Pinaceous evolution illuminated by additional diversity of Early Cretaceous seed cones

Abstract

An anatomically preserved fossil conifer seed cone has been discovered near Ono, California, providing additional evidence for the diversification of Pinaceae during the Aptian Stage of the Early Cretaceous. The specimen was measured and photographed, and then serial anatomical thin sections were prepared by the cellulose acetate peel technique. Selected peels were mounted on microscope slides, viewed, and photographed with transmitted light microscopy. Structure of the seed cone is similar to that of living and extinct representatives of the Pinaceae in the occurrence of helically arranged and imbricating foliate bract/scale complexes consisting of a small bract that subtends an ovuliferous scale bearing two inverted winged seeds on the adaxial surface. However, details of bract/scale complex vasculature, a wing that is obviously lateral to the seed body, and distinctive histological features reveal that this cone represents a new genus of extinct Pinaceae. This new genus of fossil conifers, represented by a seed cone of unique structure, further enriches the known diversity of Early Cretaceous Pinaceae. When added to the existing record of fossil seed cones, the new genus and species, Onostrobus elongatus Rothwell et Stockey, highlights knowledge that among early-diverging lineages of Pinaceae there has been considerable Cretaceous and Paleogene evolution that is reflected by variations among subtle characters that are recognizable only from anatomically preserved specimens.