Understanding the timing of mountain building and desert formation events in western North America is crucial to understanding the evolutionary history of the diverse arid-adapted biota that is found there. While many different, often conflicting descriptions exist regarding geobiotic change in western North America, little work has been done to synthesize these various viewpoints. In this paper we present several case studies that illustrate the differences in the various explanations, based on geological and paleobiological data, detailing mountain uplift and desertification in western North America. The majority of the descriptions detailing mountain building in this area fall into two major periods of uplift, the Laramide uplift (∼70—50 Ma) and the Neogene uplift (∼15—2 Ma), yet it remains unclear which of these events was responsible for the formation of the modern mountains. Like the descriptions of mountain building, various accounts exist detailing the timing of desert formation. Some authors suggest that the deserts existed as far back as 15 Ma while others propose that desert formation occurred as recently as 10,000 years ago. Based on this review of the literature, we suggest that the data on Cenozoic geomorphological evolution of the North American desert landscape is still too coarse and filled with gaps to allow for the development of a robust model of landscape evolution. Instead, this work demonstrates the need for biologists studying the North American biota to realize just how problematic some of the earth history data and models are so that they can build this uncertainty into biogeographic reconstructions.

Müllerian mimicry, in which two or more harmful species share a similar appearance for mutual benefit, is a widely appreciated, yet relatively uncommon natural phenomenon. Although Müllerian mimicry occurs in vertebrates, most studies are focused on tropical, herbivorous invertebrates. Here we identify a large Müllerian mimicry complex in North American velvet ants (Hymenoptera: Mutillidae). These are conspicuous, diurnal parasitoids of bees and wasps that defend themselves with a powerful sting. We investigate morphological and genetic variation and ask whether morphological similarities are the result of convergent evolution or shared ancestry. We find that 65 species in the velvet ant genus Dasymutilla can be placed into one of six morphologically distinct and geographically delimited mimicry rings. Müllerian colour patterns are primarily the result of independent evolution rather than shared, phylogenetic history. These convergent colour syndromes represent one of the largest known Müllerian mimicry complexes yet identified, particularly in the Northern Hemisphere.