Paleontologists have documented the first fossil evidence of foliar nyctinasty — the movements involving circadian rhythmic folding at night and opening at daytime of plant leaves or leaflets — based on a symmetrical style of insect feeding damage in gigantopterid seed-plant leaves from the Late Permian of China.
“Our findings reveal extinct plants evolved foliar nyctinastic movements at such an early stage of plant evolution, which is surprising to me,” said Dr. Zhuo Feng, a paleontologist at Yunnan University.
“Our discovery is based on an unorthodox approach,” said Dr. Stephen McLoughlin, a paleontologist at the Swedish Museum of Natural History.
“Since it is impossible to tell whether a folded leaf found in the fossil record was closed because it experienced sleeping behavior or because it shriveled and bent after death, we looked for insect damage patterns that are unique to plants with nyctinastic behavior.”
“We found one group of fossil plants that reveals a very ancient origin for this behavioral strategy.”
In 2013, the authors discovered an interesting pattern of insect damage in living plants: symmetrical holes punctured through the leaves, which they later realized looked the way they did because insects fed on the leaves while they were folded.
As this type of damage is common in nyctinastic plants, they wondered whether they could find it in fossil plants as evidence for sleeping movements.
They looked to gigantopterids, an extinct group of seed-producing plants characteristic of the Permian Cathaysian floras from about 300-250 million years ago.
They thought these plants were the best place to look because the plants are known to experience frequent attacks from plant-eating insects.
Their broad leaves with robust midvein also make insect damage easy to detect.
The first fossil gigantopterid leaf showing the symmetrical pattern they sought turned up in 2016.
“I was surprised by the distinctive pattern of the insect damage…
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