Comparison of fluoride and direct AMS radiocarbon dating of black bear bone from Lawson Cave, Missouri R. Lee Lyman 1 , Corinne N. Rosania 2 and Matthew T. Boulanger 1 1 University of Missouri, Columbia, Missouri, 2 Missouri Department of Natural Resources, Jefferson City, Missouri After a 20-year hiatus (1955–1975) during which few archaeologists discussed fluoride dating, the method again received attention in the 1980s and 1990s when some argued for its validity. As a dating method, fluoride dating depends on the rate at which fluorine ions replace hydroxyl ions in osseous tissue. The rate of replacement is influenced by the properties of the skeletal part (SP), sediment chemistry (K), and sediment hydrology (H), and the replacement rate influences estimates of time. Calibrated AMS radiocarbon assays of 10 black bear (Ursus americanus) femora from a natural-trap cave in central Missouri are weakly correlated with fluorine concentrations, determined by neutron activation analysis in the 10 femora. Despite minimal variation in SP, K, and H, results indicate fluoride dating can be considered a valid dating method only in cases when the chronological validity of its results are confirmed with independent chronometric data. As similarities in fluorine amounts across specimens increase, provenience information and bone orientation data as well as fine resolution data on K and H become critical to the application of fluoride dating. Keywords: bone dates, chronometry, fluoride dating, radiocarbon dating, Lawson Cave, black bears Introduction It has been known for more than a century and a half that the amount of fluorine in osseous tissue laying in sediment increases with age (Goodrum and Olson 2009; Middleton 1844). As a dating method, fluoride dating became well known to anthropologists, archaeologists, and paleontologists in the middle of the 20th century when it was used to demonstrate that the Piltdown Man fossils did not represent a hominid ancestor (Heizer and Cook 1954; Oakley 1951, 1953; Oakley and Hoskins 1950; Oakley and Weiner 1955; Weiner and Oakley 1954; Weiner et al. 1953). Questions were later raised about the validity of the method (Cook 1960; Cook and Ezra-Cohn 1959; McConnell 1962; Parker and Toots 1976), and the development of radiocarbon dating about the same time (Marlowe 1999; Taylor 1985, 1995) resulted in little use or discussion of fluoride dating among archaeologists for 20 years (1955–1975). For example, fluoride dating is not described in two major books on dating techniques written for archaeologists and published in the early 1970s (Michael and Ralph 1971; Michels 1973); it is simply mentioned (not described) in the context of a discussion of the Piltdown event in Michels (1973). Minimal mention in 1970s texts may, however, not be an accurate indication of the perceived validity of fluoride dating at that time. After all, Zeuner (1952), writing at a time when the method was clearly considered to be valuable, devoted a brief three paragraphs to it, all regarding its use in the Piltdown event. Whatever the case, another text on archaeological dating techni- ques published in the 1970s provides a mere three pages on fluoride dating (Fleming 1977). Few archaeologists seem to have used fluoride dating in the 1960s and 1970s; Lal (1975, 1976, 1978) was an exception. Paleontologists, on the other hand, continued in the 1970s to explore its potential, and thus learned much about the diagenetic processes and critical variables involved (e.g., Eisenbarth and Hille 1977; Parker and Toots 1980; Parker et al. 1974; Toots and Parker 1979). For this reason, and because of the less frequent occurrence of charcoal associated with naturally deposited animal remains, paleontol- ogists have continued to use fluorine analysis as a dating method (Kale et al. 1983; McFarlane and Blake 2005; Olariu et al. 2002; Pappu et al. 1994). Archaeologists used the fluoride dating method again in the 1980s and 1990s when they found the amount of fluorine in osseous tissue to occasionally correlate with independent chronological information Correspondence to: R. Lee Lyman, Department of Anthropology, 107 Swallow Hall, University of Missouri-Columbia, Columbia, MO 65211. Email: lymanr@missouri.edu 226 ß Trustees of Boston University 2012 DOI 10.1179/0093469012Z.00000000021 Journal of Field Archaeology 2012 VOL. 37 NO.3