UTILITY OF NODEXL IN INVESTIGATING PALEOECOLOGY AND PALEOBIOGEOGRAPHY OF FOSSIL DECAPOD CRUSTACEANS

NodeXL is a free, open-source template for Excel that maps social networks (nodexl.codeplex.com). It is used to analyze real time or nearly real time interactions between individual accounts on Twitter or Facebook or in email communications. The program creates various graphs or other visual displays showing the interconnectedness of individuals based upon their communication. Those with more social contacts have more connections. Here we investigated the utility of mapping decapod crustacean occurrences in NodeXL. We first mapped co-occurrences of various decapod genera within and between Campanian formations of North America, with the goal of determining whether certain decapod genera had more ore fewer generic co-occurrences, displayed as connections in NodeXL, and if they frequently occurred with the same taxa (ie. Hoploparia frequently occurs with Necrocarcinus; Tetracarcinus has few co-occurring genera). We determined that certain genera have more “connections,” that is, they frequently occurred with many other genera. Other genera had few “connections,” occurring as sole decapod occurrences within a formation or with few other genera. The number of connections between a genus and other genera may be used to drive hypotheses about ecological broadness or specialization within certain genera. We suggest that ecological generalists will demonstrate more connections than specialists and that certain environments (carbonate, fine siliciclastic, etc.) may yield a specific array of co-occurring genera. NodeXL is particularly suited to showing such connections. We further investigated the utility of plotting Maastrichtian decapod genera of North America, and then comparing the resultant co-occurring genera with those in the Campanian. Campanian genera showed more interconnectedness across faunas, such that certain genera occurred in more regions and with more genera, whereas in the Maastrichtian, fewer interconnections between and among genera occurred. Possible controls on interconnectedness may include specialization in faunas and geographic isolation due to sea level drop. We suggest that changes in both faunal associations and geographic distribution of taxa over time can be mapped in this way.