Femoral lengths and stature in Plio-Pleistocene hominids

This study reports the femoral lengths of 31 Plio-Pleistocene hominids dated between 3.1 and 0.7 million years ago, and uses those lengths to estimate stature by way of the femur-stature ratio reported by Feldesman et al. (Am. J. Phys. Anthropol. 78:219-220, 1989). By this method the average female Australopithecus afarensis is 105 cm and the average male is 151 cm. The respective values are 115 and 138 cm for A. africanus. As defined by Howell (In VJ Maglio and HBS Cooke (eds): The Evolution of African Mammals. Cambridge: Harvard University Press, 1978) and Johanson et al. (Kirtlandia 28:1-14, 1978), Homo habilis is a sexually dimorphic species, with females standing 118 cm and males 157 cm. Such apparently strong dimorphism may be due to the possibility that there are actually two species of nonrobust hominids between 2 and 1.7 m.y.a. The estimate for the female Australopithecus boisei is 124 cm and for the male, 137 cm, but these estimates are especially difficult to be certain of because there are no femora that can be positively identified as male A. boisei. Australopithecus robustus is estimated to be 110 cm (female) and 132 cm (male). African Homo erectus stood 160 cm (female) and 180 cm (male). From these estimates several generalizations are apparent. First, there is apparently strong sexual dimorphism in stature in A. afarensis and H. habilis, but less in the other species. Second, the "robust" australopithecines were relatively small statured. Third, it is apparently not true that humans have been getting progressively taller throughout their evolutionary history. Some individuals were as tall as modern humans 3 m.y.a., by 2 m.y.a. one individual stood about 173 cm, and by 1.7 m.y.a. a stature of 180+ cm was not uncommon.     

Chimpanzee variation facilitates the interpretation of the incisive suture closure in South African Plio-Pleistocene hominids

For a better understanding of early hominid growth patterns, we need to compare skeletal maturation among humans and chimpanzees. This study provides new data on variation of the incisive suture closure in extant species to facilitate the understanding of growth patterns among South African Plio-Pleistocene hominids. The complete anterior closure of the incisive suture occurs early during human life, mostly before birth. In contrast, in chimpanzees a complete anterior closure occurs mostly after the eruption of either the first permanent molars (pygmy chimpanzees) or the third molars (common chimpanzees). The first aim of this study is to test whether the patterns of closure of both the anterior and palatal components of the incisive suture in chimpanzees accurately mirror their polytypism by investigating 720 museum specimens of known geographical origin. Then we use the data gleaned from the incisive suture closure in chimpanzees to determine whether there are different growth patterns among South African Plio-Pleistocene hominids and to interpret them. Results about the pattern of incisive suture closure are consistent with the differences among chimpanzees as revealed by molecular data. Thus, the variation in chimpanzee patterns of incisive suture closure facilitates the interpretation of morphology in South African fossil hominids. In Australopithecus (Paranthropus) robustus as compared to Australopithecus africanus, the complete anterior closure and, probably, the complete palatal closure of the incisive suture occurs during early life in the same way as they occur in humans. Moreover, the closure pattern observed on Stw 53, a supposed early Homo from Sterkfontein Member 5, is similar to that seen in A. africanus and in chimpanzees. Thus, with respect to the anterior component of the incisive suture, A. africanus and Stw 53 retain the primitive feature for which A. (P.) robustus and Homo share the derived character state. Finally, it is worth noting that the Taung child does not show the robust condition. Am J Phys Anthropol 105:121–135, 1998. © 1998 Wiley-Liss, Inc.     

Early hominid body weight and encephalization

The body weight of the Plio-Pleistocene hominids of Africa is estimated by predicting equations derived from the Terry Collection of human skeletons with known body weights. About 50% of the variance in body weight can be accounted for by vertebral and femoral size. Predicted early hominid weights range from 27.6 kg (61 lb) to 54.3 kg (119 lb). The average weight for Australopithecus is 43.2 kg (95 lb) and for Homo sp. indet. from East Rudolf, Kenya, is 52.8 kg (116 lb). These estimates are consistent even if pongid proportions are assumed. Indices of encephalization show that the brain to body weight ratio in Australopithecus is above the great ape averages but well below Homo sapiens. The Homo sp. indet. represented by the KNM-ER 1470, O.H. 7 and O.H. 13 crania have encephalization indices above Australopithecus despite the greater body weight of the former.     

Mandibular postcanine dentition from the Shungura Formation,Ethiopia: Crown morphology,taxonomic allocations,and Plio-Pleistocene hominid evolution

Over 200 hominid specimens were recovered by the International Omo Expedition of 1967–1976. Despite the fragmentary nature of this primarily dental collection, these hominid remains represent a major body of evidence about hominid evolution in eastern Africa during the 2–3 myr time period. Our analysis of the Omo dental collection is based on a large comparative sample of 375 quantifiable mandibular postcanine teeth of A. afarensis, A. africanus, A. aethiopicus, A. boisei, A. robustus, and early Homo. A total of 48 isolated mandibular premolars and molars of the Omo collection spanning the 2–3 myr time period is sufficiently preserved to allow reliable serial allocations and intertaxon comparisons and is the object of study in this paper. We present taxonomic identifications of these teeth and seven other mandibular specimens preserving tooth crowns. Metric analyses of this study include cusp area and crown shape variables taken on occlusal view diagrams. Nonmetric analyses were based on simultaneous observations of all relevant material to ensure accuracy of categorical evaluations. First, a combined metric and morphological evaluation was conducted to allocate each Omo tooth to either robust or nonrobust categories. Further taxonomic affinities were then examined. Our results indicate that nonrobust and robust lineages cooccur by circa 2.7 myr. We consider the Shungura robust specimens from Members C through F to represent A. aethiopicus. A significant phenetic transformation occurs at circa 2.3 myr, with the mosaic emergence of the derived A. boisei morphology across Member G times. Characterization of the East African nonrobust lineage is more difficult because of the comparatively subtle morphological differences seen among the dentitions of A. afarensis, A. africanus, and early Homo. The earlier Members B and C nonrobust specimens are difficult to evaluate and are considered indeterminate to genus or species. Both molars and premolars from Members E through G exhibit phenetic similarities to the early Homo condition and are considered as aff. Homo sp. indet. At present, there is no indication of multiple species in the Omo nonrobust sample at any time horizon. The 2–2.4 myr Omo nonrobust specimens exhibit some similarities to the stated Homo “rudolfensis” condition in size and morphology and are likely to represent the ancestral condition of the genus Homo. The bearing of these results on interpretations of early hominid evolution and diversification is considered. © 1996 Wiley-Liss, Inc.     

Longevity and life history in hominid evolution

Under the assumption that life history in general and longevity in particular play an important part in the study of evolutionary patterns and processes, this paper focuses on predicting longevity changes across hominid evolution and attempts to throw light on the significance of such changes. We also consider some statistical arguments in the analysis of hominid life history patterns. Multiple regression techniques incorporating primate body weight and brain size data are used to predict hominied longevity and the results are compared to those in the literature. Our findings suggest that changes in hominid longevity are more likely to follow brain size than body weight, and that multiple regression techniques may be an appropriate avenue for future studies on life history variation in human evolution.     

Morphometric and meristic variation in Galician threespine stickleback populations,northwest Spain

Synopsis We evaluated morphological differentiation among populations of threespine stickleback, Gasterosteus aculeatus, from the Limia and Miño basins (Galicia, NW Spain), the river Karup (Denmark) and Aiguamolls de l’Empordà (Girona, northeast Spain), using multivariate analysis of morphometric and meristic characters. Multivariate discriminant analysis and hierarchical cluster analysis uncovered significant differences among the four main groups, between the two groups from Galicia and among populations within the Miño basin. The stickleback from Galicia differed from the Danish group in head and body armour characters. Between the Miño and Limia groups, we found differences in both head and body proportions as well as in number of gill rakers. Within the Miño basin populations varied with respect to head and body armour traits and the number of lower gill rakers. Clustering analysis divided these populations into two groups based on the latter trait: fish from the upper section of river Miño and tributaries (a lower number of lower gill rakers) and fish from the central and lower reaches of the river. Overall, morphometric traits were more useful than meristic ones; however, the two types of data provided congruent information about the morphological differentiation of stickleback populations.     

Fore- and hindlimb proportions in Plio-Pleistocene hominids.

Associated fore- and hindlimb parts of five individuals are known from the hominid Plio-Pleistocene fossil collections in Africa. Four of these have been classified as Australopithecus and show definite evidence that in comparison with humans, forelimbs were relatively large and hindlimbs were relatively small. The fourth individual, placed in the genus Homo, has human proportions. These findings do not necessarily imply locomotor differences: the forelimbs may have been relatively long in Australopithecus simply because they were as yet not completely reduced from their generalized hominoid ancestral state.     

Plantigrady and foot adaptation in African apes: implications for hominid origins.

In living primates, except the great apes and humans, the foot is placed in a heel-elevated or semi-plantigrade position when these animals move upon arboreal or terrestrial substrates. Heel placement and bone positions in the non-great ape primate foot are designed to increase mobility and flexibility in the arboreal environment. Orangutans have further enhanced foot mobility by adapting their feet for suspension and thus similarly utilize foot positions where the heel does not touch the substrate. Chimpanzees and gorillas represent an alternative pattern (plantigrady), in which the heel contacts the surface of the support at the end of swing phase, especially during terrestrial locomotion. Thus, chimpanzees and gorillas possess feet adapted for both arboreal and terrestrial substrates. African apes also share several osteological features related to plantigrady and terrestrial locomotion with early hominids. From this analysis, it is apparent that hominid locomotor evolution passed through a quadrupedal terrestrial phase.     

Variation in the pattern of cranial venous sinuses and hominid phylogeny

In 1967 Tobias noted that Australopithecus boisei cranium O.H.5 exhibited a cranial venous sinus pattern in which the occipital sinus and the marginal sinuses of the foramen magnum appeared to have replaced the transverse-sigmoid sinuses as the major venous outflow track. Specimens of A. robustus and several more recently recovered A. boisei crania also show evidence of enlarged occipital-marginal sinuses. In contrast, A. africanus and H. habilis retain a dominant transverse-sigmoid system that characterizes the great majority of extant apes and modern human cadaver samples. Pliocene A. afarensis exhibits a high frequency of occipital-marginal drainage systems. An examination of several series of precontact North American Indian crania shows that the frequency distribution of the occipital-marginal sinus pattern is spatiotemporally disjunct , ranging from 7.5% to 28%. The Late Pleistocene sample from P redmost , Czechoslovakia, also shows a very high incidence of occipital-marginal sinus patterns (approximately 45%). These observations suggest that occipital-marginal and transverse-sigmoid sinus patterns are adaptively equivalent character states. This conclusion is supported by the fact that enlarged occipital-marginal and transverse-sigmoid sinus systems often coexist on the same and/or contralateral sides of the head. It is well known that the frequencies of such adaptively neutral traits are often heavily influenced by population-specific epistatic interactions. The utilization of such traits in phylogenetic reconstruction entails a substantial risk of mistaking parallelism for synapomorphy . It is concluded that using functional-adaptive criteria in the definition of morphologic characters is a more reliable method to guide phylogeny reconstruction. In light of this, the distribution of venous sinus variants in Plio -Pleistocene hominids gives little or no basis for revising the phylogenetic scheme of Johanson and White (1979), or the functional-adaptive interpretation offered by White et al. (1981).     

Brief communication: Possible third molar impactions in the hominid fossil record

Impacted third molars affect 15%–20% of modern Americans and Western Europeans. In contrast, third molar impactions have not been reported in the early hominid fossil record. It is uncertain whether the lack of reports reflects an absence of impactions or a failure to recognize them. This communication is intended to raise awareness of the possibility of impactions by describing the appearance of impacted teeth and by noting two possible instances of impaction in early hominids. Specifically, the mandibular third molars of the Sterkfontein specimen, STS52b (Australopithecus africanus), and the left maxillary third molar of the Lake Turkana specimen, KNM-WT17400 (Australopithecus boisei), are positioned in a manner which suggests that they would not have erupted normally. Both specimens also exhibit strong crowding of the anterior dentition, providing further support for the view that these individuals lacked sufficient space for normal eruption of the third molars. Other published reports of dental crowding in the hominid fossil record are noted, and it is suggested that more attention be paid to dental impaction and dental crowding in hominid evolution. © 1993 Wiley-Liss, Inc.     

Observed and expected variation in hominid evolution

All of the major groups of fossil hominids (australopithecines, pithecanthropines, Neandertals, and early sapiens) were discovered by 1925, and therefore prior to the formulation of the synthetic theory of evolution that revolutionized the concept of the species in systematics. While these fossil finds were being made the framework for their interpretation included several assumptions: (1) that the number of living hominoid species was great, and that intraspecific variation was slight (authoritative sources recognized as many as 14 separate species of chimpanzees and 15 species of gorillas); (2) that the timescale of human evolution was brief (measured in tens or hundreds of thousands of years). As a result of these premises the consensus that hominid evolution was characterized by a large number of sympatric and synchronic species was virtually inevitable.In contrast, recent molecular studies demonstrate that genetic diversity among recent hominoids is so slight that even humans and chimpanzees differ at only about 1% of the loci that have been sampled so far; evidently, very small genetic differences can produce rather great contrasts in morphology. At the same time, geological break-throughs have increased the timescale for human evolution to several million years.It is concluded that morphological differences among fossil hominids, even if very appreciable and complex, do not necessarily reflect a great degree of either genetic or taxonomic diversity. Potential effects of evolutionary change through time should be incorporated into models of hominid evolution as a means of assessing the minimum number of lineages required to account for observed variations among hominid specimens.     

Multivariate analyses of shape variation for genetically distinct groups

Many multivariate techniques have been proprosed for the analysis of shape variation. This article discusses several approaches in the context of examining shape similarities and differences for landmark data from two genetically distinct groups. Describing and understanding these variations will help develop insight into how genetically determined differences arise and are maintained. We discuss techniques based on principal component analyses including the use of a «sheared» component as the shape component and the use of a holistic size measure for adjustment of the original log-transformed measurements. Finally we examine a recently developed morphometric technique of analysis of triangles defined by sets of three appropriate landmarks.     

Cranial capacity in hominid evolution

We present an analysis of cranial capacity of 118 hominid crania available from the literature. The crania belong to both the genusAustralopithecus andHomo and provide a clear outline of hominid cranial evolution starting at more than 3 million years ago. Beginning withA. afarensis there is a clear increase in both absolute and relative brain size with every successive time period.H.s. neandertal has an absolutely and relatively smaller brain size (1412cc, E.Q.=5.6) than fossil modernH.s. sapiens (1487cc, E.Q.=5.9). Three evolutionary models of hominid brain evolution were tested: gradualism, punctuated equilibrium, and a mixed model using both gradualism and punctuated equilibrium. Both parametric and non-parametric analyses show a clear trend toward increasing brain size withH. erectus and a possible relationship within archaicH. sapiens. An evolutionary stasis in cranial capacity could not be refuted for all other taxa. Consequently, the mixed model appears to more fully explain hominid cranial capacity evolution. However, taxonomic decisions could directly compromise the possibility of testing the evolutionary mechanisms hypothesized to be operating in hominid brain expansion.     

Mandibular size and shape variation in the hominins at Dmanisi, Republic of Georgia

The hominin fossils of Dmanisi, Republic of Georgia, present an ideal means of assessing levels of skeletal size and shape variation in a fossil hypodigm belonging to the genus Homo because they have been recovered from a spatially and temporally restricted context. We compare variation in mandible size and shape at Dmanisi to that of extant hominoids and extinct hominins. We use height and breadth measurements of the mandibular corpus at the first molar and the symphysis to assess size, and analyze shape based on size-adjusted (using a geometric mean) versions of these four variables. We compare size and shape variation at Dmanisi relative to all possible pairs of individuals within each comparative taxon using an exact resampling procedure of the ratio of D2600 to D211 and the average Euclidean distance (AED) between D2600 and D211, respectively. Comparisons to extant hominoids were conducted at both the specific and subspecific taxonomic levels and to extinct hominins by adopting both a more, and less speciose, hominin taxonomy. Results indicate that the pattern of variation for the Dmanisi hominins does not resemble that of any living species: they exhibit significantly more size variation when compared to modern humans, and they have significantly more corpus shape variation and size variation in corpus heights and overall mandible size than any extant ape species. When compared to fossil hominins they are also more dimorphic in size (although this result is influenced by the taxonomic hypothesis applied to the hominin fossil record). These results highlight the need to re-examine expectations of levels of sexual dimorphism in members of the genus Homo and to account for marked size and shape variation between D2600 and D211 under the prevailing view of a single hominin species at Dmanisi.     

Relationship of squamosal suture to asterion in pongids (Pan): relevance to early hominid brain evolution.

Based on 244 measurements of the relationship of the squamosal suture to the landmark asterion in 49 chimpanzee skulls, it is shown that in the normal lateral view the squamosal suture is very rarely inferior to asterion. In hominid crania, the squamosal suture is always well superior to asterion. Even in Pan, that part of the squamosal suture most homologous with the remnant found on the Hadar AL 162-28 Australopithecus afarensis hominid cranial fragment is very rarely inferior to asterion. Such variability suggests that Falk's (Nature 313:45-47, 1985) orientation of the Hadar specimen is incorrect; she places asterion superior to the position of the squamosal suture if projected endocranially. The implication for the brain endocast is that, however the fragment is oriented, the posterior aspect of the intraparietal (IP) sulcus is in a very posterior position relative to any chimpanzee brain. The distance from the posterior aspect of IP to occipital pole is twice as great in chimpanzee brain casts than on the Hadar AL 162-28 endocast, even though the chimpanzee brain casts are smaller in overall size. This suggests that brain reorganization, at least as exemplified as a reduction in primary visual striate cortex (area 17 of Brodmann), occurred early in hominid evolution, prior to any major brain expansion.     

Geographical variation in allometry in the guppy (Poecilia reticulata)

Variation in static allometry, the power relationship between character size and body size among individuals at similar developmental stages, remains poorly understood. We tested whether predation or other ecological factors could affect static allometry by comparing the allometry between the caudal fin length and the body length in adult male guppies (Poecilia reticulata) among populations from different geographical areas, exposed to different predation pressures. Neither the allometric slopes nor the allometric elevations (intercept at constant slope) changed with predation pressure. However, populations from the Northern Range in Trinidad showed allometry with similar slopes but lower intercepts than populations from the Caroni and the Oropouche drainages. Because most of these populations are exposed to predation by the prawn Macrobrachium crenulatum, we speculated that the specific selection pressures exerted by this predator generated this change in relative caudal fin size, although effects of other environmental factors could not be ruled out. This study further suggests that the allometric elevation is more variable than the allometric slope.     

Size variation in the postcranium ofAustralopithecus afarensis and extant species of hominoidea

The postcranial sample ofA. afarensis can be divided into two size groups. Among the best preserved elements which are represented by both morphs are the distal femur, proximal ulna, and capitate. The difference between the large and small fossil femora is similar to the difference between average male and femaleG. gorilla andP. pygmaeus. The distal femora ofH. sapiens are less sexually dimorphic while those ofP. paniscus, P. troglodytes, andH. lar are not significantly dimorphic at all. Large and small capitates and proximal ulnae ofA. afarensis differ slightly more than the highly dimorphic species of extant Hominoidea. In my sample of Amerindians, the capitate and proximal ulna are also strongly dimorphic. The two species ofPan have insignificant sexual dimorphism in these traits. There results imply that strong sexual dimorphism in body size is the primitive condition for the large bodied hominoids.