Descriptions of the lower limb skeleton of 'Homo floresiensis'
Bones of the lower extremity have been recovered for up to nine different individuals of 'Homo floresiensis' - LB1, LB4, LB6, LB8, LB9, LB10, LB11, LB13, and LB14. LB1 is represented by a bony pelvis (damaged but now repaired), femora, tibiae, fibulae, patellae, and numerous foot bones. LB4/2 is an immature right tibia lacking epiphyses. LB6 includes a fragmentary metatarsal and two pedal phalanges. LB8 is a nearly complete right tibia (shorter than that of LB1). LB9 is a fragment of a hominin femoral diaphysis. LB10 is a proximal hallucal phalanx. LB11 includes pelvic fragments and a fragmentary metatarsal. LB13 is a patellar fragment, and LB14 is a fragment of an acetabulum. All skeletal remains recovered from Liang Bua were extremely fragile, and some were badly damaged when they were removed temporarily from Jakarta. At present, virtually all fossil materials have been returned, stabilized, and hardened. These skeletal remains are described and illustrated photographically. The lower limb skeleton exhibits a uniquely mosaic pattern, with many primitive-like morphologies; we have been unable to find this combination of ancient and derived (more human-like) features in either healthy or pathological modern humans, regardless of body size. Bilateral asymmetries are slight in the postcranium, and muscle markings are clearly delineated on all bones. The long bones are robust, and the thickness of their cortices is well within the ranges seen in healthy modern humans. LB1 is most probably a female based on the shape of her greater sciatic notch, and the marked degree of lateral iliac flaring recalls that seen in australopithecines such as "Lucy" (AL 288-1). The metatarsus has a human-like robusticity formula, but the proximal pedal phalanges are relatively long and robust (and slightly curved). The hallux is fully adducted, but we suspect that a medial longitudinal arch was absent.
LB1's virtual endocast, microcephaly, and hominin brain evolution
Earlier observations of the virtual endocast of LB1, the type specimen for 'Homo floresiensis', are reviewed, extended, and interpreted. Seven derived features of LB1's cerebral cortex are detailed: a caudallypositioned occipital lobe, lack of a rostrally-located lunate sulcus, a caudally-expanded temporal lobe, advanced morphology of the lateral prefrontal cortex, shape of the rostral prefrontal cortex, enlarged gyri in the frontopolar region, and an expanded orbitofrontal cortex. These features indicate that LB1's brain was globally reorganized despite its ape-sized cranial capacity (417 cm³). Neurological reorganization may thus form the basis for the cognitive abilities attributed to 'H. floresiensis'. Because of its tiny cranial capacity, some workers think that LB1 represents a 'Homo sapiens' individual that was afflicted with microcephaly, or some other pathology, rather than a new species of hominin. We respond to concerns about our earlier study of microcephalics compared with normal individuals, and reaffirm that LB1 did not suffer from this pathology. The intense controversy about LB1 reflects an older continuing dispute about the relative evolutionary importance of brain size versus neurological reorganization. LB1 may help resolve this debate and illuminate constraints that governed hominin brain evolution.
'Homo floresiensis': a cladistic analysis
The announcement of a new species, 'Homo floresiensis', a primitive hominin that survived until relatively recent times is an enormous challenge to paradigms of human evolution. Until this announcement, the dominant paradigm stipulated that: 1) only more derived hominins had emerged from Africa, and 2) 'H. sapiens' was the only hominin since the demise of 'Homo erectus' and 'Homo neanderthalensis'. Resistance to 'H. floresiensis' has been intense, and debate centers on two sets of competing hypotheses: 1) that it is a primitive hominin, and 2) that it is a modern human, either a pygmoid form or a pathological individual. Despite a range of analytical techniques having been applied to the question, no resolution has been reached. Here, we use cladistic analysis, a tool that has not, until now, been applied to the problem, to establish the phylogenetic position of the species. Our results produce two equally parsimonious phylogenetic trees. The first suggests that 'H. floresiensis' is an early hominin that emerged after 'Homo rudolfensis' (1.86 Ma) but before 'H. habilis' (1.66 Ma, or after 1.9 Ma if the earlier chronology for 'H. habilis' is retained). The second tree indicates 'H. floresiensis' branched after 'Homo habilis'.
Conclusions: implications of the Liang Bua excavations for hominin evolution and biogeography
Excavations at Liang Bua, on the Indonesian island of Flores, have yielded a stratified sequence of stone artifacts and faunal remains spanning the last 95 k.yr., which includes the skeletal remains of two human species, 'Homo sapiens' in the Holocene and 'Homo floresiensis' in the Pleistocene. This paper summarizes and focuses on some of the evidence for 'Homo floresiensis' in context, as presented in this Special Issue edition of the 'Journal of Human Evolution' and elsewhere. Attempts to dismiss the Pleistocene hominins (and the type specimen LB1 in particular) as pathological pygmy humans are not compatible with detailed analyses of the skull, teeth, brain endocast, and postcranium. We initially concluded that 'H. floresiensis' may have evolved by insular dwarfing of a larger-bodied hominin species over 880 k.yr. or more. However, recovery of additional specimens and the numerous primitive morphological traitsm seen throughout the skeleton suggest instead that it is more likely to be a late representative of a small-bodied lineage that exited Africa before the emergence of 'Homo erectus sensu lato'. 'Homo floresiensis' is clearly not an australopithecine, but does retain many aspects of anatomy (and perhaps behavior) that are probably plesiomorphic for the genus 'Homo'. We also discuss some of the other implications of this tiny, endemic species for early hominin dispersal and evolution (e.g., for the "Out of Africa 1" paradigm and more specifically for colonizing Southeast Asia), and we present options for future research in the region.
Hominins on Flores, Indonesia, by one million years ago
Previous excavations at Mata Menge and Boa Lesa in the Soa Basin of Flores, Indonesia, recovered stone artefacts in association with fossilized remains of the large-bodied 'Stegodon florensis florensis'. Zircon fission-track ages from these sites indicated that hominins had colonized the island by 0.88 ± 0.07 million years (Myr) ago. Here we describe the contents, context and age of Wolo Sege, a recently discovered archaeological site in the Soa Basin that has 'in situ' stone artefacts and that lies stratigraphically below Mata Menge and immediately above the basement breccias of the basin. We show using 40Ar/39Ar dating that an ignimbrite overlying the artefact layers at Wolo Sege was erupted 1.02 ± 0.02 Myr ago, providing a new minimum age for hominins on Flores. This predates the disappearance from the Soa Basin of 'pygmy' 'Stegodon sondaari' and 'Geochelone' spp. (giant tortoise), as evident at the nearby site of Tangi Talo, which has been dated to 0.90 ± 0.07 Myr ago. It now seems that this extirpation or possible extinction event and the associated faunal turnover were the result of natural processes rather than the arrival of hominins. It also appears that the volcanic and fluvio-lacustrine deposits infilling the Soa Basin may not be old enough to register the initial arrival of hominins on the island.
The foot of 'Homo floresiensis'
'Homo floresiensis' is an endemic hominin species that occupied Liang Bua, a limestone cave on Flores in eastern Indonesia, during the Late Pleistocene epoch. The skeleton of the type specimen (LB1) of 'H. floresiensis' includes a relatively complete left foot and parts of the right foot. These feet provide insights into the evolution of bipedalism and, together with the rest of the skeleton, have implications for hominin dispersal events into Asia. Here we show that LB1's foot is exceptionally long relative to the femur and tibia, proportions never before documented in hominins but seen in some African apes. Although the metatarsal robusticity sequence is human-like and the hallux is fully adducted, other intrinsic proportions and pedal features are more ape-like. The postcranial anatomy of 'H. floresiensis' is that of a biped, but the unique lower-limb proportions and surprising combination of derived and primitive pedal morphologies suggest kinematic and biomechanical differences from modern human gait. Therefore, LB1 offers the most complete glimpse of a bipedal hominin foot that lacks the full suite of derived features characteristic of modern humans and whose mosaic design may be primitive for the genus 'Homo'. These new findings raise the possibility that the ancestor of 'H. floresiensi's was not 'Homo erectus' but instead some other, more primitive, hominin whose dispersal into southeast Asia is still undocumented.
Preface: research at Liang Bua, Flores, Indonesia
Excavations at Liang Bua, Flores, Indonesia, have yielded evidence for an endemic human species, 'Homo floresiensis', a population that occupied the cave between ~95-17 ka. This discovery has major implications for early hominin evolution and dispersal in Africa and Asia, attracting worldwide interest. This preface describes the rationale for the excavations in historical, geographical, and wider research contexts, as well as the methods used. It also introduces the other papers on aspects of Liang Bua research that feature in this edition of the 'Journal of Human Evolution'.
Craniofacial morphology of 'Homo floresiensis': Description, taxonomic affinities, and evolutionary implication
This paper describes in detail the external morphology of LB1/1, the nearly complete and only known cranium of 'Homo floresiensis'. Comparisons were made with a large sample of early groups of the genus 'Homo' to assess primitive, derived, and unique craniofacial traits of LB1 and discuss its evolution. Principal cranial shape differences between 'H. floresiensis' and 'Homo sapiens' are also explored metrically. The LB1 specimen exhibits a marked reductive trend in its facial skeleton, which is comparable to the 'H. sapiens' condition and is probably associated with reduced masticatory stresses. However, LB1 is craniometrically different from 'H. sapiens' showing an extremely small overall cranial size, and the combination of a primitive low and anteriorly narrow vault shape, a relatively prognathic face, a rounded oval foramen that is greatly separated anteriorly from the carotid canal/jugular foramen, and a unique, tall orbital shape. Whereas the neurocranium of LB1 is as small as that of some 'Homo habilis' specimens, it exhibits laterally expanded parietals, a weak suprameatal crest, a moderately flexed occipital, a marked facial reduction, and many other derived features that characterize post-'habilis Homo'. Other craniofacial characteristics of LB1 include, for example, a relatively narrow frontal squama with flattened right and left sides, a marked frontal keel, posteriorly divergent temporal lines, a posteriorly flexed anteromedial corner of the mandibular fossa, a bulbous lateral end of the supraorbital torus, and a forward protruding maxillary body with a distinct infraorbital sulcus. LB1 is most similar to early Javanese 'Homo erectus' from Sangiran and Trinil in these and other aspects. We conclude that the craniofacial morphology of LB1 is consistent with the hypothesis that 'H. floresiensis' evolved from early Javanese 'H. erectu's with dramatic island dwarfism. However, further field discoveries of early hominin skeletal remains from Flores and detailed analyses of the finds are needed to understand the evolutionary history of this endemic hominin species.
New wrist bones of 'Homo floresiensis' from Liang Bua (Flores, Indonesia)
The carpals from the 'Homo floresiensis' type specimen (LB1) lack features that compose the shared, derived complex of the radial side of the wrist in Neandertals and modern humans. This paper comprises a description and three-dimensional morphometric analysis of new carpals from at least one other individual at Liang Bua attributed to 'H. floresiensis': a right capitate and two hamates. The new capitate is smaller than that of LB1 but is nearly identical in morphology. As with capitates from extant apes, species of 'Australopithecus', and LB1, the newly described capitate displays a deeply-excavated nonarticular area along its radial aspect, a scaphoid facet that extends into a J-hook articulation on the neck, and a more radially-oriented second metacarpal facet; it also lacks an enlarged palmarly-positioned trapezoid facet. Because there is no accommodation for the derived, palmarly blocky trapezoid that characterizes 'Homo sapiens' and Neandertals, this individual most likely had a plesiomorphically wedge-shaped trapezoid (like LB1). Morphometric analyses confirm the close similarity of the new capitate and that of LB1, and are consistent with previous findings of an overall primitive articular geometry. In general, hamate morphology is more conserved across hominins, and the 'H. floresiensis' specimens fall at the far edge of the range of variation for 'H. sapiens' in a number of metrics. However, the hamate of 'H. floresiensis' is exceptionally small and exhibits a relatively long, stout hamulus lacking the oval-shaped cross-section characteristic of human and Neandertal hamuli (variably present in australopiths). Documentation of a second individual with primitive carpal anatomy from Liang Bua, along with further analysis of trapezoid scaling relative to the capitate in LB1, refutes claims that the wrist of the type specimen represents a modern human with pathology. In total, the carpal anatomy of 'H. floresiensis' supports the hypothesis that the lineage leading to the evolution of this species originated prior to the cladogenetic event that gave rise to modern humans and Neandertals.
Descriptions of the upper limb skeleton of 'Homo floresiensis'
Several bones of the upper extremity were recovered during excavations of Late Pleistocene deposits at Liang Bua, Flores, and these have been attributed to 'Homo floresiensis'. At present, these upper limb remains have been assigned to six different individuals - LB1, LB2, LB3, LB4, LB5, and LB6. Several of these bones are complete or nearly so, but some are quite fragmentary. All skeletal remains recovered from Liang Bua were extremely fragile, but have now been stabilized and hardened in the laboratory in Jakarta. They are now curated in museum-quality containers at the National Research and Development Centre for Archaeology in Jakarta, Indonesia. These skeletal remains are described and illustrated photographically. The upper limb presents a unique mosaic of derived (human-like) and primitive morphologies, the combination of which is never found in either healthy or pathological modern humans.