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The evolution of birds made giant cicadas better flyers
An evolutionary ‘air race’ may have been taking place in forests during the age of dinosaurs.
Fossils of giant cicadas show how they developed improved flight abilities following the evolution of birds, most likely as a response to the pressure from predation.
Insects were the first animals to evolve powered flight and dominated the air for hundreds of millions of years.
But the evolution of birds saw agile predators take to the skies, which may have spurred on the evolution of better flight performance in their insect prey.
This seems to have been the case for giant cicadas. This was a group of insects that lived from the Middle Triassic to the Late Cretaceous, with early group members appearing millions of years before the evolution of the first birds.
This allowed researchers to investigate if the evolution of birds impacted that of the insects. They found distinct changes in the wings and bodies of the giant cicadas towards the end of the Jurassic, which would have likely increased flight performance. They suspect this was in direct response to the evolution of birds at this time.
The detailed analysis of fossils spanning the evolutionary history of giant cicadas has been published in the journal Science Advances.
Professor Edmund Jarzembowski, an associate scientist at the Natural History Museum and co-author of the study, says, “Powered flight is one of the most important innovations in evolution. Insects were the Earth’s first flying animals but faced increasing competition from flying vertebrates starting in the age of the dinosaurs.”
“Giant cicadas were stout, tree-dwelling, plant-sucking bugs, with wingspans up to 15 centimetres across and could have provided a substantial meal for flying predators. They appeared in the Triassic and evolved a marked increase in flight capability, including speed and manoeuvrability, by the end of the Jurassic and the beginning of the Cretaceous periods. This coincided with the rise of birds from the Late Jurassic.”
Many species of giant cicadas have been well-preserved in the fossil record. © C. Xu/NIGPAS
How did flight performance improve in giant cicadas?
Reconstructing the flight performance and behaviour of ancient insects is notoriously difficult as it relies on having plenty of well-preserved specimens.
But giant cicadas are the ideal group to study this, due to the number of exceptionally preserved fossils spanning a variety of species across millions of years. As such, researchers were able to learn more about the relationship between the wing and body shape and flight abilities of these insects and how that changed over time.
The study looked at almost 90 species of giant cicadas to reconstruct the evolutionary history of this group. During the Late Jurassic and Early Cretaceous they found a significant transition from early cicadas to later cicadas which led to increased flight performance.
Early representatives of the group had more oval-shaped forewings and large hindwings, but this changed with the later members of the group. From the Late Jurassic, the wings became much longer and slender. The forewings were more triangular-shaped, and the hindwings became smaller. This change in wing size and shape would have increased lift, allowing for more efficient flight.
The later species of giant cicadas also had a higher muscle mass, giving them more power during flight. They also had a greater wing-to-body size ratio that was more suited to allow for higher speed and greater manoeuvrability while in flight.
Early giant cicadas (above) had more oval-shaped wings compared to later species (below), whose wings were more triangular in shape. © C. Xu/NIGPAS
An evolutionary arms race
Powered flight offers distinct advantages to animals, such as allowing them to migrate further, exploit new food sources and escape from predators. But it is also quite a rare phenomenon having only evolved in four groups of animals: bats, pterosaurs, insects and dinosaurs, which includes birds.
Insects were the first to evolve flight, and are the most species-rich group of flying animals. As a major source of food for many other animals, it is thought that insects may have evolved flight to escape predation. This same pressure might also be driving insects to improve on their flight, in a process known as an evolutionary arms race.
An evolutionary arms race develops when predators evolve better armouries and strategies to capture prey. In turn, the prey evolves better ways to evade the predators. We can see this in how the rise of bats around 50 million years ago led to the advanced evolution of hearing organs, wing shape and enhanced flight performance in moths.
Birds evolved within a group of meat-eating dinosaurs called the theropods, which includes the Velociraptor and the Tyrannosaurus. The first bird-like dinosaurs appeared around 165 to 150 million years ago during the later part of the Jurassic Period and would have been fairly small in size. Even so, they emerged as one of the dominant predators in the forest ecosystem, and many of them probably fed almost exclusively on insects.
“The conquest of the air led to faster and more agile flying animals, with innovations by one group being matched or overtaken by another, with ever-increasing refinements over time,” says Edmund.
“Giant cicadas eventually became extinct, but they nevertheless encapsulate an ancient aerial arms race spanning nearly 160 million years from start to finish!”
