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 [1, 2], 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 β-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. ©2006 Elsevier Ltd All rights reserved.
Harris, M. P., Hasso, S. M., Ferguson, M. W. J., & Fallon, J. F. (2006). The development of archosaurian first-generation teeth in a chicken mutant. Current Biology, 16(4), 371–377. https://doi.org/10.1016/j.cub.2005.12.047