East African Miocene Catarrhine Evolutionary Ecology

This dissertation assesses how East African Miocene catarrhines changed adaptively within their environments from the early to middle Miocene. This period records an important transition in catarrhine evolution that is relevant to the interpretation of later hominoid and hominin radiations. The adaptive and community restructuring of catarrhines from ~21-15 mya is posited to be associated with a shift from closed/forested habitats to more open/seasonal woodlands. However, the nature of catarrhine adaptive features and whether they reflect a response to environmental change is unclear. An analysis of the same dietary, locomotor and environmental proxies across multiple fossil localities was conducted. This dissertation has three components. First, herbivore enamel from the middle Miocene localities of Maboko and Kipsaramon was analyzed for δ13C values. These fossil enamel δ13C values are compared to enamel δ13C values from modern African herbivores to reconstruct feeding ecology and infer habitats of a sample of middle Miocene mammals. Fossil enamel δ13C values reflect a variable landscape of C3 dominated open forests/woodlands at Maboko and possibly drier and open woodland with significant amounts of C4 biomass at Kipsaramon. Second, non-cercopithecoid catarrhine dietary change is assessed across eight early and middle Miocene localities using molar shear quotients (SQs). Patterns of SQ value changes is evaluated against an environmental backdrop of herbivore enamel δ13C values from each fossil locality. The range of SQ values increases from the early to the middle Miocene, suggesting a possible increase in dietary diversity among middle Miocene catarrhines. This increase is driven by a decrease in molar shear crest development in large bodied hominoids and an increase shear crest development among nyanzapithecines. The range of variation in fossil enamel δ13C values also increased from the early to the middle Miocene. Thus, there appears to be an association between variation in herbivore feeding ecology and catarrhine diet through time. Early Miocene enamel δ13C values indicate a mosaic of C3 dominated open forest and woodland habitats, while middle Miocene sites include C4 biomass. Overall, enamel δ13C values do not support a shift from closed canopied forests to open forest and woodland habitats, contra previous environmental reconstructions. Lastly, the postcranial functional diversity of early and middle Miocene catarrhines was examined by quantifying intermediate phalangeal morphology. The relative length and curvature of 20 fossil phalanges from five early and middle Miocene sites were compared to the relative length and curvature of 30 extant anthropoid taxa of known positional behavior. Phalange relative length and curvature indicate an increase in morphological diversity, and possibly positional behavioral diversity, through time. This pattern echoes the increase in dietary diversity among middle Miocene catarrhines documented in the previous chapter. The molar and phalangeal morphological evidence suggests greater dietary and locomotor specialization in the middle Miocene of East Africa relative to the early Miocene. This study does not find evidence for a broad scale shift from closed to more open habitats as a driver of this adaptive expansion, however. Environmental reconstructions for primate rich localities using enamel δ13C values as a proxy for vegetation instead finds evidence for open forest and woodland habitats throughout the early and middle Miocene, but with a broadening of habitat heterogeneity through time. Future studies should continue to characterize habitats and their primate communities at a regional scale to better understand the ecological underpinnings of catarrhine evolution.PHDAnthropologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/151741/1/idarn_1.pd