COPEPOD MANDIBLE PALYNOMORPHS FROM THE NOLICHUCKY SHALE (CAMBRIAN, TENNESSEE): IMPLICATIONS FOR THE TAPHONOMY AND RECOVERY OF SMALL CARBONACEOUS FOSSILS

Abstract

The recent discovery of crustacean body parts among small carbonaceous fossils (SCFs) has expanded the known range of Cambrian arthropods to include comparatively derived taxa, including copepods. However, the potential for SCFs to reveal larger-scale patterns in Cambrian crustacean evolution has been unclear, because of the small number of known occurrences. Previously, Cambrian copepods were represented solely by isolated mandibles (jaws) from the Deadwood Formation of Saskatchewan, Canada (middle to late Cambrian; = Series 3 to Furongian). Herein we report a second occurrence of Cambrian copepod mandibles, of closely comparable morphology, from the approximately coeval Nolichucky Shale of Tennessee, United States. The Nolichucky specimens were recovered using standard palynological processing, whereas the larger and more articulated Deadwood specimens were recovered using a low-manipulation procedure designed for SCFs. The two datasets represent largely distinct but complementary views onto a taphonomic continuum. In general, larger and more delicate crustacean SCFs reveal phylogenetically and ecologically informative characters, but are likely to be restricted in space and time, and are often low in abundance. In contrast, robust fragments of the same body parts are more likely to be preserved and recovered, but may be unidentifiable in the absence of SCFs. Therefore, conventionally recovered palynomorphs can expand the utility of SCFs to offer a higher-fidelity account of broad-scale evolutionary patterns.