Insect pollination long before flowering plants
The first flowering plants evolved more than a hundred million years ago, while dinosaurs were still on the scene. Since then, they’ve come to dominate the world, largely outcompeting the plants that were there before, such as conifers, cycads, and ginkgoes. With some exceptions (particularly the taiga, the coniferous forests of Russia and Canada), the vast majority of the vegetation we now see are flowering plants, or angiosperms. That includes things that don’t obviously flower, like grass and oak trees.
There are a few different ideas as to why the new flowering plants did so well. Some modern ones focus on differences in the plants’ water transport: the slow seedling hypothesis says that baby angiosperms can get off to a sprint start, overshadowing competitors before they’d left the starting blocks. Making your food from sunlight might sound like an easy life, but plants have to fight for daylight, and getting on top can be the knock out blow.
Older theories tended to be more focussed on reproduction. It’s not simply a flower that officially distinguishes a flowering plant; unlike other plants, the unfertilised egg is completely enclosed, and the pollen (containing the male sex cells) has to drive a pollen tube through part of the parent plant. Their other name, angiosperms, comes from Greek words for ‘vessel’ and ‘seed’.
Flowers are, however, important. The reason for showy flowers is to attract pollinators, most commonly insects. Today, the majority of flowering plants use insects to carry their pollen, whereas most gymnosperms (the older group of plants, including conifers) are pollinated by the wind. Insects have one clear advantage over the wind: they can track down another flower of the same species, so you don’t have to produce huge amounts of pollen. This was the basis for one theory about the rise of angiosperms: they simply did pollination more efficiently.
The new work throws up a big problem with that idea. From insect fossils, it looks like there were pollinators around in the Jurassic, which had evolved together with the gymnosperms that were around at the time. If angiosperms had tried to patent working with insects to transfer pollen, there would have been prior art.
To be precise, the scientists describe several species of scorpionfly, whose mouthparts look like they evolved to suck up some sort of fluid (but blood didn’t seem to have been on their menu). And the relationships of these groups suggest that the same way of feeding evolved several times. This would all fit in with some fossil gymnosperms, which don’t seem to have been terribly well adapted for wind pollination.
As the perspective (second reference below) puts it, however: “a key piece of evidence is missing: The authors failed to find any pollen associated with these fossils.” Pollen still stuck to fossilised insects would really clinch the deal, and is worth hoping for. But if you accept that insect pollination was going on, there are other groups of insects that could also have been involved, and the story’s certainly not far fetched.
Finally, I wonder if it was really gymnosperms which those Jurassic scorpionflies were pollinating. It’s not clear just when the first flowering plants did arise, but it has been suggested that their separate lineage goes back that far. The authors argue that, because several groups of insect evolved the same feature, they must have been using a widespread group of plants, which might rule out the ancestors of today’s flowering plants.
Ren, D., Labandeira, C., Santiago-Blay, J., Rasnitsyn, A., Shih, C., Bashkuev, A., Logan, M., Hotton, C., & Dilcher, D. (2009). A Probable Pollination Mode Before Angiosperms: Eurasian, Long-Proboscid Scorpionflies Science, 326 (5954), 840-847 DOI: 10.1126/science.1178338 (Technical)
Ollerton, J., & Coulthard, E. (2009). Evolution of Animal Pollination Science, 326 (5954), 808-809 DOI: 10.1126/science.1181154 (More readable)