AN INTEGRATIVE ASSAULT ON CLAM SHRIMP ('CONCHOSTRACA'; BRANCHIOPODA; CRUSTACEA) PALEOBIOLOGY AND PHYLOGENY

Clam shrimp ('conchostracans') are a diverse group of phyllopod crustaceans with modern representatives that occur on every continent except Antarctica. Restricted to freshwater systems, the majority of modern taxa inhabit lakes, ponds and ephemeral water bodies. Although well-represented in the fossil record, the vagaries of preservation have forced paleontologists to rely on a completely different set of characters (those of the carapace) than those used by modern taxonomists (characters based on the thinly sclerotized organism within the carapace). The separation of fossil and modern clam shrimp taxonomy is further complicated by three separate fossil taxonomic systems that have arisen independently. Together, these factors all prevent a phylogenetic synthesis of the group and an understanding of their evolutionary ecology.

In an attempt to resolve these long standing issues, we have begun a multi-faceted research program that tackles the growth, variation and taphonomy of clam shrimp. Most fossil clam shrimp are represented by the carapace only. Features of the carapace, like shape and ornamentation, have been dismissed or ignored by taxonomists who work on living species, but their utility has never been tested. Preliminary work involving the application of contemporary morphometric methods has shown that the shape of the carapace can be quantified and implemented in the identification of inter- and intra-specific (sex & ontogenetic stages) morphotypes. Meanwhile, extensive study of the ornamentation suggests that, contrary to common wisdom, it is phylogenetically useful. Although patterns of ornamentation may vary through ontogeny, they vary in predictable ways.

Furthermore, unlike most other crustacea, clam shrimp undergo incomplete molting, which means they retain a complete ontogenetic record in the morphology of the carapace. To understand what these characters means, we need to have an understanding of a) how the characters are generated, b) how they grow and c) how they are affected by taphonomic processes. By conducting taphonomic and rearing experiments, we aim to assess the factors that contribute to the condition of clam shrimp remains in the fossil record. With this data, we will discover how best to interpret them and begin to formulate a much-needed comprehensive review of the specifics of clam shrimp paleontology.