Fish Faunas from the Bissekty Formation (Turonian), Uzbekistan: Insights into biogeographic connectivity and climate-driven Faunal Turnover

The Bissekty Formation (Turonian, Uzbekistan) provides new insights into the reorganization of aquatic paleocommunities that occurred during the Turonian thermal maximum, a period of significant climatic and faunal change. The assemblage includes four basal neopterygians and 13 teleosts. Teleosts are dominated by members of early diverging lineages, including Ichthyodectiformes, Elopomorpha, Osteoglossiformes, and Clupeomorpha. More derived teleosts present in the assemblage includes a characiform and an acanthomorph. The assemblage is distinctive compared to Late Cretaceous assemblages from North America in the high abundance of ichthyodectiforms and elopomorphs and both high abundance and large size of acanthomorphs. The Bissekty fish assemblages differs from preceding Cenomanian assemblages of Laurasia in the absence of two taxa that were dominant in the earlier Cenomanian assemblages, Scheenstia López-Arbarello and Sferco, 2011 (Lepidotidae) and a pycnodont, and the appearance of seven new taxa. One of the newly appearing taxa is a member of Characiformes, a group that is thought to have originated in Gondwana, adding to the evidence that the introduction of new taxa was a result, in part, of intercontinental dispersal events. All seven of the taxa that first appear in the Bissekty Formation are closely related to, or indistinguishable from, taxa present in the North American portion of Laurasia. However, only two of these are known to occur in North America during the Turonian, with the remaining taxa first occurring in North America in a step-wise pattern during the Late Cretaceous. Conversely, two of the taxa that first occur in the Turonian of the North American portion of Laurasia are absent in Asian assemblages.