When triceratops and velociraptors stalked the forests of the Cretaceous, at a time when flowering plants were just beginning to emerge, the planet was still dominated by conifers and pine trees. Now researchers have uncovered what is believed to be the oldest fossil of a pine tree ever discovered, a tiny piece of charcoal dating to around 140 million years ago, which shows that their evolution was driven – and the landscape dominated – by intense forest fires.

The discovery is helping the researchers to answer questions about how pine trees came into existence. The fossils are approximately 11 million years older than the previous record-holder, suggesting that the plants evolved much earlier than expected, and the fact that they were found within charcoal heavily suggests that their evolution has been intricately linked to wildfire for tens of millions of years. This is supported by the fact that the researchers were even able to look within the fossils to see ducts that would have carried highly flammable resin, a feature still present in modern pines.

^{Pine tree forests, such as the scot's pine one seen here, still dominate the Northern Hemisphere. Israel Hervas Bengochea/Shutterstock}

The resin is thought to aid wildfires, which are needed to allow the pine cones to germinate. This gives the seeds an advantage, because not only is the charred forest cleared of understory vegetation – and thus competition – but the ash also increases the fertility of the soil, providing vital nutrients for the developing seedlings. The thick, dead tissue surrounding the adult tree trunks prevents them from being damaged as the fires on the ground rage. During the Cretaceous, when the fossil dates to, the oxygen levels were much higher than today meaning that wildfires are thought to have been far more frequent and intense.

^{Botanists have long been puzzled as to why pines are so well adapted to forest fires, such as this one in a scot's pine forest. Viesinsh/Shutterstock}

“Pines are well adapted to fire today,” Royal Holloway’s Dr. Howard Falcon-Lang, who discovered the fossil and coauthored the paper published in the journal Geology, told BBC News. “The fossils show that wildfires raged through the earliest pine forests and probably shaped the evolution of this important tree.” The fossil specimens, which were encased in the rock gypsum, and were extracted by dissolving the rock in acid, are thought to be from trees that resembled the modern-day scots pine (Pinus sylvestris), today found across much of northern Europe and Russia.

Despite only being around half a centimeter long (0.02 inches), the researchers were able to tell a surprising amount about the ancient tree. From the small pits on the fossils surface, they are able to discern that the trees had twin pine needles, and as mentioned, by looking within the preserved twig are able to see resin ducts. Discovered in a quarry in Nova Scotia, Canada, the researchers plan on returning to the site to see if they can uncover more charcoal fossils of early pines.