Friedemann Schrenk

Growth processes in teeth distinguish modern humans from Homo erectus and earlier hominins

A modern human-like sequence of dental development, as a proxy for the pace of life history, is regarded as one of the diagnostic hallmarks of our own genus Homo. Brain size, age at first reproduction, lifespan and other life-history traits correlate tightly with dental development. Here we report differences in enamel growth that show the earliest fossils attributed to Homo do not resemble modern humans in their development. We used daily incremental markings in enamel to calculate rates of enamel formation in 13 fossil hominins and identified differences in this key determinant of tooth formation time. Neither australopiths nor fossils currently attributed to early Homo shared the slow trajectory of enamel growth typical of modern humans; rather, both resembled modern and fossil African apes. We then reconstructed tooth formation times in australopiths, in the ∼1.5-Myr-old Homo erectus skeleton from Nariokotome, Kenya, and in another Homo erectus specimen, Sangiran S7-37 from Java. These times were shorter than those in modern humans. It therefore seems likely that truly modern dental development emerged relatively late in human evolution.

Molar Macrowear Reveals Neanderthal Eco-Geographic Dietary Variation

Neanderthal diets are reported to be based mainly on the consumption of large and medium sized herbivores, while the exploitation of other food types including plants has also been demonstrated. Though some studies conclude that early Homo sapiens were active hunters, the analyses of faunal assemblages, stone tool technologies and stable isotopic studies indicate that they exploited broader dietary resources than Neanderthals. Whereas previous studies assume taxon-specific dietary specializations, we suggest here that the diet of both Neanderthals and early Homo sapiens is determined by ecological conditions. We analyzed molar wear patterns using occlusal fingerprint analysis derived from optical 3D topometry. Molar macrowear accumulates during the lifespan of an individual and thus reflects diet over long periods. Neanderthal and early Homo sapiens maxillary molar macrowear indicates strong eco-geographic dietary variation independent of taxonomic affinities. Based on comparisons with modern hunter-gatherer populations with known diets, Neanderthals as well as early Homo sapiens show high dietary variability in Mediterranean evergreen habitats but a more restricted diet in upper latitude steppe/coniferous forest environments, suggesting a significant consumption of high protein meat resources.

A new 3-d approach to determine functional morphology of cercopithecoid molars

Functional relationships between diet and tooth morphology form an integral part of primatological and paleontological research. Previously, mostly two-dimensional parameters have been used to compare and interpret the complex crown morphology of cercopithecine and colobine molars. However, as teeth are three-dimensional objects, any dimensional reduction in describing their morphology must result in loss of information. In the current study we use a high resolution optical topometric system to record crown morphology in different wear stages in order to extract three-dimensional (3-d) parameters from virtual 3-d models. Structural parameters such as relief index, occlusal surface area, enamel area and strike and dip of cusp slopes as well as wear facets can be calculated, reflecting the changing occlusal topography of molars due to attrition and abrasion. By comparing mostly fruit-eating cercopithecines and leaf-eating colobines, functional implications of tooth wear, occlusal jaw movement and resulting relief can be inferred. Our analyses show that the main differences in occlusal relief between these genera do not change with wear. Colobines maintain higher occlusal relief, whereas in cercopithecines all cusps wear flat quite rapidly. Detailed models of wear for cercopithecoid molars will be used to reconstruct diet and will enhance our knowledge of the paleoecology of Cercopithecoidea.

Wide faces or large canines? The attractive versus the aggressive primate

Hominids display marked body size dimorphism, suggestive of strong sexual selection, yet they lack significant sex differences in canine size that are commonly associated with intrasexual competition in primates. We resolve this paradox by examining sex differences in hominoid facial morphology. We show that chimpanzees, but not gorillas, exhibit clear sexual dimorphism in face width, over and above that expected based on sex differences in body size. We show that this facial dimorphism, expressed as an index, is negatively correlated with canine dimorphism among anthropoid primates. Our findings suggest that a lack of canine dimorphism in anthropoids is not owing to weak sexual selection, but rather is associated with strong sexual selection for broader face width. Enlarged cheekbones are linked with attractiveness in humans, and we propose that the evolution of a broad face and loss of large canines in hominid males results from mate choice.

Brief communication: Identification reassessment of the isolated tooth Krapina D58 through occlusal fingerprint analysis.

High variability in the dentition of Homo can create uncertainties in the correct identification of isolated teeth. For instance, standard tooth identification criteria cannot determine with absolute certainty if an isolated tooth is a second or third maxillary molar. In this contribution, using occlusal fingerprint analysis, we reassess the identification of Krapina D58 (Homo neanderthalensis), which is catalogued as a third maxillary molar. We have hypothesized that the presence/absence of the distal occlusal wear facets can be used to differentiate second from third maxillary molars. The results obtained confirm our hypothesis, showing a significant difference between second and third maxillary molars. In particular we note the complete absence of Facets 7 and 10 in all third molars included in this analysis. The presence of these facets in Krapina D58 eliminates the possibility that it is a third maxillary molar. Consequently it should be reclassified as a second molar. Although this method is limited by the degree of dental wear (i.e., unworn teeth cannot be analyzed) and to individual molars in full occlusion, it can be used for tooth identification when other common criteria are not sufficient to discriminate between second and third maxillary molars.

Relationship between cusp size and occlusal wear pattern in Neanderthal and Homo sapiens first maxillary molars.

Tooth wear studies in mammals have highlighted the relationship between wear facets (attritional areas produced during occlusion by the contact between opposing teeth) and physical properties of the ingested food. However, little is known about the influence of tooth morphology on the formation of occlusal wear facets. We analyzed the occlusal wear patterns of first maxillary molars (M1s) in Neanderthals, early Homo sapiens, and contemporary modern humans. We applied a virtual method to analyze wear facets on the crown surface of three‐dimensional digital models. Absolute and relative wear facet areas are compared with cusp area and cusp height. Although the development of wear facets partially follows the cusp pattern, the results obtained from the between‐group comparisons do not reflect the cusp size differences characterizing these groups. In particular, the wear facets developed along the slopes of the most discriminate cusp between Neanderthals and Homo sapiens (hypocone) do not display any significant difference. Moreover, no correlations have been found between cusp size and wear facet areas (with the exception of the modern sample) and between cusp height and wear facet areas. Our results suggest that cusp size is only weakly related to the formation of the occlusal wear facets. Other factors, such as, diet, food processing, environmental abrasiveness, and nondietary habits are probably more important for the development and enlargement of wear facets, corroborating the hypotheses suggested from previous dental wear studies. Anat Rec, 2011.

The early Pleistocene deciduous hominid molar FS-72 from the Sangiran dome of java, Indonesia: A taxonomic reappraisal based on its comparative endostructural characterization

OBJECTIVES Among the ten fossil hominid deciduous teeth reported so far from the Pleistocene sediments of the Sangiran Dome of Java are two isolated lower second molars: specimens PCG.2 from the Kabuh Formation and FS-72 from the Pucangan Formation. While PCG.2 appears to be certainly attributable to Homo erectus, FS-72 is somewhat more problematic, even though it is commonly listed within the Indonesian H. erectus hypodigm. Largely because of its large size, it was originally attributed to Meganthropus paleojavanicus. Subsequent study highlighted a set of metric and nonmetric crown features also found in Australopith and African early Homo (notably H. habilis) homologues. An additional problem with the taxonomic assignment of isolated teeth from the Pleistocene of Java is the presence of Pongo in these same deposits. METHODS To assess the taxonomic affinity of FS-72, we investigated its inner structure (tissue proportions and enamel-dentine junction morphology) by using techniques of 2-3D virtual imaging coupled with geometric morphometric analyses. RESULTS The results show that FS-72 has thinner enamel compared to fossil and recent humans and that its topographic repartition more closely follows the pongine pattern. It also exhibits a Pongo-like elongated morphology of the enamel-dentine junction, with proportionally lower and mesiodistally spaced dentine horns. CONCLUSIONS Given the morphological and metric similarities between fossil orangutan and H. erectus molars, we tested the hypothesis that its internal morphology more closely resembles the patterns evinced by PCG.2 and modern humans than Pongo. Accordingly, we consider that FS-72 more likely represents a dm2 of Pongo rather than Homo.

The earliest putative homo fossils

The earliest fossil remains of the genus Homo have been discovered in eastern, southeastern, and southern Africa. The sample comprises about 200 skeletal fragments attributable to about 40 individuals and assigned to two species: Homo rudolfensis (2.5–1.8 Ma) showing a combination of primitive dentition with Homo-like locomotion and Homo habilis (2.1–1.5 Ma) exhibiting a progressive reduction of tooth roots but resembling great apes rather than humans in the postcranial skeleton. Another significant difference between early Homo and the australopithecines is brain size, which was larger in early Homo than in Australopithecus but smaller than inHomo erectus. Endocasts ofH. habilis from F. Schrenk (*) • O. Kullmer Department of Paleoanthropology and Messel Research, Senckenberg Research Institute and Natural History Museum, Frankfurt, Germany e-mail: schrenk@bio.uni-frankfurt.de; ottmar.kullmer@senckenberg.de T. Bromage Department of Biomaterials and Biomimetics, New York University, College of Dentistry, New York, NY, USA e-mail: tim.bromage@nyu.edu # Springer-Verlag Berlin Heidelberg 2015 W. Henke, I. Tattersall (eds.), Handbook of Paleoanthropology, DOI 10.1007/978-3-642-39979-4_52 2145 Olduvai Gorge and Koobi Fora reveal a number of distinctive features, some of which are recognized as Homo autapomorphies. Differences in tooth wear between H. rudolfensis, with megadont teeth and more horizontal tooth abrasion, and H. habilis, with more gracile molars and higher relief in worn teeth, indicate significant differences in diet and ecology of early Homo species. The origin of the genus Homo coincided with the onset of material culture. Between ca. 2.8 and 2.5 Ma, extensive open habitats comprising more arid-tolerant vegetation developed in Africa. The selective pressures of this habitat change resulted in the increased survival of more megadont species varieties. Megadonty allowed these species to feed on harder open woodland-open savannah food items (chapter “▶Dental Adaptations of African Apes,” Vol. 2) resulting in the phyletic splitting of Australopithecus afarensis into Paranthropus and Homo lineages by ca. 2.5 Ma. An evolutionary scenario that complies with both the Habitat Theory and early hominid biogeography is provided. It delineates the association between faunal turnover and climate change and suggests a single origin for the Paranthropus lineage but separate origins for H. rudolfensis and H. habilis from A. afarensis, A. africanus, or A. sediba ancestors, respectively.

Early Hominid diversity, age and biogeography of the Malawi-Rift

Remains of earlyHomo andParanthropus have been recovered from two contemporaneous sites (Uraha and Malema) in the “Hominid Corridor” in Northern Malawi (Chiwondo Beds). Faunal dating suggests an age of 2.5–2.3 Ma for both hominids. The two specimens, a mandible attributed toHomo rudolfensis (UR 501 from Uraha), and a maxillary fragment ofParanthropus boisci. (RC 911 from Malema) known only from eastern Africa, represent the southernmost known distribution of these taxa. The biogeographic significance of these hominids from the Malawi-Rift lay in their association with the eastern African endemic animal group. Biogeographic variation in south-eastern Africa may be linked to habitat change occurring due to climate change, with maximum change occurring around 2.5 Ma.

A cercopithecoid tooth from the pliocene of Malawi

A cercopithecoid tooth which was recovered from Pliocene deposits in northern Malawi is described and identified here as cf. Parapapio sp. This is the first evidence of this taxon in the geographic corridor between the East and South African hominid bearing sites.