REGIONAL TO GLOBAL PATTERNS IN LATE CRETACEOUS SELACHIAN (CHONDRICHTHYES, EUSELACHII) DIVERSITY

Although selachian fossil remains have been studied for nearly three centuries, little is known about their evolutionary history. Recent studies have suggested different timings of early diversification events in the Late Triassic, Jurassic, and Early Cretaceous. However, Late Cretaceous selachian diversity has remained little explored despite numerous and diversified selachian assemblages known from this time interval. Sampling standardization, origination/extinction rates, and raw ordinal diversity were examined based on taxonomic occurrences in three data sets representing distinct geographical areas (Anglo-Paris Basin, northwestern Europe, and Western Interior Seaway) spanning the Cenomanian-Campanian interval. This examination allowed the identification of regional diversity events, previously reported for some invertebrate groups, but presented for the first time for a marine vertebrate group. The local mid-Cenomanian diversity drop (Anglo-Paris Basin) is interpreted as a possible consequence of changes in bottom sea water conditions related to the rapid mid-Cenomanian transgression. The Cenomanian/Turonian faunal turnover is likely to be due to various sampling biases (Anglo-Paris Basin and northwestern Europe), but a genuine extinction in the Western Interior Seaway cannot be excluded. The Santonian diversity peak synchronous with a marked global increase in seawater temperatures contrasts with the rapid temperature decrease linked with low diversity in the early Campanian.