Anthropoid versus strepsirhine status of the African Eocene primates Algeripithecus and Azibius: craniodental evidence.

Recent fossil discoveries have demonstrated that Africa and Asia were epicentres for the origin and/or early diversification of the major living primate lineages, including both anthropoids (monkeys, apes and humans) and crown strepsirhine primates (lemurs, lorises and galagos). Competing hypotheses favouring either an African or Asian origin for anthropoids rank among the most hotly contested issues in paleoprimatology. The Afrocentric model for anthropoid origins rests heavily on the >45 Myr old fossil Algeripithecus minutus from Algeria, which is widely acknowledged to be one of the oldest known anthropoids. However, the phylogenetic position of Algeripithecus with respect to other primates has been tenuous because of the highly fragmentary fossils that have documented this primate until now. Recently recovered and more nearly complete fossils of Algeripithecus and contemporaneous relatives reveal that they are not anthropoids. New data support the idea that Algeripithecus and its sister genus Azibius are the earliest offshoots of an Afro-Arabian strepsirhine clade that embraces extant toothcombed primates and their fossil relatives. Azibius exhibits anatomical evidence for nocturnality. Algeripithecus has a long, thin and forwardly inclined lower canine alveolus, a feature that is entirely compatible with the long and procumbent lower canine included in the toothcomb of crown strepsirhines. These results strengthen an ancient African origin for crown strepsirhines and, in turn, strongly challenge the role of Africa as the ancestral homeland for anthropoids.

Discovery of a highly-specialized plesiadapiform primate in the early-middle Eocene of northwestern Africa.

In this paper we report the first occurrence of an endemic African plesiadapiform primate from the early-middle Eocene locality of Glib Zegdou (Hammada du Dra, Algeria). Dralestes (new genus) is a very specialized taxon, and its closest known relative is the enigmatic and controversial genus Azibius from Gour Lazib (Hammada du Dra). We group both together as the Azibiidae (new rank). Dralestes provides the first evidence of the upper dentition in this group. Some critical dental characters, such as a postprotocingulum on upper teeth, consistently reveal a primate status for the azibiids. Dralestes exhibits, however, a very unusual configuration of the upper molars by the enlarged parastyle, the lack of a metaconule, and the ectoloph structure (preparacrista, centrocrista and postmetacrista are aligned in a high blade-like structure). The apparent dental specializations of both lower premolars and molars of azibiids (exaenodonty, large P(4) bearing sharp apical cusps, and M(1) having a highly elongated trigonid) point to potential relationships with Chronolestes and carpolestid plesiadapiforms. A phylogenetic analysis, performed on 55 dental characters scored for 19 primate genera, clarifies the euprimate status of Altiatlasius, and thus indicates that azibiids are the only known plesiadapiforms from Africa. Azibiids are the sister group of the clade carpolestids/Chronolestes in the superfamily Plesiadapoidea. However, the azibiids differ fundamentally from carpolestids by the combined lack of a centroconule and multiple buccal cusps on P(4). The exact position of both Chronolestes and azibiids in the plesiadapoids appears difficult to resolve. A basal position of Chronolestes in this superfamily cannot be ruled out because it exhibits a simple morphology of I(1) and no conule on P(3). Considering this ad hoc hypothesis, azibiids are found to lie outside a clade including carpolestids/plesiadapids/saxonellids, and they are the sister group to Chronolestes. The clade including the carpolestid, saxonellid, and plesiadapid families is characterized by the occurrence of a centroconule on P(3-4). The lack of this trait in Dralestes and Chronolestes could mean that azibiids are basal plesiadapoids that diverged before the evolution of the common ancestor of the three derived plesiadapoid families, i.e. at least around the Paleocene-Eocene boundary or more probably during the Paleocene. The report of the first offshoot in Africa of plesiadapoids enhances the role of Africa in the early primate radiation.

The anthropoid status of a primate from the late middle Eocene Pondaung Formation (Central Myanmar): tarsal evidence.

Primate dental and postcranial remains from the Eocene Pondaung Formation (Myanmar) have been the subject of considerable confusion since their initial discoveries, and their anthropoid status has been widely debated. We report here a well preserved primate talus discovered in the Segyauk locality near Mogaung that displays derived anatomical features typical of haplorhines, notably anthropoids, and lacks strepsirhine synapomorphies. Linear discriminant and parsimony analyses indicate that the talus from Myanmar is more similar structurally to those of living and extinct anthropoids than to those of adapiforms, and its overall osteological characteristics further point to arboreal quadrupedalism. Regressions of talar dimensions versus body mass in living primates indicate that this foot bone might have belonged to Amphipithecus. This evidence supports hypotheses favoring anthropoid affinities for the large-bodied primates from Pondaung and runs contrary to the hypothesis that Pondaungia and Amphipithecus are strepsirhine adapiforms.

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.