As early as 252 million years ago, some plants may have curled up their leaves at night for a cozy “sleep.”
Fossilized leaves of two now-extinct Gigantonoclea species bear signs of nyctinasty, or circadian rhythmic folding at night, researchers report February 15 in Current Biology. That would make these specimens the first known fossilized examples of this curious plant behavior, the team says.
The two leaf fossils were discovered in a rock layer in southwestern China that dates to between 259 million and 252 million years ago. In both species, the leaves were broad, with serrated edges. But most curiously, they bear oddly symmetrical holes.
Insects made those holes while feeding on the leaves while they were folded, say paleontologist Zhuo Feng of Yunnan University in Kunming, China and colleagues. Similar symmetrical patterns of insect damage in leaf fossils can be used to distinguish folding behavior from leaves that might have shriveled as the plant died, the team says.
Modern plants, including many in the legume family such as the orchid tree, that fold and unfold their leaves use specialized cells called pulvinus cells, which act somewhat like muscles (SN: 2/3/23). By shifting water from one part of the leaf to another, the cells can bloat or deflate, allowing the leaves to fold or curl.
2023-02-15 11:14:37
Article from www.sciencenews.org
For thousands of years, plants have been an integral part of the Earth’s landscapes, providing a natural beauty and crucial resources to human and animal life worldwide. A new discovery, however, suggests that the plants of ancient eras were actually quite a bit more resilient than first suspected.
Recent studies have revealed that some plants in the fossil record dating back to the late Mesozoic Era (243 to 66 million years ago) could fold their leaves up when faced with microbial attack, such as insect bites. This behavior had previously been considered an adaptive response only recently developed in the evolutionary chain of many flowering plants, but fossilized bites reveal that some species were able to fight off predators without needing to go through the usual defense mechanisms.
An international team of researchers discovered the evidence of this unusual feature when analyzing the fossilized remains of leaves and stems in a quarry of southwestern China’s Xinjiang Uygur Autonomous Region, finding small round tooth marks on the fossilized foliage. Once the team analyzed the shapes of the fossilized bites, they noticed that not only had the leaves “folded” up to escape being eaten, they had done so in such a way that the bite marks were left – preserving the evidence of their struggle for years.
The findings suggest that plants have had longer to adapt to the world around them than previously thought, with new mechanisms of self-preservation and protection coming about much earlier in their evolutionary history than expected.
This exciting discovery provides a fascinating look into how far plants have grown and adapted over the last few hundred million years, and may hint at even more remarkable findings to come.