F Rosa Rubicondior: Creationism in Crisis - Why Did Some Plants Survived The Mass Extinction That Killed The Dinosaurs? - Evolution!

Sunday 19 November 2023

Creationism in Crisis - Why Did Some Plants Survived The Mass Extinction That Killed The Dinosaurs? - Evolution!

A fossilised cycad
New Nicholas Researcher Finds Plants That Survived Dinosaur Extinction Pulled Nitrogen from Air | Duke Today

About 65 million years before creationists think Earth existed, about 75% of living species were wiped out in what is known as the K-Pg extinction event. This was caused by a massive meteor, believed to be about 9 miles wide, that hit Earth on the edge of the Yucatan peninsula in what is now Mexico, throwing up billions of tons of sulphurous dust and gas high into the atmosphere, blotting out the sun and plunging Earth into a decade or more of darkness and winter conditions.
Along with most of the animal life, most of the plants were exterminated too. Up to that point, the predominant plant life had consisted of species of cycads on which the herbivorous dinosaurs had browsed.

But just a few cycads survived. The mystery was why? What enabled those few to survive when all the others died?

Scientists now think it had something to do with the fact that the survivors all appeared to have formed an alliance with nitrogen-fixing cyanobacteria in their roots, in much the same way that legumes have. How this gave them an advantage is unknown, but it is probably no coincidence that the descendants of the survivors all have this symbiotic relationship with cyanobacteria.

This was discovered by a team of researchers led by Michael A. Kipp of the Division of Earth and Climate Sciences, Nicholas School of the Environment, Duke University, Durham, NC, USA. and is the subject of a paper in Nature Ecology & Evolution.

Knowing that modern cycads are nitrogen fixers, Professor Kipp reasoned that this means the nitrogen in their tissues is derived from atmospheric nitrogen rather than mineral nitrates in the soil, so, measuring the nitrogen isotope ratios in their fossils should tell us something about the changes in atmospheric nitrogen isotopes over time. However, he discovered that only a few species of fossil cycads had isotope signatures similar to that of living cycads because most of them were not nitrogen fixers. He also realised that those that were nitrogen fixers were the ancestors of living cycads. In other words, only the nitrogen fixers survived the K-Pg extinction.

This is an example of how evolution can give a species an unexpected advantage in a situation that was unplanned and unforeseeable, but which was so instantaneous that the process of evolution couldn’t possibly have provided a solution. So the species without that advantage went extinct and the evolutionary trajectory of those was changed forever, just as it was for the large reptiles, most of which died out, the avian dinosaurs which became birds, small mammals that became all today's mammals from pygmy shrews to blue whales, and the angiosperms which evolved into grasses and flowering plants that diversified into thousands of species, some in association with pollinating insects, birds and even bats.

First, some AI background information.
What are cycads and what is their place in the evolution of plants? Cycads are a group of seed plants that belong to the division Cycadophyta. They are ancient plants that have been around for more than 200 million years and are often referred to as "living fossils" because they have retained many primitive characteristics that were more common in the Mesozoic Era. Cycads have a unique place in the evolution of plants, and their history provides insight into the development of plant life on Earth.

Here are some key features and points about cycads and their place in plant evolution:
  1. Ancient Lineage: Cycads belong to a group of plants that dates back to the Permian period and reached their peak diversity during the Jurassic and Cretaceous periods. While they were once more widespread, today, they are a relatively small and specialized group.
  2. Gymnosperms: Cycads are gymnosperms, which means they produce seeds that are not enclosed within a fruit. The seeds are typically borne in cones, and unlike angiosperms (flowering plants), they do not produce flowers.
  3. Cycad Characteristics:
    • Cycads have large compound leaves, often referred to as pinnate leaves, which resemble those of palm trees.
    • They have a stout and woody trunk.
    • Cycads are dioecious, meaning individual plants are either male or female. Female plants produce seeds after pollination by male cones.
  4. Ecological Significance: In their prime, cycads were a significant component of terrestrial ecosystems, especially during the Mesozoic Era when dinosaurs roamed the Earth. They played a role in providing habitat and food for various organisms.
  5. Evolutionary Significance: Cycads represent an evolutionary link between ferns and gymnosperms, showcasing certain features found in both groups. Their persistence over millions of years, despite environmental changes and the rise of flowering plants, highlights their adaptability and resilience.
  6. Conservation Concerns: Many cycad species are currently endangered due to habitat destruction, over-collection for horticultural purposes, and other threats. Conservation efforts are underway to protect and preserve these ancient plants.
In summary, cycads are unique and ancient gymnosperms that have survived for hundreds of millions of years. Their evolutionary history provides valuable insights into the development of plant life on Earth, and they continue to be of interest to scientists and conservationists studying biodiversity and ecological relationships.
How the discovery was made is the subject of an article in the online magazine of Duke University, Duke Today, by Karl Leif Bates:
Once a favored food of grazing dinosaurs, an ancient lineage of plants called cycads helped sustain these and other prehistoric animals during the Mesozoic Era, starting 252 million years ago, by being plentiful in the forest understory. Today, just a few species of the palm-like plants survive in tropical and subtropical habitats.

Like their lumbering grazers, most cycads have gone extinct. Their disappearance from their prior habitats began during the late Mesozoic and continued into the early Cenozoic Era, punctuated by the cataclysmic asteroid impact and volcanic activity that marks the K-Pg boundary 66 million years ago. However, unlike the dinosaurs, somehow a few groups of cycads survived to the present.

A new study appearing Nov. 16 in the journal Nature Ecology & Evolution has concluded that the cycad species that survived relied on symbiotic bacteria in their roots, which provide them with nitrogen to grow. Just like modern legumes and other plants that use nitrogen fixation, these cycads trade their sugars with bacteria in their roots in exchange for nitrogen plucked from the atmosphere.

What originally interested lead author Michael Kipp is that the tissues of nitrogen-fixing plants can provide a record of the composition of the atmosphere they grew up in. He combines geochemistry with the fossil record to try to understand the Earth’s climate history.

Knowing already that modern cycads are nitrogen-fixers, Kipp began analyzing some very old plant fossils during his Ph.D. work at the University of Washington to see if he could get a different look at ancient atmospheres. Most of the old cycads revealed that they weren’t nitrogen-fixers, but these also turned out to be the extinct lineages.

“Instead of being a story about the atmosphere, we realized this was a story about the ecology of these plants that changed through time,” said Kipp, who spent nearly a decade on this finding, first at UW and then as a postdoctoral researcher at CalTech.

Much of what we know about ancient atmospheres comes from chemical studies of ancient sea life and sediments, Kipp said. Applying some of those methods to terrestrial plants is a new wrinkle.

“Going into the project, there were no published nitrogen isotope data from fossilized plant foliage,” Kipp said. It took a while for him to fine-tune the method and to secure samples of precious plant fossils that museum curators were reluctant to see vaporized to get the data.

“In the few fossil samples that are of surviving (cycad) lineages, and that are not so old -- 20, 30 million years -- we see the same nitrogen signature as we see today,” Kipp said. That means their nitrogen came from symbiotic bacteria. But in the older and extinct cycad fossils, that nitrogen signature was absent.

What is less clear is how nitrogen fixation helped the surviving cycads. It may have helped them weather the dramatic shift in climate or it may have allowed them to compete better with the faster-growing angiosperm plants that flourished after the extinction, “or it could be both.”

“This is a new technique that we can do a lot more with,” Kipp said.
The research team give more technical details in their paper in Nature Ecology & Evolution:

Cycads are ancient seed plants (gymnosperms) that emerged by the early Permian. Although they were common understory flora and food for dinosaurs in the Mesozoic, their abundance declined markedly in the Cenozoic. Extant cycads persist in restricted populations in tropical and subtropical habitats and, with their conserved morphology, are often called ‘living fossils.’ All surviving taxa receive nitrogen from symbiotic N2-fixing cyanobacteria living in modified roots, suggesting an ancestral origin of this symbiosis. However, such an ancient acquisition is discordant with the abundance of cycads in Mesozoic fossil assemblages, as modern N2-fixing symbioses typically occur only in nutrient-poor habitats where advantageous for survival. Here, we use foliar nitrogen isotope ratios—a proxy for N2 fixation in modern plants—to probe the antiquity of the cycad-cyanobacterial symbiosis. We find that fossilized cycad leaves from two Cenozoic representatives of extant genera have nitrogen isotopic compositions consistent with microbial N2 fixation. In contrast, all extinct cycad genera have nitrogen isotope ratios that are indistinguishable from co-existing non-cycad plants and generally inconsistent with microbial N2 fixation, pointing to nitrogen assimilation from soils and not through symbiosis. This pattern indicates that, rather than being ancestral within cycads, N2-fixing symbiosis arose independently in the lineages leading to living cycads during or after the Jurassic. The preferential survival of these lineages may therefore reflect the effects of competition with angiosperms and Cenozoic climatic change.

Apart from the small matter of this mass extinction happening about 66 million years before they think Earth existed, there is much for creationists to ignore here.

There is the evidence of an evolved ability of cycads to utilise nitrogen fixed by bacteria in their roots which somehow meant they were able to survive the decade-long 'winter', at the K-Pg boundary, and the fact that most of them lacked that ability so went extinct. It's almost exactly like their putative intelligent, omniscient designer didn't know what was about to happen, or planned to exterminate most of the cycads it had designed along with the dinosaurs it had designed, and planned to replace most of them with different life-forms which it could have designed earlier and prevented the meteor strike, if it has the powers granted to it by creationists.

In many ways, it resembles a chaotic system running without a plan and with nothing in charge.

But creationists can't allow themselves to have such thoughts in case they end up thinking they might be wrong, and they are not as important as they like to think they are.

Thank you for sharing!

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