Dental Ontogeny in Pliocene and Early Pleistocene Hominins

Until recently, our understanding of the evolution of human growth and development derived from studies of fossil juveniles that employed extant populations for both age determination and comparison. This circular approach has led to considerable debate about the human-like and ape-like affinities of fossil hominins. Teeth are invaluable for understanding maturation as age at death can be directly assessed from dental microstructure, and dental development has been shown to correlate with life history across primates broadly. We employ non-destructive synchrotron imaging to characterize incremental development, molar emergence, and age at death in more than 20 Australopithecus anamensis, Australopithecus africanus, Paranthropus robustus and South African early Homo juveniles. Long-period line periodicities range from at least 6–12 days (possibly 5–13 days), and do not support the hypothesis that australopiths have lower mean values than extant or fossil Homo. Crown formation times of australopith and early Homo postcanine teeth fall below or at the low end of extant human values; Paranthropus robustus dentitions have the shortest formation times. Pliocene and early Pleistocene hominins show remarkable variation, and previous reports of age at death that employ a narrow range of estimated long-period line periodicities, cuspal enamel thicknesses, or initiation ages are likely to be in error. New chronological ages for SK 62 and StW 151 are several months younger than previous histological estimates, while Sts 24 is more than one year older. Extant human standards overestimate age at death in hominins predating Homo sapiens, and should not be applied to other fossil taxa. We urge caution when inferring life history as aspects of dental development in Pliocene and early Pleistocene fossils are distinct from modern humans and African apes, and recent work has challenged the predictive power of primate-wide associations between hominoid first molar emergence and certain life history variables.     

First record of a parapithecid primate from the Oligocene of Kenya

Recent excavations in northwestern Kenya have recovered a vertebrate fauna of late early or early late Oligocene age. Among the mammal remains, a fragmentary lower jaw and an isolated upper molar have been attributed to a small primate, Lokonepithecus manai gen. et sp. nov. Lokonepithecus is a primitive member of the Parapithecidae and possibly most closely related to Apidium from the Fayum. The new primate from Kenya is the youngest parapithecid known and its occurrence in the Oligocene of Kenya suggests that sub-Saharan Africa probably played a major role in the evolutionary history of several groups of mammals.     

Isoform-specific O-glycosylation by murine UDP-GalNAc:polypeptide N- acetylgalactosaminyltransferase-T3, in vivo

Multiple isoforms of UDP-GalNAc:polypeptide N-acetylgalactosaminyl- transferase (ppGaNTase) have been cloned and expressed from a variety of organisms. In general, these isoforms display different patterns of tissue-specific expression, but exhibit overlapping substrate specificities, in vitro . A peptide substrate, derived from the sequence of the V3 loop of the HIV gp120 protein (HIV peptide), has previously been shown to be glycosylated in vitro exclusively by the ppGaNTase-T3 (Bennett et al. , 1996). To determine if this isoform- specificity is maintained in vivo , we have examined the glycosylation of this substrate when it is expressed as a reporter peptide (rHIV) in a cell background (COS7 cells) which lacks detectable levels of the ppGaNTase-T3. Glycosylation of rHIV was greatly increased by coexpression of a recombinant ppGaNTase-T3. Overexpression of ppGaNTase- T1 yielded only partial glycosylation of the reporter. We have also determined that the introduction of a proline residue at the +3 position flanking the potential glycosylation site eliminated ppGaNTase- T3 selectivity toward rHIV observed both in vivo and in vitro .      

New fossils of Australopithecus anamensis from Kanapoi,West Turkana,Kenya (2003–2008)

Renewed fieldwork from 2003 through 2008 at the Australopithecus anamensis type-site of Kanapoi, Kenya, yielded nine new fossils attributable to this species. These fossils all date to between 4.195 and 4.108 million years ago. Most were recovered from the lower fluvial sequence at the site, with one from the lacustrine sequence deltaic sands that overlie the lower fluvial deposits but are still below the Kanapoi Tuff. The new specimens include a partial edentulous mandible, partial maxillary dentition, two partial mandibular dentitions, and five isolated teeth. The new Kanapoi hominin fossils increase the sample known from the earliest Australopithecus, and provide new insights into morphology within this taxon. They support the distinctiveness of the early A. anamensis fossils relative to earlier hominins and to the later Australopithecus afarensis. The new fossils do not appreciably extend the range of observed variation in A. anamensis from Kanapoi, with the exception of some slightly larger molars, and a canine tooth root that is the largest in the hominin fossil record. All of the Kanapoi hominins share a distinctive morphology of the canine–premolar complex, typical early hominin low canine crowns but with mesiodistally longer honing teeth than seen in A. afarensis, and large, probably dimorphic, canine tooth roots. The new Kanapoi specimens support the observation that canine crown height, morphology, root size and dimorphism were not altered from a primitive ape-like condition as part of a single event in human evolution, and that there may have been an adaptive difference in canine function between A. anamensis and A. afarensis.     

Anterior dental evolution in the Australopithecus anamensis–afarensis lineage

Australopithecus anamensis is the earliest known species of the Australopithecus–human clade and is the likely ancestor of Australopithecus afarensis. Investigating possible selective pressures underlying these changes is key to understanding the patterns of selection shaping the origins and early evolution of the Australopithecus–human clade. During the course of the Au. anamensis–afarensis lineage, significant changes appear to occur particularly in the anterior dentition, but also in jaw structure and molar form, suggesting selection for altered diet and/or food processing. Specifically, canine tooth crown height does not change, but maxillary canines and P₃s become shorter mesiodistally, canine tooth crowns become more symmetrical in profile and P₃s less unicuspid. Canine roots diminish in size and dimorphism, especially relative to the size of the postcanine teeth. Molar crowns become higher. Tooth rows become more divergent and symphyseal form changes. Dietary change involving anterior dental use is also suggested by less intense anterior tooth wear in Au. afarensis. These dental changes signal selection for altered dietary behaviour and explain some differences in craniofacial form between these taxa. These data identify Au. anamensis not just as a more primitive version of Au. afarensis, but as a dynamic member of an evolving lineage leading to Au. afarensis, and raise intriguing questions about what other evolutionary changes occurred during the early evolution of the Australopithecus–human clade, and what characterized the origins of the group.