SEDIMENTOLOGICAL, LATITUDINAL, AND TEMPERATURE DISTRIBUTION OF TURRITELLINE GASTROPODS, CRETACEOUS-RECENT: A RETREAT FROM OR BY WARM CARBONATES, OR AN EFFECT OF SAMPLING?

Previous analysis of a data set of more than 50 fossil assemblages containing very abundant turritelline gastropods (Cerithioidea, Turritellidae) (“turritelline-dominated assemblages”; TDAs) showed a clear pattern of shifting from carbonate+clastic to only clastic sedimentary environments since the Cretaceous. These results might be due to: an evolutionary change in the environmental preferences of turritellines (either through speciation or extinction); the disappearance of warm high-nutrient carbonate environments as a result of onset of the icehouse climate regime in the mid-Cenozoic; or a fundamental bias in the preservation of carbonate environments in the fossil record or their representation amongst published data.

We have refined the details of this pattern, and normalized for sample size, using the more extensive dataset reposited in the Paleobiology Database. Analysis of more than 4,000 collections containing gastropods show that between the Cretaceous and Late Cenozoic: 1) there is a significant reduction in the proportion of carbonate sediments in the marine invertebrate fossil record in both temperate and tropical settings; 2) there is also an equally significant reduction in the relative preference of turritelline gastropods for carbonate sediments (as represented by both abundance [number of TDAs ] and number of occurrences) and increased preferences for siliciclastic sediments; and 3) turritelline occurrences show a dramatic increase in relative occurrence in tropical siliciclastic settings (1.2% to 41.5%), and were nearly absent in Cretaceous tropics when most occurrences are from temperate settings.

These results support the conclusion that turritellines shifted their sedimentologic preferences since the Cretaceous (although they also suggest that the group was never predominantly a carbonate-inhabiting taxon in the Cretaceous). They also quantify the previous conclusion that the latitudinal distribution of the group has contracted over time. This is not inconsistent with the view that they have usually preferred high-nutrient conditions, since these conditions likely were more widespread in the Cretaceous and paleolatitudinal position is not necessarily a proxy for temperature, since thermal gradients have steepened significantly since the Paleogene.