Tuesday, 5 May 2020

Evolution News - Yet Another Transitional Species

In this image of one of the new ancient species’ reproductive structures, elliptical impressions of sporangia can be seen in one row, while on the right, another row displays preserved carbonized spore masses.
Image credit: Andrew Leslie
New ancient plant captures snapshot of evolution | Stanford University.

What with their problem explaining why evolution is the only explanation for Covid-19 that doesn't leave their putative designer god looking like a malevolent, genocidal psychopath, the last thing creationists needed was another one of those annoying transitional species that so bedevil their precious dogma.

But here we are, with another one, announced just yesterday. This time an extinct plant showing evidence of transition from spores to seeds - an essential step in the evolution of the flowering plants, or angiosperms.

And once again without any effort or intent, science has again refuted creationism with evidence.

One of the major advances in plant evolution was when the gymnosperms (cone-bearing) and angiosperms (flowering) plants broke free from the constraints of the reproductive methods used by the ferns and club mosses, which required moist conditions to allow their motile male gametes to reach the sedentary female gametes.

Usually when we see heterosporous plants appear in the fossil record, they just sort of pop into existence. 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.

Andrew Leslie, co-author
Assistant professor of geological sciences
Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth).
This allowed these more advanced plants to evolve small male gametes (pollen) suitable for wind and insect distribution while the much larger female gametes contained in seeds could hold nutrients for the developing embryo plants. It also opened up access to a new range of drier environmental niches. An important step in this evolution was the transition from small, equally-sized spores to the large, female, and small, male, gametes of these higher plants.

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. 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.

Andrew Leslie, co-author
Assistant professor of geological sciences
Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth).
This paper, published yesterday in Current Biology describes what may well be a species undergoing that transition. Sadly, the full paper is paywalled, requiring a subscription, however, the Stanford University press release in the form of an article by Danielle Torrent Tucker can be read here.

She explains:

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...

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.

The fossil was found amongst a collection of about 30 small chips of rock excavated from the Campbellton Formation of New Brunswick in Canada, kept at the Smithsonian National Museum of Natural History.

So, science has closed another gap and once again, found there was no god in residence and creationists now have another transitional species to ignore because their dogma relies on the false belief that there are none.

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