Reconstructing the provenance of the hominin fossils from Trinil (Java, Indonesia) through an integrated analysis of the historical and recent excavations.

In the early 1890s at Trinil, Eugène Dubois found a hominin skullcap (Trinil 2) and femur (Trinil 3, Femur I), situated at the same level ca. 10-15 m apart. He interpreted them as representing one species, Pithecanthropus erectus (now Homo erectus) which he inferred to be a transitional form between apes and humans. Ever since, this interpretation has been questioned-as the skullcap looked archaic and the femur surprisingly modern. From the 1950s onward, chemical and morphological analyses rekindled the debate. Concurrently, (bio)stratigraphic arguments gained importance, raising the stakes by extrapolating the consequences of potential mixing of hominin remains to the homogeneity of the complete Trinil fossil assemblage. However, conclusive evidence on the provenance and age of the hominin fossils remains absent. New Trinil fieldwork yielded unmanned aerial vehicle imagery, digital elevation models, and stratigraphic observations that have been integrated here with an analysis of the historical excavation documentation. Using a geographic information system and sightline analysis, the position of the historical excavation pits and the hominin fossils therein were reconstructed, and the historical stratigraphy was connected to that of new sections and test pits. This study documents five strata situated at low water level at the excavation site. Cutting into a lahar breccia are two similarly oriented, but asynchronous pre-terrace fluvial channels whose highly fossiliferous infills are identified as the primary targets of the historical excavations (Bone-Bearing Channel 1, 830-773 ka; Bone-Bearing Channel 2, 560-380 ka), providing evidence for a mixed faunal assemblage and yielding most of the hominin fossils. These channels were incised by younger terrace-related fluvial channels (terminal Middle or Late Pleistocene) that directly intersect the historical excavations and the reconstructed discovery location of Femur I, thereby providing an explanation for the relatively modern morphology of this 'bone of contention'. The paleoanthropological implications are discussed in light of the current framework of human evolution in Southeast Asia.

Two Late Pleistocene human femora from Trinil, Indonesia: Implications for body size and behavior in Southeast Asia.

Late Pleistocene hominin postcranial specimens from Southeast Asia are relatively rare. Here we describe and place into temporal and geographic context two partial femora from the site of Trinil, Indonesia, which are dated stratigraphically and via Uranium-series direct dating to ca. 37-32 ka. The specimens, designated Trinil 9 and 10, include most of the diaphysis, with Trinil 9 being much better preserved. Microcomputed tomography is used to determine cross-sectional diaphyseal properties, with an emphasis on midshaft anteroposterior to mediolateral bending rigidity (Ix/Iy), which has been shown to relate to both body shape and activity level in modern humans. The body mass of Trinil 9 is estimated from cortical area and reconstructed length using new equations based on a Pleistocene reference sample. Comparisons are carried out with a large sample of Pleistocene and Holocene East Asian, African, and European/West Asian femora. Our results show that Trinil 9 has a high Ix/Iy ratio, most consistent with a relatively narrow-bodied male from a mobile hunting-gathering population. It has an estimated body mass of 55.4 kg and a stature of 156 cm, which are small relative to Late Pleistocene males worldwide, but larger than the penecontemporaneous Deep Skull femur from Niah Cave, Malaysia, which is very likely female. This suggests the presence of small-bodied active hunter-gatherers in Southeast Asia during the later Late Pleistocene. Trinil 9 also contrasts strongly in morphology with earlier partial femora from Trinil dating to the late Early-early Middle Pleistocene (Femora II-V), and to a lesser extent with the well-known complete Femur I, most likely dating to the terminal Middle-early Late Pleistocene. Temporal changes in morphology among femoral specimens from Trinil parallel those observed in Homo throughout the Old World during the Pleistocene and document these differences within a single site.