Liu et al. reply.

Abstract

Replying to R. C. P. Mounce & M. Wills , 10.1038/nature10266 (2011) ; D. A. Legg et al. 10.1038/nature10267 (2011) We welcome the reanalyses by Mounce and Wills 1 and Legg 2 of our paper3, and although we do not fully concur with their conclusions we are pleased that Diania has reopened the debate about key stages in arthropod evolution. We accept that the position of this fossil remains sensitive to parameters of analysis and in the original publication we conceded that our best-supported tree—Diania as sister-group to (Schinderhannes + Euarthropoda)—could be subject to change, and that the ‘walking cactus’ may have a more basal position within the overall framework of the arthropod stem-group. These alternative treatments of our data would seem to confirm this suspicion, although we find the placement of Diania in an unresolved, and extremely basal, polytomy alongside velvet worms, tardigrades and various other lobopodians similarly problematical. We do not doubt that the authors’ results1,2 are statistically well supported, but what do these cladograms tell us about the evolution of the group? Lobopodians are, by their nature, fairly simple and consequently yield few convincing synapomorphies, either with each other or with arthropods in general. As we discovered, this makes scoring a robust data matrix including both lobopodians and arthropods challenging, and we wonder whether the basal polytomies recovered here are simply due to clustering among taxa with few unequivocal apomorphies and/or much missing data.