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Chicken teeth!

Matthew P. Harris, Sean M. Hasso, Mark W. J. Ferguson & John F. Fallon: The Development of Archosaurian First-Generation Teeth in a Chicken Mutant, Current Biology 16(4), 371 -- 377 (21 February 2006)

Summary (refs removed):
"Modern birds do not have teeth. Rather, they develop a specialized keratinized structure, called the rhamphotheca, that covers the mandible, maxillae, and premaxillae. Although recombination studies have shown that the avian epidermis can respond to tooth-inductive cues from mouse or lizard oral mesenchyme and participate in tooth formation, attempts to initiate tooth development de novo in birds have failed. Here, we describe the formation of teeth in the talpid^2 chicken mutant, including the developmental processes and early molecular changes associated with the formation of teeth. Additionally, we show recapitulation of the early events seen in talpid^2 after in vivo activation of [beta]-catenin in wild-type embryos. We compare the formation of teeth in the talpid^2 mutant with that in the alligator and show the formation of decidedly archosaurian (crocodilian) first-generation teeth in an avian embryo. The formation of teeth in the mutant is coupled with alterations in the specification of the oral/aboral boundary of the jaw. We propose an epigenetic model of the developmental modification of dentition in avian evolution; in this model, changes in the relative position of a lateral signaling center over competent odontogenic mesenchyme led to loss of teeth in avians while maintaining tooth developmental potential."

The teeth were hidden under the beak.

Quote from inside the article:
"We show the initiation of tooth developmental programs as well as the formation of conical, saber-like structures on the lower jaw of the ta^2 chicken. The structures formed are similar to those seen in the first-generation teeth of the alligator in position, histological differentiation, and morphogenesis. This finding is consistent with the idea that developmental programs are hierarchical and that atavisms will reinitiate early steps before later processes of more complex teeth. Previous reports interpreted tooth formation in light of knowledge of mammalian tooth development and thus searched for the elusive chick molar. Our work demonstrates a phylogenetic framework in which to interpret the latent ability of avian embryos to form teeth apart from mammalian tooth development."