Abstract
The middle Miocene from 17 to 14 Ma was a time of elevated mammalian diversity in western North America that coincided with the regional development of topographic complexity and the last global warming interval of the Neogene. Understanding the evolutionary and ecological processes that govern past diversity trends and contribute to modern diversity gradients in relation to landscape and climate requires the integration of faunal and paleoenvironmental datasets across spatio-temporal scales. Using a variety of approaches, I analyzed small-mammal and environmental data to investigate diversity and dietary-ecology responses to changes in climate across space today and through time during the middle Miocene. I additionally utilized fossil-record simulations to assess the influence of variable preservation history on estimates of diversification rates in relation to landscape change. This thesis sheds light on how interactions between tectonic activity and climate warming influenced species richness and ecology from local to regional scales.
Highlights
A striking diversity gradient in relation to areas of high elevation and topographic complexity has been demonstrated for birds, mammals, and vascular plants, with mountains emerging as global biodiversity hotspots today (Myers et al 2000, Ruggiero and Hawkins 2008, Badgley 2010)
In North America, mammal species richness per unit area rises steeply from the low-relief Great Plains to the topographically complex intermontane west, and species’ range edges align strongly with geographic barriers (Fig. 1; Badgley and Fox 2000). This topographic diversity gradient (TDG) is the outcome of ecological, evolutionary, and biogeographic processes operating over a dynamic landscape and climate history
The evolution of western North American mammalian faunas has a complex history intimately linked with tectonic activity, climate change, and the development of topographically complex and environmentally heterogeneous habitats over the last 30 million years (Badgley et al 2014, Riddle et al 2014)
Summary
A striking diversity gradient in relation to areas of high elevation and topographic complexity has been demonstrated for birds, mammals, and vascular plants, with mountains emerging as global biodiversity hotspots today (Myers et al 2000, Ruggiero and Hawkins 2008, Badgley 2010). Peak mammal diversity in western North America and a strong TDG occurred in the middle Miocene from 18 to 14 Ma (Fig. 2; Badgley et al 2014), during an interval of intense tectonic activity that generated the topographic complexity – alternating mountain ranges and basins – that characterizes the Basin and Range Province today (McQuarrie and Wernicke 2005).
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