Plant Fossil from Early Jurassic Pushes Back Origin of Flowers

Wednesday, December 26, 2018

This is a Nanjinganthus dendrostyla fossil, showing its ovary (bottom center), sepals and petals (on the sides) and a tree-shaped top. Image credit: Fu et al, doi: 10.7554/eLife.38827.

An international team of paleontologists has identified and described a new genus and species of extinct flowering plant (angiosperm), based on over 200 specimens from the South Xiangshan Formation, China. Named Nanjinganthus dendrostyla, the newly-identified plant species dates back to more than 174 million years ago (Early Jurassic Period), making it the oldest known record of an angiosperm by almost 50 million years.

From oranges to apples, angiosperms produce most of the fruits and vegetables that we can see on display in a supermarket. While we may take little notice of the poppy fields and plum blossoms around us, how flowers came to be has been an intensely debated mystery.

The current understanding, which is mainly based on previously available fossils, is that flowers appeared about 125 million years ago in the Cretaceous period.

But not everybody agrees that this is the case. Genetic analyses, for example, suggest that flowering plants are much more ancient. Another intriguing element is that flowers seemed to have arisen during the Cretaceous ‘out of nowhere.’

“Researchers were not certain where and how flowers came into existence because it seems that many flowers just popped up in the Cretaceous from nowhere,” said study first author Dr. Qiang Fu, a researcher at the Nanjing Institute of Geology and Paleontology, China.

“Studying fossil flowers, especially those from earlier geologic periods, is the only reliable way to get an answer to these questions.”

Dr. Fu and co-authors studied 264 specimens of 198 individual flowers preserved on 34 rock slabs from the South Xiangshan Formation, an outcrop of rocks in the Nanjing region of China renowned for bearing fossils from the Early Jurassic Period.

Reconstruction of Nanjinganthus dendrostyla: (1) branches of dendroid style; (2) dendroid style; (3) sepal; (4) ovarian roof; (5) scale; (6) seed; (7) cup-form receptacle/ovary; (8) bract; (9) petal; (10) unknown organ (staminode?). Image credit: Fu et al, doi: 10.7554/eLife.38827.

The abundance of fossil samples used in the study allowed the team to dissect some of them and study them with sophisticated microscopy, providing high-resolution pictures of the flowers from different angles and magnifications.

The scientists then used this detailed information about the shape and structure of the different fossil flowers to reconstruct the features of Nanjinganthus dendrostyla.

The key feature of an angiosperm is ‘angio-ovuly’ — the presence of fully enclosed ovules, which are precursors of seeds before pollination.

Nanjinganthus dendrostyla was found to have a cup-form receptacle and ovarian roof that together enclose the ovules/seeds.

This was a crucial discovery, because the presence of this feature confirmed the flower’s status as an angiosperm.

“The origin of angiosperms has long been an academic ‘headache’ for many botanists,” said study senior author Professor Xin Wang, from the Nanjing Institute of Geology and Paleontology, China.

“Our discovery has moved the botany field forward and will allow a better understanding of angiosperms, which in turn will enhance our ability to efficiently use and look after our planet’s plant-based resources.”

The discovery is reported in the journal eLife.

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Qiang Fu et al. 2018. An unexpected noncarpellate epigynous flower from the Jurassic of China. eLife 7: e38827; doI: 10.7554/eLife.38827

Source: www.sci-news.com

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