Amazing stuff! How many mass extinctions actually happened?
Was this newly discovered episode really a mass extinction event or rather some dynamic process involving the earliest living organisms?
Are we currently living in times of an ongoing mass extinction? Hype? "Earth is currently in the midst of a mass extinction, losing thousands of species each year. "
"... in the new study, scientists at UC Riverside and Virginia Tech have found evidence of another mass extinction event that took place about 100 million years earlier than the currently accepted first. This places it during the Ediacaran period about 550 million years ago, which is when complex multicellular life really took off for the first time. ...
Fossil records from this time are murky for a number of reasons. For one, the creatures that lived then were largely soft-bodied and so didn’t fossilize too well. ...
Fossil records from this time are murky for a number of reasons. For one, the creatures that lived then were largely soft-bodied and so didn’t fossilize too well. ...
So for the new study, the researchers assembled a database of almost all known Ediacaran animals from around the world, and across the tens of millions of years of the period. They examined when these creatures lived and disappeared, as well as their environments, body sizes and shapes, diets, habits and whether they could move around or not.
In doing so, the team found that around 80% of the animals alive during the middle Ediacaran had gone extinct by the late Ediacaran. ..."
"... Although unclear whether this represents a true “mass extinction,” the percentage of organisms lost is similar to these other events, including the current, ongoing one. ...
Though it’s not clear why oxygen levels declined so precipitously at the end of the era ..."
Though it’s not clear why oxygen levels declined so precipitously at the end of the era ..."
From the significance and abstract:
"Significance
Mass extinctions are well recognized as significant steps in the evolutionary trajectory of life on this planet. Here, we document the oldest known extinction of animals and test for potential causes. Our results indicate that, like younger diversity crises, this event was caused by major shifts in environmental conditions. Particularly, we find support for decreased global oxygen availability as the mechanism responsible for this extinction. ...
Abstract
The Ediacara Biota—the oldest communities of complex, macroscopic fossils—consists of three temporally distinct assemblages: the Avalon (ca. 575–560 Ma), White Sea (ca. 560–550 Ma), and Nama (ca. 550–539 Ma). Generic diversity varies among assemblages, with a notable decline at the transition from White Sea to Nama. Preservation and sampling biases, biotic replacement, and environmental perturbation have been proposed as potential mechanisms for this drop in diversity. Here, we compile a global database of the Ediacara Biota, specifically targeting taphonomic and paleoecological characters, to test these hypotheses. Major ecological shifts in feeding mode, life habit, and tiering level accompany an increase in generic richness between the Avalon and White Sea assemblages. We find that ∼80% of White Sea taxa are absent from the Nama interval, comparable to loss during Phanerozoic mass extinctions. The paleolatitudes, depositional environments, and preservational modes that characterize the White Sea assemblage are well represented in the Nama, indicating that this decline is not the result of sampling bias. Counter to expectations of the biotic replacement model, there are minimal ecological differences between these two assemblages. However, taxa that disappear exhibit a variety of morphological and behavioral characters consistent with an environmentally driven extinction event. The preferential survival of taxa with high surface area relative to volume may suggest that this was related to reduced global oceanic oxygen availability. Thus, our data support a link between Ediacaran biotic turnover and environmental change, similar to other major mass extinctions in the geologic record."
Earth might be experiencing 7th mass extinction, not 6th 550-million-year-old creatures’ message to the present
Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition (no public access)
Diorama depicting Ediacaran-era sea creatures. (Smithsonioan Institution)
No comments:
Post a Comment