The first record of the large Cretaceous lamniform shark, Cardabiodon ricki, from North America and a new empirical test for its presumed antitropical distribution

Abstract

ABSTRACT The first occurrence of the lamniform Cardabiodon ricki is reported from the late Cenomanian of Alberta, Canada. Previously, this taxon was described from Australia and Europe and has been hypothesized in the published literature as having an antitropical distribution. Whereas the occurrence of C. ricki in Alberta seemingly supports this hypothesis, no formal methodology exists to determine if Cardabiodon had an antitropical distribution because sampling for Cenomanian fossil elasmobranchs in the tropics is poor. We offer a novel methodology to test the purported hypothesis of an antitropical distribution for Cardabiodon by examining three paleoecological aspects. We compare the range of sea surface temperatures (SST) and paleolatitudinal ranges of Cardabiodon localities to those of the extant antitropical shark, Lamna nasus, because Cardabiodon should exhibit a similar magnitude of thermal and paleolatitudinal ranges to those of L. nasus. Furthermore, the paleodistribution of Cardabiodon localities should shift with climate change. Cardabiodon is concluded to have an antitropical distribution because (1) the SST range for Cardabiodon was only slightly greater (by 1.7°C) than that recorded for L. nasus; (2) the difference in paleolatitude range for Cardabiodon was 10° latitude less than the modern range for L. nasus; and (3) the paleolatitudes of Cardabiodon localities are positively correlated with global temperature to indicate that, during warm periods, Cardabiodon was found at higher paleolatitudes in both hemispheres, but it was found at warmer, lower latitudes during cooler periods.