Functional morphology of trunk sclerites of the Cambrian lobopodian Cardiodictyon catenulum
Article
Figures
Metrics
Preview PDF
Reference
Related
Cited by
Materials
Abstract:
Cardiodictyon catenulum is a common lobopodian in the early Cambrian Chengjiang fauna. The functional morphology of its trunk sclerites has long been controversial. Here, we show that the trunk of C. catenulum has a longitudinal series of saddle-shaped sclerites, each corresponding to a body segment and extending from the dorsum to both sides of the trunk. Thus, its trunk sclerites are significantly different from those ofotherCambrian lobopodians which possessed paired or circular trunk sclerites. The trunk sclerite of C. catenulum has a conical dorsal projection at the center. The brim of each sclerite is obviously thickened and serrated, which may have in creased its overall rigidity and indicate an enhanced function of protection and defense. In this study, we also report a sieve-like microstructure on the surface of the sclerites, resembling the net-like microstructure on sclerites of Hallucigenia, Microdictyon, and Onychodictyon. The equidistantly arrayed pores are diagenetically permineralizsed with pyrite and preserved as numerous pyritized micro-tubercles. These pores might have served as exits for micro-papillae. We consider that the trunk sclerites of Cambrian lobopodians are in general with a sieve-like microstructure, which may have had protective sensory function. A single sclerite corresponding to a trunk segment in C. catenulum is an autapomorphy of the Cambrian lobopodians. The distinctive arrangement of trunk plates in C. catenulum might represent the prototype of trunk sclerites, or alternatively a derived trait, i.e., secondary fusion of paired sclerites, of early lobopodians.
