ACKNOWLEDGEMENTS

The preparation of this paper benefited from vigorous discussions with S.G. Lucas (New Mexico Museum of Natural History and Science, Albuquerque) and R.B. Sullivan (The State Museum of Pennsylvania, Harrisburg) over several decades. These colleagues generously provided dinosaur bone samples for chemical analyses, identified dinosaur fossils, provided copies of their and other publications, and have been invaluable sources of information about vertebrate paleontology. Lucas graciously agreed to be one of the USGS reviewers of the manuscript, and his review is appreciated. T.E. Williamson (New Mexico Museum of Natural History and Science), New Mexico, provided help with information and publications related to fossil-mammal collection localities in the Ojo Alamo Sandstone in the San Juan Basin. Williamson also reviewed the Vertebrate Paleontology section of this report, and his comments helped to improve that section. K. Johnson (Denver Museum of Nature and Science) reviewed the paleobotany studies of Knowlton (1924) and found them to be still valid.

U.S. Geological Survey (USGS) colleagues, F. Peterson and R.B. O'Sullivan, at the Denver Federal Center, Colorado, provided invaluable assistance in researching publications in the USGS Denver Federal Center library that were critical for this report. Peterson spent hours in the USGS field-notebook archives searching for references to dinosaur bones in the Animas Formation and succeeded in locating the field-note reference to an Animas dinosaur by J.H. Gardner, reproduced on Figure 40 of this report. Peterson, R. Keefer, and E.M. Brouwers (USGS Denver) conducted technical edits of the manuscript and greatly improved the final product. USGS colleagues R.A. Zielinski and J.R. Budahn performed the chemical analyses of the additional suite of 14 vertebrate-bone samples included in this study. Zielinski's constructive comments regarding the structure of this report and his careful review of the "Geochemistry of Vertebrate Bone Samples" section of the report improved it greatly. R.H. Tschudy (1908-1986) and D.J. Nichols, USGS palynologists, analyzed many rock samples for the author over many decades and a large part of the palynologic data base presented in this report is based on their work. Nichols also reviewed the palynology sections of this report, and his suggestions were extremely helpful. USGS palynologist N. Frederiksen deserves special recognition for being the first palynologist to identify Paleocene palynomorphs in Ojo Alamo Sandstone samples at the important San Juan River locality.

M.B. Steiner at the University of Wyoming in Laramie, provided the paleomagnetic data plot for the Mesa Portales section that has proven to be a pivotal data set for confirming the Paleocene age of the Ojo Alamo Sandstone in the San Juan Basin. E.M. Shoemaker was responsible for initiating the Mesa Portales paleomagnetic study and personally cored most of the rock samples there in an intensive week of field work in 1984, assisted by Steiner and the author. Shoemaker's encouragement and perceptive comments about the Cretaceous-Tertiary interface problem in the San Juan Basin over the years were a constant and joyful stimulus to the author in the pursuit of more and better data to help resolve this problem. K. Zeigler, Department of Earth and Planetary Sciences, University of New Mexico, reviewed the paleomagnetism section of this paper and offered insightful suggestions that greatly improved this section.

Two anonymous reviewers for Palaeontologia Electronica reviewed the manuscript and provided valuable suggestions for improving the paper. C.N. Trueman reviewed the geochemistry section of the manuscript for Palaeontologia Electronica, and his comments and suggestions improved the clarity of that section. For permission to use figures and tables, I thank the following journals and institutions: form figures from Butler and Lindsay (1985) the Journal of Geology, for figures from Lindsay et al. (1981) the American Journal of Science, for use of table 3 of Flynn (1986) and figures of Simpson (1959) The American Museum of Natural History, for use of figures from Lehman (2006) The Society of Vertebrate Paleontology.

The initial study of the paleomagnetism, radiometric ages, palynology, and vertebrate paleontology of the rock strata adjacent to the Cretaceous-Tertiary interface in the San Juan Basin was funded by a USGS Gilbert Fellowship grant awarded to the author in 1987. Those first studies provided the foundation for the geochronologic work that has continued since then by the author and the colleagues mentioned above. Bradley Scholar grants by the USGS in 2007 and 2008 helped defray some of the expenses incurred for the review and publication of this report.