The world as we know it today is hard to imagine without the rich and colorful landscapes of the plants. Among them are flowering plants, or angiosperms, which are by far the most diverse and abundant group of plants and make up over 80% of all known species, including all of our staple foods.
But the world wasn’t always like this. There was a time when the plants were almost entirely green. Then, in the time of the dinosaurs, the world blossomed splendidly.
Flowers blessed our environment with chromatic vibrancy, but they also flipped the food chains and stretched out their non-blooming predecessors. Little is known about the response of ecosystems to this sudden bloom. But now a tiny beetle that has been kept in amber for 99 million years has given a valuable clue as to how insects fed on a colorful new plant plate.
First flowers
While there is debate about when exactly angiosperms formed, there is little argument that they first became diverse about 125 million years ago in the Early Cretaceous Period.
It is believed that the explosive radiation from angiosperms that displaced gymnosperms – the reigning, flowerless proponents of the flora – caused unprecedented upheavals in terrestrial ecosystems and changed the food chain at all levels from herbivores to predators.
The largest remaining group of gymnosperms are conifers such as pine and cypress. Many gymnosperms are wind pollinated, although some produce sugary pollination drops, such as. B. fern-like cycads that maintain an ancient relationship with beetles. Flowering angiosperms surpassed most gymnosperms with their colorful and fragrant galleries that advertised their nectar to attract pollinators.
However, we know very little about the life of the earliest angiosperms. Most of the chalk flowers were obtained from burned remains that were turned into charcoal, making reconstructing their appearance a rare and difficult task. Scientists have also studied living angiosperms to reconstruct what the world’s first flower might have looked like.
The pollinators of these early flowers have remained enveloped in another mysterious layer. Today, over 80% of angiosperms rely on insects such as bees and day-flying butterflies to pollinate them. But these groups were either absent or not different in the Cretaceous Period. So who were the earliest pollinators of angiosperms?
Jurassic dusters
Before the Cretaceous period, many insects had mutual associations with plants. Some Jurassic scorpion flies had elongated jaws that are ideal for pollinating gymnosperms. Accidental amber fossils from the Early Cretaceous Period in Spain have also discovered thrips – small, slender insects – associated with the pollen of gymnosperms.
But what is the relationship between the earliest angiosperms and their insect pollinators? In paleontology, extraordinary questions call for extraordinary fossils, and it is amber that often provides them. Amber is the resin of old trees that has petrified over millions of years and preserved its contents with lifelike fidelity.
Pieces of insects and plants enclosed inside offer an incomparable window into ancient ecosystems. Scientists have amassed a unique collection of over 20,000 pieces of amber from northern Myanmar that were found in 2016. Dating back to 99 million years ago, during the golden age of angiosperm diversification, this amber preserves various insects, plants and even the occasional dinosaur remains.
As paleontologists working with amber, we need to sort out individual pieces, identify their contents, and carefully cut them open to get a clear view of the fossil inside, sometimes down to the thickness of a microscope slide. Work slowly and with surgical precision in this Jurassic Park-style adventure.
The arduous work on amber soon bore fruit. At the end of 2019, the amber from northern Myanmar produced a tumbling flower beetle (Mordellidae) with numerous angiosperm pollen grains attached to its body. This was followed by the discovery of short-winged flower beetles associated with Eudicot pollen, similar to that of water lilies – an early divergent group of angiosperms. Other discoveries were an ancient wasp that has also been linked to angiosperm pollen.
The last supper
Our study focused on a short-winged flower beetle, or Pelretes vivificus, as the new fossil was called. It’s a little over a millimeter long: a lonely speck in clear orange amber.
On closer inspection, however, we found that the beetle is associated with pollen grains: some adhere directly to its body, others are preserved in fossilized excrement pellets (coprolites). The coprolites are evidence of the beetle’s last meal and provide a unique line of evidence showing that the beetles did indeed feed on pollen and that the two were not accidentally preserved together.
To identify the pollen, we used a selection of high-tech microscopes. The pollen turned out to be the fossil genus Tricolpopollenites. This group is attributed to the Eudicots – a living group of angiosperms that includes willows, violets, and coca plants. This makes Pelretes one of the earliest angiosperm pollinators in the fossil record – and the earliest beetle with direct evidence of pollen feeding.
This tiny beetle showed that some of the earliest flowering plants had already eaten pollen on insects shortly after their rise. We now know that the association between flower beetles and angiosperms is really ancient: unbroken for at least 99 million years when the world erupted with brightly colored flowers.
This article was originally published in The Conversation
Chenyang Cai is a research fellow at the School of Earth Sciences at the University of Bristol.
