Article: Lower Cambrian cambroclaves (incertae sedis) from Xinjiang, China, with comments on the morphological variability of sclerites
Four species of cambroclave, an enigmatic group whose position within the Metazoa is unresolved, are described from the Lower Cambrian Yurtus Formation of western Xinjiang, China. Cambrodavus bicornis is similar to a number of previously described species, including C. absonus from approximately equivalent age strata of South Australia. As in many cambroclave taxa, morphological variability of individual sclerites appears to be considerable. Morphometric analysis of four populations of C. bicornis, using elliptic Fourier shape analysis (EFA), demonstrates that this technique offers considerable discriminatory power. Two samples from the upper parts of one section (Sugaitbulak) show morphological stasis. They are also readily distinguishable from two other samples, which although from near-equivalent horizons in adjacent sections on Yurtus Mountain differ significantly from one another. Zhijinites daviformis is a robust sclerite, with a strongly ribbed spine. In contrast, Parazhijinites cf. guizhouensis has a remarkably slender spine, arising from a much reduced base. Finally, Wushichites minutus is more reminiscent of other Chinese cambroclaves, notably Deiradoclavus trigonus, with a sclerite with a sub-circular base indented by a posterior notch, and a much reduced spine. Although the overall morphology of cambroclaves appears to be related to protection from predatory attack, the wide variation in basic sclerite types lacks convincing ecological explanations.