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The Early Bird Got the Cicada, Then an Evolutionary Air War Started
Fossils reveal that prehistoric cicadas’ wings evolved to help them evade hungry predators with feathers and beaks, scientists say.
Today, few critters are as abundant as cicadas. Thousands of different cicada species are found throughout the world, and some even periodically emerge by the trillions.
But the prehistoric world was not crawling with periodical swarms. The cicadas of the late Jurassic Period — which had bulkier bodies than today’s bugs and wingspans that eclipsed those of modern hummingbirds — were relatively scarce. And they were under attack from a new predator with feathery wings, claws and a toothy beak.
Early birds posed a fearsome threat. But as they responded to these competitors, cicadas evolved sleeker and more powerful wings, according to a paper published on Friday in the journal Science Advances.
Chunpeng Xu, a scientist at the Nanjing Institute of Geology and Palaeontology in China and the lead author of the new study, and his colleagues describe this evolutionary bout between predator and prey as an “air race,” and they posit that the conflict eventually improved ancient cicada diversity.
“The rise of early birds influenced the aerial ecosystem during the late Mesozoic, especially the evolution of flying insects,” he said.
Dr. Xu’s team analyzed ancient cicadas belonging to the group palaeontinidae. These insects, which resembled moths with shrunken heads, originated during the middle Triassic Period and persisted for around 160 million years into the Cretaceous Period. Like contemporary cicadas, the beefier palaeontinidae cicadas lived in trees and slurped up plant fluid.
These giant cicadas left lots of fossils, including some that preserve detailed imprints of veiny wings. The team analyzed dozens of palaeontinidae fossils found in China, Brazil and Europe.
Using the dimensions of the ancient cicadas’ wings, the researchers built a detailed evolutionary tree for the group. This revealed a clear shift between older palaeontinidae cicadas, which sported rounded, moth-like wings, and later palaeontinidae, whose triangular top wings and reduced lower wings resemble those found on modern cicadas.
Palaeontinidae cicadas with more angular wings appeared around 150 million years ago, during the late Jurassic Period. This was around when the earliest birds took flight.
To determine whether these sleeker wings helped ancient cicadas avoid avian predators, the researchers used the dimensions of the fossilized wings to model the ancient insects’ flight patterns.
They discovered that the longer, narrower wings of later cicadas generated less drag and boasted a high density of flight muscles. “This suggests that giant cicadas had evolved a significantly more advanced flight capability, including higher speed, higher efficiency and greater maneuverability,” Dr. Xu said.
He and his colleagues say these wings helped ancient cicadas not only survive the air race, but also thrive in its aftermath. When birds first emerged in the late Jurassic Period, the once plentiful palaeontinidae group became rare in the fossil record. However, the number of palaeontinidae species would rebound dramatically in the early Cretaceous Period as narrow-winged, fast-flying cicadas proliferated.
Michael Engel, a paleontologist studying ancient insects at the American Museum of Natural History in New York, said there were many examples of predator and prey duking it out in the skies. For example, when bats developed echolocation to track insects, some moths evolved to jam the sonar of approaching bats.
However, Dr. Engel is not certain that early birds caused the changes in ancient cicada wings. The fluid-sucking insects would have been vulnerable to all types of predators, including early mammals and other insects. Developing more powerful wings could have helped them take flight faster instead of engaging in high-speed aerial chases with birds.
“There is really no smoking gun for birds,” Dr. Engel said.
While there remains debate about what caused the prehistoric cicadas to fine-tune their wings, palaeontinidae were eventually driven to extinction. Dr. Xu posits that they were probably doomed by noisy upstarts: singing cicadas.
The precursors to today’s clamorous cicadas largely replaced palaeontinidae species by the end of the Cretaceous Period, when the dinosaurs were also driven to extinction. These insects’ evolutionary edge wasn’t flight aptitude, but instead their ability to communicate with one another and deposit their larvae underground.
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