Chapter 6 Cranial Shape in Asian Homo erectus: Geographic, Anagenetic, and Size-Related Variation Karen L. Baab Abstract A strong focus on the morphological differences Introduction between African and Asian H. erectus has generally overshadowed variation among populations of Asian Despite the implicit assumption of broad homogeneity H. erectus. This study explored variation in Asian H. erectus within Asian H. erectus, there is variation in the cranial using 3D geometric morphometric methods, examining morphology of the Javanese and Chinese H. erectus sam- the shape of the neurocranium, frontal bone, occipital ples. This diversity has implications for the interpretation of bone and temporal base. Analyses focused on the elucida- tion of geographic, temporal and size-related patterns of the taxonomy and evolutionary history of H. erectus. cranial shape variation in a representative sample from Although H. erectus s.l. is now known from sites across the Zhoukoudian, Sangiran, Ngandong, Sambungmacan and Old World, the initial H. erectus discoveries were from sites Ngawi. In regards to the neurocranium, geographic dif- on the Indonesian island of Java (Trinil; Dubois 1894), and ferences explained the greatest proportion of variation, from mainland China (Zhoukoudian; Black 1929). A pre- followed by geochronological age (these two factors occupation with the distinctions between African and Asian explained similar shape differences within the neurocra- H. erectus has generally overshadowed potential variation nium) and size. The temporal base, frontal and occipital within Asian H. erectus (e.g., Wood 1984, 1994; Andrews bones were strongly influenced by geography and size. 1984; Stringer 1984; Villmoare 2005). Yet, those studies Although the later Javanese and Zhoukoudian specimens that have explored differences within and among Asian were generally distinct, there was some overlap between H. erectus fossil assemblages have uncovered complex and Sangiran 2 and the northern Chinese specimens. This sometimes conflicting patterns of geographic, temporal, may suggest that isolation between the two regions did and size-related cranial variation (von Koenigswald and not occur until the Middle or Late Pleistocene or that Weidenreich 1939; Weidenreich 1943, 1951; Jacob 1975, the Sangiran hominins are morphologically close to the 1978; Sartono 1975; Rightmire 1990; Kidder and Durband common ancestor of the Zhoukoudian and later Javanese 2000, 2004; Antón 2002; Durband et al. 2005; Kaifu et al. H. erectus. The late Indonesian fossils did group together 2005, 2008; Liu et al. 2005; Baab 2007). in the principal components analyses. Yet there were subtle Some researchers have reported a robust relationship shape differences between the Sambungmacan/Ngawi fos- between morphology and geography within Asian H. erectus. sils and those from Ngandong, indicating the presence of These studies show that the Javanese and northern Chinese two similar but slightly different potentially contemporane- samples are each relatively homogenous but clearly distinct ous morphs. The Sambungmacan specimens do not appear from one another in regards to their cranial shape (Weidenreich to be morphological intermediaries between the Sangiran 1951; Picq 1990; Kidder and Durband 2000, 2004; Antón and Ngandong fossils in regards to overall cranial shape. 2002; Durband et al. 2005), despite the greater time depth of the Indonesian fossil sample. Differences have been docu- Keywords Shape variation • 3D geometric morphometrics mented in the overall shape of the cranial vault, including the • China • Indonesia • Middle Pleistocene frontal bone, occipital bone, and the temporomandibular joint (TMJ). In contrast, other studies have documented greater overlap between the Indonesian and Chinese morphologies (Rightmire 1990; Bilsborough 2000; Liu et al. 2005). Cranial shape may have changed over time both within K.L. Baab (*) Asian H. erectus as a whole as well as within regional sam- Department of Anatomical Sciences, Stony Brook University Medical Center, Stony Brook, NY 11794, USA ples (e.g., Antón 2002). It has been well-established that the e-mail: [email protected] average brain size increased over time in H. erectus s.l. C.J. Norton and D.R. Braun (eds.), Asian Paleoanthropology: From Africa to China and Beyond, Vertebrate Paleobiology 57 and Paleoanthropology, DOI 10.1007/978-90-481-9094-2_6, © Springer Science+Business Media B.V. 2010 58 K.L. Baab (Wolpoff 1984; Leigh 1992; Rightmire 2004) and within workers were implicitly supporting the presence of two or Asian H. erectus s.s. in particular (Sartono 1975; Antón and more separate lineages within Javanese H. erectus for over 1 Swisher 2001). However, it is unclear exactly how this relates Myr. Jacob (1978) extended this lineage back in time even to changes in cranial shape within this taxon, although Antón further to >1.5 Ma by arguing for an ancestor–descendent (2002) has speculated that an increase in cranial height and relationship between “Pithecanthropus modjokertensis” minimum frontal breadth were the result of increasing (which includes S 4) and “P. soloensis” (Ngandong, Sm 1, endocranial volume in the Javanese H. erectus. Santa Luca and S 17). (1980) identified several evolutionary trends in the shape of This study complements previous efforts to better char- the cranium within Asian H. erectus which he also attributed acterize and understand the degree and pattern of variation to an increase in brain size. These changes include an increase within Asian H. erectus based on linear measurements and in the breadth across the temporal squamae, a decrease in the discrete characters by focusing on an alternate source of size of the sagittal keel, a reduction of the supraorbital sulcus information: three dimensional (3D) cranial shape. Three and a more vertically oriented occipital plane. More recently, dimensional geometric morphometrics has advantages over Kaifu et al. (2008) suggested that increases in external cra- standard linear measurements in that it retains the original nial dimensions in the more recent Indonesian fossils corre- geometry of the specimens and can be used to visualize spond to increases in endocranial capacity. shape differences related to external factors such as geogra- Differences within the sites of Sangiran, Ngandong, and phy or size. Although discrete traits have proven central to Zhoukoudian have also been attributed to sexual variation the debate about the distinctiveness of Asian vs. African (e.g., Weidenreich 1943; Santa Luca 1980; Rightmire 1990; H. erectus, they have also proven quite controversial. For Wolpoff 1999). Interpretations of sexual variation must be instance, disagreements concerning individual character viewed cautiously, however, due to well-documented diffi- definitions, independence of characters, and taxonomic culties in assigning sex to individual fossils (Armelagos and distribution of characters remain unsettled (e.g., Stringer Van Gerven 1980). To avoid the risks associated with assign- 1984; Andrews 1984; Wood 1984, 1991, 1994; Hublin 1986; ing sex to the fossils, this study focused on size-related vari- Bräuer 1990; Kennedy 1991; Bräuer and Mbua 1992; ation; within Asian H. erectus, and within limited Villmoare 2005). Cranial shape, as quantified by geometric temporogeographic samples (such as Ngandong), this prob- morphometric techniques, provides a less subjective source ably corresponds to sexual variation. However, size varia- of information about cranial morphology and allows for the tion outside of these circumscribed samples must be viewed study of the shape of biological structures, rather than just a as a combination of sexual and allometric variation. Recent limited set of linear measurements. In this study the rela- work has highlighted the effect of size on certain aspects of tionship between cranial shape variation and several exter- cranial shape often used to defineH. erectus, such as occipi- nal variables, specifically geography, geological age and tal angulation and degree of postorbital constriction (Spoor cranial size, was explored using principal components and et al. 2005). multiple regression analyses. In addition, the affinities of In addition to questions which apply to the Asian H. erectus individual specimens within the Javanese sample and pos- sample as a whole, there are also areas of ambiguity related sible evolutionary relationships were also assessed using specifically to the Javanese H. erectus sample. For example, this dataset. it is unclear whether the Sambungmacan fossils form a sin- gle, homogenous sample and, if so, whether they are a good morphological intermediary between the Sangiran and Ngandong samples (Frayer et al. 1993; Wolpoff 1999; Baba Materials et al. 2003; Kaifu et al. 2008), or whether they are more closely related to the Ngandong specimens (Sartono 1975; In this study 3D landmark data were acquired from Indonesian Jacob 1975, 1978; Delson et al. 2001; Antón 2002). The less and Chinese H. erectus cranial fossils. Original specimens widely-known Ngawi specimen has also been grouped with were used when available, but casts were substituted for the the Ngandong and Sambungmacan fossils, although only Zhoukoudian, S 12, S 17 and Ngawi fossils (Table 6.1). limited morphometric comparisons have been made between Although data was collected from the well-preserved Perning Ngawi and other Indonesian H. erectus (Sartono 1990; fossil calvaria, it was not included in any analysis as a result Widianto and Zeitoun