Named Alasemenia tria, the new specimen from the Wutong Formation in the Chinese province of Anhui dates back to the Famennian stage of the the Late Devonian epoch, making it the second-earliest known winged seed.
Fertile branches and seeds of Alasemenia tria. Image credit: Wang et al., doi: 10.7554/eLife.92962.3.
Many plants need seeds to reproduce. Seeds come in all shapes and sizes and often have extra features that help them disperse in the environment.
For example, some seeds develop wings from seed coat as an outer layer, similar to fruits of sycamore trees that have two wings to help them glide in the wind.
The first seeds are thought to have evolved during the Famennian stage, between 372 and 359 million years ago.
Fossil records indicate that almost all these seeds were surrounded by an additional protective structure known as the cupule and did not have wings.
To date, only two groups of Famennian seeds have been reported to bear wings or wing-like structures, and one of these groups did not have cupules.
“The earliest-known plant seeds date back to the Late Devonian epoch,” said Peking University’s Professor Deming Wang.
“This period marks a significant evolutionary milestone in plant history, as they transitioned from spore-based reproduction, as with ferns and mosses, to seed-based reproduction.”
“However, little is known about wind dispersal in seeds during this time, as most fossils lack wings and are typically surrounded by a protective cupule.”
Professor Wang and colleagues examined Famennian seed plant fossils collected in Anhui province, China.
Assigned to a new genus and species, Alasemenia tria, the seeds are about 2.5-3.3 cm long and clearly lack a cupule, unlike most other seeds of the period.
“In fact, this is one of the oldest-known records of a seed without a cupule, 40 million years earlier than previously believed,” the paleontologists said.
“Each seed is covered by a layer of integument, or seed coat, which radiates outwards to form three wing-like lobes.”
“These wings taper toward the tips and curve outward, creating broad, flattened structures that would have helped the seeds catch the wind.”
The researchers then compared Alasemenia tria to the other known winged seeds from the Late Devonian: Warstenia and Guazia.
Both of these seeds have four wings — Guazia’s being broad and flat, and Warstenia’s being short and straight.
The scientists performed a quantitative mathematical analysis to determine which seed had the most effective wind dispersal.
This revealed that having an odd number of wings, as in Alasemenia tria, grants a more stable, high spin rate as the seeds descend from their branches, allowing them to catch the wind more effectively and therefore disperse further from the parent plant.
“Our discovery of Alasemenia tria adds to our knowledge of the origins of wind dispersal strategies in early land plants,” said Dr. Pu Huang, a researcher at the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences.
“Combined with our previous knowledge of Guazia and Warsteinia, we conclude that winged seeds as a result of integument outgrowth emerged as the first form of wind dispersal strategy during the Late Devonian, before other methods such as parachutes or plumes.”
“The three-winged seeds seen in Alasemenia tria during the Late Devonian would have subsequently been followed by two-winged seeds during the Carboniferous period, and then single-winged seeds during the Permian,” Professor Wang added.
The study was published in the journal eLife.
_____
Deming Wang et al. 2024. Alasemenia, the earliest ovule with three wings and without cupule. eLife 13: RP92962; doi: 10.7554/eLife.92962.3
Source : Breaking Science News