Abstract

Premise of the study: Characterization and phylogenetic integration of fossil angiosperms with uncertain affinities is limited, which may obscure the diversity of extinct higher taxa in the flowering plant tree of life. The order Cornales contains a diversity of extinct taxa with uncertain familial affinities that make it an ideal group for studying angiosperm turnover. Here, we describe a new extinct genus of Cornales unassignable to an extant family and conduct a series of phylogenetic analyses to reconstruct relationships of fossils across the order.
Methods: Two permineralized endocarps were collected from the Cedar District Formation (Campanian, 82-80 Ma) of Sucia Island, Washington state, USA. Fossils were sectioned with the cellulose acetate peel technique and incorporated into a morphological dataset. To assess the ability of this dataset to accurately place taxa in their respective clades, we conducted a series of phylogenetic pseudofossilization analyses. We then conducted a total-evidence analysis and a scaffold-based approach to determine relationships of fossils.
Key Results: Based on their unique combination of characters, the fossils represent a new genus, Fenestracarpa washingtonensis gen. nov. et sp. nov. Pseudofossilization analyses indicate that our morphological dataset is capable of accurately recovering taxa at the major clade level, generally with moderate to high support. The total-evidence and scaffold-based analyses recovered Fenestracarpa and other fossil genera in an entirely extinct clade within Cornales.
Conclusions: Our findings increase the reported diversity of extinct Cornales and indicate that the order’s initial radiation likely included the divergence of an extinct higher clade that endured the end-Cretaceous Mass extinction but perished during the Cenozoic.