A tiny beetle fossil shows how insects received the Earth’s earliest flowers.

 

Without the vibrant and varied landscapes of plant life, it is nearly impossible to imagine our world today. Angiosperms, also known as flowering plants, are the most abundant and diverse group of plants. They make up more than 80% of all species, plus our staple food crops.

The world wasn’t always like that. There was a time when plant life was almost entirely green. The world burst into bloom magnificently during the age of the dinosaurs.

Our environment was blessed with flowers that were chromatic and vibrant. However, they also upended food chains and overtook their nonflowering counterparts. We don’t know much about the reactions of ecosystems to sudden flowering. A tiny beetle that has been preserved in amber for 99,000,000 years is now a valuable clue as to how these insects began to eat a new variety of colourful plants.

First flowers

There are arguments about the origin of angiosperms, but it is clear that they became diverse around 125,000,000 years ago in the Early Cretaceous.

Angiosperms’ explosive radiation, which displaced gymnosperms – the dominant, flowerless champions of the plant kingdom – is believed to have caused unprecedented upheaval within terrestrial ecosystems, changing all levels of the food chain, from herbivores and their predators.

Conifers such as pines or cypresses make up the largest group of gymnosperms. Although many gymnosperms can be pollinated by wind, some produce sugar-containing pollination drops, such as the fern-like Cycads that maintain an old relationship with beetles. With their brightly scented galleries and attractive nectar, flowering angiosperms outcompeted all gymnosperms.

We know little about the early life of angiosperms. The majority of Cretaceous flowers were found in burnt remains converted to charcoal. This makes reconstructions of their appearance difficult and rare. To reconstruct the appearance of the first flower in the world, scientists have studied living Angiosperms.

These early flowers’ pollinators have been shrouded in mystery. Over 80% of angiosperms today depend on insects to pollinate them. These groups weren’t present in the Cretaceous or were not varied. Who were the first pollinators for angiosperms in the Cretaceous?

Jurassic pollinators

Before the Cretaceous, many insects were in mutualistic relationships with plants. Some Jurassic scorpionflies had elongated mouthparts that were ideal for pollinating the gymnosperms. Fortuitous fossils found in Spain’s Early Cretaceous Amber have also revealed Thrips, small, slim insects closely related to the pollen of gymnosperms.

What about the relationship between angiosperms of the earliest age and their insect pollinators. Palaeontology is a field that requires exceptional fossils. Amber often provides these exceptional fossils. Amber is the resin from ancient trees, preserved with lifelike fidelity over many millions of years.

The unique opportunity to see ancient ecosystems through tiny bits of plants and insects trapped within amber pieces is unparalleled. Researchers have accumulated a unique collection of over 20,000 amber pieces, which they discovered in northern Myanmar in 2016. This amber is from the Golden Age of Angiosperm Diversification. It dates back to 99 million years ago.

As palaeontologists working with amber, we have to sort out individual pieces and identify their content. We carefully carve them down to give a clear view of the fossil inside, sometimes down to the thickness of a microscope slide. In this Jurassic Park-like adventure, work has to be done slowly, with surgical precision.

The amber began to bear fruit after years of hard work. In late 2019, an amber sample from northern Myanmar produced a tumbling flower beetle ( Mordellidae) with many angiosperm-pollinated grains attached. The discovery of short-winged flower beetles associated with eudicot pollen, similar to the one produced by waterlilies, was next. This is an early-diverging group of angiosperms. An ancient wasp was also found to be associated with angiosperms pollen.

Last supper

The new fossil was named Pelretes viificus. Our study focused on the short-winged beetle. It measures just over one millimetre long and is a single speck in clear orange amber.

We discovered that the beetle was associated with clusters of pollen grains. Some were attached to its body directly, while others were preserved in fossilised pellets of faecal (coprolites). Coprolites provide evidence of the last meal of the beetle and are a unique piece of evidence that proves that pollen was not accidental.

We used a variety of high-tech microscopes to identify the pollen. The fossil genus Tricolpopollenites was the source of the pollen. This group can be attributed to the Euicots, a living group that includes coca, willows, and violets. Pilates is, therefore, one of the oldest pollinator angiosperms found in fossil records – and also the first beetle to show evidence of pollen feeding.

The tiny beetle’s discovery had shown that even before their rise to prominence, pollen from some of the oldest flowering plants was already being consumed by insects. We know that angiosperms and flower beetles have been associated for over 99 million years. This was when colourful flowers were exploding all around the globe.

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