ACKNOWLEDGMENTS
We thank J. Gauthier, W. Joyce, and D. Brinkman (YPM) for loan assistance and permission to sample specimens. Thanks also to W. Sanders (University of Michigan Museum of Paleontology) for preparation of the material and M. D. D’Emic (Adelphi University) and K. M. Smith (Georgia Southern University) for assistance with creating the original histological sections. M. Becerra and an anonymous reviewer greatly improved a prior version of this manuscript.