The Wagner Parsimony using morphological characters: a new method for palaeosynecological studies

NEL , A., NEL, P., PETRULEVICIUS, J. F., PERRICHOT, V., ARIA, C., PROKOP, J. Y AZAR, D.

Beijing

Congreso; V International Congress of Paleoentomology, III International Meeting on Paleoarthropodology, y IV Amber International Congress (?Fossil X3?); 2010

The analysis of global, planetary, faunistic and floristic changes during the Phanerozoic eon is very important to define the stratigraphic divisions and the major crises of biodiversity. The only available tools to study and estimate these changes are ?typological? techniques, characterizing the different geological periods by the presence/absence of fossils that are supposed to be a priori characteristic of each of them. Only a few works concern insects, or more generally terrestrial arthropods, while these constitute the most diverse groups of animals since the Late Carboniferous. Current comparisons of the faunas or floras of different geological periods (for estimations of global crises) are based on variations of percentages extracted from lists of presences versus absences of taxa (orders, families). They are currently established using groups of organisms without any precaution concerning their monophyly, which can introduce important biases. The difficulties related to the monophyly of the taxonomic groups used in the more traditional approaches are no longer a problem when using the new method of Wagner parsimony Applied to Palaeosynecology Using Morphology (WAPUM method). In the WAPUM a character is ?presence versus absence of species bearing a morphological structure?. The results obtained from use of the WAPUM minimize the number of changes among character states. Application of the WAPUM could reveal signals to confirm or object the currently available scenarios for the global changes in the evolution of past diversity and disparity of organisms (major changes or global crises of diversity). We tested and demonstrated the feasibility of the WAPUM method with two insect groups, Odonatoptera and Thripida. We could demonstrate an absence of significant changes in the odonatopteran morphology between the Upper Permian and Lower Triassic and also at the K-T boundary, but the presence of important changes at the boundary Lower - Upper Cretaceous, maybe correlated to the well-known angiosperm diversification. For the Thripida, important changes seem to have occurred at the Jurassic - Cretaceous boundary but this could be an artefact due to the lack of thrips inclusions in pre-Cretaceous amber.