News and views: Non-metric dental traits and hominin phylogeny

Abstract

Analyses of hominin dental remains conventionally include measurements of tooth crown sizes and descriptions of occlusal morphology such as minor accessory cusps, fissure patterns, and ridges (e.g., Wood, 1981, Aiello and Dean, 1990 and Bailey, 2006). Following Dahlberg, 1951 and Turner et al., 1991 developed a formal system for dividing these ‘non-metric’ aspects of dental morphology into discrete categories. This system, termed the Arizona State University Dental Anthropology System (ASUDAS), is an effective tool for discriminating among modern human populations and for assessing inter-population relationships (Scott and Turner, 1997). Other researchers later used ASUDAS to examine the evolutionary relationships of various Pleistocene hominins (Irish and Guatelli-Steinberg, 2003 and Martinón-Torres et al., 2007; but see Bailey et al., 2009). Most recently, Irish et al. (2013) used ASUDAS to assess the phylogenetic position of Australopithecus sediba, finding support for both an Au. sediba + Au. africanus clade and a clade uniting South African australopiths with Homo. However, as Kimbel (2013) has argued, there are theoretical issues with applying ASUDAS to assess phylogenetic relationships from small samples of fossil hominin dental remains. Here we explore the suitability of applying a method developed for partitioning among modern human populations to assess interspecies relationships among fossil hominins. We then discuss the ramifications of different choices made during phylogenetic estimation, including those pertaining to character weighting, clade support, and outgroup composition. We find that slight alteration of phylogenetic assumptions leads to numerous equally possible evolutionary reconstructions for Au. sediba.