A review of Theropithecus oswaldi with the proposal of a new subspecies.

Theropithecus oswaldi darti, as currently understood, is the oldest Theropithecus taxon in the fossil record and the earliest subspecies in the Theropithecusoswaldi lineage. Theropithecus oswaldi darti is typified at the site of Makapansgat in South Africa, and a similar form (T. o. cf. darti) is usually recognized at Hadar, Dikika, some Middle Awash localities, and Woranso-Mille in Ethiopia. This taxon is also tentatively believed to occur in Kenya at Kanam and Koobi Fora and in Member C of the Shungura Formation in Ethiopia. While there is a general consensus that the East African 'darti' specimens are sufficiently similar to each other, there has always been a question of whether they are too distinct from the South African type material of T. o. darti to belong to the same subspecies. Here we conduct a morphological comparison of the different samples previously assigned to T. o. darti and T. o. cf. darti. The results of our analyses overwhelmingly support the hypothesis that the East African samples are distinct from the South African ones, and they are likely distinct in geological age as well. Therefore, we propose a new subspecies designation for the material previously termed T. o. cf. darti from East Africa: Theropithecus (Theropithecus) oswaldi ecki subsp. nov. We also formally recognize Theropithecus (Theropithecus) oswaldi serengetensis (Dietrich, 1942) for specimens from Laetoli, Woranso-Mille, and perhaps Galili.

The earliest most complete skeleton of Theropithecus.

The middle Pliocene site of Woranso-Mille in the Afar Region of Ethiopia has yielded numerous significant early hominin fossils representing multiple, coexisting taxa. Here we report on another significant discovery, the oldest partial skeleton of the papionin, Theropithecus. The specimen was recovered from the Aralee Issie collection area over multiple field seasons from 2004 through 2019. The specimen was unearthed in situ from the fluvial facies of the Mesgid Dora Tuff dated to 3.66-3.57 Ma. The partial skeleton, ARI-VP-1/26, is that of a subadult male lacking a skull. In the absence of unambiguously associated craniodental remains, the male status of the specimen was established from the dimensions of the long bones in comparison to those of other Theropithecus from Woranso-Mille. ARI-VP-1/26 is noteworthy because it preserves partial hand and foot skeletons, including a complete set of metacarpals from the left side. The theropith status of ARI-VP-1/26 was established based on the detailed anatomy of the postcranial skeleton, especially the proximal and distal humerus, proximal radius, and proximal femur. The morphology of the postcranium of ARI-VP-1/26 is consistent with that of recognized Theropithecus from Woranso-Mille and, specifically, with specimens recognized as Theropithecus oswaldi cf. darti from other sites. The ratio of the lengths of the first metacarpal to metacarpals 2-5 in ARI-VP-1/26 is intermediate between that seen in extant Papio and Theropithecus. In Theropithecus gelada and Theropithecus brumpti, the pairing of pollical and indical metacarpals of near equal length contributes to the species' high opposability index and is associated with a 'manual grazing' feeding habit. Cercopithecids constitute 43% of the identified vertebrates at Aralee Issie, and T. oswaldi cf. darti is the most common mammalian species. The monkeys of Aralee Issie lived in an open shrubland habitat, but the specific reasons for their high prevalence at the site are unclear.

The anatomy of the hindlimb of Theropithecus brumpti (Cercopithecidae, Papionini): Morphofunctional implications.

Theropithecus brumpti is a primate known from numerous craniodental specimens in the Plio-Pleistocene Shungura Formation (Lower Omo Valley, Ethiopia), but the anatomy of its hindlimb is documented only by a few associated and mostly incomplete postcranial specimens. The adaptations of T. brumpti are still debated, with its substrate preferences and its use of squatting postures recently discussed based on anatomical differences when compared with its extant representative, Theropithecus gelada. Here, we describe an associated femur and tibia (L 869-1 and L 869-2) of a presumed T. brumpti male and a partial foot (L 865-1r and L 865-1t) of a male T. brumpti, dated to ca. 2.6 Ma and ca. 2.32 Ma respectively. Based on univariate and bivariate morphometric analyses, we provide new data on the morphological correlates of substrate preferences and postural behaviors of this fossil species. Our results are in agreement with previous analyses and present T. brumpti as a predominantly terrestrial primate. We demonstrate the presence of osteological correlates associated with the use of squatting behaviors in T. brumpti but also point to significant anatomical differences between this paleontological species and T. gelada. These differences blur the functional value of characters previously identified as diagnostic of T. gelada and its postural behavior. We further document the postcranial distinctiveness of the Theropithecus clade in relation to the Papio clade. This study thus provides new insights into the postcranial anatomy and paleoecology of an abundant fossil primate from the Plio-Pleistocene of eastern Africa.

First record of Theropithecus (Cercopithecidae) from the Republic of Djibouti.

We describe here several specimens of the genus Theropithecus from the southern shore of Lake Assal in the Republic of Djibouti; they are the first record of the genus from this country. We assign them to a derived stage of T. oswaldi. This identification has implications for the age of the informal 'Formation 1' from this area, which should probably be assigned to the Middle Pleistocene. In addition, the presence of T. oswaldi close to the Bab el Mandeb Strait strongly suggests that the species followed this route to India, rather than a more northern one.

Dietary niches of terrestrial cercopithecines from the Plio-Pleistocene Shungura Formation, Ethiopia: evidence from Dental Microwear Texture Analysis.

This study aims to explore the feeding ecology of two terrestrial papionins, Papio and Theropithecus from the Shungura Formation in Ethiopia, the most complete stratigraphic and paleontological record of the African Plio-Pleistocene. Two aspects were evaluated using Dental Microwear Texture Analysis: differences in diet between the extinct genera and their extant relatives, and any potential dietary fluctuations over time. Amongst more than 2,500 cercopithecid dental remains, 154 Theropithecus molars and 60 Papio molars were considered. Thirty-nine extant wild baboons and 20 wild geladas were also considered. The results show that diets of extinct monkeys from Member G already differed between genera as it is the case for their extant representatives. The shearing facets on the Theropithecus molars display significant variations in microwear textures, suggesting several dietary shifts over time. Two events point to higher intakes of herbaceous monocots (tougher than dicots foliages), at about 2.91 Ma (between members B and C) and at 2.32 Ma (between members E and F). These two events are separated by an inverse trend at about 2.53 Ma (between members C and D). Some of these variations, such as between members E and F are supported by the enamel carbon isotopic composition of herbivorous mammals and with paleovegetation evidence.

Morphology, diet, and stable carbon isotopes: On the diet of Theropithecus and some limits of uniformitarianism in paleoecology.

Geladas were long supposed to be the only living primates feeding almost entirely on graminoids and accordingly display dramatic dental and manual adaptive traits. A recent study of Theropithecus gelada, the first in a relatively undisturbed habitat, revealed a more diverse diet, also incorporating large quantities of forbs. The peculiar adaptive traits of T. gelada are also observed in extinct Theropithecus as early as 3.7 Ma. Stable carbon isotopic data of extinct Theropithecus from eastern Africa indicate that specimens older than 3 Ma consumed a significant proportion of C3 plants (on average ca. 40% of total food intake) whereas specimens younger than 2 Ma consumed more C4 plants (on average ca. 80%). Recent paleobotanical evidence suggests that C3 herbaceous plants were still present in non-negligible proportions in Plio-Pleistocene lowland tropical ecosystems. Together, the shared morphological adaptive traits of extant and extinct Theropithecus and the varied diets of extant T. gelada suggest that the paleodiets of Theropithecus may have been dominated by herbaceous plants, comprising both C3 forbs and graminoids and C4 graminoids. The changes in stable carbon isotopes could correspond to a replacement of C3 plants by C4 plants within the herbaceous strata rather than a shift from C3 woody vegetation to C4 graminoids. This synthesis highlights the need for a more exhaustive knowledge of the ecology of extant species to achieve meaningful paleodietary and paleoenvironmental reconstructions. A strong selectivity for food resources that are rare in the landscapes (as in T. gelada) should also be considered when interpreting stable carbon isotopes of extinct African mammals (and notably hominids).

New cranium of the large cercopithecid primate Theropithecus oswaldi leakeyi (Hopwood, 1934) from the paleoanthropological site of Makuyuni, Tanzania.

The Pleistocene hominin site of Makuyuni, near Lake Manyara, Tanzania, is known for fossils attributable to Homo and Acheulean artifacts (Ring et al., 2005; Kaiser et al., 2010; Frost et al., 2012). Here we describe the fossil primate material from the Manyara Beds, which includes the first nearly complete female cranium of Theropithecus oswaldi leakeyi and a proximal tibia from the same taxon. The cranium is dated to between 633 and 780 Ka and the tibia to the Pleistocene. The T. oswaldi lineage is one of the most important among Neogene mammals of Africa: it is both widespread and abundant. The size of the dentition, cranium, and tibia all confirm the previously recognized trend of increasing body size in this lineage and make their taxonomic assignments secure. The morphology of this specimen provides new insights into the evolution of this lineage through time, as well as its geographic variation and sexual dimorphism. The cranium also shows damage consistent with a mammalian carnivore, most likely a felid. The identification of this material as representing T. o. leakeyi agrees with the Middle Pleistocene age estimates for the MK4 locality in particular and the Manyara Beds in general.

Morphoarchitectural variation in South African fossil cercopithecoid endocasts.

Despite the abundance of well-preserved crania and natural endocasts in the South African Plio-Pleistocene cercopithecoid record, which provide direct information relevant to the evolution of their endocranial characteristics, few studies have attempted to characterize patterns of external brain morphology in this highly successful primate Superfamily. The availability of non-destructive penetrating radiation imaging systems, together with recently developed computer-based analytical tools, allow for high resolution virtual imaging and modeling of the endocranial casts and thus disclose new perspectives in comparative paleoneurology. Here, we use X-ray microtomographic-based 3D virtual imaging and quantitative analyses to investigate the endocranial organization of 14 cercopithecoid specimens from the South African sites of Makapansgat, Sterkfontein, Swartkrans, and Taung. We present the first detailed comparative description of the external neuroanatomies that characterize these Plio-Pleistocene primates. Along with reconstruction of endocranial volumes, we combine a semi-automatic technique for extracting the neocortical sulcal pattern together with a landmark-free surface deformation method to investigate topographic differences in morphostructural organization. Besides providing and comparing for the first time endocranial volume estimates of extinct Plio-Pleistocene South African cercopithecoid taxa, we report additional information regarding the variation in the sulcal pattern of Theropithecus oswaldi subspecies, and notably of the central sulcus, and the neuroanatomical condition of the colobine taxon Cercopithecoides williamsi, suggested to be similar for some aspects to the papionin pattern, and discuss potential phylogenetic and taxonomic implications. Further research in virtual paleoneurology, applied to specimens from a wider geographic area, is needed to clarify the polarity, intensity, and timing of cortical surface evolution in cercopithecoid lineages.

Dietary ecology of fossil Theropithecus: Inferences from dental microwear textures of extant geladas from ecologically diverse sites.

As the only extant graminivorous primate, gelada monkeys (Theropithecus gelada) offer unique insights into how hominins and other extinct primates with strong C4 isotopic signatures may have subsisted on graminoid-rich diets. Fossil Theropithecus species sharing a strong C4 signal (i.e., Theropithecus brumpti, Theropithecus darti, and Theropithecus oswaldi) have been reconstructed as predominantly graminivorous and potentially in ecological competition with contemporaneous hominins. However, inferring the breadth and variation of diet in these species (and therefore hominins) has proven problematic. Understanding how ecological variation within extant geladas impacts microwear and isotopic signatures may contribute to reconstructions of diet in fossil Theropithecus. Here, we build on a recent study at an ecologically intact tall grass ecosystem (Guassa, Ethiopia) that expanded the known diversity of gelada diets by demonstrating lower reliance on graminoids, greater consumption of forbs, and greater dietary species richness than previously described at disturbed sites. We used dental microwear texture analysis to explore how dietary variation among extant geladas may inform our understanding of the diets of fossil Theropithecus. First, we compared the dental microwear textures of geladas at Guassa to those of geladas from other sites. The microwear textures of geladas at Guassa exhibited more complexity, less anisotropy, and more variance in anisotropy and heterogeneity, reflecting the greater dietary diversity of Guassa geladas. Comparing microwear texture variables among this expanded gelada sample to those for T. brumpti, T. oswaldi, and T. darti yielded no significant differences. These results raise the intriguing possibility that data on how ecological variation and diet impact dental microwear and (possibly) isotopic signatures in extant geladas can be used to reconstruct the diets of extinct theropiths and, more broadly, hominins with strong C4 isotopic signatures. We conclude that extant gelada populations offer a powerful analog for inferring dietary variation among predominantly graminivorous fossil primates.

New fossil teeth of Theropithecus oswaldi (Cercopithecoidea) from the Early Pleistocene at Cueva Victoria (SE Spain).

The presence of Theropithecus oswaldi in Europe was first reported in 1995 from the Early Pleistocene site of Cueva Victoria (SE Spain), showing the dispersal of this genus above 30° north latitude and into Europe. Later claims of the presence in Italy of Theropithecus in the Early Pleistocene, based on vertebral remains, are controversial. Here we report four additional teeth of T. oswaldi from Cueva Victoria. These and the previously described tooth correspond to a minimum of two individuals. The presence of T. oswaldi in North Africa and SE Iberia during the Early Pleistocene suggests a possible faunal dispersal from Africa into Europe through the Straits of Gibraltar, which would have acted as a filter bridge.

A thorny question: the taxonomic identity of the Pirro Nord cervical vertebrae revisited.

The past geographic distribution of the genus Theropithecus (Primates: Cercopithecidae) is mainly restricted to Africa. Outside that continent, the earliest reported records of this genus consist of a calcaneus of cf. Theropithecus sp. from 'Ubeidiya (Israel, 1.6-1.2 Ma [millions of years ago]), as well as three associated cervical vertebrae from Pirro Nord (Italy, 1.7-1.3 Ma) attributed to Theropithecus sp. The attribution of the Pirro Nord vertebrae to this genus has been disputed on morphometric grounds, although their assignment to a large-bodied cercopithecid has remained undisputed. Here we report unpublished cervical vertebral specimens with a similar morphology and, given their significance for the paleobiogeography of Theropithecus (purportedly representing its earliest European record), we re-evaluate their taxonomic attribution. In particular, we reconsider the possibility that they belong to another non-primate mammal recorded at this site. Based on both qualitative and metric morphological comparisons, we strongly favor an alternative attribution of the cervical vertebrae from Pirro Nord to the large porcupine Hystrix refossa, which is widely documented at the site by both dentognathic and other postcranial remains. We therefore conclude that the dispersal of Theropithecus out of Africa before ca. 1 Ma (when it is recorded by dental remains from Cueva Victoria, Spain) is currently based only on the calcaneus from 'Ubeidiya tentatively attributed to this genus.

Early Pliocene Cercopithecidae from Woranso-Mille (Central Afar, Ethiopia) and the origins of the Theropithecus oswaldi lineage.

A large series of fossil cercopithecids has been recovered from the hominid-bearing Woranso-Mille site, Afar State, northeastern Ethiopia. Here we report the taxonomy of those specimens from the Am-Ado, Aralee Issie, Korsi Dora, Makah Mera, and Mesgid Dora collection areas, which are all roughly contemporaneous and dated to between 3.6 and 3.8 million years ago. This series includes a minimum of two cercopithecine and three colobine species. Theropithecus oswaldi cf. darti is by far the most common species in the assemblage, making up over 90% of identifiable cercopithecid specimens. There is also at least one other species of papionin, which cannot be currently assigned to a genus. The colobines are here allocated to Cercopithecoides cf. meaveae and two other species, one small and one large, that cannot be currently assigned to genus. The T. oswaldi cf. darti series from Woranso-Mille is both the earliest and largest identified to date. It documents the earliest occurrence of the T. oswaldi lineage and strongly suggests that parallel evolution of molar morphology has occurred within the genus between T. oswaldi and Theropithecus brumpti. Given the dominance of monkeys at Woranso-Mille, and the preponderance of Theropithecus among cercopithecids, T. o. cf. darti is likely to be the most common mammal present at the 3.6-3.8 million-years-old localities of the Woranso-Mille study area. Some explanations for this unusual occurrence are explored, and implications for the paleoenvironment at Woranso-Mille are also discussed.

Regression and simulation models for human and baboon brain parameters / Modelo regresivo y simulación para los parámetros cerebrales humanos y del babuino

The variations in morphometric parameter of mammalian brains may be influenced by process of functional complexity, evolution and adaptation. Comparative analysis of linear measurements of cerebrum in the human and baboon has shown morphometric differences. In the present study linear measurements from human and baboon cerebrum (n=10 each) were used to predict various values for human and baboon brain and body parameters through multiple regression models. The average brain weights were found to be 2.08 percent and 0.84 percent of the body weights for humans and baboons respectively. The elasticity of regression models revealed that unit percentage increase in Occipital-Frontal (OF) distance would increase the human brain weight by 66.19 percent, while the baboon brain weight would increase by 7.63 percent. The unit percentage increase in the Height of Temporal Lobe (HTL) would increase the human brain weight by 16.28 percent, while the baboon brain weight would increase by only 0.28 percent. Unit percentage increase in Frontal-Temporal (FT) distance would decrease the human and baboon brain weights by 14.04 percent and 0.46 percent respectively. Inter-species values were also predicted through simulation techniques by using the ratios of model parameters with application of programming language Python. The OF, FT and HTL values for human were found to be 2.01 times, 1.55 times and 1.91 times respectively to that of baboon.

Las variaciones en los parámetros morfométricos del cerebro de los mamíferos pueden estar influenciadas por el proceso de complejidad funcional de la evolución y adaptación. Análisis comparativo de las mediciones lineales del cerebro en el humano y babuino han puesto de manifiesto las diferencias morfométricas. En este estudio las mediciones lineales del cerebro humano y babuinos (n = 10 cada uno) fueron utilizados para predecir los valores distintivos para el cerebro de humanos y monos babuinos y los parámetros del cuerpo a través de modelos de regresión múltiple. El peso medio del cerebro resultó ser 2,08 por ciento y 0,84 por ciento del peso corporal de los seres humanos y los babuinos, respectivamente. La elasticidad de los modelos de regresión reveló que el aumento de una unidad porcentual en la distancia occipital-frontal (DE) aumentaría el peso del cerebro humano en 66,19 por ciento, mientras que el peso del cerebro babuino se incrementaría en 7,63 por ciento. El porcentaje de aumento en la altura de lóbulo temporal (HTL) aumentaría el peso del cerebro humano en 16,28 por ciento, mientras que el peso del cerebro babuino aumentaría en sólo el 0,28 por ciento. Si aumenta la distancia frontal-temporal (FT) se reduciría el peso del cerebro humano y babuinos en 14,04 por ciento y 0,46 por ciento, respectivamente. También se prevéen valores entre las especies a través de técnicas de simulación, mediante el uso de proporciones de los parámetros del modelo con la aplicación del lenguaje de programación Python. Los valores humanos de DE, FT y HTL resultaron ser 2,01, 1,55 y 1,91 veces, respectivamente con respecto a la de los babuinos.

Morphological and physiological aspects of digestive processes in the graminivorous primate Theropithecus gelada-a preliminary study.

Hindgut fermentation has been suggested to contribute significantly to the digestive process in the gelada (Theropithecus gelada). We therefore hypothesized that in an in vitro fermentation test (Hohenheim gas test, using gas production as measure of microbial digestion) inoculum based on fresh gelada feces would degrade grass to a similar degree as zebra (Equus burchelli chapmani) feces and to a higher degree than that of hamadryas baboons (Papio hamadryas). Additionally, morphology of gelada tongue, salivary glands, stomach, and intestine were examined in this study. Gas production was measured between 4 and 96 hr using animal feces incubated with 200 mg of air-dry hay or mixed concentrate sample. For grass hay, 12-hr gas production was as follows: T. gelada (19.9 ml)>Papio (18.4 ml)>Equus (15.7 ml). After 24 hr, gas production changed: Papio (35.1 ml)>T. gelada (31.9 ml)>Equus (27.9 ml). At 96 hr, Papio was unexpectedly the most effective species with the highest gas production (53.1 ml)>zebra (51.2 ml)>gelada (49.4 ml). With a concentrate standard, 12-hr gas production was as follows: T. gelada (38.5 ml)>Equus (36.8 ml) = Papio (36.4 ml). At 24 hr, gas production differed: Papio (51.7 ml)>Equus (47.0 ml) = T. gelada (46.8 ml). At 96 hr, zebra was the most effective species with the highest gas production (63.9 ml)>Papio (60 ml) = T. gelada (59.9 ml). In conclusion, the results show that the microbial population present in gelada feces is able to ferment forage and concentrate substrates in vitro, although this fermentation did not occur with the expected effectiveness. Future studies should therefore focus also on the bacteria species involved.

Morphometric variation in the papionin muzzle and the biochronology of the South African Plio-Pleistocene karst cave deposits.

Papionin monkeys are widespread, relatively common members of Plio-Pleistocene faunal assemblages across Africa. For these reasons, papionin taxa have been used as biochronological indicators by which to infer the ages of the South African karst cave deposits. A recent morphometric study of South African fossil papionin muzzle shape concluded that its variation attests to a substantial and greater time depth for these sites than is generally estimated. This inference is significant, because accurate dating of the South African cave sites is critical to our knowledge of hominin evolution and mammalian biogeographic history. We here report the results of a comparative analysis of extant papionin monkeys by which variability of the South African fossil papionins may be assessed. The muzzles of 106 specimens representing six extant papionin genera were digitized and interlandmark distances were calculated. Results demonstrate that the overall amount of morphological variation present within the fossil assemblage fits comfortably within the range exhibited by the extant sample. We also performed a statistical experiment to assess the limitations imposed by small sample sizes, such as typically encountered in the fossil record. Results suggest that 15 specimens are sufficient to accurately represent the population mean for a given phenotype, but small sample sizes are insufficient to permit the accurate estimation of the population standard deviation, variance, and range. The suggestion that the muzzle morphology of fossil papionins attests to a considerable and previously unrecognized temporal depth of the South African karst cave sites is unwarranted.

The presence of a large cercopithecine (cf. Theropithecus sp.) in the 'Ubeidiya formation (Early Pleistocene, Israel).

This study presents the discovery of a right cercopithecine calcaneus from the site of 'Ubeidiya, Israel, dated to ca. 1.6 Ma. The fossil is described and statistically compared to bones of modern and fossil cercopithecids. The specimen can be attributed to a large-bodied cercopithecine and represents a new primate taxon previously unidentified in the Early Pleistocene of the Southern Levant. Among extant genera, it is most clearly similar to calcanei of Theropithecus. However, it could also represent Paradolichopithecus, but this alternative is unlikely due to the morphological uniqueness of the latter taxon. The finding of an African taxon in the Levant suggests a circum-Mediterranean dispersal route for the taxon out of Africa, and emphasizes the importance of the Levantine corridor as a biogeographic dispersal route between Africa and Eurasia during the Early Pleistocene. Evidence for the biogeography of large-bodied primates is essential for the understanding of the dispersal routes of "Out of Africa I" taxa and can help elucidate Homo dispersal patterns in the Early Pleistocene.

Cercopithecoid cervical vertebral morphology and implications for the presence of Theropithecus in early Pleistocene Europe.

While it is recognized that the overall configuration of the vertebral column, as well as the size and shape of individual vertebrae, differ within and between primate taxa, relatively little is known about the degree to which vertebral morphology reflects a phylogenetic signal or the degree to which vertebral elements can be used in accurate taxonomic classification. Isolated vertebrae are occasionally found in fossil assemblages, and proper taxonomic identification is necessary to make inferences about the animal's biology and place it in a broader phylogenetic and evolutionary context. Recently, three large primate cervical vertebrae (C3, C5, and C6) from Pirro Nord, Italy (early Pleistocene, late Villafranchian) were attributed to the genus Theropithecus based on size comparisons with extant cercopithecoid primates (Rook et al., 2004, J. Hum. Evol. 47, 267-277). These fossils were suggested to indicate an early dispersal of this genus out of Africa around 1.6-1.3 Ma possibly co-incident with early Pleistocene dispersals of Homo. Because of the potential importance of these fossils for interpreting Theropithecus evolution and the relatively few morphological data on primate cervical vertebral morphology, we examined the size and shape of cervical vertebrae in a large sample of extant cercopithecoid taxa (n=106). Specifically, we evaluated whether subfamily and genus level assignments can be made on the basis of isolated cervical elements. Discriminant analyses reveal that scaled shape variables are good discriminators of taxonomic affinity at the subfamily level but are poor discriminators at the genus level. Least-squares regressions show that raw linear dimensions of cervical vertebral morphology are good predictors of body mass in the extant sample. Our regression results produce a likely body mass estimate of 22-38 kg for the Pirro Nord cervical vertebrae. Based on these regression estimates, the poor ability to discriminate cervical vertebrae at the genus level, and paleoenvironmental reconstructions of Pirro Nord, it is unlikely that the Pirro Nord fossils can be confidently attributed to the genus Theropithecus. These findings have important implications for recent interpretations of the nature of Theropithecus dispersal out of Africa.

Cranial allometry, phylogeography, and systematics of large-bodied papionins (primates: Cercopithecinae) inferred from geometric morphometric analysis of landmark data.

The cranial morphology of the African Old World monkeys Mandrillus, Papio, and Theropithecus (i.e., baboons) has been the subject of a number of studies investigating their systematic relationships, patterns of scaling, and growth. In this study, we use landmark-based geometric morphometrics and multivariate analysis to assess the effects of size, sex, taxonomy, and geographic location on cranial shape. Forty-five landmarks were digitized in three dimensions on 452 baboon crania and subjected to generalized Procrustes analysis (GPA), which standardizes geometric size but leaves scaling-based shape differences in the data. The resulting shape coordinates were submitted to regression analysis, principal components analysis (PCA), partial least-squares (PLS) analysis, and various clustering techniques. Scaling (shape differences correlated with size) was the largest single factor explaining cranial shape variation. For instance, most (but not all) of the shape differences between the sexes were explained by size dimorphism. However, central tendencies of shape clearly varied by taxon (both specific and subspecific) even after variations in size and sex were adjusted out. Within Papio, about 60% of the size- and sex-adjusted shape variations were explained by the geographic coordinates of the specimen's provenance, revealing a stepped cline in cranial morphology, with the greatest separation between northern and southern populations. Based on evidence from genetic studies, and the presence of at least two major hybrid/interbreeding zones, we interpret the phylogeographic pattern of cranial variation as indicating that these populations are best ranked as subspecies of a single species, rather than as two or more distinct biological species. This objective approach can be applied to other vertebrate species or species groups to help determine the taxonomic rank of problematic taxa.