Quantitative Genetics, Pleiotropy, and Morphological Integration in the Dentition of Papio hamadryas

Variation in the mammalian dentition is highly informative of adaptations and evolutionary relationships, and consequently has been the focus of considerable research. Much of the current research exploring the genetic underpinnings of dental variation can trace its roots to Olson and Miller's 1958 book Morphological Integration. These authors explored patterns of correlation in the post-canine dentitions of the owl monkey and Hyopsodus, an extinct condylarth from the Eocene. Their results were difficult to interpret, as was even noted by the authors, due to a lack of genetic information through which to view the patterns of correlation. Following in the spirit of Olson and Miller's research, we present a quantitative genetic analysis of dental variation in a pedigreed population of baboons. We identify patterns of genetic correlations that provide insight to the genetic architecture of the baboon dentition. This genetic architecture indicates the presence of at least three modules: an incisor module that is genetically independent of the post-canine dentition, and a premolar module that demonstrates incomplete pleiotropy with the molar module. We then compare this matrix of genetic correlations to matrices of phenotypic correlations between the same measurements made on museum specimens of another baboon subspecies and the Southeast Asian colobine Presbytis. We observe moderate significant correlations between the matrices from these three primate taxa. From these observations we infer similarity in modularity and hypothesize a common pattern of genetic integration across the dental arcade in the Cercopithecoidea

A Macaque Model for the Effects of Hybridization on Body Size

ObjectivesGenomics research has uncovered recurrent hybridization between hominin species, yet its morphological impact remains understudied. Non-human primate research has suggested a morphological signature of hybrid ancestry, which could be used to identify hybrids in the hominin fossil record. This pattern may include extreme size, heightened variation, and markers of developmental instability, but factors affecting these characteristics are poorly understood. Studies of non-mammalian taxa suggest that extreme morphology is more likely in early-generation hybrids and with a greater parental distance. To understand hybridization in hominins, therefore, we must use appropriate proxy taxa.Materials and methodsHere, we use Chinese × Indian Macaca mulatta hybrids with a comparable divergence time in generations to Homo sapiens/Neanderthals and wide variation in admixture. Measuring limb lengths, body length, and weight, we investigate the relationship between admixture and size/variation.ResultsCompared to previous work with more phylogenetically distant primate taxa and a focus on early generation hybrids, we found no evidence of a relationship between admixture and extreme large size, nor with increased size variation. Hybrids in our sample are relatively small but within the range of variation of the smaller parental taxon.ConclusionsOur results suggest that hybridization between closely related taxa, such as Neanderthals and H. sapiens, may lead to more subtle morphological patterns than previously anticipated. It will be necessary, however, to better understand the factors governing primate hybrid morphology before we can produce robust inferences on how hybridization has affected hominin evolution

Uniform, circular, and shallow enamel pitting in hominins: Prevalence, morphological associations, and potential taxonomic significance.

This study explores a particular form of enamel pitting originally identified in Paranthropus robustus. We call this uniform, circular, and shallow (UCS) pitting to distinguish it from more irregular and nonuniform defects often associated with enamel hypoplasia. We pose the hypothesis that UCS pitting is unique to the genus Paranthropus. We test this by investigating hominin dental remains from the ca. 3.4 Ma to ca. 1.1 Ma fossiliferous sequence at Omo, Ethiopia (n = 76) to look for evidence of UCS pitting in an assemblage that includes at least three hominin genera (Australopithecus, Paranthropus, and Homo). We also examine the correlation between UCS pitting, tooth size, enamel thickness, and cusp proportions in samples from both eastern Africa (Omo) and southern Africa (Drimolen Main Quarry ∼2.04-1.95 Ma, Swartkrans ∼1.9-1.4 Ma, and Kromdraai ∼1.95-1.78 Ma). In the Omo specimens, we found UCS pitting similar to that seen in P. robustus. While we observed this pitting on five of 24 permanent teeth and two deciduous molars from both Paranthropus aethiopicus and Paranthropus boisei, we also identified UCS pitting on five of 13 non-Paranthropus hominin permanent posterior teeth from Member B (∼3.0 Ma). Our correlation studies yielded no association between the presence of UCS pitting and variation in tooth size, enamel thickness, or cusp proportions. The consistent appearance and characteristics of UCS pitting suggest a shared etiology. Our findings also suggest that UCS pitting may result from a genetic effect related to enamel formation, potentially in association with specific environmental or dietary factors

Uniform, circular, and shallow enamel pitting in hominins: Prevalence, morphological associations, and potential taxonomic significance

This study explores a particular form of enamel pitting originally identified in Paranthropus robustus. We call this uniform, circular, and shallow (UCS) pitting to distinguish it from more irregular and nonuniform defects often associated with enamel hypoplasia. We pose the hypothesis that UCS pitting is unique to the genus Paranthropus. We test this by investigating hominin dental remains from the ca. 3.4 Ma to ca. 1.1 Ma fossiliferous sequence at Omo, Ethiopia (n = 76) to look for evidence of UCS pitting in an assemblage that includes at least three hominin genera (Australopithecus, Paranthropus, and Homo). We also examine the correlation between UCS pitting, tooth size, enamel thickness, and cusp proportions in samples from both eastern Africa (Omo) and southern Africa (Drimolen Main Quarry ∼2.04–1.95 Ma, Swartkrans ∼1.9–1.4 Ma, and Kromdraai ∼1.95–1.78 Ma). In the Omo specimens, we found UCS pitting similar to that seen in P. robustus. While we observed this pitting on five of 24 permanent teeth and two deciduous molars from both Paranthropus aethiopicus and Paranthropus boisei, we also identified UCS pitting on five of 13 non-Paranthropus hominin permanent posterior teeth from Member B (∼3.0 Ma). Our correlation studies yielded no association between the presence of UCS pitting and variation in tooth size, enamel thickness, or cusp proportions. The consistent appearance and characteristics of UCS pitting suggest a shared etiology. Our findings also suggest that UCS pitting may result from a genetic effect related to enamel formation, potentially in association with specific environmental or dietary factors

Lemudong'o: a new 6 Ma paleontological site near Narok, Kenya Rift Valley

Copyright © 2003 Elsevier Science Ltd. All rights reserved.Stanley H. Ambrose, Leslea J. Hlusko, David Kyule, Alan Deino and Martin Williamshttp://www.elsevier.com/wps/find/journaldescription.cws_home/622882/description#descriptio

History of Paleontological Research in the Narok District of Kenya

Volume: 56Start Page: 1End Page: 3

Effects of hybridization on pelvic morphology: a macaque model

Ancient DNA analyses have shown that interbreeding between hominin taxa occurred multiple times. Though admixture is often reflected in skeletal phenotype, the relationship between the two remains poorly understood, hampering interpretation of human evolution. Direct study of this relationship is often impossible due to the paucity of hominin fossils and the difficulties of retrieving ancient genetic material. Here, we use a sample of known-ancestry hybrids between two closely related nonhuman primate taxa (Indian and Chinese Macaca mulatta) to investigate the effect of admixture on skeletal morphology. We focus on pelvic shape, which has potential fitness implications in hybrids, as mismatches between maternal pelvic and fetal cranial morphology are often fatal to mother and offspring. As the pelvis is also one of the skeletal regions that differs most between Homo sapiens and Neanderthals, investigating the pelvic consequences of interbreeding could be informative regarding the viability of their hybrids. We find the effect of admixture in M. mulatta is small and proportional to the relatively small morphological difference between the parent taxa. Sexual dimorphism appears to be the main determinant of pelvic shape in M. mulatta. The lack of difference in pelvic shape between Chinese and Indian M. mulatta is in contrast to that between Neanderthals and H. sapiens, 2 despite a similar split time (in generations) between the hybridizing pairs. Greater phenotypic divergence between hominins may relate to adaptations to disparate environments, but may also highlight how the unique degree of cultural buffering in hominins allowed for greater neutral divergence. In contrast to some previous work identifying extreme morphologies in first- and second-generation hybrids, here the relationship between pelvic shape and admixture is linear. This linearity may be because most sampled animals have a multi-generational admixture history or because of relatively high constraints on the pelvis compared to other skeletal regions

A macaque model for the effects of hybridisation on body size

Objectives: Genomics research has uncovered recurrent hybridization between hominin species, yet its morphological impact remains understudied. Non-human primate research has suggested a morphological signature of hybrid ancestry, which could be used to identify hybrids in the hominin fossil record. This pattern may include extreme size, heightened variation, and markers of developmental instability, but factors affecting these characteristics are poorly understood. Studies of non-mammalian taxa suggest extreme morphology is more likely in early-generation hybrids and with a greater parental distance. To understand hybridization in hominins, therefore, we must use appropriate proxy taxa. Materials and methods: Here, we use Chinese x Indian Macaca mulatta hybrids with a comparable divergence time in generations to Homo sapiens / Neanderthals and wide variation in admixture. Measuring limb lengths, body length, and weight, we investigate the relationship between admixture and size / variation. Results: Compared to previous work with more phylogenetically distant primate taxa and a focus on early generation hybrids, we found no evidence of a relationship between admixture and extreme large size, nor with increased size variation. Hybrids in our sample are relatively small but within the range of variation of the smaller parental taxon. Conclusions: Our results suggest that hybridization between closely related taxa, such as Neanderthals and H. sapiens, may lead to more subtle morphological patterns than previously anticipated. It will be necessary, however, to better understand the factors governing primate hybrid morphology before we can produce robust inferences on how hybridization has affected hominin evolution