Reassessment of the hominid diversity in the Early-Middle Pleistocene of Indonesia

Since the first discovery of Pithecanthropus (Homo) erectus by E. Dubois at Trinil in 1891, over 200 hominid dentognathic remains have been collected from the Early-Middle Pleistocene deposits of Java, Indonesia, forming the largest palaeoanthropological collection in Southeast Asia. Most of these fossils are currently attributed to H. erectus. However, because of the substantial morphological and metric variation in the Indonesian assemblage, some robust specimens (e.g., the partial mandibles Sangiran 5 and Sangiran 6a) were formerly variably allocated to other taxa (Meganthropus palaeojavanicus, Pithecanthropus dubius, Pongo sp.). The existence of a putative “mystery ape” has also been evoked. Due to the effects of vicariance and relict survivorship accompanying phases of glacial eustasy combined with tectonic uplift and volcaniclastic deposition that periodically altered the biogeography of the Sunda region, the appraisal of palaeobiodiversity at a regional scale is difficult. To resolve the taxonomic uncertainty surrounding the contentious Indonesian hominid fossil assemblage, we applied Occlusal Fingerprint Analysis to reconstruct the chewing kinematics, and we also used various morphometric approaches to examine internal dental structures. Our results confirm the presence of Meganthropus as a Pleistocene Indonesian hominid taxon distinct from Pongo, Gigantopithecus and Homo, and further reveal that Dubois' Homo erectus paratype molars more likely belong to Meganthropus. Our analyses also suggest that Meganthropus shows greatest affinity to Lufengpithecus, and we hypothesize that these taxa are phylogenetically closely related. Thus, during the Early-Middle Pleistocene, at least three and perhaps four hominid genera inhabited what is now Indonesia: Homo, Pongo and Meganthropus, with the possible presence of Gigantopithecus. This is a higher level of diversity than previously documented and, with the newly resurrected genus Meganthropus, is particularly noteworthy for the late survival of two to three large ape lineages in Indonesia.