Crocodyliforms, ancestors of living crocodiles, were an incredibly diverse group of terrestrial and aquatic vertebrates that represent an ideal, but often overlooked, taxonomic group for biogeographic analyses. An abundance of new crocodyliform fossils from poorly sampled southern hemisphere landmasses promises to assist in addressing major gaps in knowledge concerning the biogeographic and plate tectonic history of the southern supercontinent Gondwana. Unfortunately, the evolutionary relationships of crocodyliforms are still unsettled, thus preventing meaningful biogeographic interpretation. This project seeks to clarify the evolutionary history of crocodyliforms through phylogenetic analysis; it involves critical reexamination of previously described crocodyliform species and the inclusion of new species in a comprehensive analysis.
Given the accessibility of fossil vertebrates to the public, this study provides an engaging mechanism for relating evolutionary and biogeographic questions to a wider audience. Moreover, this study will contribute to future research through the production of fossil casts and detailed morphological descriptions, images, and CT scans to be made available to other researchers. The phylogenetic dataset produced for this project will form the foundation for future work in crocodyliform evolutionary relationships. This study will also critically compare competing methods in biogeographic analysis through a comparative analysis that will provide the groundwork for ongoing investigations.
The fossil record preserves a remarkably diverse and widespread group of crocodiles much more varied than living forms, ranging from small-bodied herbivores/omnivores to large, terrestrial hypercarnivores. Features of this group, such as high diversity, widespread geography, and primarily terrestrial habit, make them a model clade for investigations into the Cretaceous biogeography of the southern, Gondwanan landmasses. However, disagreement over their evolutionary relationships makes these investigations difficult. The goal of this project was to provide detailed descriptions of several new fossil crocodile species from Africa and Madagascar and to develop a comprehensive analysis of evolutionary relationships among extinct crocodiles. The larger aim of this project was to use these results to test hypotheses surrounding the timing and sequence of the breakup of the southern, Gondwanan continents. In order to accomplish this, the project built upon previous phylogenetic (evolutionary) analyses to develop an expanded and inclusive dataset to test crocodile relationships. This award supported travel to 20 museum and university institutions around the world, providing access to specimens necessary for investigations into the comparative anatomy and evolutionary relationships of fossil crocodiles. The resulting dataset provided an organized and clarified foundation on which a study of crocodyliform phylogenetic and biogeographic analyses was conducted. The project has contributed significantly to the disciplines of paleontology and evolutionary systematics by (1) contributing detailed anatomical descriptions of poorly known and new fossil crocodyliforms from Madagascar and Africa that fill important gaps in our knowledge of the Cretaceous evolution of crocodiles; (2) providing valuable comparative information for future studies of crocodile evolution, diversification, and paleobiology; and (3) resolving relationships among several basal crocodyliform groups critical for testing biogeographic hypotheses. Results of the project indicate that the diversification and variation observed in the fossil record are directly linked to the biogeographic history of crocodyliforms. While vertebrate fossils may not be able to fully resolve continent-scale tectonics, they can be used to confirm geological and geophysical hypotheses surrounding the timing and sequence of continental breakup. Further, the evolutionary patterns observed in fossil crocodiles may be representative of large-scale patterns in other terrestrial vertebrates. As of the completion of the award period, this study has produced seven publications in peer-reviewed journals or books, four papers presented at annual scientific meetings, and twelve additional studies in various states of preparation for peer-review publications. Specifically, the support provided by this award will directly contribute to (1) the description of more than eleven new or poorly known species of fossil crocodiles; (2) a new phylogenetic (evolutionary) dataset of more than 80 fossil and living crocodiles; and (3) increased understanding of the biogeographic patterns induced by temporally large-scale tectonic events such as the breakup of Gondwana. The broader impacts of the project have thus far included more than five public lectures on fossil crocodiles and their evolution; three public lectures at international venues stressing the importance of fossils, paleontology, and research; and live broadcasts through the Denver Museum of Nature & Science’s "Scientists in Action" program to more than 800 elementary, junior high, and high school students around the country. Efforts will continue to be made to use the results of this project to inspire and educate the public through popular media and general audience presentations.
