Fossil Genera and Age of the Agaricales
The phylogeny and age of the Agaricales, and other fungi, is difficult to reconstruct from the fossil record (Taylor & Osborn 1996). Only four fossil genera of gilled mushrooms are currently accepted (Hibbett et al. 2003), with the oldest of these dating back to the mid-Cretaceous, about 90 million years ago. All are suspected to share affinities with the Agaricales. Fossil ectomycorrhizas, probably of Boletales, have been dated back to the mid-Eocene, about 50 million years ago (LePage et al. 1997). Using a molecular clock, Berbee and Taylor (1993) hypothesized that ectomycorrhizal fungi may have evolved 130 million years ago during the early Cretaceous. However, the age of the origin and diversification of the Agaricales has not been ascertained by molecular clock dating methods. The Agaricales is one of three clades, together with the Atheliales and Boletales, that appear to form one of the more derived groups of Agaricomycetes (Binder et al. 2005; Matheny et al. 2007). If cladogenesis of the sister group to the Agaricales (the Boletales) is used as an indicator (Bruns et al. 1998), then perhaps the Agaricales may have radiated simultaneously, which is estimated between 75 and 135 million years ago. Two recent studies, however, have hypothesized mid- to late-Cretaceous divergences for two genera of dark-spored Agaricales (Geml et al. 2004; Matheny and Bougher 2006), which might suggest an older radiation for the order at large.
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