ARISING FROM J. Liu et al. Nature 470, 526-530 (2011)

Liu et al. (1) described an 'armoured' lobopodian, Diania cactiformis, from the Chengjiang Lagerstatte (China; Cambrian, stage 3); this fossil bears potentially arthropod-like articulated and possibly sclerotized appendages, but lacks a sclerotized body. A cladistic analysis resolved Diania as sister-taxon to arthropods. From this phylogenetic position the authors tentatively inferred that arthropodization (sclerotization of limbs) may have preceded arthrodization (sclerotization of body elements) in arthropod evolution. Although we concur with the reasoning behind this inference, it rests on a phylogenetic placement that our analysis of the published data set does not reproduce.

Our analyses were undertaken using implicit enumeration (branch and bound) in TNT (Tree Analysis using New Technology) v.1.1 (ref. 2), first repeating the analysis of Liu et al. (1) with implied character weighting (k = 2) and additionally with equal character weighting; results are shown in Fig. 1b, c. In neither analysis was Diania resolved as sister-taxon to Arthropoda, instead belonging to an unresolved polytomy at the base of the resultant most-parsimonious trees. To confirm that the trees of Liu et al. (1) are less parsimonious, a second...