Age at first molar emergence in Pan troglodytes verus and variation in the timing of molar emergence among free-living chimpanzees Jay Kelley a, b, c, * , Gary T. Schwartz a , Tanya M. Smith c, d a Institute of Human Origins, and School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, 85287, USA b Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C., USA c Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, 02138, USA d Australian Research Centre for Human Evolution, Environmental Futures Research Institute, Griffith University, Nathan, Queensland, 4111, Australia article info Article history: Received 24 May 2019 Accepted 27 April 2020 Available online xxx Keywords: Dental development Tooth emergence Dental variation Dental histology Great apes Life history abstract Age at lower first molar (M 1 ) emergence is a commonly used proxy for inferring life-history scheduling in fossil primates, but its utility is dependent on knowing to what extent extant populations vary in this datum and how this variation correlates with the scheduling of life-history variables. Here, we address the first of these issues among extant chimpanzees. While age at M 1 emergence has been documented in several live individuals from the Kanyawara population of Pan troglodytes schweinfurthii in Uganda, it has been estimated for only one individual of Pan troglodytes verus, based on a deceased animal from the Taï Forest in C^ ote d’Ivoire. To further explore interpopulation variation in this variable in chimpanzees, and using dental histology, we calculated ages at death for two wild-shot individuals of P. t. verus with erupting M 1 , both collected in Liberia during the mid-1950s, and estimated ages at M 1 emergence from the ages at death. The overall range for these two individuals is ~4.2e4.6 yr, compared with an age of ~3.7 yr for the individual from the Taï Forest, and <2.5e3.3 yr for the several individuals of P. t. schweinfurthii. While the absolute range of ~2 yr in these samples combined is little greater than in captive chimpanzees, the disparity between the samples of P. t. schweinfurthii and P. t. verus is striking, although it cannot be determined if this disparity represents a subspecies difference or simply popu- lation differences expressed in two different subspecies. While life-history data are unavailable for the population to which the Liberian chimpanzees belonged, the difference in M 1 emergence ages between these individuals and those from Kanyawara still suggests caution when attempting even broad life- history inference in fossil apes and hominins based on age at M 1 emergence. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction The timing of permanent tooth emergence through the gingiva into the oral cavity has been frequently used to infer aspects of life history in fossil primates. Such inferences are based on primate- wide regressions relating ages at molar emergence, particularly that of the lower first molar (M 1 ), to the timing or duration of various life-history attributes among extant species (Smith, 1989; Godfrey et al., 2001; but see Smith et al., 2013). While this scale of analysis is satisfactory for making very broad inferences about the overall life-history schedules of fossil species (e.g., whether a species is more ‘ape-like’ or more ‘monkey-like’), it is limited with regard to making life-history inferences within a narrower phylo- genetic context (Robson and Wood, 2008; Machanda et al., 2015; Smith, 2016). The nature and strength of correlations established at higher taxonomic levels can change substantially, or even disappear altogether, when analysis is limited to more restricted phylogenetic groupings. Therefore, it is necessary to also examine the relationships between life-history attributes and molar emer- gence ages at scales that encompass only the species and ranges of values most relevant to the taxa of interest (e.g., Kelley and Schwartz, 2010). Ideally, this should be done using the same in- dividuals for both, as in Smith et al. (2013) and Machanda et al. (2015), although this is often not feasible. Concerning life-history inference in fossil apes and humans, there is currently a notable imbalance in the available information for extant great apes between life-history attributes on the one hand and the timing of molar emergence on the other, particularly * Corresponding author. E-mail address: jkelley.iho@asu.edu (J. Kelley). Contents lists available at ScienceDirect Journal of Human Evolution journal homepage: www.elsevier.com/locate/jhevol https://doi.org/10.1016/j.jhevol.2020.102823 0047-2484/© 2020 Elsevier Ltd. All rights reserved. Journal of Human Evolution 145 (2020) 102823