Location 
 
 The PTK site was discovered in 2012 by The Olduvai Paleoanthropology and Paleoecology Project (TOPPP) at the junction of the main and secondary branches of Olduvai Gorge (Tanzania; Fig. 1 and Supplementary Fig. 1). The site is situated ~500 m south of the well-known FLK 22 Zinjanthropus (FLK 22 Zinj) site and, to date, it is known to comprise three distinct archaeological levels (Supplementary Fig. 2). Two of these levels, corresponding to what has been defined as ‘upper Zinj’ and ‘lower Zinj’21, occur in the same clay stratum as the FLK 22 Zinj level, underlying volcanic Tuff IC, dated by 40Ar/39Ar to 1.832 + 0.003 Ma (ref. 22). PTK’s third archaeological level underlies the Zinj clay, within the tuffaceous layer known as the ‘Chapati Tuff’23, and corresponds stratigraphically to the top of the Olduvai Bed I archaeological level designated as FLK NN 2. TOPPP’s 2014 excavation of this third level at PTK yielded abundant Mode I stone artefacts and a large faunal assemblage, which includes the MHL hominin proximal phalanx OH 86, described here. 
 
 Figure 1: Geographic location of the ‘PTK’ site. The location of the new PTK site (from which the OH 86 proximal phalanx was excavated) compared with two other major and penecontemporaneous Middle Bed I (Olduvai Formation) sites of FLK 22 Zinjanthropus and FLK NN that also occur near the junction of the Main and Side Gorges. (a) Informal views of excavations at each site. (b) Relationship of the sites in aerial view; lower middle image=a panoramic view of the Gorge looking north, with PTK indicated. (c) Political map of Africa with Tanzania highlighted in black and the approximate location of Olduvai Gorge represented by white dot and a schematic plan view of sites near the junction of the Main and Side Gorges. Full size image (208 KB) Figures index 
 
 Next 
 
 Specimen identification and anatomical description 
 
 OH 86 is a complete manual proximal phalanx that is nearly entirely encased in a very thin layer of the carbonated tuffaceous silt from which it derives (that is, the ‘Chapati Tuff’; Fig. 2). Although the areal spread of this concretion on OH 86 is encompassing, its submillimetre thinness guarantees little impact on the gross measurements that we derived on the specimen and analyse and discuss in this study. Basic osteometrics of OH 86 are listed in Supplementary Table 1. On the basis of several lines of morphometric evidence (see below), as well as qualitative features, we assign OH 86 to the fifth ray of the left hand. 
 
 Applying published qualitative criteria36—including asymmetry of the specimen’s flexor ridges and distal trochlea, as well as the orientation of the latter, and its base’s palmar outline—OH 86 compares most favourably to a modern human manual proximal phalanx from ray V. Quantitative data—including head mediolateral width/base mediolateral width ratio=0.72, base mediolateral width/overall superoinferior length ratio=0.39—corroborate this qualitative diagnosis. Last, we tested this corresponding qualitative/quantitative ray assignment by conducting a discriminant function analysis of OH 86 and a comparative sample composed of modern human proximal phalanges from rays II and V (which tend to be more similar to each other because of asymmetries caused by muscle insertions, among others). This analysis confirms the results of the initial qualitative and quantitative tests, also indicating that OH 86 most probably derives from a fifth ray (with a probability six times more likely than ray II, using the seven shape variables, and with a probability 10 times more likely than ray II, using the seven raw dimensions; Supplementary Fig. 3). 
 
 Assuming that the assignment of OH 86 as a fifth proximal phalanx is correct, it must also derive from a left hand on the basis of the pattern of asymmetry of the distal condyles: in palmar and dorsal views, the presumed radial condyle projects more inferiorly than does the presumed ulnar condyle. Further, the putative ulnar basal tubercle (insertion for the hypothenar muscles) is larger and protrudes more ulnarly and proximally than does the radial basal tubercle. 
 
 Mosimann shape ratios. The overall size (as approximated by the geometric mean, GM) of OH 86 is within the range of modern humans and chimpanzees (Supplementary Fig. 4a), as it is the case of other hominins except Au. sediba (below the human range). In terms of relative length, OH 86 is in the midrange of humans and the upper range of gorillas, but below chimpanzees and monkeys (Supplementary Fig. 4b). OH 86 exhibits a MHL, dorsopalmarly short trochlea, although this value also overlaps with the lowermost range of African apes (Supplementary Fig. 4c). No trend is evident in mediolateral trochlear width, although it is worth noting that the trochlear proportions of OH 86 are virtually identical to those of the fossil Qafzeh 9 (H. sapiens; Supplementary Fig. 4d). With regard to midshaft dimensions, OH 86 is dorsopalmarly short (but still overlaps with the modern human outlier range; Supplementary Fig. 4e), and as a consequence it is also mediolaterally wider than are the midshafts of the proximal phalanges of other hominins (Supplementary Fig. 4f). Extant taxa exhibit similar values of relative basal dorsopalmar height as does OH 86 (Supplementary Fig. 4g), although Pan clearly stands out in its having relatively higher bases (but still overlapping with the remaining sample). In this respect, although all hominins fall within the modern human variation, a clear trend is evident: fossil Homo and OH 86 show very similar values, in the low interquartile range of H. sapiens, whereas all australopiths are in the upper interquartile range. Last, with regard to relative basal breadth (Supplementary Fig. 4h), modern humans (and cercopithecid monkeys) possess wider bases than do African apes. Pliocene australopiths fall in the African ape range, whereas the early Pleistocene Au. sediba, fossil Homo and OH 86 all exhibit values within the human range. 
 
 When all these dimensions of proximal phalanx form variation (that is, the seven Mosimann shape ratios and the associated GM) are summarized by means of a principal components (PCA; Fig. 3a) and a cluster (Fig. 3b) analyses, the closest form affinities of OH 86 are revealed to be with Homo. In fact, based solely on the two major axes of form variation, our PCA (Supplementary Fig. 4 and Supplementary Table 5) clearly separates H. sapiens from Pan, Gorilla and cercopithecoid monkeys (Fig. 3a). Further, although all fossils exhibit their closest form affinities to H. sapiens, OH 86 is the oldest hominin phalanx within the modern human form space (as represented by the two first axes, accounting for 90.1% of total form variation). In addition, when all dimensions of phalangeal form are summarized using an unweighted pair group method with arithmetic mean (UPGMA) dendrogram based on group centroids (Supplementary Fig. 4), it reveals a ‘Homo’ cluster nested within the ‘hominin’ group—with OH 86 being the oldest fossil in the sample placed within this ‘Homo’ cluster (Fig. 3b). In sum, modern human phalangeal form (Fig. 4 and Supplementary Table 5) is characterized by moderate relative total proximodistal length, midshaft mediolateral robusticity and overall size (that is, intermediate values of PC1, similar to Pan) in combination with a mediolaterally wide and dorsopalmarly short trochlea and base (which, together with their shorter lengths, differentiate human and Pan proximal phalanges). More specifically, the bases of Homo proximal phalanges are mediolaterally wider and dorsopalmarly shorter than are those of australopiths (Supplementary Fig. 4g,h). In addition, on the basis of trochlear shape, the intermediate phalanges of australopiths—as well as those of OH 7—are clearly distinct from those of extant and fossil Homo7. This previous finding regarding manual intermediate phalanges corresponds to our independent analyses of complete manual proximal phalanges, indicating together that modern human phalangeal morphology can be accurately characterized quantitatively. Importantly, OH 7 does not conform to the modern human characterization, even though it is penecontemporaneous with the MHL OH 86. 
 
 Figure 3: The form of the human proximal phalanx. (a) Plot showing the two major axes of proximal phalanx V form variation (that is, shape and size space). Major taxonomic groups can be distinguished (using convex hulls); OH 86 is the earliest fossil specimen within the human variation. (b) UPGMA cluster analysis summarizing eight dimensions of phalangeal form space: OH 86 is the oldest specimen within the Homo cluster. The cophenetic correlation coefficient is high (0.8681), indicating that the dendrogram is faithfully preserving the pairwise distances between the original dimensions. (These analyses exclude OH 7 because this hand skeleton does not preserve complete proximal phalanges32.) Full size image (152 KB) Previous 
 
 Figures index 
 
 Next 
 
 Figure 4: Phalangeal curvature in extant and fossil hominoids. (a) Included angle values (in degrees) in a modern and fossil sample of fifth proximal phalanges. OH 86 is (exclusively) within the modern human variation (distinct from australopiths). Boxes represent 25th and 75th percentiles, centreline is the median, whiskers represent non-outlier range and the dot is an outlier. Samples for each boxplot are Homo sapiens (n=36), Pan paniscus (n=8), Pan troglodytes (n=16), Gorilla (n=22), Pongo (n=16) and Hylobatidae (n=22). (b) The fossil hominin specimens analysed in this study are compared in lateral view. All pictures were taken from the originals with the exception of AL333-62 (cast) and ATE9-2 (modified from the literature56; Supplementary Table 4). Scale bar, 1 cm. Full size image (121 KB) Previous 
 
 Figures index 
 
 Phalangeal curvature. From functional and evolutionary perspectives, it is highly relevant that all australopith fifth proximal phalanges exhibit higher values of phalangeal curvature than do any of the extant and fossil Homo specimens (Fig. 4), denoting a biological transition in hominins towards less (if any) commitment to arboreal locomotion (at least as it is revealed from manual proximal phalanx anatomy). As with overall phalangeal form (Fig. 3), OH 86 falls exclusively within the modern human range of variation of fifth proximal phalanx curvature (Fig. 4); pooling results for curvature of all non-pollical proximal phalanges place OH 86 once again within the modern human range and in the lowermost range of Gorilla (Supplementary Fig. 5). In addition, compared with the manual phalanges of O. tugenesis, Ar. ramidus, Au. afarensis, Au. sediba, the Swartkrans hominins and OH 7—whose powerfully built flexor insertions result in proximal phalanx diaphyseal morphology that includes distinctive, palmarly concave ‘outbowing’—the diaphysis of OH 86 lacks such pronounced flexor insertions and is thus much straighter in medial and lateral views (Fig. 2). 

 The hominin finger bone likely came from the pinky finger of an adult left hand. 
 
 Scientists have discovered the oldest known fossil of a hand bone to resemble that of a modern human, and they suggest it belonged to an unknown human relative that would have been much taller and larger than any of its contemporaries. 
 
 This new finding reveals clues about when modern humanlike hands first began appearing in the fossil record, and suggests that ancient human relatives may have been larger than previously thought, researchers say in a new study. 
 
 A key feature that distinguishes humans from all other species alive today is the ability to make and use complex tools. This capability depends not only on the extraordinarily powerful human brain, but also the dexterity of the human hand. 
 
 "The hand is one of the most important anatomical features that defines humans," said study lead author Manuel Domínguez-Rodrigo, a paleoanthropologist at Complutense University of Madrid. "Our hand evolved to allow us a variety of grips and enough gripping power to allow us the widest range of manipulation observed in any primate. It is this manipulation capability that interacted with our brains to develop our intelligence." [The 10 Biggest Mysteries of the First Humans] 
 
 How the hand evolved 
 
 Past analysis of fossils of hominins — the group of species that consists of humans and their relatives after the split from the chimpanzee lineage — has typically suggested that ancient hominins were adapted for a life spent in the trees. For instance, ancient hominin hands often possessed curved finger bones that were well suited for hanging from branches. Modern humans are the only living higher primates to have straight finger bones. 
 
 Scientists have often suggested that modern hands evolved to use stone tools. However, recent hominin fossil discoveries have suggested a more complex story behind the evolution of the modern hand. For instance, the hand bones of some ancient hominin lineages are sometimes more similar to modern hands than those of more recent lineages are. 
 
 "A modernlike hand in the past would tell us when humans became fully terrestrial and when and how efficiently our ancestors used tools," Domínguez-Rodrigo told Live Science. 
 
 To learn more about the evolution of the modern hand, scientists analyzed a newly discovered hand bone dated to more than 1.84 million years ago, dug up from Olduvai Gorge in Tanzania. Previous excavations at Olduvai helped confirm that Africa was the cradle of humanity. 
 
 The new bone was probably part of the little finger of the adult left hand of an unidentified hominin lineage similar to Homo erectus, the first hominin known to regularly keep tools it made. The bone is about 1.4 inches (3.6 centimeters) long — "the same size as the equivalent bone in our hand," Domínguez-Rodrigo said. [See Photos of the Oldest Stone Tools] 
 
 The straightness and other features of this new bone suggest adaptations for life on the ground rather than in the trees. It adds to previous findings suggesting that several key features of modern human body shape emerged very early in hominin evolution. (This unknown hominin was not, however, a modern human.) 
 
 Previous research had suggested that hominins began walking on two legs about 6 million years ago, potentially helping to liberate their hands for tool use. Still, until about 2 million years ago, all known hominin hands showed a double function, allowing hominins to both climb trees and walk on two legs on the ground. (The human lineage Homo is thought to have evolved about 2 million to 3 million years ago; the oldest known extinct human species, Homo habilis, lived at least 1.8 million years ago.) 
 
 Before this oldest known hand-bone fossil was discovered, scientists weren't certain when hominin hands began looking like modern hands and became specialized for manipulation. "Our discovery fills a gap — we found out that such a modern-looking hand is at least 1.85 million years old," Domínguez-Rodrigo said. 
 
 Big hominin 
 
 These findings also reveal that this unknown hominin was larger than other hominins living at the same time or before it. If this newfound finger bone had belonged to a modern human, that person would likely be about 5 feet 9 inches (1.75 meters) tall, Domínguez-Rodrigo said. 
 
 "Why is this important? Archaeologists have gathered enough information to understand that early sites like those of Olduvai are central places where hominins repeatedly transported carcasses up to more than 350 kilograms (770 lbs.), which were obtained via hunting," Domínguez-Rodrigo said. "As a specialist on this topic, I always had trouble understanding how Homo habilis, barely taller than 1 meter (3.3 feet), could efficiently hunt animals that big." 
 
 "Now, the new discovery shows that a bigger and more modern-looking creature existed at the time these sites were formed," he added. "This makes this creature a better candidate to explain the creation of these early archaeological sites." 
 
 The scientists detailed their findings online Aug. 18 in the journal Nature Communications. 
 
 Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.
– Scientists have stumbled upon the oldest known fossil of a hand bone that looks a lot like one found in your own hand, though this one is at least 1.84 million years old. Found in Olduvai Gorge in Tanzania, the hominin bone—likely from the pinky of a left hand, reports LiveScience—is remarkable for a couple of reasons: First, it suggests the humanlike hand, which evolved to make and use tools, dates back 400,000 years earlier than scientists previously believed, UPI reports, via the study in Nature. Until this discovery, researchers weren't entirely sure when our ancestors' hands, with curved finger bones for hanging in trees, straightened out. "This bone belongs to somebody who's not spending any time in the trees at all," lead researcher Manuel Domínguez-Rodrigo tells New Scientist. He adds the hominin likely used tools more often than its predecessors. Second, the bone suggests its owner, an unidentified and possibly unknown human relative, was much taller than other hominins, standing five feet, nine inches. At about 1.4 inches long, the bone is "the same size as the equivalent bone in our hand," says Domínguez-Rodrigo. He believes the species falls somewhere between modern humans and tree-dwellers like Homo habilis—about three feet tall—and Paranthropus boisei on the evolutionary scale. The hominin's size could help explain why early sites in Olduvai include ancient animal carcasses that weighed up to 770 pounds. "I always had trouble understanding how Homo habilis...could efficiently hunt animals that big," the researcher says. "Now, the new discovery shows that a bigger and more modern-looking creature existed at the time these sites were formed." (Some argue early human hands changed little over millions of years.)