ORIGINATION AND EXTINCTION IN DECAPODA (CRUSTACEA) AT THE END-CRETACEOUS

Origination and extinction of decapod genera near the end-Cretaceous changed the diversity and faunal composition of the group in the Cenozoic. 140 decapod genera are currently recorded from the Maastrichtian. Of those, 40 became extinct (29%). 60 genera (43%) crossed into the Cenozoic, and just over half of those (32) are referred to extant genera. 40 (29%) occurred only during the Maastrichtian. In regions proximal to the Chixculub Impact Site, extinction rates were variable. In the Western Interior Seaway, 91% of genera occurring in the Maastrichtian became extinct (n =11) and along the North American Atlantic Coastal Plain, 43% of genera became extinct (n = 14). Of North Atlantic occurrences, 27% became extinct (n = 54), whereas on the west coast of North America only 14% became extinct (n = 7). On the American Gulf Coastal Plain extinction and survivorship were each at about one-third of genera. Locations with five or fewer genera exhibit variable levels of extinction, from 0% (Japan) to 66% (New Zealand). In Northern South America 2 of 3 genera became extinct. Thus, the highest extinction rates occurred proximal to Chixculub, in the Western Interior Seaway and on the Atlantic and Gulf Coastal Plains of North America. Survivorship was high in the North Atlantic comparatively, with 48% of the genera crossing into the Cenozoic. The issue of singleton genera is a problem, with the locations examined here ranging from 20-67% of genera occurring only in the Maastrichtian. About 41% of the singletons are podotrematous crabs and 30% are heterotreme crabs. Two-thirds of the K/T boundary crossing genera are shrimp, mud and ghost shrimp, and anomurans referred to extant genera. Of the genera extinct at the end of the Cretaceous, 70% were podotrematous crabs, and of those, 30% were members of Raninoida (frog crabs). These data suggest that faunal turnover within both podotrematous and heterotrematous crabs was rapid at this time, whereas evolution in lobsters and shrimps was conservative. These findings both parallel and confirm the faunal turnover of decapod crustaceans found by Schweitzer & Feldmann (2015), wherein lobsters, podotrematous crabs, and heterotrematous crabs experienced sequential rises and falls in diversity.