Revisiting the Late Cretaceous Parataxodium wigginsii flora from the North Slope of Alaska, a high-latitude temperate forest

Abstract

Reinvestigation of a Late Cretaceous plant assemblage from along the Colville River on the North Slope of Alaska reveals both that the flora is far more diverse than previously suspected, and that many specimens are anatomically preserved. The flora includes one moss, an osmundaceous fern, one species of Ginkgo, the putative conifer leaf Pityophyllum, five species of cupressaceous conifers, five dicot leaf morphotypes, and one monocot. The cupressaceous remains heretofore have been interpreted as a single taxodioid/sequoioid conifer species, Parataxodium wigginsii Arnold and Lowther. However, reexamination of the fossils reveals five different morphologies of cupressaceous ovuliferous cones, and a wide range of intergrading leafy shoot morphologies. Peel sections show excellent internal anatomy for many of the cupressaceous conifer organs, as well the moss. These fossils characterize a high-latitude deciduous flora dominated by cupressoid conifer trees, with less common dicot and Ginkgo trees, and with ground cover that includes osmundaceous ferns, monocots, and dicranalean mosses. The increased diversity of disarticulated plant parts in the assemblage demonstrates that Parataxodium wigginsii is not nearly as well understood as widely believed, and that the genus and species concepts as currently defined may be based on organs from several cupressaceous conifers. This assemblage is an outstanding example of an unusual Late Cretaceous, high-latitude, Northern Hemisphere, mixed dicot-coniferous, cool temperate, deciduous forest that existed in total darkness for a significant period each year.