60 — Polar wildfires and conifer serotiny during the Cretaceous global hothouse

This paper discusses fire-adaptive traits — features of plantlife that evolved to combat wildfire. These traits largely developed during and after the Cretaceous, a time when atmospheric oxygen was particularly high and the climate was particularly warm — both conducive to wider spread of wildfire.

Though evidence of serotiny — plants with seeds that are “triggered” to release in response to the environment rather than once the seed is fully matured — hadn’t previously been found in the fossil record, Mays et al use CT scans of fossil charcoal-rich deposits to identify morphology of plant reproductive structures. These structures, dated to the mid-Cretaceous, demonstrate that serotiny evolved during or before the mid-Cretaceous, which helps pinpoint what conditions led to serotiny, and informs our understanding of the Cretaceous environment.

The study used the Australian OPAL Reactor to record computed tomography (CT) imagery of the internal anatomy of reproductive structures from charcoal-rich deposits.

The anatomical features include thick shells — to insulate against heat and predation — and mechanisms to enable seed release in the presence of heat. (Thus, seeds are released when there is minimal ground cover and few animals remaining to eat them.)

It is significant that the fossil record has a timeline for the arrival of serotinous plant life because this helps orient us in the study of plant evolution, and strongly informs our understanding of what the world was like in the Cretaceous.