The oldest Pinus and its preservation by fire

Pinus (Pinaceae) is a diverse conifer genus that dominates Northern Hemisphere forests today and is noteworthy for its fire-adapted traits. Here we describe the oldest known fossils attributable to the genus from the Lower Cretaceous (Valanginian, ca. 133-140 Ma) part of the Chaswood Formation of Nova Scotia, Canada. Pinus mundayi sp. nov. comprises charred long-shoots, which show a constellation of derived characters including (1) axial resin ducts with thin-walled epithelial cells in the secondary xylem and phloem, (2) fenestriform or pinoid cross-field pits, and (3) helically arranged short-shoots that pass through growth ring boundaries before distally diverging into two separate needle bases. The fossils, which are interpreted as remains of an evergreen two-needle pine, provide a new constraint on timetrees of Pinaceae evolution. Their preservation as charcoal and the occurrence of resin ducts, which produce flammable terpenes in modern pines, show that Pinus has co-occurred with fire since its Mesozoic origin.