AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 140:253–264 (2009) Beyond Gorilla and Pongo: Alternative Models for Evaluating Variation and Sexual Dimorphism in Fossil Hominoid Samples Jeremiah E. Scott,1* Caitlin M. Schrein,1 and Jay Kelley2 1School of Human Evolution and Social Change, Institute of Human Origins, Arizona State University, Tempe, AZ 85287-4101 2Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, Chicago, IL 60612 KEY WORDS bootstrap; dental variation; Lufengpithecus; Ouranopithecus; Sivapithecus ABSTRACT Sexual size dimorphism in the postca- cies. Using these samples, we also evaluated molar dimor- nine dentition of the late Miocene hominoid Lufengpithe- phism and taxonomic composition in two other Miocene cus lufengensis exceeds that in Pongo pygmaeus, demon- ape samples—Ouranopithecus macedoniensis from strating that the maximum degree of molar size dimor- Greece, specimens of which can be sexed based on associ- phism in apes is not represented among the extant ated canines and P3s, and the Sivapithecus sample from Hominoidea. It has not been established, however, that Haritalyangar, India. Ouranopithecus is more dimorphic the molars of Pongo are more dimorphic than those of than the extant taxa but is similar to Lufengpithecus, any other living primate. In this study, we used resam- demonstrating that the level of molar dimorphism pling-based methods to compare molar dimorphism in required for the Greek fossil sample under the single-spe- Gorilla, Pongo,andLufengpithecus to that in the papio- cies taxonomy is not unprecedented when the compara- nin Mandrillus leucophaeus to test two hypotheses: tive framework is expanded to include extinct primates. (1) Pongo possesses the most size-dimorphic molars In contrast, the Haritalyangar Sivapithecus sample, if among living primates and (2) molar size dimorphism in it represents a single species, exhibits substantially Lufengpithecus is greater than that in the most dimorphic greater molar dimorphism than does Lufengpithecus. living primates. Our results show that M. leucophaeus Given these results, the taxonomic status of this sample exceeds great apes in its overall level of dimorphism and remains equivocal. Am J Phys Anthropol 140:253–264, that L. lufengensis is more dimorphic than the extant spe- 2009. VC 2009 Wiley-Liss, Inc. A frequently encountered problem in hominoid paleon- However, adopting a multiple-species taxonomy for a fos- tology is identification of the source of high levels of size sil sample solely on the basis of excessive size variation variation in a fossil sample (e.g., Kay 1982a,b; Lieber- relative to Gorilla and Pongo is problematic for two rea- man et al., 1988; Cope and Lacy, 1992; Albrecht and sons. First, it is not clear that the upper limit of intra- Miller, 1993; Kramer, 1993; Martin and Andrews, 1993; specific variation in extant primates is represented by Richmond and Jungers, 1995; Lockwood et al., 1996, these taxa. Among living primates, Gorilla and Pongo 2000; Plavcan and Cope, 2001; Silverman et al., 2001; are exceeded in body-mass dimorphism (and presumably Scott and Lockwood, 2004; Villmoare, 2005). While some intraspecific variation in body mass) by the African sources are relatively easily identified and controlled papionin Mandrillus sphinx (Jungers and Smith, 1997; (e.g., variation due to ontogeny or pathology), others Setchell et al., 2001). Although it has not been estab- present greater difficulty. For example, high variation in lished whether this difference is reflected in aspects of a single fossil sample can be interpreted as evidence of skeletal or dental size variation and dimorphism, data the presence of multiple species, changes in size over from other papionins, particularly Papio, indicate that at time, or marked sexual dimorphism, or some combina- least some of the members of this clade may be more tion of these factors. Determining which of these alterna- skeletally and dentally dimorphic than the great apes tives is responsible for the pattern of variation in a given (e.g., Wood, 1976; Uchida, 1996a,b; Plavcan, 2002, 2003). fossil assemblage is important because each has different Second, the upper limit of intraspecific variation may implications regarding species diversity, modes of evolu- not be represented by any extant primate. Among fossil tionary change (i.e., anagenesis vs. cladogenesis), and primates, the hominoid sample from the late Miocene social behavior. One perspective on fossil hominoid taxonomy specifies that the degree of variation in extinct species should not *Correspondence to: Jeremiah E. Scott, School of Human Evolution be greater than that in Gorilla and Pongo, the most sex- and Social Change, Institute of Human Origins, Arizona State Univer- ually dimorphic extant hominoids, which logically sity, Tempe, AZ 85287-4101, USA. E-mail: [email protected] requires rejection of a single-species hypothesis in cases where a temporally and geographically restricted fossil Received 3 July 2008; accepted 28 January 2009 sample is more variable than these great apes (e.g., Kay, 1982a,b; Lieberman et al., 1988; Martin and Andrews DOI 10.1002/ajpa.21059 et al., 1993; Teaford et al., 1993; Walker et al., 1993; see Published online 8 April 2009 in Wiley InterScience also Cope and Lacy, 1992; Cope, 1993; Plavcan, 1993). (www.interscience.wiley.com). VC 2009 WILEY-LISS, INC. 254 J.E. SCOTT ET AL. site of Lufeng, China, represents a single species— time represented by the hominoid-bearing deposits at Lufengpithecus lufengensis—that exceeds Gorilla and Lufeng is unknown, temporal variation is unlikely to be Pongo in its degree of postcanine sexual dimorphism a major component of the high level of size variation in (Kelley and Xu, 1991; Kelley, 1993; Kelley and Plavcan, L. lufengensis, given that intrasexual variation in the 1998). Establishing that the Lufeng sample represents a sample is within the range of modern species (Kelley single highly dimorphic species was made possible by and Plavcan, 1998). The fact that L. lufengensis exceeds two key characteristics of the assemblage: the sample is Pongo in its level of molar dimorphism means that it is large, comprising hundreds of teeth (e.g., Kelley and potentially more dimorphic in the molar dentition than Etler, 1989; Wood and Xu, 1991), and a number of post- any extant primate, as Pongo is commonly thought to canine dentitions have been confidently sexed using possess the greatest level of molar dimorphism among associated canines and P3s (e.g., Kelley and Xu, 1991; living primates (e.g., Mahler, 1973; Kelley and Xu, 1991; Kelley, 1993; Kelley, 1995a,b). Using the sexed specimens Kelley and Plavcan, 1998). If true, then including the (n 16 for each molar position), Kelley and colleagues Lufeng sample as part of the comparative framework for (Kelley and Xu, 1991; Kelley, 1993; Kelley and Plavcan, assessing variation in fossil primate samples becomes 1998) demonstrated that molar dimorphism in L. lufen- even more critical. gensis is so high that there is no overlap between male In fact, it has not been quantitatively verified that and female individuals in bivariate plots of mesiodistal Pongo expresses the greatest degree of molar dimor- and buccolingual dimensions. Several researchers have phism among living primates, and therefore the claim argued that the Lufeng sample contains multiple species that the degree of molar dimorphism documented in L. (e.g., Wu and Oxnard, 1983a,b; Martin, 1991; Cope and lufengensis falls outside the range observed in living pri- Lacy, 1992; Plavcan, 1993), but a mixture of two or more mate species has not been adequately tested. Thus, in species is unlikely to have produced the pattern of varia- this study, we test two hypotheses regarding molar size tion observed in the sample, unless one appeals to highly dimorphism in primates: (1) Pongo represents the upper- improbable sampling events (Kelley and Plavcan, 1998). most extreme of molar dimorphism among living pri- Thus, L. lufengensis extends the known range of intra- mates, and (2) molar dimorphism in L. lufengensis is specific size variation and sexual dimorphism in greater than that in the most dimorphic living primate the Hominoidea, at least with respect to the postcanine species. We then apply the results of these analyses to dentition. other potential instances of extreme dimorphism in the Despite initial objections based on both ontological and late Miocene hominoid fossil record—the Sivapithecus epistemological grounds (e.g., Ruff et al., 1989; Martin, material from Haritalyangar, India, and the Ouranopi- 1991; Cope and Lacy, 1992; Martin and Andrews, 1993; thecus macedoniensis material from Greece (Kelley, Plavcan, 1993; Teaford et al., 1993; Walker et al., 1993), 2005; Schrein, 2006). Specifically, we evaluate whether the idea that some fossil hominoid species were more levels of apparent sexual dimorphism (i.e., the level of dimorphic than living great apes has gained wider accep- dimorphism required if the distinct large and small size tance, and many researchers now acknowledge extreme clusters evident in the Sivapithecus and O. macedonien- dimorphism as a potential source of high measures of sis molar samples represent conspecific males and variation that must be considered when evaluating fossil females, respectively) in these fossil samples fall within samples (e.g., Plavcan, 2001; Plavcan and Cope, 2001; the limits of dimorphism established for living primates Scott and Lockwood, 2004; Schrein, 2006; Skinner et al., and L. lufengensis. 2006; Simons et al., 2007; Humphrey and Andrews, 2008).1 This is not to say that extreme dimorphism should be regarded as the null hypothesis for Miocene hominoids; rather, we are suggesting that extreme MATERIALS AND METHODS dimorphism is a viable alternative to the hypothesis that Three extant species were included in the analysis: high levels of size variation in a fossil sample indicate the western lowland gorilla (Gorilla gorilla), the Bor- the presence of multiple species. Acceptance of L. lufen- nean orangutan (Pongo pygmaeus), and the drill (Man- gensis as a single highly dimorphic species highlights drillus leucophaeus) (Table 1).