Paleobiogeography of the pectinid bivalve Neithea, and its pattern of step-wise demise in the Albian Northwest Pacific

The pectinid bivalve genus Neithea is one of the most important indicators for understanding the biogeographic relationships between the Tethyan Realm and North Pacific Province during the Cretaceous Period. Changes in temporal species diversity, endemic/widespread species composition, and origination and demise ratios of Neithea at each Cretaceous stage boundary in the Northwest Pacific were analyzed from a biogeographic perspective. Neithea is continuously present in the Northwest Pacific during the Berriasian to late Albian time interval. Species diversity reached its maximum in the late Aptian, being correlated with the global warming phase. Step-wise demise of Neithea in the Northwest Pacific during the Albian is subdivided into three stages: the late Aptian/early Albian, early Albian/middle-late Albian, and late Albian/early Cenomanian. Thereafter, Neithea disappeared in the Northwest Pacific and never reappeared. This pattern is the reverse of the Albian diversification of Neithea in the Mediterranean, and also contrary to the Mid-Cretaceous global warming trend. Demise of Neithea in the Northwest Pacific occurred simultaneously with the step-wise demise of Mesogean taxa (e.g., rudists) which strongly supports the idea that the Northwest Pacific gradually became independent from the Tethyan Realm during the Albian. It also suggests a long-term deterioration of the faunal interchange between the North Pacific Province and Tethyan Realm throughout the Late Cretaceous. This biogeographic change was possibly caused by Albian "cooling" and changes in oceanic flow/heat transport in the Northwest Pacific.