THE SICK ARTHROPODS: EVIDENCE OF PALEOPATHOLOGY FROM LOWER CAMBRIAN STRATA OF SOUTH CHINA

Naraoiids belong to a nonbiomineralizing arthropod group that is widespread and long-ranging (middle early Cambrian to late Silurian). Recently, there are new occurrences of naraoiids reported from the Balang Formation (Cambrian Series 2) in Guizhou, South China. Unlike other naraoiids, there are irregular and circular markings associated with specimens upon close examination. Although circular epibionts attached to discoidal eldoniid fossils have been reported from the younger Kaili Formation in nearby localities, these epibionts are varied in shapes and sizes (~2-10 mm in diameter), and none of them are found in association with arthropods from the same beds. Markings on Balang naraoiids are mostly circular and are less then 2 mm (most of them are less than 1 mm) in diameter. These features are affected by the soft-deformation wrinkles on cuticle, indicating the occurrence of these circular markings on cuticle preceded the deformation of cuticle due to decay. Under high magnification, there are additional features associated with the markings. In comparison with naraoiid fauna from a different locality of Balang Formation, individuals from the studied site are much smaller and bioturbation intensity is much higher in this area. Clear evidence to support wheather these markings are post-morten features or the direct cause of death is still lacking, but the latter is suggested here based on the comparison of post-morten bioturbation of soft-bodied arthropods from other Burgess Shale-type deposits.