The Early Cambrian Arthropod Guangweicaris: Its Soft Tissues and Evolutionary Significance  

Based on newly discovered fossil material with excellently preserved soft tissues, we have investigated the morphological details of the appendages of the Early Cambrian Fuxianhuia-like arthropod Guangweicaris. We discuss its phylogenetic relationships, and its bearing on the evolution of early arthropods.  Although its body segmentation is typical of Fuxianhuia-like protoarthropods, advanced characteristics of euarthropods are clearly displayed in the appendages and antennae, suggesting a key position of Guangweicaris in the transition from protoarthropods to euarthropods.    Guangweicaris is a non-trilobite arthropod documented only from the Early Cambrian Guanshan fauna of Yunnan, China.  This animal consists of 18 body tergites.  The head is composed of two tergite-bearing segments: the eye-bearing segment, and the antennal segment.  A shield-like structure is present as a widely expanded tergite, just like in other Fuxianhuia-like arthropods.  These features are considered typical characteristics of protoarthropods.  The trunk (body tergites from 3-17) is divided into two parts: the thorax, with 8 tergites; and the abdomen, comprising 7 tergites.  Three thoracic tergites are covered by the shield-like structure, the so-called “second head tergite”. Posteriorly, there is a triangular tail spine and a pair of lateral flaps (the last body tergite).

The eyes of Guangweicaris are similar to other Fuxianhuia-like arthropods (including Shankouia, Fuxianhuia and Chengjiangocaris from the Lower Cambrian Chengjiang Biota), which are thought to be borne on short, tubular stalks.  The antennae of Guangweicaris are unusual, as they are flagelliform in shape and composed of at least 23 short annuli.  This morphology is regarded as a derived euarthropod character.  Other euarthropod characters are also present in the limbs.  The limbs of Guangweicaris are neither tubular with a multi-annulated main rod, nor – as described for Fuxianhuia – like a scleritised lobopod.  Rather, the multi-jointed limbs comprise an 8-10 podomere endopod, a flap-shaped exopod, and a possible rigid basipod. 

We consider Guangweicaris as a “derived Fuxianhuia-like protoarthropod”.  This research may help reshape current hypotheses of early arthropod evolution.