Fossil provides glimpse into plant evolution

[rogue06]

To be more accurate, his 400 myo (Early Devonian) fossil from Canada is a snapshot revealing what appears to be an intermediate stage of plant reproductive biology, prior to when a terrestrial plant produced spores all the same size. When each plant produced a range of different spore sizes.

The abstract sucks, providing virtually no detail:

Source: A novel reproductive strategy in an Early Devonian plant

Bonacorsi et al. describe a new fossil from the Early Devonian that provides the earliest clear evidence for more advanced reproductive biology in land plants. The plant produced multiple spore size classes, which is an essential innovation necessary for all advanced plant reproductive strategies, including seeds and flowers.

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That's it.

And Bonacorsi is Nikole K. Bonacorsi, a visiting assistant professor at Brown University's Department of Ecology and Evolutionary Biology.

For a little more on it:

Source: Fossil captures plants in transition

A new old species from an important time

Spores.jpg
The species' reproductive structures: elliptical impressions of sporangia can be seen
in one row, while on the right another displays preserved carbonised spore masses

Scientists have discovered an ancient plant species they say provides another piece in the evolutionary jigsaw.

Dating back some 400 million years to the Early Devonian period, it produced a spectrum of spore sizes, a precursor to the specialised strategies of land plants that span the world's habitats.

As such, it is one of the most comprehensive examples of a seemingly intermediate stage of plant reproductive biology, a team led by Stanford University, US, reports in a paper in the journal Current Biology.

"Usually when we see heterosporous plants appear in the fossil record, they just sort of pop into existence," says senior author Andrew Leslie. "We think this may be kind of a snapshot of this very rarely witnessed transition period in evolutionary history where you see high variation amongst spores in the reproductive structure."

The specimens likely belong to the herbaceous barinophytes, an unusual extinct group that may be related to clubmosses.

Leslie and colleagues made the discovery while analysing a collection of fossils that had been stored at the Smithsonian National Museum of Natural History for decades.

From about 30 small chips of rock originally excavated from the Campbellton Formation of New Brunswick, Canada, they identified more than 80 reproductive structures or sporangia.

The spores themselves range from about 70 to 200 microns in diameter – about a strand to two strands of hair. While some of the structures contained exclusively large or small spores, others held only intermediate-sized spores and others held the entire range of spore sizes – possibly with some producing sperm and other eggs.

"It's rare to get this many sporangia with well-preserved spores that you can measure," Leslie says. "We just kind of got lucky in how they were preserved."

One of the most important time periods for the evolution of land plants, the Devonian witnessed diversification from small mosses to towering complex forests, the researchers say.

The development of different spore sizes, or heterospory, represents a major modification to control reproduction, a feature that later evolved into small and large versions of these reproductive units.

"Think of all the different types of sexual systems that are in flowers: all of that is predicated on having separate small spores, or pollen, and big spores, which are inside the seeds," Leslie says.

"With two discrete size classes, it's a more efficient way of packaging resources because the big spores can't move as easily as the little ones but can better nourish offspring."

The earliest plants, from between 475 million to 400 million years ago, lacked reproductive specialisation in the sense that they made the same types of spores, which would then grow into little plantlets that actually transferred reproductive cells. By partitioning reproductive resources, plants assumed more control over reproduction, according to the researchers.

The new species, together with the previously described plant group Chaleuria of the same age, represents the first evidence of more advanced reproductive biology in land plants. The next example doesn't appear in the fossil record until about 20 million years later.



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And

Source: New ancient plant captures snapshot of evolution

Summary
Researchers have discovered an ancient plant species whose reproductive biology captures the evolution from one to two spore sizes -- an essential transition to the success of the seed and flowering plants we depend on.


In a brilliant dance, a cornucopia of flowers, pinecones and acorns connected by wind, rain, insects and animals ensure the reproductive future of seed plants. But before plants achieved these elaborate specializations for sex, they went through millions of years of evolution. Now, researchers have captured a glimpse of that evolutionary process with the discovery of a new ancient plant species.

The fossilized specimen likely belongs to the herbaceous barinophytes, an unusual extinct group of plants that may be related to clubmosses, and is one of the most comprehensive examples of a seemingly intermediate stage of plant reproductive biology. The new species, which is about 400 million years old and from the Early Devonian period, produced a spectrum of spore sizes -- a precursor to the specialized strategies of land plants that span the world's habitats. The research was published in Current Biology May 4.

"Usually when we see heterosporous plants appear in the fossil record, they just sort of pop into existence," said the study's senior author, Andrew Leslie, an assistant professor of geological sciences at Stanford's School of Earth, Energy & Environmental Sciences (Stanford Earth). "We think this may be kind of a snapshot of this very rarely witnessed transition period in evolutionary history where you see high variation amongst spores in the reproductive structure."

A major shift

One of the most important time periods for the evolution of land plants, the Devonian witnessed diversification from small mosses to towering complex forests. The development of different spore sizes, or heterospory, represents a major modification to control reproduction -- a feature that later evolved into small and large versions of these reproductive units.

"Think of all the different types of sexual systems that are in flowers -- all of that is predicated on having separate small spores, or pollen, and big spores, which are inside the seeds," Leslie said. "With two discrete size classes, it's a more efficient way of packaging resources because the big spores can't move as easily as the little ones, but can better nourish offspring."

The earliest plants, from between 475 million to 400 million years ago, lacked reproductive specialization in the sense that they made the same types of spores, which would then grow into little plantlets that actually transferred reproductive cells. By partitioning reproductive resources, plants assumed more control over reproduction, according to the researchers.

The new species, together with the previously described plant group Chaleuria of the same age, represents the first evidence of more advanced reproductive biology in land plants. The next example doesn't appear in the fossil record until about 20 million years later.

"These kinds of fossils help us locate when and how exactly plants achieved that kind of partitioning of their reproductive resources," Leslie said. "The very end of that evolutionary history of specialization is something like a flower."

A fortuitous find

The researchers began analyses of the fossils after they had been stored in the collections at the Smithsonian National Museum of Natural History for decades. From about 30 small chips of rock originally excavated from the Campbellton Formation of New Brunswick in Canada by late paleobotanist and study co-author Francis Hueber, they identified more than 80 reproductive structures, or sporangia. The spores themselves range from about 70 to 200 microns in diameter -- about a strand to two strands of hair. While some of the structures contained exclusively large or small spores, others held only intermediate-sized spores and others held the entire range of spore sizes -- possibly with some producing sperm and others eggs.

"It's rare to get this many sporangia with well-preserved spores that you can measure," Leslie said. "We just kind of got lucky in how they were preserved."

Fossil and modern heterosporous plants primarily live in wetland environments, such as floodplains and swamps, where fertilization of large spores is most effective. The ancient species, which will be formally described in a follow-up paper, has a medley of spores that is not like anything living today, Leslie said.

"The overarching story in land plant reproduction is one of increased division of labor and specialization and complexity, but that has to begin somewhere -- and it began with simply producing small spores and big spores," Leslie said. "With these kinds of fossils, we can identify some ways the plants were able to do that."

Co-authors of the study are from Brown University, the University of North Carolina -- Chapel Hill and the University of Sheffield.



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[rogue06]

Disclaimer:

The fact that clubmoss is mentioned as an early terrestrial life-form is eerily similar to the earliest life, our own mossy (mossrose) and her PIN™ -- clubmoss/mossy PIN™, is entirely and wholly coincidental.

[shunyadragon]

Disclaimer:

The fact that clubmoss is mentioned as an early terrestrial life-form is eerily similar to the earliest life, our own mossy (mossrose) and her PIN™ -- clubmoss/mossy PIN™, is entirely and wholly coincidental.

Coincidance or evolved from a lower life form?