New research reveals that magic mushrooms have existed since before the dinosaurs became extinct, although exactly why fungi developed the ability to produce psychedelic compounds remains a mystery. Tracing the history of the genes that give rise to the mind-altering substance psilocybin, the study authors found that the mushroom genus Psilocybe first evolved the enzymes required to synthesize the compound almost 70 million years ago.

Around 165 different species of Psilocybe mushroom have been identified worldwide, with the majority being psychoactive. However, despite the popularity of shrooms as recreational drugs and, more recently, therapeutic tools, it took until 2017 for the genes underlying the biosynthesis of psilocybin to be identified.

As it turns out, the compound is synthesized by a quartet of enzymes that convert the amino acid tryptophan into psilocybin and whose genes are grouped together in what’s known as a biosynthetic gene cluster (BGC). Until now, though, researchers had only identified this BGC in five different Psilocybe species, making it difficult to trace the evolutionary history of these genes.

To resolve this, the study authors compared the genomes of 71 different Psilocybe mushrooms, analyzing the distribution of 2,983 genes in order to create a type of genetic family tree known as a phylogeny. Revealing where in the mushrooms’ evolutionary history different genes emerged, the resulting phylogeny indicates that the psilocybin BGC first appeared roughly 67 million years ago.

This means that magic mushrooms were around for the last million years or so of the dinosaur age, which came to a dramatic end during the Cretaceous–Paleogene extinction event. Based on the researchers’ analyses, psilocybin first appeared in wood-rotting fungi species but was later transferred to mushrooms that grow in soil and animal dung.

In spite of the profound effects of psilocybin on human consciousness, it’s clear from this study that magic mushrooms evolved long before even our earliest ancestors appeared on the scene. It’s therefore highly unlikely that the ecological function of psilocybin has anything to do with humans, so why did the compound evolve in the first place?

Given the rarity with which non-human animals have been observed consuming shrooms, the study authors say psilocybin was probably never intended for large critters. Sadly, then, the prospect of T. Rex and friends living out their last days in a psychedelic haze is slim.

On the other hand, “fungal-insect interactions are ancient and widespread and provide a more logical hypothesis for development of psilocybin as a chemical defense in mushrooms,” write the researchers. “To date, this has been the most commonly asserted hypothesis for the ecological role of psilocybin, but empirical studies are still lacking.”

Though plausible, this theory is somewhat undermined by the fact that insects regularly prey on Psilocybe mushrooms or lay eggs in them. This would suggest that either the bugs have developed a degree of immunity to psilocybin, or the compound was never meant to deter insects in the first place.

Ultimately, the researchers are unable to explain why mushrooms became psychedelic, although, whatever the reason, these findings reveal that it’s been a long old trip.

The study is published in the Proceedings of the National Academy of Sciences.