Cenozoic biogeography of Western Tethys decapod crustaceans

The fossil record is a powerful tool for documenting biogeographic histories and ancestral areas. Today, the Indo- West Pacific (IWP) is considered a centre of biodiversity, including decapod crustaceans. Renema et al. (2008) argued that today`s biodiversity hotspot in IWP has its origin in the Western Tethys (WT) and that major shifts of marine faunas occurred within the last 50 million years. A considerable part of WT is formed by the circum- Mediterranean area. During the Cenozoic it broke into several palaeogeographic areas: the Paratethys Sea, the North Sea and the Proto-Mediterranean Sea. The proposed research project is focusing on the middle to late Cenozoic palaeobiogeography of the WT decapods with the emphasis on shallow marine benthic communities and a special interest in the Miocene of the Central Paratethys because of well documented sedimentary sequences with good stratigraphic control and numerous outcrops with preserved decapod associations. A main goal is to discover testable patterns of decapods crustaceans` dispersal routes within WT and the relationship of decapod associations to other biogeographic areas. Although the role of Tethys as an ancestral area of numerous decapod taxa has already been noted in previous palaeobiogeographic studies (Feldmann & Schweitzer 2006) no detailed analysis of the Tethyan taxa has been conducted so far. Considering the long history of collecting and the currently proposed hypothesis of WT as a centre of origin and diversity during Oligocene and Early Miocene times (Harzhauser et al. 2007), decapods are promising tool for tracking faunal shifts in the geological past. The research programme is planned as a two-year project at NHMW. The first year will be focused on building the database and will be concluded with publication of taxonomic revisions resulted from the examination of the material. The second year will be focused on the palaeobiogeographic analyses. A database will be compiled from published and newly collected material. Critical revision of the systematic placement of previously established taxa will ensure systematic coherence. The analyses will use only decapods. In this respect use of the decapods provides a mean by which to independently test patterns derived from analyses of other groups of organisms. For better evaluation of the potential of decapods several different methods will be employed. Examined associations will be compared using a binary coefficient based on presence/absence of taxa. Similarity between studied areas based on their taxonomic composition will be analysed using clustering analysis and ordination (PCA). Using Parsimony Analysis of Endemicity times-sliced series of stratigraphically coeval data will be analysed separately to show changing relationships between sample areas and biotas over successive time horizons. By using time controls provided by fossil decapod associations we will learn more about the relationships of areas with complex histories, such as WT. Using these data, dispersal theories based on extant decapods only (Groeneveld et al. 2007; Sotelo et al. 2009) can be put to a test.

During the last thirty million years, Europe experienced dramatic geographical changes. In addition to the Mediterranean Sea in the South, there was the vast Paratethys Sea spreading across large parts of Central and Eastern Europe. Marine organisms, including decapod crustaceans, i.e. crabs, lobsters and shrimps, migrated between the Mediterranean, the Paratethys and the East Atlantic Ocean via intermittent connections. The research project was focused on the palaeobiogeography of decapods, thus, on the affinities and interactions of decapod faunas between respective areas in different time periods. Extensive data collecting provided a basis for estimation of decapod species diversity within the last thirty million years; altogether 392 decapod species in 178 genera were recorded.The main results of the project are the first palaeobiogeographic analyses based exclusively on decapods from the area of today's Europe. Several conclusions were drawn from them: During the Oligocene and Early Miocene (3416 million years ago) decapod faunas of the Paratethys in general had more affinities to the Atlantic Ocean than to the Mediterranean. These relationships probably reflect remains of relatively uniform marine faunas from the time before the Oligocene (>34 million years ago) when organisms could migrate freely across vast areas of today's Europe. During the Early and Middle Miocene (2312 million years ago),when the Paratethys and the Mediterranean became well-separated seas, Mediterranean decapod species migrated into the Paratethys, but taxa that had evolved in the Paratethys did not spread to the Mediterranean. As a result, in the Paratethys numerous endemic species evolved by the Middle Miocene (1612 million years ago). Later, the Paratethys shrunk and transformed to a lacustrine system Lake Pannon which hosted the last remains of the marine decapod faunas approximately 10 million years ago, as suggested by indirect evidence of their fossil burrows.Based on the data from different groups of organisms, the investigated area has been proposed to represent a centre of biodiversity, a so called biodiversity hotspot, in the geological past. Here new species evolved and spread into adjacent areas. Today, such biodiversity hotspot is located in the Indo-West Pacific. Decapods do not necessarily show a simple pattern of directional migration of marine organisms from the area of today's Europe to the Indo-West Pacific. In future studies, a contraction of a much larger biodiversity hotspot rather than a shift should be considered as possible explanation for the patterns observed.The present project delivered novel insights into the palaeobiodiversity and palaeobiogeography of Europe and the Mediterranean Region, since only minor attention has been paid on fossil decapods in biogeographic studies so far.. The results of the project thus represent an important advancement in the field of marine palaeobiology, both within Europe and internationally.