A CRYPTIC EXTINCTION EVENT: DISAPPEARANCE OF MULTIPLE LARGE MARINE FISH SPECIES IN THE EARLY CAMPANIAN NORTH AMERICAN INTERIOR SEAS

Nearly synchronous disappearance of several widely-distributed, large marine (> 4 m) fishes in the early Campanian, ca. 82-78 Myr, suggests an unrecognized event in the Late Cretaceous marine fossil record. These extinctions were distributed among selachian, teleost and coelacanth species, and among multiple trophic strategies. Included among these extinctions were the two largest Cretaceous predaceous selachian species, Cretoxyrhina mantelli and Cretodus crassidens. Also going extinct at this time was the widely distributed predaceous teleost Xiphactinus audax, the suspension-feeding coelacanth Megalocoelacanthus dobiei, and the last surviving species of the molluscivorous genus Ptychodus. Cretoxyrhina and Ptychodus extinctions occurred at the generic level, whereas, in contrast, Xiphactinus audax was apparently replaced by the equally large species X. vetus, and Cretodus crassidens was apparently replaced, at least at the generic level, by several much smaller species such as C. borodini.

The cause of these major changes in the marine megafauna remains cryptic, since the extinctions range among taxa, feeding strategies, and include both apparent replacements and non-replacements by new, congeneric species. The precise timing of the extinction events is also difficult to constrain because of a quirk in the North American marine fossil record: highly fossiliferous deposits in the Western Interior Seaway tend to be skewed toward Turonian through Santonian ages, e.g. in the Niobrara Formation. In contrast, along the Atlantic Coastal Plain, Late Cretaceous marine deposits tend to yield fossils mostly of late Campanian and Maastrichtian ages. Fortunately, the marine record in Alabama and western Georgia incorporates fossiliferous deposits ranging from Santonian through Campanian, which help to elucidate the faunal changes and includes all of the extinct species and their apparent replacement taxa.