SCORPION TAPHONOMY: IMPLICATIONS FOR DISTINGUISHING FOSSIL SCORPION MOLTS AND CARCASSES

Scorpions are terrestrial chelicerates with a prosoma (head), seven mesosomal (body) segments, and five metasomal (tail) segments. Scorpions have a fossil record reaching back to the Silurian, when they were aquatic, but there is very little literature on fossil scorpions. The taphonomy of scorpions (both modern and fossil) has not been systematically documented, even though these data could be applied to gaining a better understanding of true paleoarthropod diversity (an accurate estimate of biodiversity must distinguish between molts and carcasses) and better understanding the role of arthropods in paleoecosystems. The purpose of this study is to develop criteria to distinguish between fossil scorpion carcasses and molts, by studying the taphonomy of modern scorpions (following the experimental design of Babcock, on modern horseshoe crabs, and Briggs and Kear, on shrimp, among others).

Nine scorpion carcasses were allowed to decay for different lengths of time, under both aerobic and anaerobic conditions. To date, two carcasses have been tumbled in inoculated freshwater to the point of total disarticulation, and have had the order of disarticulation of exoskeletal elements noted. Patterns of disarticulation and breakage of exoskeletal elements have been catalogued for 14 scorpion molts. Comparison of these initial data has revealed similarities and differences between extant scorpion molts and carcasses that may be useful in distinguishing fossil scorpion molts and carcasses. Of particular interest are body posture, order of appendage disarticulation, and position of the chelicerae. The size of the specimen appears to affect scorpion taphonomy; for example, body posture (curved vs. straight) is an effective criterion for distinguishing molts from carcasses most reliably only among the larger specimens.

Among extant arthropods, scorpions possess the body plan most similar to the extinct eurypterids (and scorpions were at one point aquatic with a body plan that differed very little from the terrestrial body plan). Therefore, scorpions are a reasonable analogue for studies of taphonomy and ecdysis of euypterids. It is likely that this work on scorpion taphonomy will have important implications for studies of eurypterid paleobiology. This work was supported by a grant from the N-C Section of the GSA.