Hadar Hominids Research Articles

The Os Navicular of Humans, Great Apes, OH 8, Hadar, and Oreopithecus: Function, Phylogeny, and Multivariate Analyses

Abstract To clarify fossil hominid behavior and phylogeny, and to test the accuracy of basing these studies on single bones, navicular measurements of Olduvai and Hadar hominids, Oreopithecus, and a representative sample of humans and great apes were compared. The measurements chosen for comparison quantify the relative orientation, articular area, and curvature of the navicular facets. The measurements demonstrate that the OH 8 navicular belongs to a rigid foot with an adducted hallux and a strong commitment to terrestriality. The Hadar naviculars belong to a foot which lacked a fixed longitudinal plantar arch and had at least a degree of hallucal opposability comparable to that of mountain gorillas. The Oreopithecus navicular belongs to a mobile foot with a widely divergent hallux committed to arboreal behaviors. Multiple discriminant and canonical variate analyses of navicular measurements emphasize the uniqueness of Oreopithecus and the similarities between OH 8 and humans, and between Hadar and Afric...

Functional, morphogenetic and phylogenetic significance of conjunction between cardioid foramen magnum and enlarged occipital and marginal venous sinuses

AbstractA quarter of a century ago the study of Australopithecus boisei, a hyper‐robust ape‐man first found at Olduvai Gorge in Tanzania (Tobias, 1967), revealed that in A. boisei and A. robustus the drainage of the intracranial venous sinuses had occurred predominantly by means of enlarged occipital and marginal venous sinuses, instead of, or as a supplement to, the customary hominoid pattern of drainage by way of the transverse and sigmoid sinuses. Later the Hadar hominids (usually assigned to A. afarensis) were found to show similar selective drainage through enlarged occipital and marginal sinuses. The same 1967 study led to the discovery of a hitherto unrecorded pattern of the foramen magnum which was broad, truncated, almost heart‐shaped or cardioid and which occurred in some of the early hominids (A. boisei, probably A. robustus). In a new study on Hadar casts, the senior author has concluded that, in these Ethiopian hominids as well, the shape of the foramen magnum was most probably cardioid.Thus, in A. boisei and probably in A. robustus and Hadar, we have the remarkable association of enlarged occipital and marginal sinuses and of cardioid foramina magna. This conjunction we propose is not fortuitous, but results from a functional and morphogenetic correlation between the two sets of traits. A careful study of the contents of the foramen magnum leads us to infer that the occurrence of enlarged occipital and marginal sinuses drastically modified the pattern of drainage of the blood around the foramen magnum, with consequential changes in the shape of the foramen, especially of its anterior and posterolateral margins. The occurrence of this uniquely different, shared‐derived (synapomorphic) character complex in these three groups of early hominids provides further evidence that they had seemingly become specialised away from the lineage leading to later hominids of the genus Homo.

Sexual dimorphism in Australopithecus afarensis

This study reassesses body weight sexual dimorphism in A. afarensis by applying equations that predict body weight from hindlimb joint size in a comparative sample of modern apes and humans. The resulting estimates show a level of body size dimorphism in this fossil hominid to be below that seen in modern gorillas or orang-utans, greater than modern species of Pan, and well above modern H. sapiens. This degree of dimorphism fits with the behavioral model proposed by Foley & Lee, 1989 in which A. afarensis lived in large kin-related multimale groups with females that are not kin-related. The moderate level of body size sexual dimorphism found in this study removes one objection to the lumping of all Hadar hominids into a single species.

The capitular joint of the first rib in primates: A re‐evaluation of the proposed link to locomotion

Evidence exists that in Australopithecus afarensis the head of the first rib articulated with the body of the first thoracic vertebra but not with the body of the seventh cervical vertebra (Ohman, 1983, 1986). Thus, the Hadar hominid would have differed from most primates, in which both these vertebrae are involved in formation of the first costal capitular joint. Indeed, Ohman (1986) has claimed that a univertebral pattern is unique to modern and fossil hominids among primates. He offered various theories on the adaptive significance of this trait, chief among which was a link to freeing the upper limb from any role in locomotion. Believing that Ohman's statement about the distribution of the univertebral pattern in living forms was based on inadequate samples, we have compiled data on the first costal capitular joint in a wider range of primate genera. Our observations demonstrate that the univertebral pattern, rather than being unique to hominids, is common among siamangs, occurs in an occasional gibbon, and is typical of the larger indriids. Consequently, one can no longer accept any contention that the univertebral first costal capitular joint of A. afarensis implies that it did not use its upper limbs for locomotion. Rather, the formation of this joint is correlated with orthogrady and body size. We discuss a possible explanation of this correlation in terms of movement of the first rib during breathing in an orthograde primate, be it one that stands on two legs, swings by two arms, or clings to trunks using all four appendages.

Evidence for a dual pattern of cranial venous sinuses on the endocranial cast of Taung (Australopithecus africanus).

According to published accounts, an enlarged occipital-marginal sinus system is absent in Australopithecus africanus, although it occurs in high frequencies in A. robustus, A. Boisei, and Hadar hominids commonly designated A. afarensis. In this report, we describe, for the first time, an enlarged occipital-marginal sinus system on the endocranial cast of the Taung specimen, which is part of the holotype of A. africanus. In addition, well-developed right transverse and sigmoid sinuses are represented on the Taung endocast. The various components of the dual venous sinus system on the Taung endocast are measured, and the system is compared to those of other fossil hominids. The compresence of a lateral sinus system and enlarged occipital and marginal sinuses occurs in two Hadar specimens, 2 specimens of A. robustus crassidens, 1 A. boisei specimen, and several early H. sapiens crania. Hence, the presence of strong transverse sinus impressions in a fragmentary specimen may not be interpreted as an indication that an enlarged occipital-marginal sinus system was not present in the original specimen. Conversely, lack of transverse sinus grooves in a fragmentary specimen does provide indirect evidence than an enlarged occipital-marginal system would probably have been present in the whole specimen, as in 2 specimens of A. boisei. Including Taung, enlarged occipital and marginal sinuses occur in 1 out of 5, or 20%, of A. africanus specimens. This figure compares well with the range of mean frequencies in modern human cranial series (1.5 to 28%), but is much lower than are the frequencies for A. boisei, A. robustus, and the Hadar hominids.(ABSTRACT TRUNCATED AT 250 WORDS)

Status ofAustralopithecus afarensis

Australopithecus afarensis Johanson in Hinrichsen (New Sci. 78(1105):571, 1978) is now accepted by many workers as an East African early hominid species showing marked sexual dimorphism dating to between 2.8 and 3.8 million years before present (my BP) and possibly as early as 5.0 my BP. It is best known in the latter part of this time range, at Hadar, and is here most phenetically similar to the South African A. africanus. In the earlier part of its time range, at Laetoli and Middle Awash, the morphology of the species is less well known. Much debate has surrounded the taxonomy, dating, morphological adaptations, and phylogenetic interpretation of the Laetoli and Hadar hominids. Some questions, such as the geological age of the sites, are close to resolution. Other questions hinge on whether the Laetoli and Hadar fossil samples are drawn from one biological population or species or from more than one. At present the balance of evidence suggests attribution of the Laetoli and Hadar fossils to a single species. Different emphases in functional morphological studies have led to differences in interpretations of taxonomy, phylogeny, function, and behavior. Various lines of evidence document that A. afarensis engaged in humanlike bipedal locomotion, but its postcranial morphology also documents that the species' locomotor adaptation differed from that of Homo, perhaps toward a more climbing and arboreal adaptation. Cladistic relations between A. afarensis and A. robustus/boisei are unresolved. A. afarensis does appear to be an appropriate ancestor for the A. africanus-Homo lineage.

Hominid footprints at Laetoli: facts and interpretations.

The history of discovery and interpretation of primate footprints at the site of Laetoli in northern Tanzania is reviewed. An analysis of the geological context of these tracks is provided. The hominid tracks in Tuff 7 at Site G in the Garusi River Valley demonstrate bipedality at a mid-Pliocene datum. Comparison of these tracks and the Hadar hominid foot fossils by Tuttle has led him to conclude that Australopithecus afarensis did not make the Tanzanian prints and that a more derived form of hominid is therefore indicated at Laetoli. An alternative interpretation has been offered by Stern and Susman who posit a conforming "transitional morphology" in both the Tanzanian prints and the Ethiopian bones. The present examines both hypotheses and shows that neither is likely to be entirely correct. To illustrate this point, a reconstruction of the foot skeleton of a female A. afarensis is undertaken, and the results are compared to the Laetoli tracks. We conclude that A. afarensis represents the best candidate for the maker of the Laetoli hominid trails.

Ages of tuff beds at East African early hominid sites and sediments in the Gulf of Aden

The early hominids of East Africa were dated by determining the ages of tuff beds at the sites. Despite much research using palaeomagnetic and K/Ar-dating techniques, some of those ages are still controversial1,2. To obtain independent age estimates for these tephra layers, we have examined cores from DSDP Sites 231 and 232 in the Gulf of Aden (Fig. 1a) which consist mainly of calcareous nannofossil ooze, but also contain rare tephra horizons3 dated by interpolation from the established nannofossil stratigraphy (Fig. 1b). Chemical analysis confirms that the identity and sequence of these horizons is the same as that at the East African sites. We conclude that the age of the Tulu Bor Tuff is <3.4 Myr and hence that the Hadar hominid specimens are also <∼3.4 Myr old.

Interpretations of the magnetostratigraphy of the Hadar hominid site, Ethiopia

As part of an investigation to determine the age of the hominidbearing strata of the Hadar Formation of Ethiopia we have determined the magnetostratigraphy of two separate sections of the strata. Two major zones of reversed polarity occur within the predominantly normally magnetized sequence, one at the top and the other in the middle. There are difficulties with the absolute age determinations of volcanic units within the strata which result in uncertainties in correlating the Hadar magnetostratigraphy with the standard magnetic reversal time scale. The age of the upper part of the section is established by the BKT-2 tuff at ∼2.8 Myr (refs 1–4). The K–Ar dating of the Kadada Moumou basalt which lies in the middle of the sequence yields variable results ranging from 3.1 to 3.6 Myr (refs 1–4). Regional geochemical5 and bio-stratigraphical6 studies suggest the younger age for the Kadada Moumou basalt. We show here that this is also the age that results in the most consistent interpretation of the observed magneto-stratigraphy of the formation, which is that the Hadar Formation was deposited during the Gauss Normal epoch and that the two reversals represent the Kaena and Mammoth events within that epoch.

Arboreality and bipedality in the Hadar hominids.

Numerous studies of the locomotor skeleton of the Hadar hominids have revealed traits indicative of both arboreal climbing/suspension and terrestrial bipedalism. These earliest known hominids must have devoted part of their activities to feeding, sleeping and/or predator avoidance in trees, while also spending time on the ground where they moved bipedally. In this paper we offer new data on phalangeal length and curvature, morphology of the tarsus and metatarsophalangeal joints, and body proportions that further strengthen the argument for arboreality in the Hadar hominids. We also provide additional evidence on limb and pedal proportions and on the functional anatomy of the hip, knee and foot, indicating that the bipedality practiced at Hadar differed from that of modern humans. Consideration of the ecology at Hadar, in conjunction with modern primate models, supports the notion of arboredality in these earliest australopithecines. We speculate that selection for terrestrial bipedality may have intensified through the Plio-Pleistocene as forests and woodland patches shrunk and the need arose to move increasingly longer distances on the ground. Only with Homo erectus might body size, culture and other factors have combined to 'release' hominids from their dependence on trees.

Body proportions, skeletal allometry and locomotion in the hadar hominids: a reply to Wolpoff

Wolpoff, 1983a , Wolpoff, 1983b ) has challenged the interpretation of relative limb proportions and locomotion offered by Jungers (1982) for Australopithecus afarensis in comparison to modern humans of similar body size. In this reply, we demonstrate that Wolpoff's conclusions are based on several misconceptions about the biomechanics and energetics of bipedalism and a misapplication of the allometric approach. Compared with modern humans (pygmies) of comparably small size (measured as cstimated body weight and as a linear variable correlated to body weight in modern humans), “Lucy” (AL 288-1) possesses very short hindlimbs outside of the known human range and which are proportioned most similarly to small-bodied African apes. By contrast, relative humerus length of Lucy can be matched precisely in a skeletal sample of human pygmics. A similar combination of relative limb lengths appears to exist in the larger individuals of A. afarensis and probably characterizes all gracile australopithecines (including STS 14). The functional implications of interlimb proportions, relative fore-and hindlimb lengths and relative foot length for locomotor biomechanics in A afarensis are also examined. The original interpretations put forth by Jungers (1982) are reaffirmed and strengthened by new data and appropriate analyses.

Revisions of K/Ar ages for the Hadar hominid site, Ethiopia

Conventional K/Ar age measurements are reported for two volcanic units from the hominid-bearing Hadar Formation. These ages represent revision of previously published ages for the BKT-2 tephra and the Kadada Moumou basalt. BKT-2 is revised from 2.65 to 2.9 Myr BP and the Kadada Moumou basalt is revised from 3.0 to 3.6 Myr BP.

Evolution of hominid bipedalism and prehensile capabilities

In this paper, I present an updated version of the hylobatian model for the proximate ancestors of the Hominidae. The hylobatians are hypothesized to have been relatively small creatures that were especially adapted for vertical climbing on tree trunks and vines and for bipedalism on horizontal boughs. They were no more disposed toward suspensory behaviours than are modern chimpanzees and bonobos. According to this evolutionary scenario, bipedalism preceded the emergence of the Hominidae. The earliest hominids would be recognized as diurnally terrestrial bipeds that stood with full extension of the knee joints and walked with greater extension of the lower limbs than is common in non-human primates that are induced to walk bipedally on the ground. The wealth of hominid fossils from the Hadar Formation, Ethiopia, and the Laetolil Formation, Tanzania, are generally compatible with the hylobatian model. They show that by ca . 4 Ma B.P. habitually terrestrial, bipedal hominids had evolved from arboreal ancestors. The Hadar hominids had curved fingers and toes, strong great toes and thumbs, and other features that suggest that they were rather recently derived from arboreal hominids and that they probably continued to enter trees, perhaps for night rest and some foraging. The hominid hand bones from Hadar evince no features that are distinctly related to knuckle-walking. They relate neatly to counterparts in the hand of O.H. 7, a specimen that was found with stone tools. However, there is no evidence that the Hadar hominids of 3 Ma ago engaged in tool behaviour.