PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3486, 45 pp., 26 ®gures, 8 tables October 27, 2005 An Early Miocene Dome-Skulled Chalicothere from the ``Arikaree'' Conglomerates of Darton: Calibrating the Ages of High Plains Paleovalleys Against Rocky Mountain Tectonism ROBERT M. HUNT, JR.1 CONTENTS Abstract ....................................................................... 2 Introduction .................................................................... 2 Geologic Setting ................................................................ 3 Systematic Paleontology ........................................................ 12 Age of the Dome-Skulled Chalicothere ........................................... 28 The ``Arikaree'' Conglomerates of N.H. Darton ................................... 32 Post-Laramide Evolution of the Rocky Mountains ................................. 39 Acknowledgments ............................................................. 42 References .................................................................... 42 1 Department of Geosciences, W436 Nebraska Hall, University of Nebraska, Lincoln, NE 68588-0549 (
[email protected]). Copyright q American Museum of Natural History 2005 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3486 ABSTRACT Fragmentary skeletal remains discovered in 1979 in southeastern Wyoming, associated with a mammalian fauna of early Hemingfordian age (;18.2 to 18.8 Ma), represent the oldest known occurrence of dome-skulled chalicotheres