A reanalysis of the early Holocene frontal bone from Aitape, New Guinea.
The Aitape frontal bone is compared to 13 late Pleistocene/early Holocene Australian crania as well as two modern samples comprised of 101 modern Australian and 126 modern New Guinea crania. These crania are compared using canonical variates analysis and Mahalanobis distances, the latter of which is examined for statistical significance using random expectation statistics. The results show that Aitape shares shape characteristics of a longer, flatter frontal with ancient Australians. Modern populations differ from both Aitape and the ancient Australians in having generally shorter, more curved frontals.
Keywords: Australia, New Guinea, Sahul, Holocene, terminal Pleistocene, Aitape
The Aitape frontal was discovered in 1929 during petroleum prospecting operations (Nason-Jones 1930; Fenner 1944). The specimen consists of a nearly complete frontal bone and an additional associated cranial fragment (Fenner 1944). While early interpretations of the site stratigraphy placed the specimen in the Pleistocene (Hossfeld, 1949), later radiocarbon dates suggested an age of approximately 5000 years BP for the skull (Hossfeld 1964, 1965). Despite being somewhat younger than initially suspected, the Aitape frontal remains a valuable source of information about early populations inhabiting Sahul. Analysis of Aitape has been limited apart from the description contributed by Fenner (1944). Since that initial publication, a number of other terminal Pleistocene and early Holocene crania have been found in Australia and our appreciation of variation in those populations has improved considerably. The present study is an analysis of Aitape in light of this expanded sample, furthering our understanding of variability in early Sahul populations.
Aitape was located during a geological survey of the Barida Range in Northern New Guinea (Hossfeld 1949). The cranial material was found in a fossiliferous lenticle contained within the Upper Wanimo Group, a soft, blue, fossiliferous mudstone that is overlain by a layer of coarse gravel beds (Hossfeld 1949, 1965). A variety of foraminifera and gastropods were collected during the original 1929 survey as well as a later expedition undertaken in 1962 to reexamine the stratigraphy of the Aitape site (Hossfeld 1965). The paleoecological evidence suggests a coastal mangrove swamp that was exposed at low tide and periodically flooded by a shallow, muddy protected sea (Hossfeld 1965). While initial interpretations of the geology at the site suggested the frontal was deposited during sea-level fluctuations at some stage in the Pleistocene (Hossfeld 1949), later radiocarbon dates indicate a Holocene date for the deposits containing them (Hossfeld 1964, 1965). A date on coconut shell was reported as 4555 _+ 80 BP, and two carbonized wood fragments yielded dates of 4915 +_ 65 BP and 5070 _+ 140 BP (Hossfeld 1965). Further tests on the uranium content of the skull fragments also provided results consistent with a Holocene age (Hossfeld 1965).
Aitape consists of a nearly complete frontal bone that has darkened to a chocolate brown (Figure 1). The specimen retains the anterior portions of both parietal bones and includes an unattached fragment consisting of frontal and articulated sphenoid (Fenner 1944). The nasal sutures are well preserved, as is the suture for the right zygomatic process of the frontal. In addition, the coronal suture and several centimeters of the sagittal suture are also present between the adjacent parietal bones. The anterior sections of both temporal lines are present, and these are well developed. Vault thickness of Aitape is similar to that noted for a sample of modern Australians (Fenner 1944). Fenner (1944: 353) diagnosed Aitape as coming from a female of perhaps 45 years of age, and found "no evidence that it belonged to an individual differing greatly from the modern Australian aboriginal (southern type)". A craniometric analysis comparing the Aitape frontal to a number of modern groups from Australia and New Guinea was carried out using five measurements (Chiles 1996). The results indicated male status for Aitape (contra Fenner 1944), and found no close associations between it and any modern samples.
The Aitape frontal represents one of the few ancient human specimens from New Guinea, and it is broadly contemporary with a number of important mid-Holocene remains from Australia. The Mossgiel, Green Gully, Lake Nitchie and Cossack individuals from southern Australia all date to <6500 BP (Pardoe 1993), and each has been examined by various workers attempting to understand variation in Australian populations during the Pleistocene/Holocene (Macintosh 1963; 1976a, 1976b; Thorne 1977; Freedman and Lofgren 1979; Pardoe 1993). These endeavors have not included Aitape despite its availability for more than 70 years. This is almost certainly due to a focus on Australia, where greater attention has been generated due to more intensive archaeological exploration and greater numbers of skeletal remains, and as a result the prehistory of New Guinea has received less scrutiny. The Aitape frontal provides an opportunity to examine cranial variation within greater Sahul during the early Holocene. In addition, comparisons with both fossil and modern populations from the region will offer some insights about the patterns of change in the frontal bone during the past 5000 years in New Guinea.
[FIGURE 1 OMITTED]
Materials and methods
The cranial sample used for this project includes Aitape; Cohuna; Kow Swamp 1,2, 3, 5, 6, 7; Keilor, Lake Nitchie; Nacurrie 1 and 2; and WLH 19. Modern comparative samples were provided by the 101 modern Australians measured by Howells (1973) and an additional 127 modern New Guinea crania measured by the lead author. The variables used are Frontal Chord (FRC), Frontal Subtense (FRS) and Bistephanic Breadth (STB) as defined by Howells (1973). Due to the extremely fragmentary nature of the fossil material, variables were selected based on their presence on Aitape. Measurements for Aitape were taken on the original specimen by AD. Measurements from the fossil Australians were taken by AD on high quality casts due to the repatriation of the original fossils, and were checked on available published data. Data for Kow Swamp 2, 3, and 6 were taken from Thorne (1975), data for WLH 19 were taken from Webb (1989), and data for the Nacurrie crania were obtained from M. Westaway (pers. comm.). The modern New Guinea crania are housed at the Field Museum of Natural History, Chicago. These crania come from ten different populations along the Sepik Coast near the Aitape site.
Canonical variates analysis with random expectation statistics
It is well known that fossil specimens present a number of problems for multivariate statistical analyses. To minimize these, the data set from Howells (1973), minus the Australian sample used here for comparison, is used to estimate a within group covariance matrix. While under ideal circumstances the covariance matrix should reflect variation similar to that of the subjects under examination, this is clearly impossible in the case of fossil crania. The Howells data set is the best alternative currently available, providing a pooled covariance matrix from 28 samples of modern humans.
Canonical variates analyses and Mahalanobis distances are computed for the fossil samples after Jantz and Owsley (2001). One analysis is performed using three variables, the maximum number of measurements held in common between the individuals analyzed. The variables are transformed using the Darroch and Mosimann (1985) shape adjustment technique. When employing this method, each variable for each individual (row in the data matrix), is divided by the geometric mean for all variables. This results in a dimensionless shape variable. The practical effect of this technique is to remove isometric size.
Measurements are limited to length, breadth, and curvature of the frontal bone. Although the measurements in their raw form may be moderately to highly correlated, the approach used here insures that only the independent information of each variable contributes to the Mahalanobis distance, at least to the extent that the modern covariance matrix applies to the ancient crania. Consequently, the Mahalanobis distances quantify shape variation in sagittal and coronal planes of the vault.
Once the canonical variates and Mahalanobis distances have been calculated, the crania can be compared to one another by the use of random expectation statistics. Through this method, the distance between pairs of individuals randomly selected from a population will be distributed as [square root of]/(2p-1) with a variance of 1, where p is the number of dimensions (Defrise-Gussenhoven 1967). This random expectation statistic can be used to determine whether the distance between any two crania exceeds that expected between individuals drawn from a single population in the Howells data set (Jantz and Owsley 2001). Furthermore, any distance greater than 1.96 standard deviations above the random expectation value reflects statistical significance by a one-tailed test (Jantz and Owsley 2001).
Our test examines the shape of the frontal bone using canonical variates analysis on three variables. The plot generated by this analysis is shown in Figure 2, and the Mahalanobis distances obtained are shown in Table 1. The first canonical variate accounts for 63.5% of the variation in this test, and it is primarily influenced by a very high positive loading (.9998) on the frontal chord and a high negative loading on the frontal subtense. The second canonical variate accounts for the remaining 36.5% of the variation, and it is primarily influenced by a very high positive loading (.9978) on bistephanic breadth and a moderately high negative loading on frontal subtense. As a result, this analysis is separating crania with relatively long, flat frontals from those with shorter and more curved frontals along variate 1, while variate 2 is separating relatively broader, flatter frontals from those that are narrower and more curved.
[FIGURE 2 OMITTED]
The plot of these results (Figure 2) shows a broad distribution of crania along the first canonical variate. Both modern cranial samples are grouped together in a broad point cloud on the left side of the plot. Aitape falls just to the right of the cluster of modern crania, with the Australian fossils Kow Swamp 3, Nacurrie 2, and Mossgiel slightly more widely separated from the distribution of modern crania. Keilor and Lake Nitchie fall well within the modern grouping, while Kow Swamp 2, 6, and WLH 19 are located on the edges of the modern distribution. Cohuna, Nacurrie 1, and Kow Swamp 1 are clustered to the far right of the plot well away from any other crania in the analysis. This positioning reflects the exceptionally long and flat frontals that characterize these specimens. Many scholars allege that these individuals have been artificially deformed due to these fairly extreme characteristics in the frontal (Brothwell 1975; Brown 1987, 1989; Anton & Weinstein 1999; Durband 2008); a position that could be supported by the present results. Kow Swamp 5 likewise occupies a remote section of the plot due to its relatively long frontal combined with an exceptionally low frontal subtense and broad bistephanic breadth. Kow Swamp 5 is also widely believed to have been artificially deformed (e.g. Brothwell 1975; Brown 1987; Anton and Weinstein 1999; Durband 2008). With notable exceptions like Kow Swamp 2, Keilor, and Lake Nitchie, the Australian fossils and Aitape generally show longer and flatter frontal bones than the modern crania.
The Mahalanobis distances, provided in Table 1, provide further illumination on the patterns presented in the plot. Aitape is statistically significantly separated from 34.6% (35/101) of the modern Australian sample and 45.7% (58/127) of the modern New Guinea sample. Among the more ancient individuals, Aitape is statistically significantly separated from Cohuna, Nacurrie 1, and Kow Swamp 1,2 and 5. Lake Nitchie, Keilor, and Kow Swamp 2, all of whom fall amongst the modern human point cloud in the plot, are statistically significantly separated from very few modern crania in either sample. Keilor and Lake Nitchie are both likewise separated from a similar list of fossil crania, with each being statistically significantly distant from Cohuna, Mossgiel, Nacurrie 1 and 2 and Kow Swamp 1, 3, and 5. Lake Nitchie is also statistically significantly separated from Kow Swamp 7. Kow Swamp 2 is statistically significantly distant from every ancient specimen in the analysis except for Keilor and Lake Nitchie. It has been suggested by Thorne (1975) that Kow Swamp 2 is likely a much younger burial than the other Kow Swamp remains, and the results of this test do indicate a frontal bone shape in that specimen that is more similar to the modern crania and differs strongly from the other ancient Australians. Befitting their more remote locations on the plot, Cohuna, Nacurrie 1, and Kow Swamp 1 and 5 are statistically significantly separated from all of the modern crania and the majority, if not all, of the other fossil specimens in the analysis.
The results of this study demonstrate some morphological similarities between the Aitape frontal and other broadly contemporaneous individuals from Sahul. As with most ancient crania from the region, Aitape shows a relatively longer and flatter frontal than is typically seen in local modern populations. In the canonical variates plot Aitape fell outside of the combined modern distribution and adjacent to several ancient Australian crania along the first factor. This patterning has identified a frontal shape in Aitape that is atypical for modern populations in the region but similar to many early Australians.
The Mahalanobis distances generated in this analysis suggest that Aitape may be slightly more similar in shape to modern Australian populations than with recent New Guineans. Aitape showed fewer statistically significant distances with the modern Australian sample than with the modern New Guinea sample, 34.6% to 45.7% respectively. This pattern is unexpected, and could suggest that frontal bone shape in modern New Guinean populations has changed slightly more relative to the form seen in the early inhabitants of Sahul. Indeed, the ancient Australian crania in our sample tend to share greater similarities in shape with modern Australians and higher numbers of statistically significant distances with the modern New Guinean sample (Table 1). These patterns could reflect isolation and genetic drift in the modern New Guinean groups relative to the modern Australians. Further discoveries of ancient crania on New Guinea could help test these apparent patterns highlighted by our analysis.
Despite the fragmentary nature of the Aitape frontal, and the paucity of measurements available as a result of its preservation, our results do provide some interesting, but tentative, conclusions. First, that the Aitape frontal shares a similar morphology with other late Pleistocene/early Holocene occupants of Sahul, despite being located several thousand kilometers from any of the early Australian populations sampled through these crania. These findings suggest that frontal bone shape was fairly homogenous throughout Sahul for several millennia. More recently, modern New Guinean crania appear to show a slightly greater divergence in frontal bone shape from the ancient pattern than is seen in modern Australians.
Several potential mechanisms have been invoked to explain the evolutionary trends in Australian cranial samples during the late Pleistocene and early Holocene. These include climate changes after the Last Glacial Maximum (e.g. Brown, 1989; Bulbeck, 2001), changing demographic trends and population structure (e.g. Pardoe, 1988), and even a propensity towards physical violence in dispute resolution (Brown, 1989). Based on the small surviving fragments of Aitape, the lack of any other material of similar antiquity at the site, and the great distance between Aitape and the highest density of ancient Australian remains, we feel it would be premature to endorse any of these hypotheses based on the results reported here.
We thank Simon Poraituk, Alois Kuaso, and the Papua New Guinea National Museum (PNGNM) for permission to study the Aitape frontal. Andy Fairbairn was instrumental in establishing contact with the PNGNM and his assistance is also greatly appreciated. Susan Whitby and Mike Picketing of the National Museum of Australia provided access to the Aitape frontal and assistance during data collection. Dan Rayner helped with data collection and the photographs of the Aitape frontal used in this paper. Alan Thorne and Denise Donlon allowed ACD to study casts of fossil Australians in their care. Michael Westaway gave us unpublished data on the Nacurrie crania. John Terrell provided access to the modern New Guinea cranial sample at the Field Museum, and Will Pestle facilitated ACD's work at the museum. Meredith Tarczynski and Krista Schroeder assisted with data collection at the Field Museum. Richard Jantz provided his DISPOP computer program to run the canonical variates analysis and also answered many questions.
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Department of Sociology, Anthropology, and Social Work, Texas Tech University, MS 41012, Holden Hall 158, Lubbock, TX 79409-1012, USA. email@example.com
Table 1: Mahalanobis distances obtained for the three variable canonical variates test. Leftmost column indicates the number of statistically significant distances obtained between that specimen and the modern Australian (n=101) and New Guinea samples (n=127). Distances >3.692 are statistically significant at the P=0.05 level and are shown in bold type. Aust NG 35 58 Aitape 0.000 14 18 WLH19 1.059 0.000 101 127 Cohuna 4.794 5.776 0.000 4 7 Keilor 3.390 2.344 8.097 0.000 76 104 Mossgiel 1.504 2.561 3.427 4.892 101 127 Nacurrie1 5.048 6.058 0.503 8394 78 104 Nacurrie2 1.273 2.270 3.523 4.610 0 1 Nitchie 3.414 2.838 8.021 2.433 101 127 KS1 5.752 6.759 1.054 9.093 12 10 KS2 5.028 4.087 9.823 2.042 34 30 KS3 1.004 2.041 3.802 4384 101 127 KS5 5.943 6.026 5.946 7.178 36 46 KS6 2.079 1.225 6318 2.023 61 77 KS7 1.262 1.405 4.780 3.432 Aitape WLH19 Cohuna Keilor Aust 35 14 101 4 76 0.000 101 3.621 0.000 78 0.594 3.789 0.000 0 4597 8.186 4.616 0.000 101 4323 0.703 4.491 8.879 0.000 12 6.459 10.067 6301 2.409 10.771 34 0.568 4.046 0.335 4.293 4.749 101 6.047 6.448 5504 8.799 6.800 36 3.461 6.669 3.020 3.529 7351 61 2.159 5.135 1.620 4.238 5.815 Mossgie1 Nacurrie1 Nacurrie2 Nitchie KS1 Aust 35 14 101 4 76 101 78 0 101 12 0.000 34 6.025 0.000 101 9.199 5.749 0.000 36 4.045 2.896 5331 0.000 61 5356 1.607 4.739 1.539 0.000 KS2 KS3 KS5 KS6 KS7
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|Author:||Durband, Arthur C.; Creel, Jody A.|
|Publication:||Archaeology in Oceania|
|Date:||Apr 1, 2011|
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