ABSTRACT

In a recent article in this journal, Fassett (2009) concludes that dinosaur fossils of Paleocene age are present in the San Juan Basin of New Mexico-Colorado. However, we argue that, based on existing data, Fassett has failed to produce compelling evidence to support this conclusion. In the San Juan Basin, only one arguably reworked dinosaur bone (an isolated hadrosaur femur) is stratigraphically above undisputed Paleocene pollen, so palynology does not demonstrate Paleocene dinosaurs in the San Juan Basin. Nor does magnetostratigraphy, because Fassett's disregard of a major unconformity above the dinosaur-bearing Naashoibito Member renders questionable his use of an uninterrupted magnetostratigraphy to assign a Paleocene age to dinosaur fossils in that unit. Moreover, Fassett's article failed to adequately dismiss the broadly held conclusions that: (1) the Cretaceous-Tertiary boundary is within the Ojo Alamo Sandstone; (2) the dinosaur-dominated vertebrate fossil assemblage of the lower Ojo Alamo Sandstone (Alamo Wash local fauna of the Naashoibito Member) is of Maastrichtian age; and (3) the isolated, water-worn and/or fragmentary dinosaur bones from the overlying Kimbeto Member are reworked from underlying Cretaceous strata.

Spencer G. Lucas, New Mexico Museum of Natural History and Science, 1801 Mountain Rd. NW, Albuquerque, NM 87104,
Robert M. Sullivan, Section of Paleontology and Geology, The State Museum of Pennsylvania, 300 North Street, Harrisburg, PA 17102-0024
Steven M. Cather, New Mexico Bureau of Geology & Mineral Resources, New Mexico Institute of Mining & Technology, 801 Leroy Place, Socorro, NM 87801
Steven E. Jasinski, Section of Paleontology and Geology, The State Museum of Pennsylvania, 300 North Street, Harrisburg, PA 17102-0024.
Denver W. Fowler, Museum of the Rockies, Montana State University, 600 West Kagy Boulevard, Bozeman, MT 59717
Andrew B. Heckert, Department of Geology, Appalachian State University, ASU Box 32067, Boone, NC 28608-2607
Justin A. Spielmann, New Mexico Museum of Natural History and Science, 1801Mountain Rd. NW, Albuquerque, NM 87104
Adrian P. Hunt, New Mexico Museum of Natural History and Science, 1801Mountain Rd. NW, Albuquerque, NM 87104

KEYWORDS: Paleocene dinosaurs, San Juan Basin, vertebrate biochronology, palynology, lithostratigraphy, magnetostratigraphy