I found an interesting paper that is in early online edition with Science. The paper is titled "Impacts of the Cretaceous terrestrial revolution and KPg extinction on mammalian diversification" by Meredith et al. (2011). Unfortunately, I was unable to access the PDF yesterday at school (database failure I suppose) so I will have to base my discussion on the abstract.
The authors constructed a "molecular supermatrix" and used it to build a large mammalian phylogeny using multiple fossil calibrations. Importantly, they find support for the "long fuse" model of mammalian diversification, which predicts that the mammalian orders we know today diversified after the KPg boundary. These results seem to agree with Bininda-Emonds et al. (2007) The delayed rise of present day mammals in that both studies show long evolutionary fuses. However, they appear to disagree on one important point, the impact of the KPg boundary on mammalian diversification. Meredith et al. (2011) state that their phylogeny suggests that the KPg extinctions and subsequent opening of niches was very important in the diversification of modern mammals. In contrast, Bininda-Emonds (2007) do not find a significant effect of the KPg mass extinction.
Meredith et al. (2011) suggest that their methods are superior and the reason for this difference in interpretation. For those of you who do not know, Bininda-Emonds (2007) used supertree analyses. Essentially, many trees from the literature are glued together (I assure it is more complex than this). Meredith et al. (2011) use a "molecular supermatrix." I am not presently aware of what a molecular supermatrix is besides that it is a large matrix based on molecular data. As a result, I have no basis for judging which method would be "most accurate." My "gut feeling" is to agree with Meredith et al. because I can envision the component trees of a supertree coming from very divergent sources, some more reliable than others. I will return to this issue once I have accessed the full Meredith et al. (2011) article, however.
Were Bininda-Emonds et al. actually able to rule out a significant effect of the K-Pg extinction, or did they "not find a significant effect" in the sense that their results were inconclusive? If the latter, I wouldn't really say the studies "disagree"...
ReplyDeleteTheir tree is not consistent with the KPg boundary having a significant effect. Their results are definitely not inconclusive. They state that " The pulse of mammalian diversification immediately after the K/T event was mainly or wholly in groups that
ReplyDeletedeclined subsequently or died out, without contributing markedly
to those lineages with extant descendants, for which the diversification rate remained flat across the boundary."
The difference is that both studies support a long fuse model but the length of the fuses in Bininda-Emond's paper are not related to the KPg boundary while Meredith's are.But I have yet to fully read this paper.