Abstract:
Current diversity is the result of macroevolutionary processes of origination and extinction of lineages through time. Here we make use of a fossil-calibrated molecular-clock phylogeny of modern squirrel genera to estimate both rates of 'birth' and 'death', and the net rate of accumulation of lineages since the origin of the squirrel family (Sciuridae) 36 Ma. As a family, the Sciuridae have exhibited modest rates of diversification in comparison with other mammalian clades. Within the Sciuridae, lineages of squirrels have accumulated at higher rates in geographically localized subclades in the tropics of different continents. The rate is strikingly high in the Sciurini of South America, which first entered and radiated within that continent comparatively recently (less than 3 Ma). It is noteworthy that the most rapidly diversifying groups are also relatively young. Because extinctions lag behind originations, the effects of extinction are not yet detectable in relatively recent radiations. The balance of origination and extinction is fragile, and is likely to become more so if increases in extinction due to habitat destruction, climate change and other human activity are not mitigated.
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