A morphometric analysis of pliopithecoid maxillary molar cusp peripheralization Andrew C. Holmes, Jacqueline Garnett, David R. Begun Department of Anthropology, The University of Toronto Introduction Results The is a superfamily of catarrhine known from fossil sites across Eurasia from 18-8 Ma. The most well known and best documented pliopithecoid A B clades are the and the Crouzelidae. Despite extensive study, most diagnostic features used to differentiate these groups have remained qualitative.1,2,3,4 This analysis uses geometric measurements to quantify upper molar cusp peripheralization. Our results confirm previous qualitative descriptions and show that crouzeliids have more peripheralized upper molar cusps compared with pliopithecids. We conclude that increased upper molar cusp peripheralization is a derived trait unique to the Crouzeliidae. Materials M1 and M2 were selected because they provide a comprehensive comparative sample of pliopithecoid upper dentition and are known to be phylogenetically informative (M1 n=28, M2 n=30)5 .

Pliopithecidae Crouzeliidae Outgroup Pliopithecidae Crouzeliidae Outgroup Figure 3. ROPA measurements for M1 (A) and M2 (B).

2 A B Table 2. M angle Mann-Whitney U results M2 (Angle A) Pliopithecidae Crouzeliidae Crouzeliidae 0.86 Crouzeliidae Outgroup 0.05 0.09 M2 (Angle B) Pliopithecidae Crouzeliidae Crouzeliidae Crouzeliidae 0.42 a b Pliopithecidae Outgroup Outgroup 0.82 0.61 M2 (Angle C) Pliopithecidae Crouzeliidae 2 Figure 1. M a) platyodon (Göriach 1453) b) hernyaki (SMNS 6089) Pliopithecidae Crouzeliidae 0.04 Our sample represents seven species currently assigned to three pliopithecoid clades: Outgroup Outgroup 0.08 0.004 Crouzeliidae, Pliopithecidae, and Dionysopithecidae (Table 1). Dionysopithecidae (D. M2 (Angle D) Pliopithecidae Crouzeliidae shuangoensis, P. jianghuaiensis) are the earliest, most primitive branch of the Crouzeliidae 0.27 pliopithecoids6. We combined these taxa with two earlier African species, Outgroup 0.76 0.19 Propliopithecus haeckeli and Lomorupithecus harrisoni, to create an outgroup useful for Figure 4. Principal Components Analysis of Length-Breadth (MD/BL) determining whether cusp peripheralization is a primitive or a derived trait for the and ROPA indices for M1 (A) and M2 (B). Pliopithecoidea. Table 1. Taxa used in this analysis. Discussion Pliopithecidae Crouzeliidae Outgroup Our results show that the Crouzeliidae have significantly higher ROPA values for M1 and M2 when compared with the Pliopithecus piveteaui Anapithecus hernyaki Dionysopithecus shuangouensis Pliopithecidae and the outgroup (<0.05). Pliopithecids and the outgroup did not significantly differ (Figure 3). Among the Pliopithecus canmatensis Laccopithecus. robustus Platodontopithecus jianghuaiensis Crouzeliidae, Laccopithecus has the most peripheralized cusps, particularly so in the M2. Consequently, crouzeliid ROPA Pliopithecus zhanxiangi Barberapithecus huezeleri Propliopithecus zeuxis values show a greater range of variation compared with the pliopithecids or the outgroup (Figure 3B, Figure 4B). Even Pliopithecus platyodon Lomorupithecus harrisoni with this large range of variation, pliopithecid and outgroup M2 values are markedly lower and do not overlap vindobonensis substantially with those of the Crouzeliidae. Few differences were found in angular cusp measurements among Methods taxonomic categories. The one exception is the M2 cusp angle C (metacone), which is significantly smaller for crouzeliids compared with pliopithecids and the outgroup (<0.05, Table 2). In crouzeliids, the metacone is buccally displaced and We collected a series of linear, closer to the perimeter of the occlusal surface, which in turn causes the metacone angle to be smaller. angular, and area measurements of We used PCA to investigate group specific molar shape patterns by analyzing MD/BL and ROPA (Figure 4). In M1 the molar specimens using ImageJ 1.8.0 B majority of variance is accounted for in PC1 (84%), but in M2 the variance is more evenly split (PC1 = 54%). Because PC1 7 imaging software (Figure 2). High A is loaded primarily by MD/BL and PC2 by ROPA this means that peripheralization can be seen more strongly in M2 than resolution photographs were used M1. Crouzeliids differ significantly from pliopithecids and the outgroup in molar cusp peripheralization, suggesting that (Nikon D7100 with a 60mm Micro OPA increased peripheralization is a crouzeliid synapomorphy. lens). Total Crown Base Area (TCBA) MD is measurement of the total occlusal surface area, and Occlusal Polygon Conclusion C D Area (OPA) is a measurement of a Crouzeliids have more peripheralized upper molar cusps than other pliopithecoids, Propliopithecus and Lomorupithecus, polygon that is created by suggesting that this is a synapomorphy. As both crouzeliids and pliopithecids have been described as primarily connecting the major upper molar frugivorous, the functional significance of cusp peripheralization is not clear and requires further analysis. cusps. When dentin was exposed on a cusp, we estimated the cusp apex BL as being in the center of the exposed Acknowledgments Figure 2. Barberapithecus huerzeleri IPS 1724c dentin8,9. We used the index of OPA Thank you to Museum National d’Histoire Naturelle, Institut Català de Paleontologia Miquel Measurements: Mesiodistal length (MD), Buccolingual relative to TCBA (Relative Occlusal Crusafont, Hungarian Institute of Geology and Geophysics, Naturhistoriches Museum Wien, breadth (BL), TCBA (Total Crown Base Area), OPA Universalmuseum Joanneum, Universität Tübingen, Naturkundemuseum Stuttgart Museum Polygon Area or ROPA) to quantify (Occlusal Polygon Area), Cusp A (Protocone), Cusp B cusp peripheralization (figure 2). (Paracone), Cusp C (Metacone), Cusp D (Hypocone). am Löwentor, Christine Argot, Madelaine Böhme, Ursula Gölich, Dominique Gommery, Martin Angle measurements for OPA were Mesial is up. 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