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Nature

400-million-year-old fossil hints at plant evolution

Madrid / A new species of plant that lived about 400 million years ago has allowed researchers to know more about the evolutionary process that gave rise to the current complex forms of plant reproduction, which went through millions of years of evolution.

A study from Stanford University (USA) published by Current Biology indicates that the fossil possibly belongs to the herbaceous bryophytes and corresponds to the early Devonian, according to a statement.

This new species is, according to the team, one of “the most complex examples of an apparently intermediate stage in the reproductive biology of plants”, which produced different sizes of spores, which is a precedent in the specialization strategies of land plants around the world.

For Stanford professor of geological science and lead author of the research, Andrew Leslie, the discovery may be “a kind of snapshot of that transition period, very rarely witnessed in the history of evolution, in which a high variety of spores in the reproductive structure ”.

The division of spores and the reproduction of plants

The first plants, between 475 and 400 million years old, lacked reproductive specialization because they manufactured the same spore sizes; but by dividing the spores, the plants assumed more control over their reproduction.

One of the most important time periods for the evolution of land plants, the Devonian, witnessed the diversification of small mosses into large and complex forests.

The development of different spore sizes (heterospore) represents an important modification to control reproduction, a characteristic that later evolved in small and large versions of these reproductive units.

The first evidence

The new species, together with the “Chaleuria” type of plants, represents the first evidence of a more advanced reproductive biology in terrestrial plants, since the following example does not appear in the fossil record until 20 million years later.

“This type of fossil helps us locate when and how exactly plants achieved that type of division in their reproductive resources,” explains Leslie, for whom “the end of that evolutionary history of specialization is something like a flower.”

The researchers analyzed fossils that had been stored for decades in the collections of the National Museum of Natural History of the United States.

Rock samples excavated in Canada

From some 30 rock samples excavated in Canada, they identified more than 80 reproductive structures, containing spores 70 to 200 microns in diameter, the equivalent of approximately one or two hairs.

While some of the reproductive structures contained exclusively large or small spores, others had only intermediate size and some had all measures.

“It’s rare to get as many sporangia with well-preserved spores that can be measured,” says Leslie, who believes the team had been lucky because of the way they had been preserved.

This recently described ancient plant species “presents a mixture of spores that is unlike anything that exists today.”

“The general history of the reproduction of land plants is one of greater division of labor, specialization and complexity, but that has to start at some point, that is, the simple production of small and large spores,” concludes the researcher. (May 6, 2020, EFE / PracticaEspañol)

(Automatic translation)

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