Terrence Ritzman

New hominin remains from Uzbekistan

Although the Paleolithic occupations of Uzbekistan and the neighboring foothill regions of Tajikistan and Kazakhstan are well-documented, almost no hominin fossil material has been discovered in the area since Teshik-Tash 1 in 1938. Here we describe and offer a preliminary comparative framework for hominin remains that were recovered in 2003 from two Middle Paleolithic sites in Uzbekistan, Obi-Rakhmat Grotto and Anghilak Cave. The description of Teshik-Tash as a Neandertal and the preponderance of lithic assemblages identified as Mousterian in character has supported the interpretation of the region as the eastern-most extent of the Neandertal range. The material from Obi-Rakhmat (OR-1), a subadult represented by part of a permanent maxillary dentition and a fragmentary cranium, expresses a relatively Neandertal-like dentition coupled with more ambiguous cranial anatomy. The remains from Anghilak Cave include a non-diagnostic, diminutive right fifth metatarsal (AH-1). These findings are important additions to the Central Asia hominin fossil record.

The Gross Anatomy of the Original and Regenerated Tail in the Green Anole (Anolis carolinensis)

This study investigates the gross anatomy of the original and the regenerated tail in the green anole (Anolis carolinensis). Dissections were conducted on 24 original and 13 regenerated tails. While the extrinsic muscles of the original tail in A. carolinensis are similar to those in other known Anolis lizard species, the extent of the origins of m. caudofemoralis longus and m. caudofemoralis brevis is more restricted. These differences may underlie variation in locomotor performance among anole ecomorphs. The intrinsic muscles of the original tail are also described, confirming previous findings and documenting new details, including muscle origins and insertions and the range of intraspecific variation. A comparison of the intrinsic muscles of the original tail and the regenerated tail muscles reveals key differences, such as the lack of interdigitating muscle segments and intramuscular septa in the regenerated tail. These findings, along with the replacement of interlocking vertebrae with a stiff, cartilaginous rod, suggest that important functional differences exist between the original and regenerated tail. In particular, the regenerated tail is predicted to be less capable of coordinated, fine movements. Studies of the physical properties and range of motion of the original and regenerated tail are required to test this hypothesis. This atlas of tail anatomy in A. carolinensis represents a key resource for developmental and genetic studies of tail regeneration in lizards, as well as studies of anole evolution and biomechanics. Anat Rec,, 2012.

A 3-D geometric morphometric study of intraspecific variation in the ontogeny of the temporal bone in modern Homo sapiens

This study addresses how the human temporal bone develops the population-specific pattern of morphology observed among adults and at what point in ontogeny those patterns arise. Three-dimensional temporal bone shape was captured using 15 landmarks on ontogenetic series of specimens from seven modern human populations. Discriminant function analysis revealed that population-specific temporal bone morphology is evident early in ontogeny, with significant shape differences among many human populations apparent prior to the eruption of the first molar. As early as five years of age, temporal bone shape reflects population history and can be used to reliably sort populations, although those in closer geographic proximity and molecular affinity are more likely to be misclassified. The deviation of cold-adapted populations from this general pattern of congruence between temporal bone morphology and genetic distances, identified in previous work, was confirmed here in adult and subadult specimens, and was revealed to occur earlier in ontogeny than previously recognized. Significant differences exist between the ontogenetic trajectories of some pairs of populations, but not among others, and the angles of these trajectories do not reflect genetic relationships or final adult temporal bone size. Significant intrapopulation differences are evident early in ontogeny, with differences becoming amplified by divergent trajectories in some groups. These findings elucidate how the congruence between adult human temporal bone morphology and population history develops, and reveal that this pattern corresponds closely to that described previously for facial ontogeny.

Is Central Asia the Eastern Outpost of the Neandertal Range? A Reassessment of the Teshik-Tash Child

Since its discovery in southeastern Uzbekistan in 1938, the Teshik-Tash child has been considered a Neandertal. Its affinity is important to studies of Late Pleistocene hominin growth and development as well as interpretations of the Central Asian Middle Paleolithic and the geographic distribution of Neandertals. A close examination of the original Russian monograph reveals the incompleteness of key morphologies associated with the cranial base and face and problems with the reconstruction of the Teshik-Tash cranium, making its Neandertal attribution less certain than previously assumed. This study reassesses the Neandertal status of Teshik-Tash 1 by comparing it to a sample of Neandertal, Middle and Upper Paleolithic modern humans, and recent human sub-adults. Separate examinations of the cranium and mandible are conducted using multinomial logistic regression and discriminant function analysis to assess group membership. Results of the cranial analysis group Teshik-Tash with Upper Paleolithic modern humans when variables are not size-standardized, while results of the mandibular analysis place the specimen with recent modern humans for both raw and size-standardized data. Although these results are influenced by limitations related to the incomplete nature of the comparative sample, they suggest that the morphology of Teshik-Tash 1 as expressed in craniometrics is equivocal. Although, further quantitative studies as well as additional sub-adult fossil finds from this region are needed to ascertain the morphological pattern of this specimen specifically, and Central Asian Middle Paleolithic hominins in general, these results challenge current characterizations of this territory as the eastern boundary of the Neandertal range during the Late Pleistocene.

Mandibular ramus shape of Australopithecus sediba suggests a single variable species

The fossils from Malapa cave, South Africa, attributed to Australopithecus sediba, include two partial skeletons-MH1, a subadult, and MH2, an adult. Previous research noted differences in the mandibular rami of these individuals. This study tests three hypotheses that could explain these differences. The first two state that the differences are due to ontogenetic variation and sexual dimorphism, respectively. The third hypothesis, which is relevant to arguments suggesting that MH1 belongs in the genus Australopithecus and MH2 in Homo, is that the differences are due to the two individuals representing more than one taxon. To test these hypotheses, we digitized two-dimensional sliding semilandmarks in samples of Gorilla, Pan, Pongo, and Homo, as well as MH1 and MH2. We document large amounts of shape variation within all extant species, which is related neither to ontogeny nor sexual dimorphism. Extant species nevertheless form clusters in shape space, albeit with some overlap. The shape differences in extant taxa between individuals in the relevant age categories are minimal, indicating that it is unlikely that ontogeny explains the differences between MH1 and MH2. Similarly, the pattern of differences between MH1 and MH2 is inconsistent with those found between males and females in the extant sample, suggesting that it is unlikely that sexual dimorphism explains these differences. While the difference between MH1 and MH2 is large relative to within-species comparisons, it does not generally fall outside of the confidence intervals for extant intraspecific variation. However, the MH1-MH2 distance also does not plot outside and below the between-species confidence intervals. Based on these results, as well as the contextual and depositional evidence, we conclude that MH1 and MH2 represent a single species and that the relatively large degree of variation in this species is due to neither ontogeny nor sexual dimorphism.

Ontogenetic Variation in the Mandibular Ramus of Great Apes and Humans

Considerable variation exists in mandibular ramus form among primates, particularly great apes and humans. Recent analyses of adult ramal morphology have suggested that features on the ramus, especially the coronoid process and sigmoid notch, can be treated as phylogenetic characters that can be used to reconstruct relationships among great ape and fossil hominin taxa. Others have contended that ramal morphology is more influenced by function than phylogeny. In addition, it remains unclear how ontogeny of the ramus contributes to adult variation in great apes and humans. Specifically, it is unclear whether differences among adults appear early and are maintained throughout ontogeny, or if these differences appear, or are enhanced, during later development. To address these questions, the present study examined a broad ontogenetic sample of great apes and humans using two‐dimensional geometric morphometric analysis. Variation within and among species was summarized using principal component and thin plate spline analyses, and Procrustes distances and discriminant function analyses were used to statistically compare species and age classes. Results suggest that morphological differences among species in ramal morphology appear early in ontogeny and persist into adulthood. Morphological differences among adults are particularly pronounced in the height and angulation of the coronoid process, the depth and anteroposterior length of the sigmoid notch, and the inclination of the ramus. In all taxa, the ascending ramus of the youngest specimens is more posteriorly inclined in relation to the occlusal plane, shifting to become more upright in adults. These results suggest that, although there are likely functional influences over the form of the coronoid process and ramus, the morphology of this region can be profitably used to differentiate among great apes, modern humans, and fossil hominid taxa. J. Morphol. 275:661–677, 2014.

Facing the facts: The Runx2 gene is associated with variation in facial morphology in primates

The phylogenetic and adaptive factors that cause variation in primate facial form-including differences among the major primate clades and variation related to feeding and/or social behavior-are relatively well understood. However, comparatively little is known about the genetic mechanisms that underlie diversity in facial form in primates. Because it is essential for osteoblastic differentiation and skeletal development, the runt-related transcription factor 2 (Runx2) is one gene that may play a role in these genetic mechanisms. Specifically, polymorphisms in the QA ratio (determined by the ratio of the number of polyglutamines to polyalanines in one functional domain of Runx2) have been shown to be correlated with variation in facial length and orientation in other mammal groups. However, to date, the relationship between variation in this gene and variation in facial form in primates has not been explicitly tested. To test the hypothesis that the QA ratio is correlated with facial form in primates, the current study quantified the QA ratio, facial length, and facial angle in a sample of 33 primate species and tested for correlation using phylogenetic generalized least squares. The results indicate that the QA ratio of the Runx2 gene is positively correlated with variation in relative facial length in anthropoid primates. However, no correlation was found in strepsirrhines, and there was no correlation between facial angle and the QA ratio in any groups. These results suggest that, in primates, the QA ratio of the Runx2 gene may play a role in modulating facial size, but not facial orientation. This study therefore provides important clues about the genetic and developmental mechanisms that may underlie variation in facial form in primates.

Craniomandibular form and body size variation of first generation mouse hybrids: A model for hominin hybridization

Hybridization occurs in a number of mammalian lineages, including among primate taxa. Analyses of ancient genomes have shown that hybridization between our lineage and other archaic hominins in Eurasia occurred numerous times in the past. However, we still have limited empirical data on what a hybrid skeleton looks like, or how to spot patterns of hybridization among fossils for which there are no genetic data. Here we use experimental mouse models to supplement previous studies of primates. We characterize size and shape variation in the cranium and mandible of three wild-derived inbred mouse strains and their first generation (F1) hybrids. The three parent taxa in our analysis represent lineages that diverged over approximately the same period as the human/Neanderthal/Denisovan lineages and their hybrids are variably successful in the wild. Comparisons of body size, as quantified by long bone measurements, are also presented to determine whether the identified phenotypic effects of hybridization are localized to the cranium or represent overall body size changes. The results indicate that hybrid cranial and mandibular sizes, as well as limb length, exceed that of the parent taxa in all cases. All three F1 hybrid crosses display similar patterns of size and form variation. These results are generally consistent with earlier studies on primates and other mammals, suggesting that the effects of hybridization may be similar across very different scenarios of hybridization, including different levels of hybrid fitness. This paper serves to supplement previous studies aimed at identifying F1 hybrids in the fossil record and to introduce further research that will explore hybrid morphologies using mice as a proxy for better understanding hybridization in the hominin fossil record.