Over a decade ago, researchers analyzing fossils from the Late Pleistocene deposits of Liang Bua cave on the Indonesian island of Flores announced the discovery of a new extinct, diminutive species they named Homo floresiensis. It likely lived between 17,000 and one million years ago and stood about a meter tall. However, some contend that the remains belong to short or perhaps even disfigured members of our own species. Now, according to a new analysis of teeth from multiple individuals spanning several species and continents, these so-called “hobbits” are indeed a separate species. The findings are published in PLOS ONE this week.
Previous work revealed that H. floresiensis exhibits unusually small body and brain sizes for a Late Pleistocene Homo, as well as a mix of primitive, advanced, and unique skeletal features. For example, its cranial shape was like that of H. erectus, but it had the upper versus lower limb proportions of Australopithecus. While this unique mosaic clearly has significant evolutionary meaning, researchers can’t agree on what that would be.
To investigate, a team led by University of Tokyo’s Yousuke Kaifu conducted extensive comparisons with multiple teeth (including measurements such as crown size and contour) from H. floresiensis, H. habilis from about two million years ago, early H. erectus from the Indonesian island of Java dating back about a million years ago, and 490 H. sapiens. The dental remains from multiple individuals indicate that H. floresiensis had primitive canines and premolars but advanced molars – a combination of dental traits that haven’t been seen in any other species of hominin (a lineage that includes us and our direct ancestors).
The primitive aspects are comparable to H. erectus from the Early Pleistocene, while some of the molar morphologies appear to be even more progressive than those of modern humans. This contradicts the earlier claim of an entirely modern human-like dental morphology, but it also doesn’t support the hypothesis that H. floresiensis originated from a much older H. habilis or Australopithecus-like, small-brained hominin that’s currently unknown in the Asian fossil record.
The dentition of H. floresiensis isn’t just a simple, scaled-down version of earlier hominins. Instead, the results support an alternative hypothesis that H. floresiensis derived from an earlier Asian H. erectus population, and then they experienced substantial body and brain size dwarfism living on an isolated island setting.
Mandibular dentitions of H. floresiensis (LB) and selected Early Pleistocene Homo specimens: early Javanese H. erectus (Sangiran) and H. habilis (OH). 2015 Kaifu et al.