Researchers Uncover Evidence of What May Be Earth’s First Mass Animal Extinction

Ever since the Cambrian blast 538.8 million years earlier– a time when most of the animal phyla we’re familiar with today were established– 5 significant mass extinction events have whittled down the biodiversity of all creatures, great and tiny.

Researchers from the United States have uncovered proof of one happening earlier, around 550 million years ago during a period referred to as the Ediacaran.

Animals were soft-bodied

Though the seas teemed with a few familiar animals like sponges and jellyfish, most life during this early time of biological history would seem alien to us currently.

Many of the animals were soft-bodied. Some appeared more like plant fronds stuck in place. Others had some form of shell.

Virginia Tech paleobiologist

Virginia Tech paleobiologist Scott Evans and associates compiled data on uncommon fossils of the squishier kinds of animals from around the world dated to the Ediacaran. They found unexpected shifts in biodiversity that had before been spotted weren’t simple sampling biases.

Because softer body parts generally do not fossilize as immediately as harder, much more mineralized bits of anatomy, researchers usually have suspected a relative lack of soft-bodied creatures in the Ediacaran’s later phases are simply the result of a failure to be protected.

But the global fossil record suggests otherwise

The team discovered that there was an overall rise in biodiversity between the earlier and middle stages of the Ediacaran, called the Avalon (575 to 560 million years back) and White Sea stages (560 to 550 million years back).

“We discover significant differences in the feeding mode, life habit, ecological tier, and maximum body dimension between the Avalon and White Sea assemblages,” the group writes in their paper.

In between these 2 time periods, more smaller mobile animals appeared that fed upon the microbial mats that dominated the seafloors. Previously many of the animals were stuck-in-place (sessile) filter feeders.

Feeding modes did not change in this form between the White Ocean and the last stage, called as the Nama (550 to 539 million years ago). Instead, a staggering 80 percent of species appeared to vanish between these 2 stages of the Ediacaran.

Earlier research

Earlier research has recommended that this decrease may have been the outcome of mobile animals that burrowed or left trace fossils, which considerably changed the environment and slowly changed sessile filter feeders. This new proof suggests that was not the case.

Feeding modes

All kinds of feeding modes and life habits experienced similar losses, with just 14 genera still observed in the Nama out of 70 recognized teams from the earlier White Sea stage. If more newly developed species had taken over, there just would have been temporal overlap between the recent and the old species. This wasn’t observed, the team argue, ruling out biotic replacement.

“The decrease in diversity between these assemblages is indicative of an extinction event, with the percentage of genera lost comparable to that experienced by aquatic invertebrates during the ‘Huge 5’ mass extinctions,” Evans and colleagues write.

Many of the White Sea animals that survived the extinction event and stayed in the Nama period were large, frond-like organisms with a high surface area-to-volume ratio. This could be a sign these animals were adapting to deal with a decrease in oceanic oxygen.

Low-oxygen atmospheres

“By maximizing the relative proportions of cells in straight contact with seawater, great surface-area taxa would have been comparatively better adapted to stay alive in low-oxygen atmospheres,” the team describes.

Additionally, current geochemical evidence supports this idea, with a 2018 study finding signs of extensive ocean anoxia that covered more than twenty percent of the seafloor at the end of the Ediacaran.

“Hence, our data sustain a link in between Ediacaran biotic turnover and environmental change, comparable to other major mass terminations in the geologic record,” the team ends.

It´s become an all too familiar story.

Read The Original Article on Science Alert

Read more: In A First, Investigators Found An Uncommon Mineral That Comes Straight From Earth’s Lower Mantle