Cusp size, sexual dimorphism, and heritability of cusp size in twins.

Overall measures of mandibular molars reflect the combined size contributions of the component cusps and ridges. Until now, the size hierarchy of primary and permanent mandibular molar cusps remained unclear. This paper utilizes the relative plane surface areas (basal area dimensions) of the individual molar cusps, as assays of cusp size to demonstrate cusp size variations within populations, antimere cuspal variations, sexual dimorphism, and, the heritability of cusp size. Duplicate dental casts from 199 pairs of like-sexed twins provide the raw dats. Defined anatomic landmarks on the occlusal surfaces were reduced to X-Y rectangular coordinates prior to the computation of the basal areas dimensions. The results establish a cusp size hierarchy specific for molar type, i.e., five-cusped molars with a distal fovea and distal marginal ridge (5fd), five-cusped molars without a distal fovea and without a distal marginal ridge (5o), and four-cusped molars (4c). Sexual dimorphism in cusp size is apparent in 5fd molar cusped but not in 5o molar cusps. However, males have a significantly higher frequency of 5fd molars. Females have a higher frequency of smaller 5o and 4c molars which have fewer crown components. Moreover, female 5o molars have cusps as large as or larger than 5o male molor cusps. Right-side-left-side differences exist between antimere cusps based on relatively low correlations. The mirroring of molor types occurs infrequently. When observed, most intrapair differences for cusp size, using F-ratios, indicate a low component of hereditary variability.     

下颌第二恒磨牙C形根管的离体实验研究

目的：寻找一种预备C形根管的有效器械,提高下颌第二恒磨牙的治愈率。方法：选用80颗具有C形根管的下颌第二恒磨牙,选择四种器械进行根管预备,第一组用不锈钢K锉,第二组用不锈钢K锉和手用镍钛器械,第三组用机用镍钛器械,第四组用超声根管治疗仪,预备中均用3％双氧水和生理盐水交替反复冲洗根管,预备后用Vitapex糊剂和牙胶尖冷侧压方法充填根管,观察根充后X线片和根尖微渗漏情况,评价充填效果。结果：四种器械根充后微渗漏有明显差异（P〈0．05）。结论：不锈钢K锉和手用镍钛器械联合应用及超声根管治疗仪为预备C形根管的有效器械。     

下颌第二恒磨牙C 形根管的离体实验研究

目的:寻找一种预备C形根管的有效器械,提高下颌第二恒磨牙的治愈率。方法:选用80颗具有C形根管的下颌第二恒磨牙,选择四种器械进行根管预备,第一组用不锈钢K锉,第二组用不锈钢K锉和手用镍钛器械,第三组用机用镍钛器械,第四组用超声根管治疗仪,预备中均用3%双氧水和生理盐水交替反复冲洗根管,预备后用Vitapex糊剂和牙胶尖冷侧压方法充填根管,观察根充后X线片和根尖微渗漏情况,评价充填效果。结果:四种器械根充后微渗漏有明显差异(P<0.05)。结论:不锈钢K锉和手用镍钛器械联合应用及超声根管治疗仪为预备C形根管的有效器械。     

Alleged synapomorphy of the M1/I1 eruption pattern in robust australopithecines and Homo: evidence from high-resolution computed tomography

Ever since Broom and Robinson (1951) published their claim that the eruption pattern of permanent incisors in robust australopithecines was most similar to that of modern man and different from that of gracile australopithecines and apes, the accuracy of this observation has been the subject of periodic debate (e.g., Wallace: Ph.D. thesis, 1972; Dean: Am. J. Phys. Anthropol. 67:251-257, 1985; Grine: Am. J. Phys. Anthropol. 72:353-359, 1987). Part of the problem is that the developing incisors in one of the specimens most crucial to this argument (SK61) are difficult to visualize clearly by conventional radiographic techniques because of the heavy mineralization in the fossil. This study reanalyzes SK 61 by high-resolution computed tomography in order to contribute to the final resolution of its incisor development. Grine's (op. cit.) assessment of the incisors as the deciduous ones, not the permanent ones, is fully confirmed. This fact, in conjunction with the observation that permanent incisor root formation had only just commenced in this specimen, further weakens the argument of M1/I1 eruption pattern synapomorphy between Homo and robust australopithecines.     

A geometric morphometric analysis of hominin upper first molar shape

Recent studies have revealed interesting differences in upper first molar morphology across the hominin fossil record, particularly significant between H. sapiens and H. neanderthalensis. Usually these analyses have been performed by means of classic morphometric methods, including the measurement of relative cusp areas or the angles defined between cusps. Although these studies have provided valuable information for the morphological characterization of some hominin species, we believe that the analysis of this particular tooth could be more conclusive for taxonomic assignment. In this study, we have applied geometric morphometric methods to explore the morphological variability of the upper first molar (M(1)) across the human fossil record. Our emphasis focuses on the study of the phenetic relationships among the European middle Pleistocene populations (designated as H. heidelbergensis) with H. neanderthalensis and H. sapiens, but the inclusion of Australopithecus and early Homo specimens has helped us to assess the polarity of the observed traits. H. neanderthalensis presents a unique morphology characterized by a relatively distal displacement of the lingual cusps and protrusion in the external outline of a large and bulging hypocone. This morphology can be found in a less pronounced degree in the European early and middle Pleistocene populations, and reaches its maximum expression with the H. neanderthalensis lineage. In contrast, modern humans retain the primitive morphology with a square occlusal polygon associated with a round external outline.     

Paleopediatrics: Or when did human infants really become human?

Modern human children take about twice as long as their closest biological relative, the chimpanzee, to mature. One standard explanation for the evolution of “delayed maturation” at an early stage of human evolution is that it provided the time necessary for immature individuals to learn complex skills, most notably those relating to tool-making abilities. However, after comparing dental maturational profiles of early hominids from South Africa (who apparently did make and use stone tools) (Susman [1994] Science 265:1570–1573) to those of extant humans and chimpanzees, we find no evidence to document an association between “delayed maturation” and tool-making abilities in the early stages of human evolution. This also suggests that the assumed association between prolonged childhood dependency and other behaviors often associated with the advent of tool-making such as cooperative hunting, food sharing, home bases, sexual division of labor, etc., is also suspect. Instead, we must look for other, or additional, selective pressures for the evolution of “delayed maturation,” which may postdate the australopithecine radiation. © 1995 Wiley-Liss, Inc.     

Molar scaling in strepsirrhine primates

We examined how maxillary molar dimensions change with body and skull size estimates among 54 species of living and subfossil strepsirrhine primates. Strepsirrhine maxillary molar areas tend to scale with negative allometry, or possibly isometry, relative to body mass. This observation supports several previous scaling analyses showing that primate molar areas scale at or slightly below geometric similarity relative to body mass. Strepsirrhine molar areas do not change relative to body mass(0.75), as predicted by the metabolic scaling hypothesis. Relative to basicranial length, maxillary molar areas tend to scale with positive allometry. Previous claims that primate molar areas scale with positive allometry relative to body mass appear to rest on the incorrect assumption that skull dimensions scale isometrically with body mass. We identified specific factors that help us to better understand these observed scaling patterns. Lorisiform and lemuriform maxillary molar scaling patterns did not differ significantly, suggesting that the two infraorders had little independent influence on strepsirrhine scaling patterns. Contrary to many previous studies of primate dental allometry, we found little evidence for significant differences in molar area scaling patterns among frugivorous, folivorous, and insectivorous groups. We were able to distinguish folivorous species from frugivorous and insectivorous taxa by comparing M1 lengths and widths. Folivores tend to have a mesiodistally elongated M1 for a given buccolingual M1 width when compared to the other two dietary groups. It has recently been shown that brain mass has a strong influence on primate dental eruption rates. We extended this comparison to relative maxillary molar sizes, but found that brain mass appears to have little influence on the size of strepsirrhine molars. Alternatively, we observed a strong correlation between the relative size of the facial skull and relative molar areas among strepsirrhines. We hypothesize that this association may be underlain by a partial sharing of the patterning of development between molar and facial skull elements.     

Hominids' taxonomy. Three levels of discussion

Paleoanthropology plays a significant role in the study of man and the research of his past. As we all know, the anthropologists in the last century followed the alternative trends of multiplying and reducing the number of taxonomic names. The present paper presents three different levels of taxonomic discussion concerning fossil hominids. These levels belong to different orders: empirical, theoretical and psychological, and they do not exist in isolation from each other. On the contrary, they are connected and interdependent. It shall also be argued that taxonomic controversies described below arise from both objective and subjective factors.     

Gladysvale: First early hominid site discovered in South Africa since 1948

We report here the discovery of fossil hominid teeth at Gladysvale, near Johannesburg in the southern Transvaal. This find makes the site the seventh in South Africa to yield australopithecine remains and the first new early hominid-bearing locality to be found in this region since 1948. Apart from the hominid specimens, our excavations at Gladysvale have added appreciably to the abundant Plio-Pleistocene fauna previously recorded from the cave deposit. The fauna indicates that savanna conditions prevailed during deposition of at least part of the fill. Preliminary faunal dating gives an age of deposition of between c1.7 and c2.5 mya. © 1993 Wiley-Liss, Inc.     

Basicranial anatomy of Plio-Pleistocene hominids from East and South Africa

The results of a metrical analysis of the basicranium of 19 Plio-Pleistocene fossil hominid crania are presented. The sample includes crania attributed to Australopithecus africanus, Australopithecus boisei, and robustus, and Homo erectus as well as crania whose attribution is still under discussion. These results confirm significant differences between the cranial base patterns of the "gracile" and "robust" australopithecines and the three crania attributed to Homo erectus have a pattern which resembles that of modern humans. None of the crania examined from East Africa sites have base patterns which resemble that of the "gracile" australopithecines. The crania KNM-ER 407 and 732 have patterns which are compatible with them being smaller-bodied females of Australopithecus boisei; KNM-ER 1470 and 1813 have base patterns which most closely resemble that of Homo erectus. The cranial base pattern of KNM-ER 1805 is compatible with its inclusion in either Australopithecus boisei or Homo. When account is taken of the immaturity of Taung, the evidence of its cranial base pattern suggests that if it had reached adulthood it would have resembled the "gracile" australopithecine crania from Sterkfontein and Makapansgat.     

The eruption pattern of the permanent incisors and first permanent molars in Australopithecus (Paranthropus) robustus

This study aims to reassess the claim that the eruption sequence of the permanent incisor and first permanent molar teeth of Australopithecus (Paranthropus) robustus is identical with that in modern Homo sapiens. Eight fossil hominid mandibles of equivalent dental developmental age were chosen for comparative study. Emphasis has been placed upon the comparative timing of events within the growth period rather than eruption sequence alone. The results of this study indicate that Homo sapiens and Australopithecus (Paranthropus) robustus share the same pattern of permanent molar and incisor eruption and that this is significantly different from the pattern of eruption shared by the great apes, Australopithecus africanus and Australopithecus afarensis.     

Increase of tooth size in prehistoric coastal Peru, 10,000 B.P.-1,000 B.P.

Teeth increase in size during a 9,000-year period in an archaeologically derived, radiocarbon dated sample of skeletons from a geographically restricted area of coastal Peru. Although cultural change is extensive, including the transition to food production and pottery making, teeth do not reduce as predicted under these conditions by Brace's Probable Mutation Effect. Since most of the dental literature dealing with size change of teeth focuses upon dental reduction, hypotheses explaining why teeth increase through time are not well developed. No obvious selective forces explaining size increase are apparent in the present data. Attrition decreases through time. The increase in tooth size in this collection may be a function of overall cranialfacial size increase, which (pending further data) may be related to a general body size increase.     

The unusual cranial attributes of KNM-ER 1805 and their implication for studies of sexual dimorphism inHomo habilis

A principal components analysis (PCA) of basicranial measurements (Thompson 1991) isolated KNM-ER 1805 as having the highest Principal Component (PC) score on PCI of all the fossil hominids. Two measurements with high loadings on PCI were B12 and B13 and these two measurements indicate the relative positions of the foramina ovale (FO) and infratemporal crests (IT) to the tympanic bone (TP). The object of this study was to compare the two measurements of KNM-ER 1805 with those of other early fossil hominids as well as a sample of extant hominoids. The comparison involved the raw measurements, the index of the two measurements, the coefficient of variation, and a t-test. The results of this comparison showed that KNM-ER 1805 had more forwardly placed foramina ovale than any of the comparative specimens. KNM-ER 1805 possesses a number of other unique features which differentiate it from other hominids including a persistent metopic suture, the form of the premolar roots, and the form of the asterionic region. These apparent unique features mean that KNM-ER 1805 is unlikely to represent an “average” maleHomo habilis and so is an inappropriate model for the male morph of that species.     

Homologies of the anterior teeth in Indriidae and a functional basis for dental reduction in primates

In a recent paper Schwartz ('74) proposes revised homologies of the deciduous and permanent teeth in living lemuriform primates of the family Indriidae. However, new evidence provided by the deciduous dentition ofAvahi suggests that the traditional interpretations are correct, specifically: (1) the lateral teeth in the dental scraper of Indriidae are homologous with the incisors of Lemuridae and Lorisidae, not the canines; (2) the dental formula for the lower deciduous teeth of indriids is 2.1.3; (3) the dental formula for the lower permanent teeth of indriids is 2.0.2.3; and (4) decrease in number of incisors during primate evolution was usually in the sequence I3, then I2, then I1. It appears that dental reduction during primate evolution occurred at the ends of integrated incisor and cheek tooth units to minimize disruption of their functional integrity.     

How large were the australopithecines?

Stature of the African early hominids is estimated from most of the available fragments of fossil long bones by means of regression analysis. The average height of the South African gracile australopithecines is predicted to be 145.1 cm (4′9″) where n = 4 and of the South African robust forms, 152.7 cm (5′) where n = 3. The East African early hominids are somewhat taller (x = 163.0 cm or 5′4″, where n = 7). Variability in stature is high even within the same site which is probably a reflection of fairly strong sexual dimorphism in body size. Evidence is presented which suggests that at least in one form of early hominid the size proportions of fore- and hindlimbs are different than in modern man. There is also evidence that average stature may have increased through time. The most significant of these findings is that the two forms of early hominids in South Africa are possibly more similar in stature than is usually cited. This does not imply necessarily that the two forms did not differ significantly in robustness or weight.     

Some comments on the case for Early Pleistocene hominids in South-Eastern Spain

Several sites in the Orce Basin have revealed evidence of the presence of hominids in the Early Pleistocene. These remains are dated to over 1.0 million years, while they may be as old as 1.6 million years. The skeletal remains from Venta Micena in the Orce Basin show a molecular “fossil protein” pattern which aligns them with hominids, but not with equids. This is supported by the anatomical evidence of the two humeral shafts from theEstrato Blanco in the Venta Micena deposits. The biparieto-occipital partial calvaria shows some unusual features if VM-0 is a hominid specimen. the presence of a prominent crest on the internal surface of the occipital fragment adjacent to the point lambda is decidedly unusual for a modern human calvaria. Moreover, theimpressions gyrorum, in the region where the superior parietal lobule of the cerebral hemisphere abutted against the calvaria, point to a bipartite superior parietal lobule with anterior and posterior moieties which, on the endocast, are clearly separated by a depression that represents a sulcus. These morphological traits are rather puzzling if VM-0 is a hominid, and at first they led me to hesitate over the anatomical identification of VM-0. However, the studies of Campillo (1989) and of Campillo and Barcelo (1986) suggest that the features of the fragment VM-0 are compatible with those of a hominid. Because I believe that we do not possess sufficient information on the variability of the endocranial and ectocranial manifestations of the sagittal suture and of its variance with age of the individual, in different hominid species and different equid species, I have not adduced this pattern as evidence in support or rebuttal of the hominid status of VM-0.