Fir Trees & Building the World of the Distant Past

Understanding when and where a group of species evolved tells a story of the world they emerged into.

This past week, I had an interesting new scientific paper come across my desk, on the systematics of fir trees – genus Abies in the Pine family. I realize fir tree systematics is not what the average person might consider compelling reading, but if you look past the statistical tests and lines of code, systematics can be great reading for the imagination. In this paper, the researchers reconstructed the speciation pulse (a period of time when a bunch of species came into existence fairly quickly) of fir trees native to the Mediterranean Basin, then dated it using fossils. The main finding of the paper was that this burst had actually happened millions of years earlier than had been supposed.

The really neat part is how they then used this finding to paint a picture of the world when fir trees were colonizing the Mediterranean. At the time these fir trees diversified, what we now think of as the Mediterranean climate, temperate and favourable to biodiversity, didn’t exist, and wouldn’t for tens of millions of years yet. At this time, the Oligocene-Miocene boundary, around 23 million years ago, the global climate had been cooling for some time, which favoured the expansion of gymnosperms like firs. A single ancestor came to the Mediterranean from Asia and quickly (for trees) spread through the whole of the Mediterranean Basin, leaving a dozen or so new species in its wake. This was going on at a time when the first apes were evolving and glasslands were just forming for the first time. The Andes didn’t exist yet and Australia was moving northward and drying out. What we now know about Mediterranean fir trees adds a new detail to this picture of a world very different from, but turning into, our own.

In my own work on the systematics of the Dialiinae, I’ve always been captivated by a genus called Labichea. It’s a group of about 14 shrubs native to Queensland, Australia. The earlier evolving species of the genus have pinnate leaves with broad leaflets, sort of like walnut trees (but smaller and more oval). From this, there is an evolutionary progression to species with fewer leaflets, becoming long and thin, covered with hairs to keep the wind from pulling water away form the surface. They become tougher and more leathery to the touch. In one species, the leaflets have narrowed and curled up on themselves so much that they are, for all intents and purposes, needles now. Lining these species up next to one another is like watching a plant evolve and adapt to an increasingly hot, dry Australian outback in real time.

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Labichea stellata, one of the intermediate forms, with tough, leathery, narrow leaves adapted to a hot, dry climate.

Studying the morphology – the physical form – of a plant will tell you a lot about the challenges of the place it evolved and what it had to survive to make it to today, but reconstructing the evolutionary tree of a group creates a sort of speculative saga of a group of species changing as the world changed and it pushed out to new territories and new niches. 

I think that’s the difference between finding science a collection of dry facts and finding it utterly compelling to learn about… knowing that you need to see the forest rather than just the trees, and to find the story of life that all those facts come together to tell you.

 

[Note to sharp readers: yes, I know those are not fir trees in the image. But those are definitely the mists of time you’re seeing between them.]

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