A new distal fibular fragment of <i>Homo floresiensis</i> and the first quantitative comparative analysis of proximal and distal fibular morphology in this species

The hindlimb skeleton of the holotype (LB1) of Homo floresiensis is relatively complete and includes both fibulae, which despite being well preserved have yet to be subject to a quantitative comparative analysis with other hominids. A new distal fragment of a fibula has also been recovered from the H. floresiensis-bearing sediments at Liang Bua (Flores, Indonesia). In this study, we used 3D geometric morphometrics (3DGM) to quantify detailed aspects of the external shape and articular facet morphology of the proximal and distal ends of these H. floresiensis fibulae. The comparative sample included fibulae from 57 extant great apes (Pongo, Gorilla, and Pan), 41 recent and fossil Homo sapiens, five Australopithecus afarensis, and five Neandertals. Shape variation was analyzed using principal component analysis of Procrustes coordinates, and mean differences among taxa were tested using a Procrustes ANOVA with a randomization procedure. Size comparisons were made using centroid size and tested via correlations with principal component scores. Results demonstrate that H. floresiensis fibulae possess the absolute smallest mean linear dimensions and mean centroid sizes among our comparative sample. The proximal and distal fibular ends of H. floresiensis exhibit four key features adapted for obligate bipedalism while also displaying a suite of plesiomorphic traits shared with extant great apes and A. afarensis that, compared with that of H. sapiens and Neandertals, suggest a more versatile ankle joint with a greater range of motion and enhanced load-bearing capabilities of the fibula. Our results are consistent with other aspects of the H. floresiensis lower limb, such as long feet relative to the femur and a long forefoot relative to the hindfoot, that together suggest an australopith-like locomotor repertoire that included both obligate bipedalism and climbing.