Pollen Fossils Reveal Flowering Plants to Have Emerged 100 Million Years Earlier
A new study suggests flowering plants to have emerged 100 million years before previous estimates. The findings were published in the Oct. 1 issue of the journal Frontiers in Plant Science.
Flowering plants (angiosperms) are believed to have evolved from long extinct, gymnosperm vegetation, related to cycads, conifers, Ginkgos and Gnetales. Gymnosperms are seed-producing plant forms that have unenclosed, or “naked,” seeds. This contrasts against flowering plants, which harbor their seeds within an enclosed ovary.
Professor Peter Hochuli, working at the University of Zürich, explained that flowering plants were the final group of plants to have evolved on planet Earth, before going on to discuss their impact on mankind. Without angiosperms, Hochuli explains that the lush, modern ecosystems of today would likely not exist, and neither would humanity.
Were Angiosperms Cretaceous or Triassic in Origin?
The prevailing notion is that flower-like structures first made their emergence during the Cretaceous period, around 130 to 140 million years back, whilst the dinosaurs wandered our planet. A continuous sequence of fossilized pollen grains derived from flowering plants had been observed, dating back to this period; therefore, it was generally accepted that the first angiosperms materialized during this period.
However, a new group of researchers claim to have identified evidence that calls this estimate into question. Previous approximations have been based around investigation of fossilized plant remains; unfortunately, old fossils are extraordinarily difficult to find for flowering plants, making molecular studies rare and highly inconclusive.
On this basis, a team working at the University of Zürich, Switzerland, performed studies into drilling cores, at two different location in Switzerland. Peter Hochuli, and his colleague Susanne Feist-Burkhardt, discovered pollen grains remarkably similar in appearance to the fossilized pollen from some of the first recorded flowering plants.
Pollen grains are tiny, durable structures that are in abundance; these properties make it far easier to locate fossilized pollen grains than delicate plants or leaves.
The crew then used Confocal Laser Microscopy to generate high-resolution imagery of six different forms of collected pollen grain. This form of microscopy enabled scientists to acquire in-focus images of specimen samples, at various depths (optical sectioning). The various images were then aggregated to provide a 3-dimensional reconstruction of the intricate specimens.
The presence of six pollen grain types hints at high diversification between the flowering plants, which were thought to be almost 250 million years old. Based upon these findings, the earliest angiosperms were likely to have dated right back to the Triassic period, suggesting they were approximately 100 million years older than first anticipated.
These findings go a long way to solving an ambiguity that has long plagued the minds of the scientific community, who thought it strange that flowering plants were able to dominate Earth in such a short period of time. Even Charles Darwin described the origins of modern angiosperms as an “abominable mystery.”
It’s thought that plants evolved in this manner to include mobile animals in their reproduction. Various plants produced attractive, brightly colored flowers to gain the attention of animals and enable efficient dissemination of their pollen. However, thus far, the researchers remain uncertain as to what conditions could have been imposed upon gymnosperms to potentially spur on the evolution of the flowering plants that dominate today.
During the Triassic period, bees would not have existed. Therefore, the authors posit that various insects may have been responsible for pollination, including beetles.
Other Study Findings
Hochuli and Feist-Burkhardt also performed another study in 2004, which investigated the relationship between pollen, derived from flowering plants. During this research study, the pair reported the finding of pollen grains that were of “angiosperm-like morphologies from marine Middle Triassic sediments of the Boreal Realm…”
Meanwhile, a separate study, performed by Xin Wang and colleagues, entitled Schmeissneria: A missing link to angiosperms?, found fossils with angiospermous qualities, dating back to the Jurassic age. Specifically, they found that a Jurassic genus of plant, called Schmeissneria, might actually be an angiosperm.
Professor Peter Hochuli explained that his team’s study represented a significant step forward in our attempts to understand the origins of flowering plants:
“We believe that even highly cautious scientists will now be convinced that flowering plants evolved long before the Cretaceous.”
Even though the researchers’ microscopy of the pollen fossils suggests flowering plants to have emerged 100 million years earlier than expected, further investigation is needed to cement their conclusions.
By: James Fenner