Ratings

No competing interests declared.

The specimen documented in this paper is undoubtedly an important fossil, particularly because it is the most complete adapoid primate skeleton known to date. Although other, partial adapoid skeletons are known (hence 4/5 stars in the "insight" category), Darwinius will be a valuable data point for future studies of primate evolution.

The proposed placement of Darwinius and adapoids with haplorhines will likely be disputed by future workers, particularly due to the absence of a comprehensive cladistic analysis incorporating the new specimen. Cladistic analysis is not perfect (it is relatively easy to pick and choose characters to support any topology), but it would allow another evaluation of the new taxon's (controversial) relationships. Furthermore, it would be interesting to see how other fossil haplorhines (e.g., Eosimias) now fall out in light of the new data. This was not completely evaluated in the paper, unfortunately. In the absence of a parsimony analysis, it is possible to imagine alternative scenarios in which some characters of Darwinius are homoplasies rather than synapomorphies with haplorhines. Additionally, some of the synapomorphies described here probably will be reinterpreted by other workers, which could further affect the hypothesis for where Darwinius lies phylogenetically. So, I have only rated the paper 2/5 stars for reliability.

I have rated the paper 4/5 stars for style, in light of the clear prose and numerous detailed figures within the paper.

Competing interests declared: member of PLoS ONE editorial board

No competing interests declared.

No competing interests declared.

No competing interests declared.

While this paper does a fine job of description of the fossil specimen, two serious weaknesses compromise the phylogenetic conclusions of this paper. (i) Absence of comparisons with fossil primates that have been shown by rigorous phylogenetic analysis to be stem anthropoids and stem tarsiers (Kay, R.F., Ross, C.F., Williams, B.A., 1997. Anthropoid origins. Science 275, 797-804; Ross, C., Williams, B.A., Kay, R.F., 1998. Phylogenetic analysis of anthropoid relationships. Journal of Human Evolution 35, 221-306; Seiffert, E.R., Simons, E.L., Clyde, W.C., Rossie, J.B., Attia, Y., Bown, T.M., Chatrath, P., Mathison, M.E., 2005. Basal Anthropoids from Egypt and the Antiquity of Africa's Higher Primate Radiation. Science 310(5746), 300-304; Bajpai, S., Kay, R.F., Williams, B.A., Das, D.P., Kapur, V.V., Tiwari, B.N., 2008. The oldest Asian record of Anthropoidea. Proceedings of the National Academy of Sciences 105(32), 11093-11098) makes it impossible to determine character polarities of the major primate crown groups. (ii) The assertion that Darwinius is more closely related to extant Haplorhini than to extant Strepsirrhini (note mis-spelling in Figure S7) can only be maintained in absence of a rigorous and comprehensive phylogenetic analysis of the new fossil using all the available evidence (see above references). No doubt such analyses will be forthcoming from other workers. At present, however, it is safe to say that, as Franzen et al. note, Darwinius is best viewed as a cercamoniin adapoid. Contrary to Franzen et al., however, cercamoniins are most parsimoniously viewed as stem strepsirrhines, not stem haplorhines.

No competing interests declared.