Small-bodied humans from Palau, Micronesia

Abstract

Newly discovered fossil assemblages of small bodied Homo sapiens from Palau, Micronesia possess characters thought to be taxonomically primitive for the genus Homo.

Background: Recent surface collection and test excavation in limestone caves in the rock islands of Palau, Micronesia, has produced a sizeable sample of human skeletal remains dating roughly between 940-2890 cal ybp.

Principle findings: Preliminary analysis indicates that this material is important for two reasons. First, individuals from the older time horizons are small in body size even relative to "pygmoid" populations from Southeast Asia and Indonesia, and thus may represent a marked case of human insular dwarfism. Second, while possessing a number of derived features that align them with Homo sapiens, the human remains from Palau also exhibit several skeletal traits that are considered to be primitive for the genus Homo.

Significance: These features may be previously unrecognized developmental correlates of small body size and, if so, they may have important implications for interpreting the taxonomic affinities of fossil specimens of Homo.

Figure 1. Map of Palau indicating the position of the Rock Islands to the south and southwest of the large island of Babeldaob.

The caves discussed in this paper are found on western and eastern edges of the Rock Islands. Specific locations of the caves are not given for security reasons.

Figure 2. Reconstruction from a field map of the southern aspect of Ucheliungs Cave.

The area where a 1×1 meter test excavation was made is indicated by the excavation square. The Position of Original Specimens marks the location where the first fossil were discovered by LRB. The Embedded Skull indicates the position of a more complete cranial specimen encased in dense flowstone.

Figure 3. A field map of Omedokel Cave.

Numbers 100–102 indicate the approximate position of samples of bone collected that yielded successful radiocarbon dates (see Supplementary Data S1). The position of the embedded skull shown in Supplementary Data S5 is indicated.

Figure 4. Stratagraphic column of the Ucheliungs Cave Excavation Square noted in Figure 2.

Successful radiocarbon dates were obtained from human bone in levels 1–5 (see Supplementary Data S1).

Figure 5. Comparison of the two innominates from Palau to that of a modern adult female of average stature (c162 cm).

From left to right – modern human pelvis (top is from the right, bottom is from the left), B:OR-15:18-009 and B:OR-15:18-087. Top: posterolateral view; bottom: lateral view. Maximum iliac breadth can be calculated for both. Calcium carbonate obscures part of the acetabulum of B:OR-15:18-009. Scale bar 1 cm.

Figure 6. Three tali from Palau (left) illustrating variation in size and shape.

The “Little Foot” talus (right) - from a very small bodied early hominin from Sterkfontein, South Africa - is included for comparison. From left to right B:OR-15:18-010 the largest talus collected; B:OR-15:18-011 illustrating a medium sized talus from Palau; B:OR-15:18-039 representing a smaller bodied individual; Little Foot. Of nine tali recovered, at least two individuals have some joint dimensions smaller than those of Little Foot. Scale bar 1 cm.

Figure 7. Interorbital breadth (mm) versus orbital breadth (mm) in Australasians.

Filled circles: Palauan specimens; filled squares: sample means for recent human males; open squares: sample means for recent human females; open triangle; sample mean for Andamanese pygmy females; dotted line: orbital breadth value for LB1 (from supplemental data in [1]). Least squares regression line (y = 0.0624x+18.913, r = 0.1044) based on recent human sample means only. Recent human data representing Australian, Melanesian, Polynesian, western Pacific and Far Eastern populations from WW Howells .

Figure 8. Frontal and lateral-oblique views of B:OR-15:18-001 (Right, top and bottom) and B:OR-14:8-005 (Left, top and bottom), illustrating two adult specimens with inflated glabellae and thickened lateral superciliary arches.

In B:OR-15:18-005 the inflated glabellar region gives rise to curved and laterally extending projections that are continuous with thickened lateral superciliary arches, creating a moderately projecting, double curved supraorbital torus. Specimen B:OR-14:8-001 has an inflated glabellar area and thickened superciliary arches continuing laterally. However, in this specimen the inflated glabellar region is not continuous with the superciliary arches and does not give the appearance of continuous brow ridges.

Figure 9. Occlusal and lateral views of B:OR-14:8-122 (top left and top middle) and B:OR-14:8-771 (bottom left and right), illustrating two adult specimens with reduced chins in the Palauan sample.

B:OR-14:8-122 lacks a vertical keel as well as the distended inferior margin, and consequently lacks the T-shaped mental trigone and associated mental fossae characteristic of modern human chins. The cross section (top right) - approximately through the symphysis - clearly shows the reduction of the chin in this individual. Although part of the symphyseal region of B:OR-14:8-771 is missing, the lack of swelling of the inferior margin at the level of the canine suggests a highly reduced mental eminence. B:OR-14:8-771 also exhibits a congenitally absent third molar, a feature also common in the Palauan sample.

Figure 10. Palauan mandible B:OR-15:18-083 illustrating a number of characters common in the sample, including dental crowding of the anterior teeth, incisiform canines, caniniform premolars, large tooth size, and absence of a third molar.