Seafood Salad: A diverse latest Cretaceous flora from eastern Montana

Abstract

Abstract The Cretaceous-Paleogene boundary (KPB) marks a mass extinction resulting in global biotic turnover. Exposures of the Hell Creek Formation in northeastern Montana contain some of the most well-studied vertebrate localities recording this mass extinction; however, very little is known of the floral record in this area. As part of an effort to reconstruct floral changes across the KPB in northeastern Montana, this study presents a taxonomically diverse flora from the Seafood Salad locality, located ~65\xa0m below the KPB in the Hell Creek Formation, Garfield County, Montana. Leaves, stems, and reproductive structures (e.g., cones and seeds) are preserved as compression and impression fossils in massive, bedded siltstones and very fine sandstones. Seafood Salad is significant in that it represents a “pre-disaster” community approximately 1.3 m.y. before the Cretaceous-Paleogene mass extinction. We interpret the plants in these deposits as reflecting a local riparian community. The vegetation was taxonomically diverse and dominated by angiosperm trees; it also included abundant conifer specimens of a few taxa and relatively few ginkgoes and ferns. We describe 34 morphotypes and propose taxonomic affinities to modern groups and to fossil taxa from contemporaneous-age deposits in Montana and North Dakota. The Seafood Salad flora shares several taxa with other Late Cretaceous floras of the Western Interior, but substantial differences in taxonomic composition and relative abundances among these assemblages indicate that regional plant communities in the latest Cretaceous were spatially heterogeneous, rapidly changing, or both.