Liang Bua 'Homo floresiensis' mandibles and mandibular teeth: A contribution to the comparative morphology of a new hominin species

Abstract

In 2004, a new hominin species, 'Homo floresiensis', was described from Late Pleistocene cave deposits at Liang Bua, Flores. 'H. floresiensis' was remarkable for its small body-size, endocranial volume in the chimpanzee range, limb proportions and skeletal robusticity similar to Pliocene 'Australopithecus', and a skeletal morphology with a distinctive combination of symplesiomorphic, derived, and unique traits. Critics of 'H. floresiensis' as a novel species have argued that the Pleistocene skeletons from Liang Bua either fall within the range of living Australomelanesians, exhibit the attributes of growth disorders found in modern humans, or a combination of both. Here we describe the morphology of the LB1, LB2, and LB6 mandibles and mandibular teeth from Liang Bua. Morphological and metrical comparisons of the mandibles demonstrate that they share a distinctive suite of traits that place them outside both the 'H. sapiens' and 'H. erectus' ranges of variation. While having the derived molar size of later 'Homo', the symphyseal, corpus, ramus, and premolar morphologies share similarities with both 'Australopithecus' and early 'Homo'. When the mandibles are considered with the existing evidence for cranial and postcranial anatomy, limb proportions, and the functional anatomy of the wrist and shoulder, they are in many respects closer to African early 'Homo' or 'Australopithecus' than to later 'Homo'. Taken together, this evidence suggests that the ancestors of 'H. floresiensis' left Africa before the evolution of 'H. erectus', as defined by the Dmanisi and East African evidence.