KOSKOBILO (SPAIN) – THE RICHEST CRETACEOUS DECAPOD LOCALITY IN THE WORLD?

During the mid-Cretaceous, several reefs developed in the present-day area of western Navarra (northern Spain). The mid-Cretaceous reefs are part of the Albian-Cenomanian Albinez unit within the Eguino Formation. The Koskobilo quarry is situated within the Aldoirar patch reef and was discovered and visited during recent fieldwork in the summers of 2008 and 2009. The main reef builders are corals and algae; associated fossils include anomuran and brachyuran decapod crustaceans, bivalves, benthic foraminifera, and echinoderms. This outcrop yielded a varied and remarkably rich decapod fauna consisting of crabs and squat lobsters. Although research on the fauna is still in progress, based on the huge collection of many hundreds of decapod specimens, it is estimated that the total number of species from this outcrop is about 30. Another rich exposure bearing decapods in close proximity to the Aldoirar reef is the Mt. Orobe patch reef, which yielded 23 decapod species. Preliminary observations indicate that many of the species reported from Mt. Orobe also can be found in Koskobilo. In addition, several new species have been encountered at Koskobilo. For comparison, there is no locality with Cretaceous sediments known to us that has yielded more than thirty decapod species. The Koskobilo locality might, thus, be the richest decapod locality in the world for the Cretaceous. Moreover, the Spanish Eguino Formation might be the richest Cretaceous formation containing decapods. The high number of decapod species most likely was facilitated by the many different habitats within the reef. Fieldwork was partly supported by NSF grant EF0531670 to Feldmann and Schweitzer.