, flying pterosaurs, crocodiles and birds all are classified within the diverse archosaur group of reptiles.
The mutant chicken teeth, as for crocodile and alligator choppers, are less complex than human and other mammalian teeth, but Harris said "they do a very fine job for their purpose," which is to rip through fish and animal flesh.
He theorized that relatives of modern birds lost their teeth to reduce weight and drag in flight. These bird ancestors also lost some of their bone mass, probably for the same reason. Harris said beaks were not necessarily worse than teeth for pulverizing food.
He said beaks "come quite close to grinding function" in tests, and "the beak proves to be quite versatile."
Scott Gilbert, a professor of biology at Swarthmore College and a leading scholar on the history and theory of evolution and development, told Discovery News the discovery indicated "that for teeth to occur in mammals and alligators, two sets of cells have to come together — those cells that give the tooth forming instructions, and those cells that can respond to them. In chicks, the responding cells don't meet the signaling cells, but in the mutant chick, the jaw has changed and these two groups of cells are brought together again."
Gilbert added that atavisms, or vestiges of physical characteristics that no longer appear or develop, occur in other animals, even humans.
"For instance, some humans have a mutation that enables hair to grow luxuriously all over their body, including their faces," Gilbert said.
