Hypocone

Abstract: Few dental anthropological studies have investigated the associations between tooth crown size and crown traits in humans using quantitative methods. We tested several hypotheses about overall crown size, individual cusp areas, and expression of Carabelli cusps in human permanent first molars by obtaining data from standardized occlusal photographs of 308 Australians of European descent (171 males and 137 females). Specifically, we aimed to calculate the areas of the four main molar cusps, and also Carabelli cusp, and to compare the relative variability of cusp areas in relation to timing of development. We also aimed to compare cusp areas between males and females and to describe how Carabelli cusp interacted with other molar cusps. Measurements included maximum crown diameters (mesiodistal and buccolingual crown diameters), the areas of the four main cusps, and the area of Carabelli cusp. The pattern of relative variability in absolute areas of molar cusps corresponded with their order of formation, the first-forming paracone displaying the least variation, and the last-forming Carabelli cusp showing the greatest. Overall crown size and areas of individual cusps all showed sexual dimorphism, with values in males exceeding those in females. Sexual dimorphism was smallest for paracone area and greatest for Carabelli cusp area. Overall crown size and cusp areas were larger in individuals displaying a Carabelli cusp, especially the hypocone area. Although the combined area of the protocone and a Carabelli cusp was greater in cuspal forms than noncuspal forms, protocone area alone was significantly smaller in the former. Our findings lead us to propose that, in individuals with the genotype for Carabelli trait expression, larger molar crowns are more likely to display Carabelli cusps, whereas molars with smaller crowns are more likely to display reduced forms of expression of the trait. We suggest that the pattern of folding of the internal enamel epithelium in developing molar crowns, particularly in the protocone region, can be modified by a developing Carabelli cusp.

Abstract: The dentition of a Mesolithic population (8,000–11,000 years old) from Wadi Halfa, Sudan, can be characterized as morphologically complex, massive and relatively free from pathology except that associated with extreme wear. Maxillary incisors show shoveling. All of the maxillary molars show some development of the hypocone. Supernumerary cusps appear frequently. Almost one-half of the second lower molars observed show distally located third cusps. Over one-half of the maxillary third molars show an extra cusp. A high percentage of mandibular molars show six cusps. Overall the teeth from this population compare favorably in size with those of an Australian aborigine tribe and are slightly larger than the teeth of the Neanderthaloids from Skūhl. The teeth show wear of a degree greater than that found in present day Eskimo or Australian aborigine groups. This data may be interpreted as indicating that this Mesolithic group was subjected to rigorous selective pressures favoring large and/or morphologically complex teeth. This pressure was apparently intensive wear, presumably caused by the inclusion of large amounts of grit in the diet through the eating of vegetable food macerated on coarse grinding stones.

Abstract: Two remarkably complete skulls and associated mandibles from the late early Eocene of the Yuhuangding Formation of Hubei Province, central China, are described as a new genus and species of rodent, Exmus mini, and referred to the early ctenodectyloid family Cocomyidae. This is a small rodent in the size range of the early Eocene Asian Cocomys. Dental characters that link Exmus with other cocomyids include: non-molariform P4; cheek teeth increasing in size posteriorly; lower molar ectolophid weak or absent; and lower molar hypoconulid distinct, enlarged on m3. Cranial characters linking Exmus and Cocomys include: skull shape and proportions, including a short rostrum and large orbit; sagittal crest absent; large optic canal, confluent between the orbits; and no petrosal shelf posterior to the caudal tympanic process of the petrosal. Differences from Cocomys are numerous and include: absence of conules on P4 and loss of the protoconule on the upper molars; tiny meta-cone and hypocone on P4; molarif...