Chapter 17 - Fossil Seeds With Affinities to Austrobaileyales and Nymphaeales From the Early Cretaceous (Early to Middle Albian) of Virginia and Maryland, USA: New Evidence for Extensive Extinction Near the Base of the Angiosperm Tree

Abstract

Early Cretaceous seeds from Virginia and Maryland, USA, part of a diverse complex of exotestal seeds in Early Cretaceous mesofossil floras from North America and Europe, provide new evidence of extensive extinction among early angiosperms. The seeds are assigned to a new genus, Nitaspermum, with six species: N. taylorii, N. hopewellense, N. crassum, N. virginiense, N. marylandense, and Nitaspermum sp. All seeds are small, anatropous, bitegmic, and exotestal, with the exotesta composed of a single layer of short, columnar sclerenchyma with strongly folded walls. Nitaspermum shows features of extant Austrobaileyales (Illiciaceae) and Nymphaeales but also critical differences precluding assignment to extant families. These discoveries are consistent with predictions from molecular phylogenetics that indicate the differentiation of Illiciaceae and Nymphaeales early in angiosperm evolution, but the diversity of such seeds underlines the extent to which the pattern of extant angiosperm diversity has been shaped by widespread extinction early in angiosperm evolution.