Variation among the Dmanisi hominins: Multiple taxa or one species?

OBJECTIVES

There is continuing controversy over the number of taxa documented by the Dmanisi hominins. Variation may reflect age and sex differences within a single population. Alternatively, two (or more) distinct species may be present. Our null hypothesis states that just one population is represented at the site.

MATERIALS AND METHODS

We assess the likely sources of variation in endocranial capacity, craniofacial and mandibular morphology, and the expression of characters related to aging and sex dimorphism. We use the coefficient of variation and a modified version of Levene's test for equal variances to compare trait variation at Dmanisi with that in fossil hominins and modern Homo sapiens from Africa.

RESULTS

Skull 5 presents a low, massive vault, and a muzzle-like lower face. Other individuals have larger brains and more globular vaults. Despite such variation, the five crania share numerous features. All of the mandibles possess marginal tubercles, mandibular tori, and a distinctive patterning of mental foramina. Relative variation at Dmanisi is comparable to that in selected reference groups. Further growth anticipated in Skull 3, age-related remodeling affecting the D2600 mandible, pathology, and sex dimorphism can account for much of the interindividual variation observed. The preponderance of evidence supports our null hypothesis.

DISCUSSION

Sources of the variation within ancient Homo assemblages remain poorly understood. Skull 5 is a very robust male, with a brain smaller than that of both a juvenile (Skull 3) and a probable female (Skull 2). Skull 1 has the largest brain, but cranial superstructures do not clearly mark this individual as male or female. It is likely that the Dmanisi hominins represent a single paleospecies of Homo displaying a pattern of sex dimorphism not seen in living hominids.

A complete skull from Dmanisi, Georgia, and the evolutionary biology of early Homo

The site of Dmanisi, Georgia, has yielded an impressive sample of hominid cranial and postcranial remains, documenting the presence of Homo outside Africa around 1.8 million years ago. Here we report on a new cranium from Dmanisi (D4500) that, together with its mandible (D2600), represents the world's first completely preserved adult hominid skull from the early Pleistocene. D4500/D2600 combines a small braincase (546 cubic centimeters) with a large prognathic face and exhibits close morphological affinities with the earliest known Homo fossils from Africa. The Dmanisi sample, which now comprises five crania, provides direct evidence for wide morphological variation within and among early Homo paleodemes. This implies the existence of a single evolving lineage of early Homo, with phylogeographic continuity across continents.

Postcranial evidence from early Homo from Dmanisi, Georgia

The Plio-Pleistocene site of Dmanisi, Georgia, has yielded a rich fossil and archaeological record documenting an early presence of the genus Homo outside Africa. Although the craniomandibular morphology of early Homo is well known as a result of finds from Dmanisi and African localities, data about its postcranial morphology are still relatively scarce. Here we describe newly excavated postcranial material from Dmanisi comprising a partial skeleton of an adolescent individual, associated with skull D2700/D2735, and the remains from three adult individuals. This material shows that the postcranial anatomy of the Dmanisi hominins has a surprising mosaic of primitive and derived features. The primitive features include a small body size, a low encephalization quotient and absence of humeral torsion; the derived features include modern-human-like body proportions and lower limb morphology indicative of the capability for long-distance travel. Thus, the earliest known hominins to have lived outside of Africa in the temperate zones of Eurasia did not yet display the full set of derived skeletal features.

A fourth hominin skull from Dmanisi, Georgia

Newly discovered Homo remains, stone artifacts, and animal fossils from Dmanisi, Republic of Georgia, provide a basis for better understanding patterns of hominin evolution and behavior in Eurasia ca. 1.77 million years ago. Here we describe a fourth skull that is nearly complete, lacking all but one of its teeth at the time of death. Both the maxillae and the mandible exhibit extensive bone loss due to resorption. This individual is similar to others from the site but supplies information about variation in brain size and craniofacial anatomy within the Dmanisi paleodeme. Although this assemblage presents numerous primitive characters, the Dmanisi skulls are best accommodated within the species H. erectus. On anatomical grounds, it is argued that the relatively small-brained and lightly built Dmanisi hominins may be ancestral to African and Far Eastern branches of H. erectus showing more derived morphology.

Anatomical descriptions, comparative studies and evolutionary significance of the hominin skulls from Dmanisi, Republic of Georgia

Evidence for ancient hominin occupation in Eurasia comes from Dmanisi in the Georgian Caucasus. Stratigraphic and sedimentological arguments, geochemical observations, paleomagnetic sampling and radiometric dates all point to the conclusion that bones and artifacts were deposited at this site during a brief interval following the close of the Olduvai Subchron (1.77 million years ago). In this report we present further descriptive and comparative studies of the D2280 braincase, the D2282 partial cranium, now linked with the D211 mandible, and the skull D2700/D2735. The crania have capacities ranging from 600 cm3 to 775 cm3. Supraorbital tori and other vault superstructures are only moderately developed. The braincase is expanded laterally in the mastoid region, but the occiput is rounded. The pattern of sagittal keeling is distinctive. D2700 displays a prominent midfacial profile and has a very short nasoalveolar clivus. Also, the M3 crowns are reduced in size. Although there is variation probably related to growth status and sex dimorphism, it is appropriate to group the Dmanisi hominins together. With the possible exception of the large D2600 mandible, the individuals are sampled from one paleodeme. This population resembles Homo habilis in brain volume and some aspects of craniofacial morphology, but many of these features can be interpreted as symplesiomorphies. Other discrete characters and measurements suggest that the Dmanisi skulls are best placed with H. erectus. There are numerous similarities to individuals from the Turkana Basin in Kenya, but a few features link Dmanisi to Sangiran in Java. Some traits expressed in the Dmanisi assemblage appear to be unique. Reconstructing the evolutionary relationships of these ancient populations of Africa and Eurasia is difficult, as the record is quite patchy, and determination of character polarities is not straightforward. Nevertheless, the evidence from anatomical analysis and measurements supports the hypothesis that Dmanisi is close to the stem from which H. erectus evolved.

Human foot bones from Klasies River main site, South Africa

The caves at Klasies River contain abundant archaeological evidence relating to human evolution in the late Pleistocene of southern Africa. Along with Middle Stone Age artifacts, animal bones, and other food waste, there are hominin cranial fragments, mandibles with teeth, and a few postcranial remains. Three foot bones can now be added to this inventory. An adult first metatarsal is similar in size and discrete anatomical features to those from Holocene burials in the Cape Province. A complete and well-preserved second metatarsal is especially long and heavy at midshaft in comparison to all Holocene and more recent South African homologues. A large fifth metatarsal is highly distinctive in its morphology. In overall size, these pedal elements resemble specimens from late Pleistocene sites in western Asia, but there are some differences in proportions. The fossils support earlier suggestions concerning a relatively high level of sexual dimorphism in the African Middle Stone Age population. Squatting facets on the two lateral metatarsals appear to indicate a high frequency of kneeling among members of this group. The new postcranial material also underlines the fact that the morphology of particular skeletal elements of some of the 100,000-year-old Klasies River individuals falls outside the range of modern variation.

Anthropology: the earliest toothless hominin skull

The site of Dmanisi in the Eurasian republic of Georgia has yielded striking hominin, faunal and archaeological material as evidence for the presence of early Homo outside Africa 1.77 million years ago, documenting an important episode in human evolution. Here we describe a beautifully preserved skull and jawbone from a Dmanisi hominin of this period who had lost all but one tooth several years before death. This specimen not only represents the earliest case of severe masticatory impairment in the hominin fossil record to be discovered so far, but also raises questions about alternative subsistence strategies in early Homo.

Brain size and encephalization in early to Mid-PleistoceneHomo

Important changes in the brain have occurred during the course of human evolution. Both absolute and relative size increases can be documented for species of Homo, culminating in the appearance of modern humans. One species that is particularly well-represented by fossil crania is Homo erectus. The mean capacity for 30 individuals is 973 cm(3). Within this group there is substantial variation, but brain size increases slightly in specimens from later time periods. Other Middle Pleistocene crania differ from those of Homo erectus. Characters of the facial skeleton, vault, and cranial base suggest that fossils from sites such as Arago Cave in France, the Sima de los Huesos in Spain, Bodo in Ethiopia, Broken Hill in Zambia, and perhaps Dali in China belong to the taxon Homo heidelbergensis. Ten of these mid-Quaternary hominins have brains averaging 1,206 cm(3) in volume, and many fall beyond the limits of size predicted for Homo erectus of equivalent age. When orbit height is used to construct an index of relative brain size, it is apparent that the (significant) increase in volume documented for the Middle Pleistocene individuals is not simply a consequence of larger body mass. Encephalization quotient values confirm this finding. These changes in absolute and relative brain size can be taken as further corroborative evidence for a speciation event, in which Homo erectus produced a daughter lineage. It is probable that Homo heidelbergensis originated in Africa or western Eurasia and then ranged widely across the Old World. Archaeological traces indicate that these populations differed in their technology and behavior from earlier hominins.

A new skull of early Homo from Dmanisi, Georgia

Another hominid skull has been recovered at Dmanisi (Republic of Georgia) from the same strata in which hominid remains have been reported previously. The Dmanisi site dated to approximately 1.75 million years ago has now produced craniofacial portions of several hominid individuals, along with many well-preserved animal fossils and quantities of stone artifacts. Although there are certain anatomical differences among the Dmanisi specimens, the hominids do not clearly represent more than one taxon. We assign the new skull provisionally to Homo erectus (=ergaster). The Dmanisi specimens are the most primitive and small-brained fossils to be grouped with this species or any taxon linked unequivocally with genus Homo and also the ones most similar to the presumed habilis-like stem. We suggest that the ancestors of the Dmanisi population dispersed from Africa before the emergence of humans identified broadly with the H. erectus grade.

New human teeth from Middle Stone Age deposits at Klasies River, South Africa

Since 1984, the main site at Klasies River has been re-investigated. Human remains, animal bones and stone artefacts have been collected from the LBS, SAS and other stratigraphic members, and these discoveries help to establish the antiquity of anatomically near-modern populations practicing a Middle Stone Age way of life on the southern coast of Africa. Several teeth found in the lower SAS levels in 1989-1991 can be matched in recent South African populations. Two complete upper molars representing one individual have crowns that are relatively short mesiodistally. These specimens are small in comparison to black South African homologues, but MD and BL dimensions fall close to the averages for San burials. This evidence confirms that several of the Klasies individuals have very small molars, while others have cheek teeth that are close to the upper limits for size variation in recent Africans. The new material is in keeping with the view that sex dimorphism within this Middle Stone Age population may be pronounced.

Additional human fossils from Klasies River Mouth South Africa

A fragmentary temporal bone and partial atlas from the Middle Stone Age (MSA) at Klasies River Mouth (KRM) are described and analyzed. The atlas (SAM-AP 6268) is comparable to Levantine "Early Modern", Neandertal and recent human vertebrae. The temporal (SAM-AP 6269) is similar to recent African homologues except that the posteromedial wall of the glenoid fossa is composed entirely of the squamous temporal, a situation that appears to be infrequent among other Pleistocene fossils. The KRM glenoid fossa is also mediolateraly broad and anteroposteriorly short in comparison with many, but not, all recent specimens. Nevertheless, the KRM temporal is decidedly modern, both morphologically and metrically, by comparison with other Pleistocene specimens. The limited evidence provided by this bone is consistent with that of other MSA cranial remains from this site in suggesting an overall, if somewhat ambiguous pattern of morphological modernity.

Evidence from facial morphology for similarity of Asian and African representatives of Homo erectus

It has been argued that Homo erectus is a species confined to Asia. Specialized characters displayed by the Indonesian and Chinese skulls are said to be absent in material from eastern Africa, and individuals from Koobi Fora and Nariokotome are now referred by some workers to H. ergaster. This second species is held to be the ancestor from which later human populations are derived. The claim for two taxa is evaluated here with special reference to the facial skeleton. Asian fossils examined include Sangiran 4 and Sangiran 17, several of the Ngandong crania, Gongwangling, and of course the material from Zhoukoudian described by Weidenreich ([1943] Palaeontol. Sin. [New Ser. D] 10:1-484). African specimens compared are KNM-ER 3733 and KNM-ER 3883 from Koobi Fora and KNM-WT 15000 from Nariokotome. Hominid 9 from Olduvai is useful only insofar as the brows and interorbital pillar are preserved. Neither detailed anatomical comparisons nor measurements bring to light any consistent patterns in facial morphology which set the African hominids apart from Asian H. erectus. Faces of the African individuals do tend to be high and less broad across the orbits. Both of the Koobi Fora crania but not KNM-WT 15000 have nasal bones that are narrow superiorly, while the piriform aperture is relatively wide. In many other characters, including contour of the supraorbital torus, glabellar prominence, nasal bridge dimensions, internasal keeling, anatomy of the nasal sill and floor, development of the canine jugum, orientation of the zygomaticoalveolar pillar, rounding of the anterolateral surface of the cheek, formation of a malar tubercle, and palatal rugosity, there is variation among individuals from localities within the major geographic provinces. Here it is not possible to identify features that are unique to either the Asian or African assemblages. Additional traits such as a forward sloping "crista nasalis," presence of a "sulcus maxillaris," a high (and massive) cheek coupled with some flexion of the malar pillar, and a posterior position for the incisive canal are present in all groups. These characters seem to be plesiomorphic, in comparison to the derived states evolved in later humans. Much or all of the variation in facial form can be attributed to sex dimorphism and/or local differentiation of populations within the Asian and African geographic regions. Metric differences among the fossils are comparable to those documented in a subset of recent H. sapiens, and there is no evidence that the Pleistocene specimens show greater dispersion than expected within a single species. This finding is generally in keeping with observations made on other parts of the cranium, lower jaw, and teeth. All of the hominids can be placed in H. erectus. Although its phylogenetic origins remain obscure, this lineage must be rooted in Africa. The species flourished for a long time. At several sites in China, H. erectus is known from deposits of the later Middle Pleistocene, while at Ngandong in Indonesia, archaic people may have survived even into the Late Pleistocene (Swisher et al. [1996] Science 274:1870-1874). The Ngandong fossils may record the last appearance of the lineage.

Variation among early Homo crania from Olduvai Gorge and the Koobi Fora region

Fossils recognized as early Homo were discovered first at Olduvai Gorge in 1959 and 1960. Teeth, skull parts and hand bones representing three individuals were found in Bed I, and more material followed from Bed I and lower Bed II. By 1964, L.S.B. Leakey, P.V. Tobias, and J.R. Napier were ready to name Homo habilis. But almost as soon as they had, there was confusion over the hypodigm of the new species. Tobias himself suggested that OH 13 resembles Homo erectus from Java, and he noted that OH 16 has teeth as large as those of Australopithecus. By the early 1970s, however, Tobias had put these thoughts behind him and returned to the opinion that all of the Olduvai remains are Homo habilis. At about this time, important discoveries began to flow from the Koobi Fora region in Kenya. To most observers, crania such as KNM-ER 1470 confirmed the presence of Homo in East Africa at an early date. Some of the other specimens were problematical. A.C. Walker and R.E. Leakey raised the possibility that larger skulls including KNM-ER 1470 differ significantly from smaller-brained, small-toothed individuals such as KNM-ER 1813. Other workers emphasized that there are differences of shape as well as size among the hominids from Koobi Fora. There is now substantial support for the view that in the Turkana and perhaps also in the Olduvai assemblages, there is more variation than would be expected among male and female conspecifics. One way to approach this question of sorting would be to compare all of the new fossils against the original material from Olduvai which was used to characterize Homo habilis in 1964. A problem is that the Olduvai remains are fragmentary, and none of them provides much information about vault form or facial structure. An alternative is to work first with the better crania, even if these are from other sites. I have elected to treat KNM-ER 1470 and KNM-ER 1813 as key individuals. Comparisons are based on discrete anatomy and measurements. Metric results are displayed with ratio diagrams, by which similarity in proportions for several skulls can be assessed in respect to a single specimen selected as a standard. Crania from Olduvai examined in this way are generally smaller than KNM-ER 1470, although OH 7 has a relatively long parietal. In the Koobi Fora assemblage, there is variation in brow thickness, frontal flattening and parietal shape relative to KNM-ER 1470.(ABSTRACT TRUNCATED AT 400 WORDS)

The Lake Ndutu cranium and early Homo sapiens in Africa

The partial cranium from Lake Ndutu, near Olduvai Gorge in northern Tanzania, has generally been viewed as Homo erectus, although points of similarity to H. sapiens have also been recognized. Bones of the vault are in fact quite thick, and the cranium is small. Length and breadth dimensions are comparable to those of earlier H. erectus from Koobi Fora and Ileret, and the Ndutu individual is more similar in size to O.H. 12 than to O.H. 9. Unfortunately, the facial skeleton and frontal bone are very incomplete, and little useful information can be obtained from these parts of the existing reconstruction. The parietals are also damaged, but the left temporal is more satisfactorily preserved, and the occiput is nearly complete. Occipital morphology, mastoid shape, and characteristics of the glenoid cavity and tympanic plate probably provide the best available guide to affinities of the Ndutu hominid. In many of these features the cranium resembles Broken Hill, Elandsfontein, and other African fossils referred to archaic H. sapiens. There are some similarities to modern humans also, but no ties to the Neanderthals of Europe. Allocation of Ndutu to an African subspecies of H. sapiens seems most appropriate, even if the pattern of relationships between such archaic populations and recent humans is still unclear.

Middle Pleistocene hominids from Olduvai Gorge, northern Tanzania

Cranial, dental, and mandibular remains of eight Olduvai hominids are described in detail. Four individuals were recovered in situ in Beds II to IV, while three more are most probably derived from Bed IV, the Masek Beds and the Lower Ndutu Beds. One specimen is of uncertain provenance. Deposits from which the fossils were collected range from late Lower Pleistocene to Middle Pleistocene in age. Of particular interest are three fragmentary lower jaws, which can be compared to mandibles of Homo erectus known from localities in Northwest Africa and China. Olduvai hominid 22, a nearly complete half mandible with crowns of P3-M2 in place, shares many anatomical features with fossils from Ternifine and Choukoutien. This individual is also similar to a jaw from the Kapthurin Formation west of Lake Baringo, Kenya. How best to interpret these comparisons is not clear, but in view of marked similarities between specimens representing geographically diverse populations from different time periods, it may be unwise to rely on mandibular evidence alone to document the presence of regional lineages. Gradual change and continuity within a sequence of Northwest African Homo fossils has been endorsed by many workers, but such hypotheses cannot be tested adequately with the fragmentary jaws available.

Florisbad and human population succession in Southern Africa

The human cranium recovered at Florisbad in 1932 is compared with other Sub-Saharan African hominid remains from Broken Hill, the Omo and Klasies River Mouth. The Florisbad frontal is very broad, but despite this breadth and differences in zygomatic form, there is a definite resemblance to archaic Homo sapiens from Broken Hill. There is also some similarity to both Omo I and Omo II, while fragmentary remains from Klasies River are more lightly built and hence more modern in appearance. These impressions are strengthened by measurement and statistical analysis, which demonstrates that Florisbad and Broken Hill are distant from recent African populations. Even if Florisbad is less archaic than the earlier (Middle Pleistocene?) hominid, it is not noticeably Bushman-like. New dates suggestive of early Upper Pleistocene antiquity also place Florisbad securely in a lineage containing Broken Hill, and there is no evidence to support special ties with any one group of living Africans.

New studies of post-Pleistocene human skeletal remains from the Rift Valley, Kenya

Prehistoric human crania from Bromhead's Site, Willey's Kopje, Makalia Burial Site, Nakuru, and other localities in the Eastern Rift Valley of Kenya are reassessed using measurements and a multivariate statistical approach. Materials available for comparison include series of Bushman and Hottentot crania. South and East African Negroes, and Egyptians. Up to 34 cranial measurements taken on these series are utilized to construct three multiple discriminant frameworks, each of which can assign modern individuals to a correct group with considerable accuracy. When the prehistoric crania are classified with the help of these discriminants, results indicate that several of the skulls are best grouped with modern Negroes. This is especially clear in the case of individuals from Bromhead's Site, Willey's Kopje, and Nakuru, and the evidence hardly suggests post-Pleistocene domination of the Rift and surrounding territory by "Mediterranean" Caucasoids, as has been claimed. Recent linguistic and archaeological findings are also reviewed, and these seem to support application of the term Nilotic Negro to the early Rift populations.