Long-term erosion and subsidence cause dramatic alterations in the physical and ecological features of oceanic islands. Although oceanic islands have been extensively used as models for the study of speciation, little attention has been given to investigating evolutionary patterns in old volcanic islands that have suffered severe climatic degradation. The spider genus Dysdera has diversified across the Canary Islands and has evolved endemisms in the low-elevation, xeric eastern islands, which sharply contrast with the younger, higher, and more humid western islands. A combined phylogenetic analysis of seven mitochondrial and nuclear genes reveals that the eastern Canaries were colonized twice, although only one lineage underwent in situ diversification. Origins of the speciose lineage remain obscure, but probably preceded diversification of present-day Iberian and North African species. A second colonization of the eastern Canaries from North Africa has occurred in more recent times. Molecular analyses reveal several instances of geographically coherent cryptic lineages further supported by morphometric evidence. Analyses of diversification rates suggest deceleration of diversification over the course of time, and this is compatible with increasing extinction rates due to drastic yet continuous ecological changes. Extinction may also explain incongruent patterns of morphological differentiation and species coexistence. Despite a general trend towards community impoverishment, there is also evidence for recent speciation events linked to ecological shifts, which may illustrate the origins of nonspeciose relic lineages on islands. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 589–615.