| dcterms.abstract | Cercopithecoidea is the superfamily within the order Primates representing Old World Monkeys. Cercopithecoids are relatively rare in the fossil record prior to the middle Miocene. However, since the PlioPleistocene, cercopithecoids have undergone a diversification making them one of most ecological diverse groups of primates today. Although cercopithecoids are ecologically and behaviorally diverse, their locomotor behavior is not considered specialized and their postcrania reflect a generalized quadrupedal locomotor repertoire. Many cercopithecoids today are considered " semi-terrestrial" meaning that they are efficient on the ground and in the trees. However, the colobines are almost exclusively arboreal and committed terrestriality is thought to have evolved at least twice in the papionins. Based primarily on interpretations of the mid-Miocene fossil monkey <italic>Victoriapithecus</italic>, it has been argued that the last common ancestor (LCA) of cercopithecoids engaged in terrestrial behavior and that arboreality has been secondarily evolved in the colobines, some guenons and various macaques. <italic>Victoriapithecus</italic>, the proposed sister taxon to crown Cercopithecoidea, has been reconstructed as semi-terrestrial. In 2010, a skeleton of <italic>Microcolobus</italic>, a proposed stem colobine was described as primarily arboreal, suggesting that the earliest colobines were not terrestrial and the arboreality in the clade was inherited from the LCA of crown colobines. This work also challenges the hypothesis that the ancestral cercopithecoid was semi-terrestrial. Lack of resolution on the pattern of locomotor evolution in cercopithecoids is compounded by the absence of taxonomically comprehensive, quantitative assessments of form-function relationships and conflicting perspectives generated by a multitude of more restrictive studies. This dissertation seeks to examine the associations between morphology and locomotor behavior in cercopithecoids with the ultimate goal of improving resolution on the pattern of locomotor transitions throughout the evolution of Cercopithecoidea. Chapter 2 summarizes a morphometric study of the humerus, femur, astragalus, and calcaneus of a sample of 52 anthropoid primates using recently developed phylogenetic comparative methods. The results from this chapter document several associations between morphology and behavior supporting previous research on the functional morphology of cercopithecoids. The major findings from this chapter are that " primarily arboreal" and " primarily terrestrial" cercopithecoids are well separated by many morphometric features but " semi-terrestrial" cercopithecoids overlap in their morphology with each of the more specialized groups. The lack of consistently " intermediate" trait values for " semi-terrestrial" cercopithecoids leads to the conclusion that they are not united by a consistent set of " intermediate" functional demands. Instead the pattern suggests that different " semi-terrestrial" taxa may differ in the degree to which functional demands of terrestriality versus arboreality have influenced the morphology of any given feature. Therefore it is unlikely that the extent of terrestrial behavior can be reliably determined in fossil taxa that lack extreme and/or consistent specialization for either terrestriality or arboreality throughout the skeleton. Although this chapter suggests that locomotor reconstructions of fossil cercopithecoids may not be highly specific in the exact amount of time a species spent in the ground or in the trees, the morphological associations can still inform us of a fossil species general locomotor behavior. First, given the separation between primarily arboreal and primarily terrestrial extant cercopithecoids, it should be possible to determine if a fossil species was highly arboreal or terrestrial. Second, if a fossil species falls into the intermediate space between primarily arboreal and primarily terrestrial cercopithecoids, or if this taxon has a pattern of morphology that suggests arboreality in some features but terrestriality in others, then this species should be considered as flexible in its locomotor behavior as many " semi-terrestrial" cercopithecoids are today. The associations between morphology and behavior and the locomotor diversity of extant cercopithecoids presented in this chapter, form the basis for the fossil reconstruction in Chapter 3. Seventeen fossil stem and crown cercopithecoids are studied in Chapter 3 and their most likely locomotor reconstructions are presented. <italic>Victoriapithecus</italic> is reconstructed as considerably more arboreal than previous work has suggested. Nonetheless, the data also suggest that <italic>Victoirpaithecus</italic> would likely have engaged in a limited amount terrestrial behavior. Most elements from <italic>Victoriapithecus</italic> are classified as arboreal, but the distal humerus is consistently classified as semi-terrestrial due to a relatively dorsally projecting medial epicondyle. <italic>Micrcolobus</italic> is classified consistently to the arboreal group supporting previous work on this species. Given that <italic>Victoriapithecus</italic> probably engaged in a substantial amount of arboreal behavior and that <italic>Microcolobus</italic> was probably primarily arboreal, this chapter suggests that the LCA of crown cercopithecoid was arboreal, with a limited amount of terrestrial behavior possible. Importantly, this implies that in most respects, the LCA of crown colobines inherited arboreality from the LCA of crown cercopithecoids, with a possible increase in commitment to an arboreal lifestyle (i.e., colobines did not " re-evolve" arboreality). Of the other fossil cercopithecoids studied, species that have been previously interpreted as arboreal, such as <italic>Paracolobus</italic> and <italic>Rhinocolobus</italic> are also reconstructed as arboreal in this study. Similarly, this study's reconstructions of <italic>Theropithecus oswaldi</italic> support previous work suggesting that this species was committed to terrestriality. However, many species previously interpreted as terrestrial, such as <italic>Cercopithecoides</italic>, <italic>Dolichopithecus</italic>, and <italic>Theropithecus brumpti</italic> are found to have included some arboreal behavior in their locomotor repertoire. Extensive previous work has consistently suggested " semi-terrestriality" in <italic>Mesopithecus</italic> and this study supports a reconstruction of <italic>Mesopithecus</italic> as arboreal with some limited amount of terrestrial behavior. Although this chapter suggests that the LCA of crown cercopithecoids was arboreal and presents reconstructions for fossil cercopithecoids, the pattern of locomotor transitions throughout cercopithecoid evolution can only be loosely hypothesized from the fossil record. Chapter 4 uses ancestral state reconstruction (ASR) methods to more rigorously test hypotheses concerning the timing and number of transitions to terrestriality in cercopithecoids. Chapter 4 presents the results from ASR analyses that reconstruct 30 nodes along an anthropoid phylogeny. Crown Anthropoidea, crown Catarrhini, crown Cercopithecoidea, and crown Colobinae are consistently reconstructed as arboreal by all analyses. However, the other nodes, including crown Cercopithecinae, crown Cercopithecini, crown Papionini, crown Papionina, and crown <italic>Macaca</italic> are classified inconsistently to different locomotor groups across different analyses. Examining the character evolution of morphological features provides information to be considered in conjunction with classification analyses from Chapter 3. ASR suggests that the morphology of crown Cercopithecoidea is associated with arboreal behavior and that this morphology is retained in crown Colobinae. The morphology of crown Cercopithecinae shows a shift from the state of crown Cercopithecoidea to more terrestrial behavior with this shift continuing in crown Papionini. Relative to crown Cercopithecinae, the morphology of crown Cercopithecini is shifted more towards increasing arboreality. Overall, the results of Chapter 4 support an arboreal LCA for crown Cercopithecoidea and crown Colobinae with the evolution of committed terrestrial behavior first appearing in crown Cercopithecinae. This dissertation documents the morphological diversity in the cercopithecoid postcranium and presents several features that exhibit a morphological continuum with respect to substrate preference. Using this morphometric dataset, the locomotor behavior of fossil stem and crown cercopithecoids and hypothetical ancestors are reconstructed. The findings of this dissertation suggest that early cercopithecoids were arboreal with committed terrestriality evolving in the late Miocene during cercopithecine evolution. The transition to increased use of terrestrial behavior at around 10 million years ago coincides with global cooling that began in the late Miocene. | |
