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RE: Chicken teeth!

Great! First we have to worry about chickens with bird flu, and now
killer chickens with teeth! 

Kenneth Carpenter, Ph.D.
Curator of Lower Vertebrate Paleontology/
Chief Preparator
Department of Earth Sciences
Denver Museum of Nature & Science
2001 Colorado Blvd.
Denver, CO 80205
Phone: 303-370-6392
Fax: 303-331-6492
for PDFs of some of my publications, as well as information of the Cedar
Mountain Project: 

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu] On Behalf
Of David Marjanovic
Sent: Tuesday, February 21, 2006 4:12 PM
Subject: 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
Our work demonstrates a phylogenetic framework in which to interpret the
latent ability of avian embryos to form teeth apart from mammalian tooth