The hand of Australopithecus sediba

Here we describe the functional morphology of the Australopithecus sediba hand, including the almost complete hand of the presumed female Malapa Hominin (MH) 2 skeleton and a single, juvenile metacarpal from the presumed male MH1 skeleton. Qualitative and quantitative comparisons with extant hominids and fossil hominins, ranging from Ardipithecus to early Homo sapiens, reveal that Au. sediba presents a unique suite of morphological features that have not been found in any other known hominin. Analyses of intrinsic hand proportions show that the MH2 hand has a thumb that is longer relative to its fingers than recent humans and any other known hominin. Furthermore, the morphology of the hamatometacarpal articulation suggests that the robust fifth metacarpal was positioned in a slightly more flexed and adducted posture than is typical of Neandertals and humans. Together, this morphology would have facilitated opposition of the thumb to the fingers and pad-to-pad precision gripping that is typical of later Homo. However, the remarkably gracile morphology of the first ray and the morphology of the lateral carpometacarpal region suggest limited force production by the thumb. The distinct scaphoid-lunatecapitate morphology in MH2 suggests a greater range of abduction at the radiocarpal joint and perhaps less central-axis loading of the radiocarpal and midcarpal joints than is interpreted for other fossil hominins, while the morphology of the hamatotriquetrum articulation suggests enhanced stability of the medial midcarpal joint in extended and/or adducted wrist postures. The MH2 proximal phalanges show moderate curvature and, unusually, both the proximal and intermediate phalanges have well-developed flexor sheath ridges that, in combination with a palmarly-projecting hamate hamulus, suggest powerful flexion and that some degree of arboreality may have been a functionally important part of the Au. sediba locomotor repertoire. Finally, the MH1 and MH2 third metacarpals differ remarkably in their size and degree of robusticity, but this variation fits comfortably within the sexual dimorphism documented in recent humans and other fossil hominins, and does not necessarily reflect differences in function or hand use. Overall, the morphology of the current Au. sediba hand bones suggests the capability for use of the hands both for powerful gripping during locomotion and precision manipulation that is required for tool-related behaviors, but likely with more limited force production by the thumb than is inferred in humans, Neandertals, and potentially Homo naledi

The neurocranium of Ekweeconfractus amorui gen. et sp. nov. (Hyaenodonta, Mammalia) and the evolution of the brain in some hyaenodontan carnivores

This project forms part of the NSF-funded Research on East African Catarrhine and Hominoid Evolution (REACHE) Project and is REACHE Paper #16. Fieldwork by The West Turkana Miocene Project was funded by NSF award BCS 1241817 to JBR, the Natural Sciences and Engineering Research Council of Canada, and the University of Calgary.</p

CORRECTIONS

Hand bones from a single individual with a clear taxonomic affiliation are scarce in the hominin fossil record, which has hampered understanding the evolution of manipulative abilities in hominins. Here we describe and analyze a nearly complete wrist and hand of an adult female [Malapa Hominin 2 (MH2)] Australopithecus sediba from Malapa, South Africa (1.977 million years ago). The hand presents a suite of Australopithecus-like features, such as a strong flexor apparatus associated with arboreal locomotion, and Homo-like features, such as a long thumb and short fingers associated with precision gripping and possibly stone tool production. Comparisons to other fossil hominins suggest that there were at least two distinct hand morphotypes around the Plio-Pleistocene transition. The MH2 fossils suggest that Au. sediba may represent a basal condition associated with early stone tool use and production

CT Scans of UW 88–866 in oblique (left) and lateral (right) views.

<p>Again, note the strong maxillary ridges, deep maxillary fossae, strong temporal lines, and tall malar region, distinctive of <i>P</i>. <i>angusticeps</i> males.</p

Comparison of selected morphological features in "small-bodied" <i>Papio</i> species.

<p><b>Notes:</b> Results from one-way ANOVA with Tukey's Honestly Significant Difference post-hoc comparisons for those variables with equal variances and Games-Howell post-hoc comparisons for those variables with unequal variances. Because orbit height, orbit area, and malar height all scale allometrically, the most meaningful comparisons are among taxa of similar body size. The estimated mass for <i>P</i>. <i>angusticeps</i> averages ~21 kg for males and ~15 for females [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133361#pone.0133361.ref039" target="_blank">39</a>]. <i>P</i>. <i>izodi</i> is estimated at ~20 kg for males and ~15 for females [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133361#pone.0133361.ref039" target="_blank">39</a>]. The most similar extant taxon in terms of body mass is <i>P</i>. <i>h</i>. <i>cynocephalus</i>, ~23 kg for males and 12.5 kg for females, which is why <i>P</i>. <i>h</i>. <i>cynocephalus</i> is used in the above comparisons. All specimens were pooled regardless of sex in order to increase sample size. For sex-specific values, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133361#pone.0133361.t003" target="_blank">Table 3</a>. n.s. = non-significant. Note that <i>P</i>. <i>angusticeps</i> and <i>P</i>. <i>h</i>. <i>cynocephalus</i> are both significantly different from <i>P</i>. <i>izodi</i>, but not from each other. Results for all comparisons are the same if UW 88–886 is included in the <i>P</i>. <i>angusticeps</i> sample. Orbit height defined as the maximum distance between the inferior and superior orbit borders. Orbit width defined as the maximum distance between the lateral and medial orbit borders. Orbit area is defined as orbit width x orbit height. Malar height defined as the distance between orbitale inferior/zygoorbitale and zygomaxillare inferior. Relative malar height defined as malar height/orbit height. <i>P</i>. <i>angusticeps</i> specimens include CO 100, CO 135A/B, CO 101, GV 4040, and HGD 1249. <i>P</i>. <i>izodi</i> specimens include TP 12, SAM 11728, T10, T13, UCMP 125854, UCMP 125855, UCMP 125856, STS 262, T89-11-1, and SWP UN-2. Values for each taxon represent averages. Numbers in parentheses represent estimates. For boxplots with ranges, see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133361#pone.0133361.g004" target="_blank">Fig 4</a> and Table A in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133361#pone.0133361.s001" target="_blank">S1 Dataset</a>.</p><p>Comparison of selected morphological features in "small-bodied" <i>Papio</i> species.</p

Comparison of morphology in UW 88–886 (left), <i>P</i>. <i>angusticeps</i> males (CO 100, center), and <i>P</i>. <i>izodi</i> males (TP 89-11-1, right).

<p>Top: Lateral view, specimens scaled to approximately the same cranial height. Note the tall malar region (black bar), prominent maxillary ridges and deep maxillary fossae (white arrows) in UW 88–886 and <i>P</i>. <i>angusticeps</i> compared with <i>P</i>. <i>izodi</i>. Bottom: Dorsal view, specimens scaled to approximately the same cranial width. Note the longer, narrower muzzle in <i>P</i>. <i>angusticeps</i> compared to <i>P</i>. <i>izodi</i>, and again the prominent maxillary ridges and deep maxillary fossae in UW 88–886 and <i>P</i>. <i>angusticeps</i> compared with <i>P</i>. <i>izodi</i>.</p

Available craniometric comparisons in <i>P</i>. <i>angusticeps</i>, UW 88–886, <i>P</i>. <i>h</i>. <i>cynocephalus</i>, and <i>P</i>. <i>izodi</i>.

<p>Top Row: Boxplots of orbit height considering UW 88–886 separately (left) and within <i>P</i>. <i>angusticeps</i> (right). Note that <i>P</i>. <i>izodi</i> has significantly taller orbits than both <i>P</i>. <i>angusticeps</i> and <i>P</i>. <i>h</i>. <i>cynocephalus</i>. UW 88–886 has tall orbits compared to other <i>P</i>. <i>angusticeps</i> specimens, but within a reasonable range of expected variation for a species. Middle Row: Boxplots of orbit area (mm²) considering UW 88–886 separately (left) and within <i>P</i>. <i>angusticeps</i> (right). <i>P</i>. <i>izodi</i> has significantly larger orbits than <i>P</i>. <i>angusticeps</i>, but a non-significant difference compared to <i>P</i>. <i>h</i>. <i>cynocephalus</i>. The difference between <i>P</i>. <i>angusticeps</i> and <i>P</i>. <i>h</i>. <i>cynocephalus</i> is also non-significant. UW 88–886 appears to have large orbits compared to other <i>P</i>. <i>angusticeps</i> specimens, but again within a reasonable range of expected variation for a species. Bottow Row: Boxplots of relative malar height considering UW 88–886 separately (left) and within <i>P</i>. <i>angusticeps</i> (right). <i>P</i>. <i>izodi</i> has a significantly shorter malar height compared to <i>P</i>. <i>angusticeps</i> and <i>P</i>. <i>h</i>. <i>cynocephalus</i>, but the difference between <i>P</i>. <i>angusticeps</i> and <i>P</i>. <i>h</i>. <i>cynocephalus</i> is non-significant. UW 88–886 is closest to the average of other <i>P</i>. <i>angusticeps</i> specimens. See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133361#pone.0133361.t002" target="_blank">Table 2</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133361#pone.0133361.g005" target="_blank">Fig 5</a>.</p

<i>Papio</i> Cranium from the Hominin-Bearing Site of Malapa: Implications for the Evolution of Modern Baboon Cranial Morphology and South African Plio-Pleistocene Biochronology

<div><p>A new partial cranium (UW 88-886) of the Plio-Pleistocene baboon <i>Papio angusticeps</i> from Malapa is identified, described and discussed. UW 88-886 represents the only non-hominin primate yet recovered from Malapa and is important both in the context of baboon evolution as well as South African hominin site biochronology. The new specimen may represent the first appearance of modern baboon anatomy and coincides almost perfectly with molecular divergence date estimates for the origin of the modern <i>P</i>. <i>hamadryas</i> radiation. The fact that the Malapa specimen is dated between ~2.026–2.36 million years ago (Ma) also has implications for the biochronology of other South African Plio-Pleistocene sites where <i>P</i>. <i>angusticeps</i> is found.</p></div