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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2010.05.001 Byline: Benjamin Sames (a)(b)(c), Richard L. Cifelli (c), Michael E. Schudack (b) Keywords: Cordilleran foreland basin; nonmarine Early Cretaceous; Ostracoda; biostratigraphy; chronostratigraphy; early Mammalia Abstract: The timespan represented by the hiatus between nonmarine Upper Jurassic (Early Berriasian?) and unconformably overlying Lower Cretaceous deposits throughout the North American Western Interior foreland basin has been under discussion for the entire 20th century and remains controversial to date. Ongoing research in revision of Early Cretaceous nonmarine ostracods of some respective North American formations leads to a breakthrough concerning the verification of their biostratigraphic utility as well as their subsequent application. These ostracods are not as endemic as hitherto believed and can be used for supraregional and regional correlation, as well as improvement of the age determination of North American units. New results strongly suggest a maximum age of Late Berriasian to Valanginian ([approximately equal to]142-138Ma) for the lower part of the Lakota (Black Hills area, South Dakota) and Cedar Mountain (Utah) formations. A pre-Aptian maximum age for the Lakota Formation is supported by early mammals. These biostratigraphic results affect the correlatable formations as well, and therefore have broad implications on basin-related geologic and paleontologic topics that are overviewed and discussed herein. The central issue hampering an integrated synthesis of the foreland basin is its yet imprecise chronostratigraphic framework and documentation. Temporal relationships between the gologic processes of the basin and their control factors are still insufficiently calibrated or controversial. Detailed ongoing revision of North American Early Cretaceous nonmarine ostracods demonstrates their applicability, utility, and further potential as tool for improvement of the chronostratigraphy of the Western Interior foreland basin at both small and large scales. These ostracods also foster understanding of animal (e.g. early mammals and dinosaurs) and plant (angiosperms) evolution on the North American continent and show promise of providing age determinations for single-sample horizons in the near future. Author Affiliation: (a) Universitat Wien, Institut fur Palaontologie, Geozentrum, Althanstrasse 14, 1090 Wien, Austria (b) Freie Universitat Berlin, Institut fur Geologische Wissenschaften, Fachrichtung Palaontologie, Malteserstr. 74-100, 12249 Berlin, Germany (c) Sam Noble Oklahoma Museum of Natural History, 2401 Chautauqua Avenue, Norman, OK 73072, USA Article History: Received 31 August 2009; Accepted 11 May 2010