John G. Fleagle

Stratigraphic placement and age of modern humans from Kibish, Ethiopia.

In 1967 the Kibish Formation in southern Ethiopia yielded hominid cranial remains identified as early anatomically modern humans, assigned to Homo sapiens . However, the provenance and age of the fossils have been much debated. Here we confirm that the Omo I and Omo II hominid fossils are from similar stratigraphic levels in Member I of the Kibish Formation, despite the view that Omo I is more modern in appearance than Omo II. 40Ar/39Ar ages on feldspar crystals from pumice clasts within a tuff in Member I below the hominid levels place an older limit of 198 ± 14 kyr (weighted mean age 196 ± 2 kyr) on the hominids. A younger age limit of 104 ± 7 kyr is provided by feldspars from pumice clasts in a Member III tuff. Geological evidence indicates rapid deposition of each member of the Kibish Formation. Isotopic ages on the Kibish Formation correspond to ages of Mediterranean sapropels, which reflect increased flow of the Nile River, and necessarily increased flow of the Omo River. Thus the 40Ar/39Ar age measurements, together with the sapropel correlations, indicate that the hominid fossils have an age close to the older limit. Our preferred estimate of the age of the Kibish hominids is 195 ± 5 kyr, making them the earliest well-dated anatomically modern humans yet described.

Locomotion and Posture of the Malayan Siamang and Implications for Hominoid Evolution

Wild, adult siamang were observed for over 800 h in lowland dipterocarp forest in the Krau Game Reserve, Pahang, West Malaysia. Siamang use four patterns of locomotion: brachiation, climbing, bipedalism and leaping. The pattern of locomotion used by the siamang varies with the size of arboreal supports and with major behavioral activity. Travel is primarily by brachiation along large boughs. Locomotion during feeding is primarily climbing among small branches. In feeding, siamang use suspensory postures among small supports and seated postures on large supports. Comparison of siamang locomotion and posture with that of other apes suggest that quadramanous climbing during feeding is the basic hominoid locomotor adaptation.

Old World Monkeys

Living catarrhine primates are distinguished from platyrrhine by several anatomical features, including a reduced number of premolar teeth. There are two groups of catarrhines, cercopithecoid monkeys and hominoid apes (including humans). Old World monkeys, or cercopithecoids, are found in Africa and Asia, and contain two distinct radiations, cercopithecines and colobines. Cercopithecines are predominantly frugivorous and include two groups. Macaques, baboons, geladas, mangabeys, and mandrills are relatively large monkeys and all except macaques are restricted to Africa. Guenons and related taxa are smaller monkeys found only in Africa. The leaf-eating colobines are found in both Africa and Asia. As a group, Old World monkeys are all diurnal and predominately quadrupeds and leapers. They include arboreal and terrestrial species. Most live in single male groups, multi-male groups, or larger complex societies. Phylogenetic relations among cercopithecoids are generally well-resolved, but hybridization has been widespread in the evolution of the group.

The phyletic position of the Parapithecidae

Abstract The Parapithecidae are a group of primitive anthropoid primates known only from the early Oligocene Jebel Qatrani Formation of Fayum, Egypt. Since the initial discovery of the group early in the century, their phyletic position relative to other higher primates has been ambiguous and the subject of considerable debate. Various authors have considered the parapithecids as the sister taxon of (1) Old World monkeys, (2) all other Old World anthropoids; (3) platyrrhines; or (4) all other higher primates. Although there are anatomical features that can be advanced to support each of these views, parapithecids lack a number of anatomical features that characterize all other anthropoids and are best considered the most primitive higher primates. Such a phyletic position for parapithecids involves fewer evolutionary parallelisms and reversals in anthropoid evolution than does any other phylogeny. This suggests that the origin of anthropoids from prosimians was most probably in Africa.

Size and Adaptation in Primates

Living primates vary in size from species averaging less than 100 g to some averaging well over 100 kg (Fig 1). The fossil record provides evidence of both much larger and much smaller species (e.g., Fleagle, 1978; Gingerich et al., 1982; Gunnell, 1983; Simons and Ettel, 1970). There is no doubt that much of the diversity that these species show in structure, physiology, behavior, and ecology is intimately related to differences in body size (e.g., Schmidt-Nielson, 1975; Clutton-Brock and Harvey, 1983). The details of this relationship are the domain of allometry. Thus, in its broadest sense, allometry is the study of the relationship between size and adaptation.

The Fayum Primate Forest Revisited

In Oligocene times, the Fayum area of northern Egypt was a subtropical to tropical lowland coastal plain with damp soils and seasonal rainfall that supported an abundance and variety of vegetation, including lianes (large vines), tall trees, and possibly mangroves, and a large and varied vertebrate fauna. The Oligocene marine strandline was close by and principal Jebel Qatrani Formation streams were probably brackish several kilometers inland due to tidal incursions. Sediments of the Jebel Qatrani Formation were deposited by several large meandering streams, associated with minor but sometimes extensive floodbasin ponds. These rocks provide no evidence for the former existence, in early Tertiary time, of a “Proto-Nile” River. Large accumulations of silicified fossil logs in the Jebel Qatrani Formation are autochthonous and the logs were transported only a short distance before burial. The Oligocene higher primates Aegyptopithecus, Propliopithecus, Parapithecus , and Apidium lived in this paleoenvironment and postcranial remains of Aegyptopithecus and Apidium demonstrate that these animals were arboreal. This scenario for the paleoenvironment of the Fayum area in Oligocene times differs greatly from the nearly treeless, sparsely vegetated, semiarid sahelien Oligocene Fayum paleoenvironment populated by terrestrial primates that was recently proposed by Kortlandt (1980) .

Oligocene mammals from Ethiopia and faunal exchange between Afro-Arabia and Eurasia

Afro-Arabian mammalian communities underwent a marked transition near the Oligocene/Miocene boundary at approximately 24 million years (Myr) ago. Although it is well documented that the endemic paenungulate taxa were replaced by migrants from the Northern Hemisphere, the timing and evolutionary dynamics of this transition have long been a mystery because faunas from about 32 to 24 Myr ago are largely unknown. Here we report a late Oligocene fossil assemblage from Ethiopia, which constrains the migration to postdate 27 Myr ago, and yields new insight into the indigenous faunal dynamics that preceded this event. The fauna is composed of large paenungulate herbivores and reveals not only which earlier taxa persisted into the late Oligocene epoch but also demonstrates that one group, the Proboscidea, underwent a marked diversification. When Eurasian immigrants entered Afro-Arabia, a pattern of winners and losers among the endemics emerged: less diverse taxa such as arsinoitheres became extinct, moderately species-rich groups such as hyracoids continued into the Miocene with reduced diversity, whereas the proboscideans successfully carried their adaptive radiation out of Afro-Arabia and across the world.

The First Humans – Origin and Early Evolution of the Genus Homo

Part I. Retrospectives and Theoretical Perspectives 1. Early humans: of whom do we speak? Richard E. Leakey 2. Homo habilis - a premature discovery: remembered by one of its founding fathers, 42 years later Phillip V. Tobia 3. Where does the genus Homo begin, and how would we know? Bernard Wood Part II. Craniodental Perspectives on Taxonomy and Systematics 4. The origin of Homo William H. Kimbel 5. Comparisons of Early Pleistocene skulls from East Africa and the Georgian Caucasus: evidence bearing on the origin and systematics of genus Homo G. Philip Rightmire and David Lordkipanidze 6. Phenetic affinities of Plio-Pleistocene Homo fossils from South Africa: molar cusp proportions Frederick E. Grine, Heather F. Smith, Christopher P. Heesy and Emma J. Smith Part III. Postcranial Perspectives on Locomotion and Adaptation 7. Evolution of the hominin shoulder: early Homo Susan G. Larson 8. Brains, brawn, and the evolution of human endurance running capabilities Daniel E. Lieberman, Dennis M. Bramble, David A. Raichlen and John J. Shea 9. Interlimb proportions in humans and fossil hominins: variability and scaling William L. Jungers Part IV. Perspectives on Development, Diet and Behavior 10. Growth and development of the Nariokotome youth, KNM-WT 15000 M. Christopher Dean and B. Holly Smith 11. Dental evidence for diets of early Homo Peter S. Ungar and Robert S. Scott 12. Origins and adaptations of early Homo: what archaeology tells us Helene Roche, Robert J. Blumenschine and John J. Shea Part V. Environmental and Ecological Perspectives 13. Plio-Pleistocene EastAfrican pulsed climate variability and its influence on early human evolution. Mark A. Maslin and Martin H. Trauth 14. Tracking ecological change in relation to the emergence of Homo near the Plio-Pleistocene boundary. Kaye E. Reed and Samantha M. Russak 15. Ecology of Plio-Pleistocene mammals in the Omo-Turkana Basin and the emergence of Homo. Rene Bobe and Meave G. Leakey 16. Biogeochemical evidence for the environments of early Homo in South Africa Matt Sponheimer and Julia Lee-Thorp Part VI. Summary Perspective on the Workshop 17. The first humans: a summary perspective on the origin and early evolution of the genus Homo. Frederick E. Grine and John G. Fleagle

The recognition and evaluation of homoplasy in primate and human evolution.

Homoplasy has been a prominent issue in primate systematics and phylogeny for as long as people have been studying human evolution. In the past, homoplasy, in the form of parallel evolution, was often considered the dominant theme in primate evolution. Today, it receives blame for difficulties in phylogenetic analysis, but is essential in the study of adaptation. This paper reviews the history of study of homoplasy, methods of defining homoplasy, and methodological and biological factors that generate homoplasy. A post hoc definition of homology and homoplasy, based on patterns of character distributions and their congruence or incongruence on a cladogram, is the most consistent method of recognizing these phenomena. Defined this way, homology and homoplasy are mutually exclusive. However, when different levels of analysis are examined, it is seen that homoplasy at one level, such as adult phenotype, often exists simultaneously with homology at a different level, such as developmental process. Thus, in some cases, patterns of homoplasy may point to underlying similarities that reflect the shared heritage of a particular clade. This is an old concept that is being renewed on the strength of recent trends in developmental biology. Factors that influence homoplasy include character definition and a host of biological factors, such as developmental constraints, allometry, and adaptation. These interact with one another to provide explanations of homoplastic patterns. Because of the repetition of events, explanations of homoplastic features are often more reliable than those for homologous features, and serve as effective tests for hypotheses of evolutionary process. In some cases, particular explanations of homoplasy lead to generalizations about the likelihood of homoplasy in a type of structure. The structure may be adaptive or highly epigenetic, or it may belong to an anatomical system considered to be more prone to homoplasy than others. However, our review shows that these generalizations are usually based on theory, and contradictory expectations can be developed under different theoretical models. More rigorous empirical studies are necessary to discover what, if any, generalizations can be made about the likelihood of homoplasy in different types of characters.

Locomotion and Posture

Apart from marsupials and edentates, there is no order of mammals, living or fossil, which displays a greater diversity of locomotor and postural adaptations than extant primates. With body weight varying from about 100 grams to 200 kilograms, the Order Primates includes leapers, climbers, brachiators, knuckle-walkers and a variety of arboreal and terrestrial quadrupeds. Despite the interest which primate positional behaviour has engendered in anatomists, anthropologists and zoologists throughout this century, we still understand very little about the relationships between locomotor and postural behaviour on the one hand, and basic aspects of these animals’ biology, such as gross diet and use of forest structure on the other.