Postcranial Measurements Research Articles

Testing the accuracy of the SexEst software for sex estimation in a modern Greek sample

AbstractSex estimation from human skeletal remains is fundamental in osteoarcheology and forensic anthropology. The increasing availability of reference skeletal collections across the world has allowed the development of morphological and metric methods for skeletal sex estimation, some of which may be implemented in specialized computer software. The present study aims to evaluate the freely available SexEst software, which utilizes cranial and postcranial measurements, and different classification models for sex estimation, on a contemporary Greek population comprising of 227 (126 males and 101 females) adult individuals. After the calculation of intra‐observer error to assess the repeatability of the measurements, the proposed variables were tested for classification accuracy individually and in different combinations. Based on the results, the postcranial models outperformed the cranial ones in all cases and can be adequately applied on a Greek population sample. The light gradient boosting (LGB) algorithm yielded the highest correct classification rates when no missing values exist, while the linear discriminant analysis (LDA) models should only be used when dealing with missing data. The highest classification accuracy for a 0.65 posterior probability threshold was reached when utilizing a combination of postcranial variables (89.67%), while the lowest was achieved with the cranial measurement “Glabella‐occipital length” (45.00%). The same models yielded the highest and lowest accuracy for a 0.5 probability threshold, with values of 92.96% and 67.73%, respectively. Combining variables yielded higher accuracies in both skeletal regions, suggesting that the software would be more helpful in cases of intact skeletons. The loss of classification accuracy due to population specificity further corroborates the need to include different ancestries in sex estimation software.

The postmortem fate of osteometric measurements: taphonomic alteration of landmarks and its implication for biological profiling

The aim of this research was to identify the measurements that are most frequently retrieved from buried skeletal remains to create the most applicable discriminant functions for osteometric assessments. The study sample was composed of 644 adult skeletons from IV-III BC Italy (Pontecagnano). All burials were in the supine position and individuals were buried either directly in the ground or in large stone coffins. The burial context did not present any environmental conditions that could have a detrimental effect on bonepreservation either in general or differentially between anatomical regions. Due to its complexity, the skull was divided in different regions (two macro areas and five regions, plus the mandible), while the long bones and scapula were examined as anatomical units. The results show that cranial measurements cannot be reliably used for anthropological analyses, as main landmarks are frequently affected by taphonomic factors. Given the higher frequency of their preservation, postcranial measurements are more appropriate for the creation of usable discriminant functions for the construction of biological profiles.

Predicting body mass in Ruminantia using postcranial measurements.

Size plays an important role in mammalian ecology. Accurate prediction of body mass is therefore critical for inferring aspects of ecology in extinct mammals. The unique digestive physiology of extant ruminant artiodactyls, in particular, is suggested to place constraints on their body mass depending on the type of food resources available. Therefore, reliable body mass estimates could provide insight into the habitat preferences of extinct ruminants. While most regression equations proposed thus far have used craniodental predictors, which for ungulates may produce misleading estimates based on indirect relationships between tooth dimensions and size, postcranial bones support the body and may be more accurate predictors of body mass. Here, I use phylogenetically informed bivariate and multiple regression techniques to establish predictive equations for body mass in 101 species of extant ruminant artiodactyls based on 56 postcranial measurements. Within limb elements, stepwise multiple regression models were typically preferred, though bivariate models often received comparable support based on Akaike's information criterion scores. The globally preferred model for predicting mass is a model including both proximal and distal width of the humerus, though several models from the radioulna received comparable support. In general, widths of long bones were good predictors, while lengths and midshaft circumferences were not. Finally, I show that where the best elements for prediction are unavailable for fossil taxa, selection of the model with lowest percent prediction error for the lowest level clade to which the fossil can be assigned could be a productive and novel way forward for predicting mass and subsequently aspects of ecology in fossil mammals.

Evaluating growth in Macrospondylus bollensis (Crocodylomorpha, Teleosauroidea) in the Toarcian Posidonia Shale, Germany

AbstractThe study of how organisms grow is a fundamental aspect of palaeontology. Growth in teleosauroids is poorly understood and little studied, especially in an ontogenetic sense. We investigate growth rates of the most common and abundant teleosauroid, Macrospondylus bollensis, in which a large sample of multiple body sizes is available from the Posidonienschiefer Formation (Posidonia Shale) of southwestern Germany. We perform linear regression analyses on 62 specimens of Macrospondylus (16 juveniles, 7 subadults and 39 adults) using 21 cranial and postcranial measurements. Our results show that juvenile, subadult and adult individuals have near‐isometric or isometric growth throughout much of the body. Notably, we find that in Macrospondylus: (1) the femur grows at a faster rate than the skull and hindlimb zeugopodium; (2) the forelimb and hindlimb grow at the same rate; and (3) there is distinct ontogenetic signal in the growth of the orbit and supratemporal fenestra. We also find that limb scaling in Macrospondylus is somewhat comparable to that seen in the extant gavialids Gavialis gangeticus and Tomistoma schlegelii. Last, we examine evolutionary allometry in skull length relative to body size in Crocodylomorpha using femoral length as a proxy, which shows a near‐isometric trend. Non‐thalattosuchian crocodylomorphs (with the exception of one pholidosaurid and one dryosaurid taxon) are differentiated from thalattosuchians due to their shorter skulls, as previously suggested, but the scaling relationship with femur length remains unchanged.

SexEst: An open access web application for metric skeletal sex estimation

AbstractSkeletal sex estimation is an essential step in any osteoarcheological study; hence, several metric and morphological methods have been developed for this purpose, employing different skeletal elements. This paper has a dual purpose: (1) test the performance of several machine learning classification models for skeletal sex estimation using worldwide samples of cranial and postcranial measurements and (2) present a free web application for the implementation of the models that exhibit the highest accuracy so that the sex of unknown skeletons can be straightforwardly estimated. Regarding the first objective, using the Goldman database of postcranial metrics and the William W. Howells craniometric database, machine learning classification models were constructed for sex prediction. The models were optimized with respect to their hyperparameters and cross‐validated reaching accuracies ranging from 80.8%–89.5% for the postcranial data and 81.2%–87.7% for the cranial data. The models offering the highest rates of correct sex classification (Extreme Gradient Boosting, Light Gradient Boosting, and Linear Discriminant Analysis) were then selected to construct an open access and open source web application, SexEst, for predicting the sex of unknown skeletons.

The case of hip dysplasia of an adult from the Roman Period site of Velebit (Serbia)

Objective: This study is designed to reveal the diagnosis of a rare hip condition with an estimation of the possible cause of death. Materials: Archaeological site of Velebit dated between the 3rd and 4th century AD is located in northern Serbia. Grave No 24 differs from others in the unusual position of the skeletal remains in situ. Methods: The bioanthropological analyses included an estimation of skeletal preservation, cranial and postcranial skeletal measurements, estimation of sex and age at the moment of death, dental analysis and a paleopathological examination. This skeleton was analysed for signs of bone disease, using diagnostic paleopathological procedures comprising gross examination and CT scanning. Results: The results revealed that the analysed male individual was 40 to 55 years of age. The bioanthropological analyses showed two deformities of the pelvic bones, each on the outer surface, located posteriorly and superiorly of the acetabular area. The observed lesions were characterised as type 4 of developmental dysplasia of the hip. In addition, a sharp lesion was observed in the right posterior region of squama of the occipital bone. Conclusions: Our results clearly suggest that this individual had been suffering from hip dysplasia. The possible cause of death could be the observed head lesion. In addition, there is no skeletal conformation of unfavourable living conditions related to physiological stress and diet.

Cephalic Index of Adult Igbo’s in Imo State, Nigeria

Cephalic index is of great importance to anatomists, anthropologists and even to forensic scientists, in the determination of head shapes and for medicolegal cases. Cranial and post cranial measurements have typically been used to describe individuals and to compare groups. This study aims at obtaining the Cranial indices of adults Igbos in Imo state, which will help build the forensic database and in identification of age, gender, racial differences in recent and ancient humans, and in the diagnoses of certain developmental disorders of the skull, such as Craniosynostosis, Hydrocephalus, and Postural deformation. Also to correlate the results of males with that of females. One thousand, One hundred and fifty eight (1158) subjects comprising of five hundred and seventy nine (579) males and females respectively, ages 18-52 years. The measurements were done manually with the use of transparent graded ruler, measuring tapes, gliding and sliding calipers or flexible tapes. The following parameters were measured; cranial length, cranial breadth, since Cephalic Index=Cranial breadth/cranial length x 100. The mean cranial length and breadth were 172±92.89 and 160.46±27.65 respectively. The result for males Cranial Length (CL), Cranial Breadth (CB), were respectively 173.93±18.75, 161.05±17.21. The result for females Cranial Length (CL), Cranial Breadth (CB), were respectively; 171.76±30.06, 159.88±35.11. These results were used to calculate the various Cephalic Index; mean Cephalic Index (CI) was 97.26±21.55. The males Cephalic Index (CI) was100.23±26.23, and female Cephalic Index (CI) was 94.29±14.94, Analysis of the results was done using independent t-test and Pearson bivariate correlation. These tests were carried out using Statistical Package for Social Sciences (SPSS version 25). Microsoft office excel was also used during data processing. Analysis showed that there was a significant difference in the mean values of females and males. The result from this study shows that Adults in Imo state are Brachycephalic. This study is a great contribution to the forensic, anthropology, anatomical and medical database.

Sex estimation from knee breadth dimensions in a Finnish population.

Sex estimation is an important part of osteological analysis of skeletons and forensic identification process. Traditionally cranial and pelvic traits are utilized for accurate sex estimation. However, post-cranial measurements have also been proven to accurately estimate sex especially from robust bones such as the femur. In this study, we investigated the potential of knee breadth dimensions in sex estimation in a Finnish population. To conduct this study we utilized a study sample (n=1654) belonging to the Northern Finland Birth Cohort 1966. All individuals were 46years of age at the time of the examination. Three knee breadth dimensions were measured from subjects' knee posteroanterior radiographs: femoral biepicondylar breadth (FBEB), mediolateral breadth of the femoral condyles (FCML), and mediolateral breadth of the tibial plateau (TPML). Sex estimation was performed using logistic regression. The study clearly demonstrated that all three measurements were different between males and females. Sectioning points for individual knee breadth measurements were 82.9mm for FBEB, 76.6mm for FCML and 75.4mm for TPML. The classification rates ranged from 90.9% to 93.6%. The less commonly used measurements of FCML and TPML showed higher accuracy than FBEB in sex estimation. Our study confirmed that knee breadths can be successfully utilized to improve sex estimation in cases where the skeleton is only partially preserved and other major components of sex estimation are absent. We can also provide new standards for sex estimation from the knee joint in a Finnish population.

Adjusting posterior probabilities to meet predefined accuracy criteria: A proposal for a novel approach to osteometric sex estimation

The osteometric methods are the most reliable way to estimate the sex of skeletons when DNA analysis is not used. However, as osteometric studies usually ignore the overlap in male and female skeletal dimensions, they rarely achieve accuracy sufficient for forensic application. To resolve this issue, recent studies suggest sex estimation only when posterior probability (pp) is greater than 0.95, but that approach does not always provide sufficient accuracy and creates a large proportion of unsexed skeleton. Thus, our study aimed to explore whether it is possible to adjust pp on skeletal measurements with pronounced sexual dimorphism to meet 95% accuracy and to enable sex estimation on a reasonable proportion of individuals. From 207 skeletons, we included 65 postcranial measurements and selected 10% of variables with the highest sexual dimorphism. We computed univariate and bivariate discriminant functions using pp threshold of 0.5, 0.95, and the threshold required to achieve accuracy of ≥ 95%. Discriminant functions with pp=0.5 obtained accuracy of 85%–93%, while those with pp≥0.95 and adjusted posterior probabilities obtained 94%–99%. However, we showed that by selecting a particular threshold, sex could be estimated on a greater proportion of individuals than for pp≥0.95: 42%–86% vs. 24%–62% for univariate and 69%–95% vs. 49%–78% for bivariate functions. Therefore, when developing sex estimation models, we suggest not to use fixed pp level, but to adjust pp to achieve 95% accuracy and to minimize the percentage of unsexed skeletons.

Metsamor in Armenia: the sixth season of fieldwork in 2018

Archaeological exploration of the eastern part of the settlement in Metsamor in 2018 uncovered several rectangular structures. Most of these structures were dated to the early Iron Ages I and II. Roman-period graves were recorded in the ruins of the Iron Age settlement. An anthropological assessment of human remains from three of the burials (sex, age, cranial and postcranial measurements as well as the selected paleopathologies) is presented in the appendix.

Comparative functional skeletal morphology among three genera of shrews: implications for the evolution of locomotor behavior in the Soricinae (Eulipotyphla: Soricidae)

AbstractThe clade comprising the soricid tribes Blarinellini (Blarinella) and Blarinini (Blarina and Cryptotis) is notable within the Soricidae (Eulipotyphla) for the large proportion of reportedly semifossorial species. To better define locomotor modes among species in these two tribes, we quantified purported locomotor adaptations by calculating 23 functional indices from postcranial measurements obtained from museum specimens of Blarina and Blarinella and published measurements for 16 species of Cryptotis. We then analyzed relative ambulatory–fossorial function of each species using principal component analyses and mean percentile rank (MPR) analysis of the indices. Species within the Blarinellini–Blarinini clade exhibit a graded series of morphologies with four primary functional groupings that we classified as “ambulatory,” “intermediate,” “semifossorial,” and “fossorial.” To obtain a preliminary overview of evolution of locomotor modes in this group, we mapped MPRs on a composite phylogeny and examined the resulting patterns. That analysis revealed that the most recent common ancestor of the Blarinellini–Blarinini clade most likely had an intermediate or semifossorial locomotor morphology. Individual subclades subsequently evolved either more ambulatory or more fossorial morphologies. Hence, evolution of locomotor traits within this clade is complex. Multiple shifts in locomotor mode likely occurred, and no single directional tendency is apparent either among the major modes or in levels of complexity.

Sex Estimation from Postcranial Measurements in Filipino Mortuary Remains

Filipino populations are under-studied in the field of forensic anthropology. The development of population-specific analyses for those of Filipino descent is critical in an increasingly globalized world with a growing diaspora of Filipino individuals. The objectives of this study are to broaden our knowledge of sexual dimorphism and to contribute to standard forensic methods.The sample consisted of 39 adult individuals (25 males and 14 females) of Filipino ancestry from the Manila North Cemetery in Manila, Philippines. Using this sample, discriminant function models for sex estimation that generated the highest separation power were generated. These models were cross-validated using a .632+ bootstrap method with 1,000 iterations. Humeral head diameter and anterior-posterior diameter of the radius produced the highest accuracy (>99%) for sex discrimination. Multivariate models were shown to be more powerful than univariate models. The results are discussed in the context of inter-population differences in sexual dimorphism.

Cranial and Postcranial Metric Sex Estimation in Modern Thai and Ancient Native American Individuals

Historically, morphometric standards used in forensic anthropology and bioarchaeology were derived from individuals of African and European descent, along with ancient Native Americans. However, it is unlikely that these standards can be accurately applied to modern Asian populations, and they may introduce error into biological profiles. Due to different population histories, it is hypothesized that ancient Native American and modern Thai individuals are morphometrically distinct. This study investigates the differences in sexual dimorphism between 102 Native American adults and 100 Thai individuals, 17 to 96 years old. A total of 30 cranial, 8 mandibular, and 58 postcranial measurements were compared between the two groups. Using independent t-tests, MANOVAs, univariate sectioning points, and linear discriminant functions, the Native American and Thai samples were found to be significantly different in the expression of sexual dimorphism for many elements. Further, measurements tested in Spradley and Jantz’s (2011) American Black and American White discriminant function equations produce correct classification biases of –91.0–100.0% and often fail to correctly classify Native American and Thai individuals. Therefore, the metric sex estimation methods developed on non-Asian populations do not adequately classify Native American and Thai individuals, thereby underscoring the importance of population-specific equations. The population-specific statistics developed for the Native Americans correctly classify 48.1–93.8% (univariate) and 70.8–94.1% (multivariate) of individuals, while those developed for the Thai correctly classify 47.8–93.0% (univariate) and 63.2–100.0% (multivariate). The most discriminating elements are population dependent: the humerus, clavicle, and tibia work best for Native Americans, while the os coxa, ulna, and scapula perform best for Thai individuals.

Body mass estimates of the earliest possible hominins and implications for the last common ancestor

Many hypotheses regarding the paleobiology of the earliest possible hominins, Orrorin tugenensis and Ardipithecus ramidus, are dependent upon accurate body mass estimates for these taxa. While we have previously published body mass predictions for Orrorin and Ardipithecus, the accuracies of those estimates depend on the assumption that the postcranial skeletal dimensions and body masses of these taxa followed scaling patterns that were similar to those observed in modern humans. This assumption may not be correct because certain aspects of postcranial morphology in Orrorin and Ardipithecus differ from modern humans, and suggest that their overall body plans might be unique but more similar to modern non-human great apes than to modern humans. Here we present individual body mass predictions for O. tugenensis and Ar. ramidus assuming that they followed postcranial scaling patterns similar to those of chimpanzees. All estimates include individual prediction intervals as measures of uncertainty. In addition, we provide equations for predicting body mass from univariate postcranial measurements based on the largest sample (n = 25) yet compiled of common chimpanzee skeletons with known body masses, which is vital for calculating prediction intervals for individual fossils. Our results show that estimated body masses in Orrorin and Ardipithecus are generally larger when derived from a chimpanzee-like scaling pattern compared to estimates that assume a human-like pattern, though the prediction intervals of the two sets of estimates overlap. In addition, the more complete of the two known Orrorin femora has an overall scaling pattern that is more similar to common chimpanzees than to modern humans, supporting the application of a non-human great ape comparative model. Our new estimates fall near the male (Ardipithecus) average and in between the male and female averages (Orrorin) for wild-caught common chimpanzees. If a chimpanzee-like pattern of scaling between postcranial dimensions and body mass did exist in these earliest hominins, our results suggest the large body masses found in some early australopiths were already present in taxa near the origins of our lineage, and perhaps also in the Pan-Homo last common ancestor.

The relationship of age, activity, and body size on osteoarthritis in weight-bearing skeletal regions

This study examined the simultaneous impact of multiple underlying factors on OA expression in weight-bearing joints of the vertebrae and lower limb of a modern European skeletal sample (Lisbon and Sassari). OA was evaluated using standard ranked categorical scoring; composite OA scores derived through principal component analysis. Body size was calculated from postcranial measurements; torsional strength (J) of the femoral midshaft was calculated from three-dimensional surface models, size standardized and used as a proxy for activity. A standard multiple regression was applied.In all regions, the linear combination of age, body mass, stature, and J was significantly related to differences in OA. Across all joints, age was the strongest predictor; neither body size, nor activity variables demonstrated a statistical relationship with OA at the lumbar or knee; J demonstrated a negative correlation with pelvic OA.Variation in OA can be explained by age, stature, body mass, and structural adaptation related to habitual use. The negative correlation between femoral torsional strength with OA suggests that long-term, repetitive physical work capacity in childhood may be protective against OA development later in life. The multifactorial aetiology of OA requires incorporating multiple lines of evidence to interpret individual or population health from bone samples.

Sacrifice Horse Remains from Late Bronze-Early Iron Age of South Moldova: A Study of Dental and Limb Bone Morphology

The article describes dental and postcranial remains of ancient domestic horses of various individual ages from the archaeological monuments of Belozerla Culture Novosiolovca-1 and Olanesti (Southern Moldova). Upper cheek teeth of the horses under study are characterized by relatively long and variable in shape protocone. Single preserved metacarpal and metatarsal bones from Novosiolovca-1 are quite elongated and slender, showing a close resemblance to the mean measurement values of horse remains from Late Bronze age and Early Iron Age from Southeast Europe. Phalanxes of the horses from Novosiolovca-1 and Olanesti are comparatively slender and elongated. Generally, the postcranial measurements of the horses under study correspond to the semi-thin legged type with average height in withers (144-136 cm). One of horse individuals from Novosiolovca-1 shows a specific wear of second upper molar caused by a snaffle bit.

Body mass estimation for †Cyonasua (Procyonidae, Carnivora) and related taxa based on postcranial skeleton

Procyonidae were the first northern placental carnivorans that reached the Neotropics. They are represented by two extinct genera: †Cyonasua and †Chapalmalania (late Miocene – early Pleistocene). Postcranial elements are only known for †Cyonasua and related taxa (†Parahyaenodon argentinus and †Tetraprothomo argentinus). To obtain highly reliable allometric equations for body mass estimations of fossil procyonids, we performed least squares regressions (multiple and bivariate lineal models) using 51 postcranial linear measurements. The extant sample included 124 taxa corresponding to nine families of Carnivora, with body mass data from the literature. We obtained about 63 equations from diverse combinations of postcranial measurements; 14 of them were selected using several reliability indexes as criteria. Our results show that body masses calculated for †Cyonasua range between 12.63 and 28.45 kg, †P. argentinus was estimated at 14.41 kg, while †T. argentinus at 25.31 kg. Thus, the body mass of †Cyonasua would have been at least twice as high as the mean of the extant procyonid Procyon cancrivorus. †Cyonasua was probably able to fend off predators and quite capable of climbing slowly on thick-enough branches. Other palaeoecological and palaeobiological inferences are discussed.

Subadult sex estimation from diaphyseal dimensions.

Many studies on subadult sex estimation focus on elements that express sexually dimorphic features in adults. In contrast, diaphyseal dimensions have been shown to display sex-specific differences prior to adolescence. The current study evaluates the use of diaphyseal dimensions in subadult sex estimation. Eighteen postcranial measurements from six long bones were collected on Lodox Statscan radiographic images of 1,310 modern South African children between birth and 12 years of age. Linear (LDA) and flexible discriminant analysis (FDA) and logistic regression were employed with single and multiple variable models with age both included and excluded from the model. Bootstrapped cross-validation was employed because some of the multiple variable subsets had small sample sizes. Each of the bootstrapped accuracies has an associated 95% confidence interval demonstrating the ranges in classification. Classification methods utilizing multiple variables achieved the highest bootstrapped classification accuracies (70% to 93%). The inclusion of age in the models did not consistently increase or decrease the classification accuracies. Proximal and distal breadth measurements were consistently recognized as important measurements in model creation. FDA yielded the highest overall accuracies, but the logistic regression presented with overall smaller bootstrapped 95% confidence intervals. Quantifiable sex differences were discovered in the appendicular skeleton of children between birth and 12 years of age. The high classification accuracies were likely due to using numerous predictor variables from multiple skeletal elements, which were optimized for classification using FDA. To facilitate application, a graphical user interface, KidStats, was developed.

Spatial and temporal variation of body size among early Homo

The estimation of body size among the earliest members of the genus Homo (2.4–1.5Myr [millions of years ago]) is central to interpretations of their biology. It is widely accepted that Homo ergaster possessed increased body size compared with Homo habilis and Homo rudolfensis, and that this may have been a factor involved with the dispersal of Homo out of Africa. The study of taxonomic differences in body size, however, is problematic. Postcranial remains are rarely associated with craniodental fossils, and taxonomic attributions frequently rest upon the size of skeletal elements. Previous body size estimates have been based upon well-preserved specimens with a more reliable species assessment. Since these samples are small (n < 5) and disparate in space and time, little is known about geographical and chronological variation in body size within early Homo.We investigate temporal and spatial variation in body size among fossils of early Homo using a ‘taxon-free’ approach, considering evidence for size variation from isolated and fragmentary postcranial remains (n = 39). To render the size of disparate fossil elements comparable, we derived new regression equations for common parameters of body size from a globally representative sample of hunter-gatherers and applied them to available postcranial measurements from the fossils.The results demonstrate chronological and spatial variation but no simple temporal or geographical trends for the evolution of body size among early Homo. Pronounced body size increases within Africa take place only after hominin populations were established at Dmanisi, suggesting that migrations into Eurasia were not contingent on larger body sizes. The primary evidence for these marked changes among early Homo is based upon material from Koobi Fora after 1.7Myr, indicating regional size variation. The significant body size differences between specimens from Koobi Fora and Olduvai support the cranial evidence for at least two co-existing morphotypes in the Early Pleistocene of eastern Africa.

Evidence for unusual size dimorphism in a fossil ailurid

A second nearly complete skeleton of the fossil ailurid Pristinailurus bristoli was recently recovered from the Hemphillian (late Miocene) Gray Fossil Site of northeast Tennessee. It appears to be significantly larger than the previously known skeleton of P. bristoli, which was surprising as the living red panda Ailurus fulgens is thought to be generally monomorphic, including between sexes. Here the presence of significant size difference in the geometric means of cranial and postcranial measurements and canine area in the two specimens of P. bristoli is tested relative to the distribution of size differences in intersex and intrasex pairs of A. fulgens. The presence of sexual dimorphism in these dimensions is also assessed in A. fulgens using t-tests. We report the first evidence of sexual dimorphism in both upper and lower canine area in A. fulgens. We also found evidence of significantly greater body size difference in the two specimens of P. bristoli than that present in A. fulgens. This could reflect a variety of causes, including the presence of multiple species or subspecies, a greater range of ecologically driven variability, or the presence of sexual dimorphism. We argue tentatively for sexual dimorphism as the most plausible explanation for the apparent size range of P. bristoli. Ethan L. Fulwood. Department of Anthropology, University of Tennessee, Knoxville, Tennessee 37865 USA Current Address: Department of Evolutionary Anthropology, Duke University, Durham, North Carolina 27708 USA ethan.fulwood@duke.edu Steven C. Wallace. Department of Geosciences, Don Sundquist Center of Excellence in Paleontology, East Tennessee State University, Johnson City, Tennessee 37614 USA wallaces@mail.etsu.edu