Intrinsic hand proportions of euarchontans and other mammals: implications for the locomotor behavior of plesiadapiforms

Arboreal primates have distinctive intrinsic hand proportions compared with many other mammals. Within Euarchonta, platyrrhines and strepsirrhines have longer manual proximal phalanges relative to metacarpal length than colugos and terrestrial tree shrews. This trait is part of a complex of features allowing primates to grasp small-diameter arboreal substrates. In addition to many living and Eocene primates, relative elongation of proximal manual phalanges is also present in most plesiadapiforms. In order to evaluate the functional and evolutionary implications of manual similarities between crown primates and plesiadapiforms, we measured the lengths of the metacarpal, proximal phalanx, and intermediate phalanx of manual ray III for 132 extant mammal species (n=702 individuals). These data were compared with measurements of hands in six plesiadapiform species using ternary diagrams and phalangeal indices. Our analyses reveal that many arboreal mammals (including some tree shrews, rodents, marsupials, and carnivorans) have manual ray III proportions similar to those of various arboreal primates. By contrast, terrestrial tree shrews have hand proportions most similar to those of other terrestrial mammals, and colugos are highly derived in having relatively long intermediate phalanges. Phalangeal indices of arboreal species are significantly greater than those of the terrestrial species in our sample, reflecting the utility of having relatively long digits in an arboreal context. Although mammals known to be capable of prehensile grips demonstrate long digits relative to palm length, this feature is not uniquely associated with manual prehension and should be interpreted with caution in fossil taxa. Among plesiadapiforms, Carpolestes, Nannodectes, Ignacius, and Dryomomys have manual ray III proportions that are unlike those of most terrestrial species and most similar to those of various arboreal species of primates, tree shrews, and rodents. Within Euarchonta, Ignacius and Carpolestes have intrinsic hand proportions most comparable to those of living arboreal primates, while Nannodectes is very similar to the arboreal tree shrew Tupaia minor. These results provide additional evidence that plesiadapiforms were arboreal and support the hypothesis that Euarchonta originated in an arboreal milieu.     

The hand structure of Carnotaurus sastrei (Theropoda,Abelisauridae): implications for hand diversity and evolution in abelisaurids

Abstract: Carnotaurus sastrei is an abelisaurid dinosaur from the Late Cretaceous of Argentina that has very reduced, but robust, forelimbs and derived hands with four digits, including a large, conical‐shaped metacarpal IV lacking an articulation for a phalanx. The analysis presented in this work highlights a series of additional autapomorphies of C. sastrei. For example, the proximal phalanges are longer than the metacarpals in digits II and III, and digit III includes only one phalanx besides the ungual. The hand of Carnotaurus shares several features with those of Aucasaurus and Majungasaurus, but the hands of the latter genera also display autapomorphies, indicating that the diversity in abelisaurid hand structure is similar to the diversity of cranial protuberances of these dinosaurs.     

Pattern profile analysis of hominid and chimpanzee hand bones

In a study designed to complement morphological research on hominid hand bones, length and width measurements of the thumb, index, and middle rays were obtained from radiographs of modern human hands. These rays are primary in precision-gripping postures and are therefore the ones most relevant for investigating evolutionary changes in fine manipulation. Pattern profile analysis allows individuals or samples to be plotted against a reference sample in standard deviation units, or Z-scores. It provides an indication of how different measurements are from modern human averages, while taking into consideration the degree of variation present within modern human samples. A pattern profile for chimpanzees is clearly distinct from humans but quite similar to that of a bonobo, demonstrating the promise of pattern analysis. Partial pattern profiles of several of the more complete early hominid bones from Hadar, Swartkrans, and Olduvai (O.H. 7) are presented and compared. Hadar bones are long and wide at midshaft relative to articular widths; both body-size effects and functional differences are likely. Thumb distal phalanges from Swartkrans and Olduvai both have relatively small base widths, but they differ in other proportions. Two first metacarpals from Swartkrans show distinct patterns. The profiles of La Ferrassie I and Shanidar IV show the characteristically large Neanderthal distal phalanges. Profiles of Skhūl IV and P?edmost III are alike in some regions with reference to modern North American white males, though they are less similar overall than are those of the two Neanderthals. © 1995 Wiley-Liss, Inc.     

Metacarpophalangeal pattern profiles in Venezuelan and northern Caucasoid samples compared

Comparison of hand long-bone lengths and variances in published measurements of North American Caucasoid, Venezuelan, and English individuals, and of their metacarpophalangeal pattern profiles (MPP), revealed systematic differences between samples from infancy through adulthood. The variances of Venezuelan males tend to be larger than those of Americans, especially under 9 years of age. The same trend was observed for females, but to a lesser degree. The English sample showed variance similar to that of Venezuelans and Americans. Below 7 years of age, bones of Venezuelans were longer than those of Americans, except the distal phalanges, which always were longer in the latter, as were all bones after age 17. The index finger's middle and distal phalanges of Americans were relatively longer than the other bones at all ages. Females also showed this general trend, though not as clearly. Venezuelan adults had longer first and second metacarpals and proximal phalanges than the English adult homologs. American adults had all bones longer than those of English adults. The English adults showed a "typical" MPP, characterized by shorter proximal phalanges, both when compared with Venezuelan and with American adults. Genetic rather than environmental causes are likely as an explanation for these differences. This warned us against the indiscriminate use of any "standard" sample from a different population to establish objective profile patterns and sizes in abnormal cases, as illustrated with one example.     

Comparative and functional morphology of hominoid fingers.

Comparisons of hominoid metacarpals and phalanges reveal differences, many of which are closely linked to locomotor hand postures. The African apes display features of the metacarpals and phalanges which distinguish them from the other Hominoidea. These features are most evident in digits III and IV. The orangutan hand is demonstrably less well adapted to knuckle-walking and is distinctive in its adaptation to power and hook grasping of vertical and horizontal supports, respectively. Orangutan fingers possess a "double-locking" mechanism (Napier, '60), and a slight ulnad shift in the axis of the hand which results in lengthened phalanges of ray IV. Hylobatid apes are more like orangutans in their finger morphology than any of the other Hominoidea, but exhibit unique features of their own. These include elongate phalanges of fingers II-V. Human metacarpals II-V form two sets composed of II-III, and IV-V. The heads of both metacarpals II and III are characterized by axial torsion. This reflects the enhanced manipulatory role of the third finger in humans. Human distal phalanges are unique in the development of pronounced apical tufts. Multivariate analysis of metacarpal III and proximal III yields variables that array the extant apes along an arboreal-terrestrial axis, from hylobatid apes to male gorillas. The positions of taxa on this discriminant concur with observations on the locomotion of free-ranging apes.     

Functional and morphological affinities of the subadult hand (O.H. 7) from Olduvai Gorge.

Study of the O.H. 7 hand was based primarily on morphological comparisons with a large series of hand skeletons of extant hominoid primates. Most of the hand elements are fragmentary or have missing epiphyses and only comparisons based on qualitative morphological observations are possible. The distal phalanges are complete, however, and were analyzed metrically utilizing univariate and multivariate statistical techniques. To compensate for size differences among the Hominoidea a number of size adjustments were employed. None of the adjustments were totally satisfactory from theoretical and practical standpoints and none completely eliminated the influence of size. There is no entirely satisfactory procedure to eliminate size and it is advisable to use several techniques that are not closely related, to compare the results and interpret them with caution. In certain features the wrist and fingers resemble those of African apes; in others they are more like modern human hands; in still others they are unique. The scaphoid and the proximal articular surface of the trapezium retain ape-like features, as do the proximal and middle phalanges. The pollical carpometacarpal joint and the distal phalanges are closer in morphology to those of modern humans. The scaphoid, proximal phalanges and middle phalanges of rays II-V indicate a hand capable of a strong power grip. A number of features of the thumb and the distal phalanges suggest that the O.H. 7 individual was capable of more precise manipulation that extant apes. FLK NN-A, a first distal phalanx, does not closely resemble the first distal phalanx of any of the living Hominoidea. Multivariate distance analysis indicates, however, that it is closest in overall morphology to the pollical distal phalanx of modern humans. In some features not included in the metric analysis, FLK NN-A also resembles the hallucial distal phalanx of modern humans.     

A resampling approach and implications for estimating the phalangeal index from unassociated hand bones in fossil primates

Primate fossil assemblages often have metacarpals and phalanges from which functional/behavioral interpretations may be inferred. For example, intrinsic hand proportions can indicate hand function and substrate use. But, estimates of intrinsic hand proportions from unassociated hand elements can be imperfect due to digit misattribution. Although isolated metacarpals can be identified to a specific digit, phalanges are difficult to assign to a specific ray. We used a resampling approach to evaluate how estimates of intrinsic hand proportions are affected by such uncertainty. First, the phalangeal index—intermediate phalanx length plus proximal phalanx length divided by metacarpal length—for the third digit was calculated for associated specimens of terrestrial, semiterrestrial, and arboreal taxa. We then used resampling procedures to generate distributions of “composite digits” based on resampled ratios in which phalanges from the second, fourth, and fifth rays, and from different individuals, were chosen randomly. Results confirm that the phalangeal index for associated third digits significantly discriminates groups. We also found that resampled ratios had significantly lower means, indicating that using composite digits is prone to systematic underestimation. Resampled ratios also generated distributions with greater variance around the means that obscured distinctions between groups, although significant differences between the most arboreal and terrestrial taxa are maintained. We conclude that using unassociated phalanges to calculate a phalangeal index is prone to sampling bias. Nevertheless, a resampling approach has the potential to inform estimates of hand proportions for fossil taxa, provided that the comparative sample is constrained to mimic the fossil composition. Am J Phys Anthropol 151:280–289, 2013. © 2013 Wiley Periodicals, Inc.     

Ecomorphology of the cervid intermediate phalanx and its implications for palaeoenvironmental reconstruction

This paper reports on newly developed ecomorphological models for the cervid intermediate phalanx. Using a geometric morphometric approach, we quantitatively assess the overall gracility of the bone, the depth and concavity of the proximal articulation and the roundness and symmetry of the distal articulation in the intermediate phalanx, to establish relationships between morphology, locomotor behavior and environment. The morphology of the phalanx was found to vary along a gradient from gracile phalanges with shallow proximal articulations in forms adapted to yielding substrate, to robust phalanges with deeper proximal articulations in taxa adapted to firm substrate. Phylogeny and allometry are accounted for using regressions and phylogenetic comparative methods. Although the results indicate phylogeny explains part of the morphological variation, overall the shape of the intermediate phalanx appears mainly driven by differences in function. Consequently, this element promises to be a useful palaeoenvironmental proxy that can be applied on fossil assemblages with cervid remains.     

Principal component analysis of the elongation of metacarpal and phalangeal bones

A hypothesis that the first principal component computed from the covariance matrix of logarithms reflected the specific growth rates of corresponding bones was taken to analyze the growth pattern of the tubular bones of the hand. The total length of 19 tubular bones of the right hand was measured on standardized radiographs of Japanese children (33 boys, 33 girls). Metacarpals in boys and bones of the fifth digit in girls showed higher growth coefficients. The second, third and fourth proximal, and the third and fourth middle phalanges showed lower coefficients for both sexes. These observations suggest the signs of proximal row dominance in boys and of fifth ray dominance in girls in the elongation of the hand bones. A marked sex difference was found in the fifth middle phalanx. In girls the growth coefficients of this bone was much larger than any other bones, but was moderate in boys.     

Metric dimensions of the proximal phalanges of the human hand and their relationship to side, position, and asymmetry

The anatomy of the proximal phalanges of the human hand has been widely described. Nevertheless, when consulting osteology and anatomy publications, the general opinion of researchers is that siding and allocating the proximal phalanges with regard to finger position is difficult, if not impossible. We provide morphological criteria for determining the side of the proximal phalanges and a metric means of allocating a phalanx to a specific finger. This paper also quantifies the absolute and directional asymmetry found in phalanges within this sample. The sample studied consists of three groups, one modern and two archaeological. To investigate these, three measurements were taken—maximum length, maximum width at the base and maximum width at the head. It was found that phalanges could be assigned correctly to the side and finger of origin in 100% of the cases when the five phalanges of a given hand were present, and that this result dropped to 92% when allocating isolated phalanges. The means of the measurements taken were larger in the modern group and a constant relationship between the greater basal width of the second and the fourth proximal phalanges was found.     

广西侗族手指指毛的分布

本文调查了广西三江侗族18至50岁农民和学生279人(男153、女126)的手指指毛分布。结果说明,近侧和中间指节除发现一例女性没有指毛以外,其余均有指毛,远侧指节无指毛。男女两性间指毛的出现率无明显差异,左右手指指毛分布基本上对称。     

Notches in the non-epiphyseal ends of the metacarpals and phalanges in children of four South African populations

The incidence of notches in the non-epiphyseal ends of the shafts of the metacarpals and phalanges was determined from radiographs of the left hand of 1,303 Pretoria school-children aged 6 to 11 years. The group included White, Negro, Coloured and Indian children. The notches represent vestiges of supernumerary epiphyses or pseudo-epiphyses. Notching of one or more of the metacarpals or phalanges was found in 88.9% of White children, 77.1% of Negro children, 84.3% of Coloured children and 78.8% of Indian children. Notches were most common in metacarpal I followed in declining order of frequency by metacarpal II, metacarpal V, middle phalanx V and proximal phalanx I. Notches were rare in other sites. The mean number of notches per subject was significantly higher in males than in females in all four population groups. However, the sex differences appear to be due mainly to earlier obliteration of notches in females. The findings in White children suggest that there is no significant relationship between metacarpal and phalangeal notching and skeletal maturation rate. Notches are significantly more common in Pretoria Whites than in relatively poorly nourished Pretoria Negro children. It is concluded that the occurrence of notches is a normal phenomenon accompanying the ossification of the hand skeleton and that notching is related neither to retardation in skeletal development nor to undernutrition.     

Neanderthal hand and foot remains from Moula‐Guercy,Ardèche,France

The hand and foot remains from Moula‐Guercy cave (Ardèche, France) comprise 24 specimens of Eemian age (ca. 120 ka). The specimens include primarily complete elements, which are rare among the Moula‐Guercy postcrania. The hand remains have several characteristic Neanderthal traits including a laterally facing (parasagittally oriented) second metacarpal‐capitate articulation, a short styloid process, a wide proximal articular surface on the third metacarpal, and absolutely expanded apical tuberosities on the distal hand phalanges relative to modern humans. The foot remains include several incomplete elements along with an antimeric pair of naviculars, a medial cuneiform and cuboid, and a single complete element from each of the distal segments (one each: metatarsal, proximal foot phalanx, intermediate foot phalanx, distal foot phalanx). Consistent among the specimens are relatively wide diaphyses for length in the metatarsals and phalanges and large and prominent muscle attachments, both consistent with previously published Neanderthal morphology. The hand and foot collection from Moula‐Guercy is an important dataset for future studies of Neanderthal functional morphology, dexterity, and behavior as it represents a previously undersampled time period for European Neanderthals. Am J Phys Anthropol 152:516–529, 2013. © 2013 Wiley Periodicals, Inc.     

Aquatic Adaptation and Swimming Mode Inferred from Skeletal Proportions in the Miocene Desmostylian Desmostylus

Desmostylians are enigmatic, extinct, semiaquatic marine mammals that inhabited coastlines of the northern Pacific Rim during the late Oligocene through middle Miocene. Principal components analysis (PCA) of trunk and limb proportions provides a rational multivariate context for separating living semiaquatic mammals on three orthogonal axes: a size axis (PC-I), a degree of aquatic adaptation axis (PC-II), and a forelimb- versus hind-limb-dominated locomotion axis (PC-III). The necessary skeletal measurements are available for Desmostylus hesperus but not for other desmostylians. Among species similar in size to Desmostylus in the study set, the one most similarly proportioned is the polar bear. Projection of Desmostylus on PC-II shows it to have been more aquatic than a polar bear (indicated by its relatively short ilium and femur, combined with relatively long metapodals and phalanges). Projection of Desmostylus on PC-III suggests that its aquatic locomotion was even more forelimb-dominated than that of a bear (indicated by its relatively long metacarpal III and corresponding proximal phalanx, combined with a relatively short metatarsal III and corresponding proximal phalanx). Desmostylians were different from all living semiaquatic mammals, and desmostylians are properly classified in their own extinct order, but their skeletal proportions suggest that bears provide an appropriate baseline for imagining what desmostylians were like in life.     

Trabecular Architecture of the Manual Elements Reflects Locomotor Patterns in Primates

The morphology of trabecular bone has proven sensitive to loading patterns in the long bones and metacarpal heads of primates. It is expected that we should also see differences in the manual digits of primates that practice different methods of locomotion. Primate proximal and middle phalanges are load-bearing elements that are held in different postures and experience different mechanical strains during suspension, quadrupedalism, and knuckle walking. Micro CT scans of the middle phalanx, proximal phalanx and the metacarpal head of the third ray were used to examine the pattern of trabecular orientation in Pan, Gorilla, Pongo, Hylobates and Macaca. Several zones, i.e., the proximal ends of both phalanges and the metacarpal heads, were capable of distinguishing between knuckle-walking, quadrupedal, and suspensory primates. Orientation and shape seem to be the primary distinguishing factors but differences in bone volume, isotropy index, and degree of anisotropy were seen across included taxa. Suspensory primates show primarily proximodistal alignment in all zones, and quadrupeds more palmar-dorsal orientation in several zones. Knuckle walkers are characterized by having proximodistal alignment in the proximal ends of the phalanges and a palmar-dorsal alignment in the distal ends and metacarpal heads. These structural differences may be used to infer locmotor propensities of extinct primate taxa.     

An Early Pleistocene human pedal phalanx from Swartkrans,SKX 16699, and the antiquity of the human lateral forefoot

In order to assess the antiquity of derived human lateral (lesser) toe morphology, the SKX 16699 Early Pleistocene pedal proximal phalanx from Swartkrans (South Africa) was compared to samples of pedal phalanges attributed to Pliocene/Pleistocene australopithecines, Homo naledi and Late Pleistocene Homo. In contrast to australopith lateral phalanges, the SKX 16699 phalanx exhibits an absolutely (and probably relatively) short length, limited plantar diaphyseal curvature, proximal-to-midshaft and mid-dorsoplantar flexor sheath insertions, and a marked proximodorsal orientation of the metatarsal facet. SKX 16699 is intermediate between the australopith phalanges and later Homo ones in its modest dorsal diaphyseal curvature and mid-dorsoplantar metatarsophalangeal collateral ligament insertion areas. Its diaphyseal robustness is similar to that of Homo phalanges, but overlaps the range of later australopith ones. This combination of features and the close morphological affinities of SKX 16699 to later Homo proximal pedal phalanges suggest the emergence of a distinctly human lateral forefoot by the initial Early Pleistocene.     

The Developmental Origins of Mosaic Evolution in the Primate Limb Skeleton

The central hypothesis of this paper is that basic properties of vertebrate limb development bias the generation of phenotypic variation in certain directions, and that these biases establish focal units, or regions, of evolutionary change within the primate hand and foot. These focal units include (1) a preaxial domain (digit I, hallux or pollex, metapodial and proximal phalanx), (2) a postaxial domain (metapodials and phalanges of digits II?CV), and (3) a digit tip domain (terminal phalanges and nails/claws of rays I?CV). The existence of these focal units therefore provides a mechanistic basis for mosaic evolution within the hand and foot, and can be applied to make specific predictions about which features of the limb skeleton are most likely to be altered in primate adaptive radiations over time. Examination of the early primate fossil record provides support for this model, and suggests that the existence of variational tendencies in limb development has played a major role in guiding the origin and evolution of primate skeletal form.     

Mechanical advantages of the Neanderthal thumb in flexion: a test of an hypothesis

It has been proposed that the pollical phalangeal length proportions of the Neanderthals provided them with a greater mechanical advantage relative to recent humans for their pollical flexor muscles in power grips across the interphalangeal (IP) joint at the expense of the mechanical advantage of those pollical flexor muscles in precision grips at the finger tip. To test these related hypotheses, we compared the pollical load arm dimensions (phalanx lengths) to power arm dimensions (dorsopalmar articular heights) for the European and Near Eastern Neanderthals and for European and Amerindian samples of recent humans. It was found, initially, that the proximal articular height of the pollical distal phalanx is a poor predictor of the power arm at the IP articulation, even though the proximal articular height of the pollical proximal phalanx was an adequate indicator of the power arm size at the metacarpophalangeal (MCP) joint. In addition, differences in distal pollical ulnar deviation at the IP joint appeared to make little difference in the mechanical advantage comparisons. More importantly, the relative shortness of Neanderthal proximal pollical phalanges and the relative lengthening of their distal pollical phalanges was confirmed, and it was determined that, despite some minor differences in articular dimensions between Neanderthals and recent humans, these pollical phalangeal length contrasts translated into significant differences in mechanical advantages for the flexor muscles across the MCP and IP articulations.     

Tubular hand bone growth during the latter half of the prenatal period: an allometric analysis

The growth of the 19 tubular hand bones from fetal months 5 to 9 was studied by the allometric method. The hand bones were carefully dissected under a low power stereoscopic microscope. The length and breadth of all bones was found to be monophasic in relation to crown-rump length. In general, maximum bone and ossified shaft lengths in the same row group demonstrate similar allometric coefficients. The specific growth rate of ossified shaft length for all fetal hand bones is greater than the growth rate of maximum length. The highest allometric coefficients for both maximum length and ossified shaft length were obtained from the middle phalanges. The shape of the metacarpals and distal phalanges becomes thinner, while the other bones become thicker or maintain their length-breadth ratio. The relative growth pattern of the first proximal phalanx differed from the middle phalangeal group of the other digits. This suggests that current nomenclatures for the three bones of the pollex is appropriate.     

从中指骨长度推算身高的研究

作者对近年在华南地区收集的,已知生前身高的汉族成年男性骨骼的中指骨近节、中节进行了测量。用直线回归方程、多元回归方程对从中指骨长度推算身高进行了研究。并用50例国人骨骼标本对这些推算身高的方法作了检验。结果表明,中指骨与四肢大型长骨,以及从中指骨长度推算身高的直线回归方程与多元回归方程,对推算身高的价值都是相同的。