ANIMATING AMMONITES: USING GIS TO ILLUSTRATE CHANGES IN ABUNDANCE THROUGH THE WESTERN INTERIOR SEAWAY

The Western Interior Seaway (WIS) was an ecologically diverse seaway that divided North America during the Late Cretaceous. Its strata preserve a wealth of marine fossils that are vital for understanding many aspects of paleoecology and macroevolution. Here we combine information on abundance, along with geographic occurrences, in a Geographic Informations System (GIS) to study biogeography within the WIS. A similar approach has recently been applied by the Cornell lab of Ornithology and ebird to look at how bird species change their ranges over the course of seasons, and our work represents the first scaling of this approach to the fossil record and across geological time scales. The Scaphitidae, a major group of WIS ammonites, are the focal group. These comprise an ideal study organism as they are extremely diverse, well sampled, and were ecologically important denizens of the WIS. We use the GIS in conjunction with animations to present predictions about biogeographic dynamics and abundance models in the group, by temporal stage. The dataset used data obtained from Integrated Digitized Biocollections (iDigBio) that were subsequently pruned to remove specimens with limited taxonomic information or that were less well localized spatially and/or temporally. The remaining dataset contained approximately 13,000 specimens. The abundance model maps could reflect either preferred habitats of species, zones of intense paleontological sampling, or prominent outcrop belts. Comparisons with maps of the WIS and outcrop belts through time appear to support the habitat hypothesis, although additional research is needed. This type of GIS approach can also be used to explore changes in abundance distributions within clades through time, as well as differences between clades. Further, modeling patterns of abundance distribution may help reveal organismal dispersal distances in long extinct taxa, and how these for instance differed between ammonites and nautiloids. Information about such parameters will be very valuable in subsequent macroevolutionary studies.