::::::::I agree that if you want to cite Sahney et al. (2010), you can mention increase in biodiversity, but you should not argue that it is exponential on that basis, so Petter is right about this. Another, not negligible problem that I mentioned above is using family counts as a proxy of biodiversity (very imprecise at best), but that does not mean the paper cannot be cited. I disagree a bit with Peter's perspective on the relevance of the lissamphibian data; sure, lissamphibians account for about 7000 extant species of tetrapods, so that is less than a third of the total. But extant Tetrapoda are composed of two sister-taxa: Lissamphibia and Amniota. There is strong evidence for exponential diversification in Lissamphibia, but not in Amniota. There is strong evidence of impact of biological crises in Amniota, but not on Lissamphibia. In my opinion, the differences in patterns, as currently documented, are such that biodiversity of evolution of the group should distinguish between what happened in both clades. That was part of the reason why I introduced the two citations (Marjanovic & Laurin 2008 and Ward et al. 2005).