Christoph P. E. Zollikofer

A new hominid from the Upper Miocene of Chad, Central Africa

The search for the earliest fossil evidence of the human lineage has been concentrated in East Africa. Here we report the discovery of six hominid specimens from Chad, central Africa, 2,500 km from the East African Rift Valley. The fossils include a nearly complete cranium and fragmentary lower jaws. The associated fauna suggest the fossils are between 6 and 7 million years old. The fossils display a unique mosaic of primitive and derived characters, and constitute a new genus and species of hominid. The distance from the Rift Valley, and the great antiquity of the fossils, suggest that the earliest members of the hominid clade were more widely distributed than has been thought, and that the divergence between the human and chimpanzee lineages was earlier than indicated by most molecular studies.

A Complete Skull from Dmanisi, Georgia, and the Evolutionary Biology of Early Homo

A Heady Find In the past two decades, excavations at the archaeological site at Dmanisi, Georgia, have revealed hominin fossils from the earliest Pleistocene, soon after the genus Homo first dispersed beyond Africa. Lordkipanidze et al. (p. 326; see the cover) now describe a fossil cranium from the site. Combined with mandibular remains that had been found earlier, this find completes the first entire hominin skull from this period. An early Pleistocene adult skull illuminates the evolution and morphology of the first hominins outside Africa. 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 worlds 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.

Virtual cranial reconstruction of Sahelanthropus tchadensis

Previous research in Chad at the Toros-Menalla 266 fossiliferous locality (about 7 million years old) uncovered a nearly complete cranium (TM 266-01-60-1), three mandibular fragments and several isolated teeth attributed to Sahelanthropus tchadensis . Of this material, the cranium is especially important for testing hypotheses about the systematics and behavioural characteristics of this species, but is partly distorted from fracturing, displacement and plastic deformation. Here we present a detailed virtual reconstruction of the TM 266 cranium that corrects these distortions. The reconstruction confirms that S. tchadensis is a hominid and is not more closely related to the African great apes. Analysis of the basicranium further indicates that S. tchadensis might have been an upright biped, suggesting that bipedalism was present in the earliest known hominids, and probably arose soon after the divergence of the chimpanzee and human lineages.

New material of the earliest hominid from the Upper Miocene of Chad

Discoveries in Chad by the Mission Paléoanthropologique Franco-Tchadienne have substantially changed our understanding of early human evolution in Africa. In particular, the TM 266 locality in the Toros-Menalla fossiliferous area yielded a nearly complete cranium (TM 266-01-60-1), a mandible, and several isolated teeth assigned to Sahelanthropus tchadensis and biochronologically dated to the late Miocene epoch (about 7 million years ago). Despite the relative completeness of the TM 266 cranium, there has been some controversy about its morphology and its status in the hominid clade. Here we describe new dental and mandibular specimens from three Toros-Menalla (Chad) fossiliferous localities (TM 247, TM 266 and TM 292) of the same age. This new material, including a lower canine consistent with a non-honing C/P3 complex, post-canine teeth with primitive root morphology and intermediate radial enamel thickness, is attributed to S. tchadensis. It expands the hypodigm of the species and provides additional anatomical characters that confirm the morphological differences between S. tchadensis and African apes. S. tchadensis presents several key derived features consistent with its position in the hominid clade close to the last common ancestor of chimpanzees and humans.

Neanderthal brain size at birth provides insights into the evolution of human life history

From birth to adulthood, the human brain expands by a factor of 3.3, compared with 2.5 in chimpanzees [DeSilva J and Lesnik J (2006) Chimpanzee neonatal brain size: Implications for brain growth in Homo erectus. J Hum Evol 51: 207–212]. How the required extra amount of human brain growth is achieved and what its implications are for human life history and cognitive development are still a matter of debate. Likewise, because comparative fossil evidence is scarce, when and how the modern human pattern of brain growth arose during evolution is largely unknown. Virtual reconstructions of a Neanderthal neonate from Mezmaiskaya Cave (Russia) and of two Neanderthal infant skeletons from Dederiyeh Cave (Syria) now provide new comparative insights: Neanderthal brain size at birth was similar to that in recent Homo sapiens and most likely subject to similar obstetric constraints. Neanderthal brain growth rates during early infancy were higher, however. This pattern of growth resulted in larger adult brain sizes but not in earlier completion of brain growth. Because large brains growing at high rates require large, late-maturing, mothers [Leigh SR and Blomquist GE (2007) in Campbell CJ et al. Primates in perspective; pp 396–407], it is likely that Neanderthal life history was similarly slow, or even slower-paced, than in recent H. sapiens.

Genomic evidence for the Pleistocene and recent population history of Native Americans

Genetic history of Native Americans Several theories have been put forth as to the origin and timing of when Native American ancestors entered the Americas. To clarify this controversy, Raghavan et al. examined the genomic variation among ancient and modern individuals from Asia and the Americas. There is no evidence for multiple waves of entry or recurrent gene flow with Asians in northern populations. The earliest migrations occurred no earlier than 23,000 years ago from Siberian ancestors. Amerindians and Athabascans originated from a single population, splitting approximately 13,000 years ago. Science, this issue 10.1126/science.aab3884 Genetic variation within ancient and extant Native American populations informs on their migration into the Americas. INTRODUCTION The consensus view on the peopling of the Americas is that ancestors of modern Native Americans entered the Americas from Siberia via the Bering Land Bridge and that this occurred at least ~14.6 thousand years ago (ka). However, the number and timing of migrations into the Americas remain controversial, with conflicting interpretations based on anatomical and genetic evidence. RATIONALE In this study, we address four major unresolved issues regarding the Pleistocene and recent population history of Native Americans: (i) the timing of their divergence from their ancestral group, (ii) the number of migrations into the Americas, (iii) whether there was ~15,000 years of isolation of ancestral Native Americans in Beringia (Beringian Incubation Model), and (iv) whether there was post-Pleistocene survival of relict populations in the Americas related to Australo-Melanesians, as suggested by apparent differences in cranial morphologies between some early (“Paleoamerican”) remains and those of more recent Native Americans. We generated 31 high-coverage modern genomes from the Americas, Siberia, and Oceania; 23 ancient genomic sequences from the Americas dating between ~0.2 and 6 ka; and SNP chip genotype data from 79 present-day individuals belonging to 28 populations from the Americas and Siberia. The above data sets were analyzed together with published modern and ancient genomic data from worldwide populations, after masking some present-day Native Americans for recent European admixture. RESULTS Using three different methods, we determined the divergence time for all Native Americans (Athabascans and Amerindians) from their Siberian ancestors to be ~20 ka, and no earlier than ~23 ka. Furthermore, we dated the divergence between Athabascans (northern Native American branch, together with northern North American Amerindians) and southern North Americans and South and Central Americans (southern Native American branch) to be ~13 ka. Similar divergence times from East Asian populations and a divergence time between the two branches that is close in age to the earliest well-established archaeological sites in the Americas suggest that the split between the branches occurred within the Americas. We additionally found that several sequenced Holocene individuals from the Americas are related to present-day populations from the same geographical regions, implying genetic continuity of ancient and modern populations in some parts of the Americas over at least the past 8500 years. Moreover, our results suggest that there has been gene flow between some Native Americans from both North and South America and groups related to East Asians and Australo-Melanesians, the latter possibly through an East Asian route that might have included ancestors of modern Aleutian Islanders. Last, using both genomic and morphometric analyses, we found that historical Native American groups such as the Pericúes and Fuego-Patagonians were not “relicts” of Paleoamericans, and hence, our results do not support an early migration of populations directly related to Australo-Melanesians into the Americas. CONCLUSION Our results provide an upper bound of ~23 ka on the initial divergence of ancestral Native Americans from their East Asian ancestors, followed by a short isolation period of no more than ~8000 years, and subsequent entrance and spread across the Americas. The data presented are consistent with a single-migration model for all Native Americans, with later gene flow from sources related to East Asians and, indirectly, Australo-Melanesians. The single wave diversified ~13 ka, likely within the Americas, giving rise to the northern and southern branches of present-day Native Americans. Population history of present-day Native Americans. The ancestors of all Native Americans entered the Americas as a single migration wave from Siberia (purple) no earlier than ~23 ka, separate from the Inuit (green), and diversified into “northern” and “southern” Native American branches ~13 ka. There is evidence of post-divergence gene flow between some Native Americans and groups related to East Asians/Inuit and Australo-Melanesians (yellow). How and when the Americas were populated remains contentious. Using ancient and modern genome-wide data, we found that the ancestors of all present-day Native Americans, including Athabascans and Amerindians, entered the Americas as a single migration wave from Siberia no earlier than 23 thousand years ago (ka) and after no more than an 8000-year isolation period in Beringia. After their arrival to the Americas, ancestral Native Americans diversified into two basal genetic branches around 13 ka, one that is now dispersed across North and South America and the other restricted to North America. Subsequent gene flow resulted in some Native Americans sharing ancestry with present-day East Asians (including Siberians) and, more distantly, Australo-Melanesians. Putative “Paleoamerican” relict populations, including the historical Mexican Pericúes and South American Fuego-Patagonians, are not directly related to modern Australo-Melanesians as suggested by the Paleoamerican Model.

Locomotor anatomy and biomechanics of the Dmanisi hominins

The Dmanisi hominins inhabited a northern temperate habitat in the southern Caucasus, approximately 1.8 million years ago. This is the oldest population of hominins known outside of Africa. Understanding the set of anatomical and behavioral traits that equipped this population to exploit their seasonal habitat successfully may shed light on the selection pressures shaping early members of the genus Homo and the ecological strategies that permitted the expansion of their range outside of the African subtropics. The abundant stone tools at the site, as well as taphonomic evidence for butchery, suggest that the Dmanisi hominins were active hunters or scavengers. In this study, we examine the locomotor mechanics of the Dmanisi hind limb to test the hypothesis that the inclusion of meat in the diet is associated with an increase in walking and running economy and endurance. Using comparative data from modern humans, chimpanzees, and gorillas, as well as other fossil hominins, we show that the Dmanisi hind limb was functionally similar to modern humans, with a longitudinal plantar arch, increased limb length, and human-like ankle morphology. Other aspects of the foot, specifically metatarsal morphology and tibial torsion, are less derived and similar to earlier hominins. These results are consistent with hypotheses linking hunting and scavenging to improved walking and running performance in early Homo. Primitive retentions in the Dmanisi foot suggest that locomotor evolution continued through the early Pleistocene.

New evidence from Le Moustier 1: Computer-assisted reconstruction and morphometry of the skull

In this study, we present a new computerized reconstruction of the Le Moustier 1 Neanderthal skull and discuss its significance for Neanderthal growth and variability. Because of the precarious state of preservation of the original material, we applied entirely noninvasive methods of fossil reconstruction and morphometry, using a combination of computed tomography, computer graphics, and stereolithography.

Computer-assisted paleoanthropology

Paleoanthropologists are confronted by a steadily growing number of fossil specimens exhibiting diversity in both apparent morphology and state of preservation. Studying this material to answer phylogenetic and functional questions requires extensive qualitative assessment accompanied by quantitative evaluation of large volumes of data. Over the past decade, major new developments in both respects have been made possible through the advent of medical imaging technologies, most notably computer tomography (CT), and through concomitant progress in computer graphics technology. In paleoanthropology, these techniques offer noninvasive tools for visualization of inaccessible regions of the skeleton, computer‐assisted reconstruction of fragmentary fossil specimens, and morphometric or biomechanical analysis of data derived from CT images. A series of CT based studies has already yielded new insights into character differences between fossil hominid species.

Peştera cu Oase 2 and the cranial morphology of early modern Europeans

Between 2003 and 2005, the Peştera cu Oase, Romania yielded a largely complete early modern human cranium, Oase 2, scattered on the surface of a Late Pleistocene hydraulically displaced bone bed containing principally the remains of Ursus spelaeus. Multiple lines of evidence indicate an age of ≈40.5 thousand calendar years before the present (≈35 ka 14C B.P.). Morphological comparison of the adolescent Oase 2 cranium to relevant Late Pleistocene human samples documents a suite of derived modern human and/or non-Neandertal features, including absence of a supraorbital torus, subrectangular orbits, prominent canine fossae, narrow nasal aperture, level nasal floor, angled and anteriorly oriented zygomatic bones, a high neurocranium with prominent parietal bosses and marked sagittal parietal curvature, superiorly positioned temporal zygomatic root, vertical auditory porous, laterally bulbous mastoid processes, superiorly positioned posterior semicircular canal, absence of a nuchal torus and a suprainiac fossa, and a small occipital bun. However, these features are associated with an exceptionally flat frontal arc, a moderately large juxtamastoid eminence, extremely large molars that become progressively larger distally, complex occlusal morphology of the upper third molar, and relatively anteriorly positioned zygomatic arches. Moreover, the featureless occipital region and small mastoid process are at variance with the large facial skeleton and dentition. This unusual mosaic in Oase 2, some of which is paralleled in the Oase 1 mandible, indicates both complex population dynamics as modern humans dispersed into Europe and significant ongoing human evolution once modern humans were established within Europe.