Early species developed much faster than previously thought, research shows

Early species developed much faster than previously thought, OHIO research shows
Building block model of the earth system that produced the Great Ordovician Biodiversificaiton Event. Figure from Stigall et al., 2019. Credit: Christian Rasmussen

When Earth's species were rapidly diversifying nearly 500 million years ago, that evolution was driven by complex factors including global cooling, more oxygen in the atmosphere, and more nutrients in the oceans. But it took a combination of many global environmental and tectonic changes occurring simultaneously and combining like building blocks to produce rapid diversification into new species, according to a new study by Dr. Alycia Stigall, Professor of Geological Sciences at Ohio University.

She and fellow researchers have narrowed in a specific time during an era known as the Ordovician Radiation, showing that actually developed rapidly during a much shorter time frame than previously thought. The Great Biodiversification Event where many new species developed, they argue, happened during the Darriwilian Stage about 465 million years ago. Their research, "Coordinated biotic and abiotic change during the Great Ordovician Biodiversification Event: Darriwilian assembly of early Paleozoic ," was published in Palaeogeography, Palaeoclimatology, Palaeoecology as part of a special issue they are editing on the Great Ordovician Biodiversification Event.

New datasets have allowed them to show that what previously looked like species development widespread over time and geography was actually a pulse.Picture a world before the continents as we know them, when most of the land mass was south of the equator, with only small continents and islands in the vast oceans above the tropics. Then picture forming over the southern pole. As the ice caps form, the ocean recedes and local, isolated environments form around islands and in seas perched atop continents. In those shallow marine environments, new species develop.

Then picture the ice caps melting and the oceans rising again, with those new species riding the waves of global diversification to populate new regions. The cycle then repeats producing waves of new species and new dispersals.

Lighting the Spark of Diversification

The early evolution of animal life on Earth is a complex and fascinating subject. The Cambrian Explosion (between about 540 to 510 million years ago) produced a stunning array of body plans, but very few separate species of each, notes Stigall. But nearly 40 million years later, during the Ordovician Period, this situation changed, with a rapid radiation of species and genera during the Great Ordovician Biodiversification Event.

The triggers of the GOBE and processes that promoted diversification have been subject to much debate, but most geoscientists haven't fully considered how changes like or increased oxygenation would foster increased diversification.

A recent review paper by Stigall and an international team of collaborators attempts to provide clarity on these issues. For this study, Stigall teamed up with Cole Edwards (Appalachian State University), a sedimentary geochemist, and fellow paleontologists Christian Mac ├śrum Rasmussen (University of Copenhagen) and Rebecca Freeman (University of Kentucky) to analyze how changes to the physical earth system during the Ordovician could have promoted this rapid increase in diversity.

In their paper, Stigall and colleagues demonstrate that the main pulse of diversification during the GOBE is temporally restricted and occurred in the Middle Ordovician Darriwilian Stage (about 465 million years ago). Many changes to the physical earth system, including oceanic cooling, increased nutrient availability, and increased atmospheric oxygen accumulate in the interval leading up to the Darriwilian.

These physical changes were necessary building blocks, but on their own were not enough to light the spark of diversification.

The missing ingredient was a method to alternately connect and isolate populations of through cycles of vicariance and dispersal. That spark finally occurs in the Darriwilian Stage when ice caps form over the south pole of the Ordovician Earth. The waxing and waning of these ice sheets caused sea level to rise and fall (similar to the Pleistocene), which provided the alternate connection and disconnection needed to facilitate rapid diversity accumulation.

Stigall and her collaborators compared this to the assembly of building blocks required to pass a threshold.

Explore further

Rise in oxygen levels links to ancient explosion of life, researchers find

More information: Alycia L. Stigall et al, Coordinated biotic and abiotic change during the Great Ordovician Biodiversification Event: Darriwilian assembly of early Paleozoic building blocks, Palaeogeography, Palaeoclimatology, Palaeoecology (2019). DOI: 10.1016/j.palaeo.2019.05.034
Provided by Ohio University
Citation: Early species developed much faster than previously thought, research shows (2019, August 15) retrieved 18 September 2019 from https://phys.org/news/2019-08-early-species-faster-previously-thought.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Aug 16, 2019
Look up RNA World Hypothesis on youtube. It's produced by Spoken Clearly, a collaboration that includes the National Science Foundation. It's truly excellent work. Everyone should see it, at least twice.

Aug 17, 2019
If the Great Ordovician Biodiversification Event happened within 10 Myrs and mostly difersified species, while the Cambrian Explosion happened within 30 Myrs and mostly diversified body plans, maybe we call the former "the explosion" and rename the latter to the Cambrian Event...

Aug 17, 2019
Look up RNA World Hypothesis on youtube. It's produced by Spoken Clearly, a collaboration that includes the National Science Foundation.

Good! But is easier to find by searching "Stated Clearly" [ https://www.youtu...nYFCZ9Yg ]. The good part is the ribozyme and its evolution (whether in vivo or in vitro) part, but beware that it is a US/NASA video so is heavily weighted for biochemistry and against geology/biology where the most interesting evidence is found. (Say, evolutionary tree pathway back to geology, or the RNA/DNA replication in vent environments that these researchers did not mention - video from 2016, the same year PCR free RNA replication was discovered.)

The RNA/protein cell hypothesis (as ancestor to modern DNA/protein cells) is even stronger, and they did not relate the evidence very well. E.g. RNA is a metabolic precursor to DNA and sits at the center of metabolism (ATP), of protein production and of the oldest protein transport machinery.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more