Bringing together otolith and skeleton fossil record: the case of Old-World Cyprinodontiformes

Toothcarps (Cyprinodontiformes) are a highly diverse group of freshwater fish found worldwide. Their fossil record known until now is particularly rich in Eurasia, with few examples from Africa, and spans from the Late Eocene to the Pliocene. Although not as diverse as their extant relatives, approximately 76 fossil species have been described, of which 16 (21%) are based on skeletons with otoliths (“ear stone”) in situ, 24 (32%) are skeletons only, and 35 (46%) are based solely on otoliths. Linking skeletal with otolith-based findings can only be done in rare cases where fossils are found with otoliths in situ and/or when information from extant relatives is available. However, the lack of otolith knowledge from extant families and fragmented data of the fossil record has hindered the integration of skeletal and otolith-based fossil record. By gathering new morphometric, meristic and osteological data from fossil and extant species, together with a literature review, we started to investigate the skeletal and otolith-based fossil species to better understand the evolutionary and biogeographic history of toothcarps. The newly produced and compiled data suggest that the fragmentation of the Tethys Sea and the formation of its related basins (Paratethys) together with the development of various lake systems during the Oligocene and Miocene appear to have promoted the diversification and expansion of Eurasian toothcarps. Furthermore, we found some evidence that representatives of African and East Asian families, whose fossil record is very poor (apart from one family), may also have been present in Eurasia during this time.