Homo floresiensis: microcephalic, pygmoid, Australopithecus, or Homo?

The remarkable partial adult skeleton (LB1) excavated from Liang Bua cave on the island of Flores, Indonesia, has been attributed to a new species, Homo floresiensis, based upon a unique mosaic of primitive and derived features compared to any other hominin. The announcement precipitated widespread interest, and attention quickly focused on its possible affinities. LB1 is a small-bodied hominin with an endocranial volume of 380-410 cm3, a stature of 1m, and an approximate geological age of 18,000 years. The describers [Brown, P., Sutikna, T., Morwood, M.J., Soejono, R.P., Jatmiko, Wayhu Saptomo, E., Awe Due, R., 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431, 1055-1061] originally proposed that H. floresiensis was the end product of a long period of isolation of H. erectus or early Homo on a small island, a process known as insular dwarfism. More recently Morwood, Brown, and colleagues [Morwood, M.J., Brown, P., Jatmiko, Sutikna, T., Wahyu Saptomo, E., Westaway, K.E., Awe Due, R., Roberts, R.G., Maeda, T., Wasisto, S., Djubiantono, T., 2005. Further evidence for small-bodied hominins from the Late Pleistocene of Flores, Indonesia. Nature 437, 1012-1017] reviewed this assessment in light of new material from the site and concluded that H. floresiensis is not likely to be descended from H. erectus, with the genealogy of the species remaining uncertain. Other interpretations, namely that LB1 is a pygmy or afflicted with microcephaly, have also been put forward. We explore the affinities of LB1 using cranial and postcranial metric and non-metric analyses. LB1 is compared to early Homo, two microcephalic humans, a 'pygmoid' excavated from another cave on Flores, H. sapiens (including African pygmies and Andaman Islanders), Australopithecus, and Paranthropus. Based on these comparisons, we conclude that it is unlikely that LB1 is a microcephalic human, and it cannot be attributed to any known species. Its attribution to a new species, Homo floresiensis, is supported.