Frequency variations of discrete cranial traits in major human populations. II. Hypostotic variations

Cranial morphology in metopism: A comparative geometric morphometric study

BACKGROUND

Cranial sutures are active bone growth sites and any alteration in their normal formation, patency and closure influences the overall cranial morphology. This comparative study aims to establish whether the cranial shape and size are significantly modified when metopic suture persists into adulthood using geometric morphometric analyses.

METHODS

The sample consisted of 63 metopic and 184 non-metopic dry adult male crania. Three-dimensional polygonal models of the crania were generated using a hand-held laser scanner Creaform VIUscan. A total of 50 landmarks were digitized on the three-dimensional models and eight landmark configurations delineating the cranium and its compartments were constructed and analyzed. Geometric morphometric analyses were applied to investigate separately the size and shape differences between the metopic and non-metopic series in each of the landmark configurations.

RESULTS

Significant size differences were established solely in the neurocranium, but not in its total size, rather in its parts. The size modification was expressed by an enlargement of the anterior part of the neurocranium at the expense of the middle and posterior ones. All investigated landmark sets differed significantly between the series regarding the shape. In metopic series, the shape alteration was mainly in a mediolateral widening and an anteroposterior shortening contributing to a more rounded overall shape of the cranium.

CONCLUSIONS

The slight modification of the cranial morphology in metopism suggests that the metopic suture persistence is not an isolated variation limited to the frontal bone. It is rather a complex condition associated with a combination of specific phenotypic characteristics.

Evaluation of ancestry from human skeletal remains: a concise review

Ancestry assessment represents a major component of forensic anthropological analysis of recovered human remains. Interpretations of ancestry, together with other aspects of the biological profile, can help narrow the search of missing persons and contribute to eventual positive identification. Such information can prove useful to authorities involved in the identification and investigative process since many lists of missing persons have a reference to this parameter. Recent research has strengthened available methodologies involving metric, non-metric morphological as well as chemical and genetic approaches. This review addresses the new anthropological techniques that are now available, as well as the complex historical context related to ancestry evaluation.

A new analysis interpreting Nilotic relationships and peopling of the Nile Valley

The process of the peopling of the Nile Valley likely shaped the population structure and early biological similarity of Egyptians and Nubians. As others have noted, affinity among Nilotic populations was due to an aggregation of events, including environmental, linguistic, and sociopolitical changes over a great deal of time. This study seeks to evaluate the relationships of Nubian and Egyptian groups in the context of the original peopling event. Cranial nonmetric traits from 18 Nubian and Egyptian samples, spanning Lower Egypt to Lower Nubia and approximately 7400 years, were analyzed using Mahalanobis D² as a measure of biological distance. A principal coordinates analysis and spatial-temporal model were applied to these data. The results reveal temporal and spatial patterning consistent with documented events in Egyptian and Nubian population history. Moreover, the Mesolithic Nubian sample clustered with later Nubian and Egyptian samples, indicating that events prior to the Mesolithic were important in shaping the later genetic patterning of the Nubian population. Later contact through the establishment of the Egyptian fort at Buhen, Kerma's position as a strategic trade center along the Nile, and Egyptian colonization at Tombos maintained genetic similarity among the populations.

Non-metric variation of the middle phalanges of the human toes (II-V): long/short types and their evolutionary significance

The human lateral toes are characterised by extreme reduction compared with other primates, and in particular other hominoids. Some phalangeal non-metric variants have been well identified in humans, in particular: triphalangeal/biphalangeal patterns, and the presence/absence of phalangeal secondary centres of ossification. The purpose of the present study was to describe and analyse an original non-metric variation of the middle phalanges of the lateral toes. The material consisted of 2541 foot radiographs that came from 2541 different European adult individuals. Two morphological types of the middle phalanx were defined as a simple binary trait: long type (L) and short type (S). In feet with a triphalangeal pattern in all lateral toes (1413 cases), a mediolateral increasing gradient was observed in the occurrence of type S: 8.1% in II; 30.7% in III; 68.4% in IV; and 99.1% in V. In feet with a biphalangeal pattern in one or more lateral toes (III-V; 1128 cases), type S occurred more frequently than in triphalangeal feet. Of the 30 theoretical arrangements of the L/S types in the lateral toes (II-V) in a complete foot, only 13 patterns were observed. Seven patterns represented 95.6% of the population: LLSS (20.9%), LLLS (17.1%), LSS (15.9%), SSS (14.5%), LSSS (12.7%), LLS (10.1%) and SSSS (4.4%). Type L can be interpreted as the primitive pattern (plesiomorphy), and type S as a derived pattern (apomorphy) that seems specific to the human species (i.e. autapomorphy). Within the specific evolution of the human foot in relation to the acquisition of constant erect posture and bipedalism, the short type of the middle phalanges can reasonably be considered as directly linked to the reduction of the lateral toes.

A new anatomic trait for identifying the mendosal suture in young children: the mendosal-lambdoidal angle

PURPOSE

Radiologic diagnosis of skull fractures in young children is difficult due to numerous accessory sutures. This is especially true around the occipital bone because it has more than one ossification center. Normal anatomic variants, such as the mendosal suture, may be misinterpreted as a skull fracture. We investigated the anatomic traits of the mendosal suture in young children.

METHODS

We retrospectively evaluated 52 children, aged between 1 month and 4 years, who had undergone head computed tomography with three-dimensional reconstructions. We evaluated the presence or absence of the mendosal suture. If present, then we measured the length of the suture and the angle between the lambdoidal and mendosal suture lines.

RESULTS

The presence of the mendosal suture was bilateral in 12 children and unilateral in 5 children. The mendosal suture had a mean length of 13.9 ± 3.4 mm on the right side and 11.2 ± 4 mm on the left side. The angle between the mendosal and lambdoidal sutures had a mean value of 54.2° ± 11° for the right side and 53.6° ± 13.9° for the left side. The 95 % confidence interval for the mean value of the angle had a lower and upper bounds of 48° and 60° on the right side and 46° and 61° on the left side, respectively.

CONCLUSIONS

The angle between mendosal and lambdoidal suture lines may help radiologists to identify the mendosal suture.

An examination of Nubian and Egyptian biological distances: support for biological diffusion or in situ development?

Many authors have speculated on Nubian biological evolution. Because of the contact Nubians had with other peoples, migration and/or invasion (biological diffusion) were originally thought to be the biological mechanism for skeletal changes in Nubians. Later, a new hypothesis was put forth, the in situ hypothesis. The new hypothesis postulated that Nubians evolved in situ, without much genetic influence from foreign populations. This study examined 12 Egyptian and Nubian groups in an effort to explore the relationship between the two populations and to test the in situ hypothesis. Data from nine cranial nonmetric traits were assessed for an estimate of biological distance, using Mahalanobis D(2) with a tetrachoric matrix. The distance scores were then input into principal coordinates analysis (PCO) to depict the relationships between the two populations. PCO detected 60% of the variation in the first two principal coordinates. A plot of the distance scores revealed only one cluster; the Nubian and Egyptian groups clustered together. The grouping of the Nubians and Egyptians indicates there may have been some sort of gene flow between these groups of Nubians and Egyptians. However, common adaptation to similar environments may also be responsible for this pattern. Although the predominant results in this study appear to support the biological diffusion hypothesis, the in situ hypothesis was not completely negated.

Characterization of biological diversity through analysis of discrete cranial traits

In the present study, the frequency distributions of 20 discrete cranial traits in 70 major human populations from around the world were analyzed. The principal-coordinate and neighbor-joining analyses of Smith's mean measure of divergence (MMD), based on trait frequencies, indicate that 1). the clustering pattern is similar to those based on classic genetic markers, DNA polymorphisms, and craniometrics; 2). significant interregional separation and intraregional diversity are present in Subsaharan Africans; 3). clinal relationships exist among regional groups; 4). intraregional discontinuity exists in some populations inhabiting peripheral or isolated areas. For example, the Ainu are the most distinct outliers of the East Asian populations. These patterns suggest that founder effects, genetic drift, isolation, and population structure are the primary causes of regional variation in discrete cranial traits. Our results are compatible with a single origin for modern humans as well as the multiregional model, similar to the results of Relethford and Harpending ([1994] Am. J. Phys. Anthropol. 95:249-270). The results presented here provide additional measures of the morphological variation and diversification of modern human populations.

Dental variation of Ryukyu islanders: a comparative study among Ryukyu, Ainu, and other Asian populations

The presence or absence of 24 nonmetric dental traits was examined to investigate the inter- and intraregional variation of Ryukyu Islanders. We compared the dentition of the Kadena sample from the central district of Okinawa Island in the Ryukyu Island chain to those of samples from Nakijin from the northern district of the same Okinawa Island, Tokunoshima, another island of the Ryukyu Island chain, main-island Japanese in Kagoshima and Tokyo, Hokkaido Ainu, Atayal in Taiwan, and Pashtuns and Tajiks in Afghanistan. Many traits of the Ryukyu Islanders were found to be close to those of the main-island Japanese; however, several were intermediate between those of the main-island Japanese and the Ainu or Atayal. The intraregional variation in the Ryukyu Islanders was comparable to that in the main-island Japanese. This result supports the influence of a complex gene flow to the Ryukyu Islanders, as suggested by some genetic studies. Among the populations compared here, that closest to the Ainu was the population of Tokunoshima.

Inca bone in forensic autopsy: a report of two cases with a review of the literature

Complete tripartite and complete asymmetric bipartite bones were, respectively, found in the interparietal region of the occipital bone in two forensic autopsy cases that we encountered. These isolated bones are called the Inca bones, or interparietal bones, which occasionally occur as a result of incomplete fusion of the ossifying nuclei during the developmental course. The Inca bones were detectable on ante-mortem cranial radiographs in these two cases. We review the embryological background of this variation, discuss the significance of this variation in forensic medicine, and additionally, present a review of the frequencies of other non-metrical characteristics of the skulls that may be detectable at the time of autopsy.

Frequency variations of discrete cranial traits in major human populations. III. Hyperostotic variations

Seven discrete cranial traits usually categorised as hyperostotic characters, the medial palatine canal, hypoglossal canal bridging, precondylar tubercle, condylus tertius, jugular foramen bridging, auditory exostosis, and mylohyoid bridging were investigated in 81 major human population samples from around the world. Significant asymmetric occurrences of the bilateral traits were detected in the medial palatine canal and jugular foramen bridging in several samples. Significant intertrait associations were found between some pairs of the traits, but not consistently across the large geographical samples. The auditory exostosis showed a predominant occurrence in males. With the exception of the auditory exostosis and mylohyoid bridging in a few samples, significant sex differences were slight. The frequency distributions of the traits (except for the auditory exostosis) showed some interregional clinality and intraregional discontinuity, suggesting that genetic drift could have contributed to the observed pattern of variation.

Frequency variations of discrete cranial traits in major human populations. IV. Vessel and nerve related variations

This concludes a series of descriptive statistical reports on discrete cranial traits in 81 human populations from around the world. Four variants classified as vessel and nerve related characters were investigated: patent condylar canal, supraorbital foramen; accessory infraorbital foramen; and accessory mental foramen. A significant asymmetric occurrence without any side preference was detected for the accessory mental foramen. Significant intertrait associations were found between the accessory infraorbital and supraorbital foramina in the panPacific region and Subsaharan African samples. The intertrait associations between the accessory infraorbital foramen and some traits classified as hypostotic were found mainly in the samples from the western part of the Old World, and those as hyperostotic traits in the samples from eastern Asian and the related population samples. With a few exceptions. the occurrence of a patent condylar canal and a supraorbital foramen was predominant in females, but the accessory infraorbital and accessory mental foramina were predominant in males. The frequency distributions of the traits showed interregional clinality and intraregional discontinuity. A temporal trend was found in the Northeast Asian region in the frequencies of the accessory infraorbital and accessory mental foramina. The diversity of modern human discrete cranial traits may at least in part be attributable to differential retention or intensification from an ancestral pattern.