Beetle in Amber Offers Insight Into Drift of Ancient Continents

Wednesday, October 31, 2018

The fossil beetle, Propiestus archaicus, preserved in amber. (Field Museum/Shuhei Yamamoto)

A 99 million-year-old beetle trapped in amber offers scientists hints about how Earth’s landmasses were arranged long ago, according to a paper published in the Journal of Systematic Paleontology.

“This is a very rare find,” Field Museum researcher and lead author Shuhei Yamamoto said. “This fossil helps us understand life in the Mesozoic era,” he said. “We need to think about everything from that time, both big and small.”

Yamamoto obtained the penny-sized piece of Burmese amber from Hukawng Valley in northern Myanmar, near China’s southern border, in 2016. He had a hunch the three-millimeter insect trapped inside the amber could help him show why our world looks the way it does now.

Yamamoto used sandpaper to carefully polish the amber just enough to make the beetle clearly visible.

“It was very exciting, because the cutting process is very sensitive,” Yamamoto said. “If you cut too fast or apply too much pressure, you destroy the inclusion inside very quickly.”

Once the amber was polished and the beetle was clearly visible, Yamamoto and his colleagues studied the beetle to determine its closest living relatives. Yamamoto found the insect, smaller than the phone-end of an iPhone charger, was a new species to science and a relative of insects alive today that live under tree bark.

The fossil beetle is one of the oldest known members of its family. Its name, Propiestus archaicus, refers to the fact that it’s an ancient relative of the flat rove beetles in the Piestus genus that now dominate South America, with the exception of one species in southern Arizona. But the fossil beetle was found in Myanmar, literally on the other side of the globe from these places.

It hasn’t always been that way.

While dinosaurs roamed much of Earth 99 million years ago during the Late Cretaceous, Propiestus – with its flattened body and short legs – was busy conquering smaller turf underneath the bark of rotting trees. Its long, slender antennae were the clear giveaway to Yamamoto that Propiestus had lived in this environment similar to the modern-day flat rove beetles.

“The antennae probably had a highly sensitive ability as a sensory organ,” Yamamoto said, as smaller hair-like structures attached perpendicular to the antennae would have increased its ability to feel out its surroundings. “There wouldn’t have been a lot of space available in the beetle’s habitat, so it was important to be able to detect everything,” he explained.

Millions of years ago, Myanmar and South America were actually quite close to each other, all fused together as part of the megacontinent Gondwanaland which formed when the earlier megacontinent Pangea broke apart. Gondwanaland itself eventually broke apart, helping to form the continents we recognize on a map today.

Scientists have a clear sense of which of today’s continents and subcontinents comprised Gondwanaland and made up its sister continent Laurasia. However, the detailed timing and pattern of Gondwanaland’s split into smaller continents is disputable.

Searching for supporting or contrasting evidence means analyzing fossils, some as small as Propiestus, to compare their similarities to other organisms discovered across the globe that might have inhabited the same space long ago.

“Like koalas and kangaroos today, certain animals that we think lived in Gondwanaland are only found in one part of the world. Although Propiestus went extinct long ago, our finding probably shows some amazing connections between Southern Hemisphere and Myanmar,” Yamamoto said.

“Our finding fits well with the hypothesis that, unlike today, Myanmar was once located in the Southern Hemisphere.”

Many inclusions in Burmese amber that have been researched in the last 15 years, including Propiestus, show signs that show traits in common with insects from Gondwanaland. By studying these tiny creatures trapped in amber, we’re finding answers to the questions about Earth’s structure and the life it supported millions of years ago.

Many small insects that lived during the Cretaceous died at the hands of tree sap that engulfed the bugs and hardened into amber. The trapped bugs fossilized and remained frozen for millions of years, unaffected by the passage of time. The hardened amber, covered by soil, decayed leaves, and other organic material, eventually blended in with its surroundings.

Because of this, amber in nature doesn’t look like it does in jewelry–in fact, it doesn’t look like anything special at all. The small clumps of unpolished amber look like rocks and only those experienced in amber identification, mostly local miners, are able to find them.

After miners extract the amber, the clumps are either sold into the jewelry trade or to scientists like Yamamoto to study the creatures frozen inside.