Even without body parts that allow movement, new research shows — for the first time — that some of the first animals on Earth managed to be selective about where they lived.
These creatures from the Ediacaran period, roughly 550 million years ago, are soft-bodied animals with odd shapes that live in the sea. Researchers have long considered it ambiguous.
“It’s not like studying dinosaurs, which are related to the birds we can observe today,” said Philip C. Bowen, a UC Riverside paleontology graduate student and lead author of the new study. “With these animals, since we have no contemporary descendants, we are still working out basic questions about how they lived, such as how they reproduced and what they ate.”
For this specific research project, the researchers focused on understanding where the animals spent their lives in the sea.
The ancient sea was also quite a strange place compared to marine environments today. It was dominated by a mat on the sea floor made up of bacteria and layers of other organic matter. In addition, predatory creatures were uncommon.
Given the exotic nature of the Ediacaran land, the researchers were surprised to find an animal that lived the way barnacles do today. new paleobiology The paper details how Obamus Coronatus, named after the former US president, chose to live in certain parts of the sea floor in the company of other Obamus.
The animal averaged half an inch in diameter and was “in the shape of a French donut with ribbons on top,” Boin said. It didn’t move on its own, and it’s likely that it spent its entire life in its favorite spot at the bottom of the sea.
“We’re thinking about very old animals and you probably wouldn’t expect them to be so selective. But Obamus only happens when there’s a thick mat, which is a very evolved way of making a living for something so old,” he said. Mary Drewser, UCSD Distinguished Professor of Paleontology, and co-author of the study.
In 2018, Drosser’s lab named Obamus in honor of Barack Obama’s passion for science. Her group discovered them at an unusual, well-preserved fossil site in the Australian outback, in what is now called Nelpina Ediakkara National Park.
A series of storms buried Nelpina’s Ediacaran sea floor in layers of sediment, helping to preserve sandstone impressions of entire animal communities that lived together there. “In this way, we can put together whole ecosystems,” Drosser said. “Looking at them is like diving into the bottom of an ancient sea, rather than looking at a single animal in a fish tank.”
For this project, the research team selected three animals that were found in relatively large numbers in Nelbina, and examined how they were distributed geographically.
The other animals, Tribrachydium and Rogoconnet, are also non-motile creatures that have no recent descendants. “They are three-dimensionally symmetrical, like the Mercedes-Benz logo,” Boin said. “And they would have lived their whole lives embedded in the bottom of the sea, as did Obamus.”
The distribution of these two other animals was varied. Sometimes they can be found living in the company of other creatures like themselves, but not in every case. However, Obamus showed a clear preference.
“This is really the first example of an Ediacaran creature selective in its habitat, and the first example of a microscopic animal doing so,” Puan said. “But how did they get where they wanted to go? That’s a question we don’t know the answer to yet.”
The research team hypothesizes that Obamus was likely motivated by the need to reproduce.
“There are a limited number of reproductive strategies out there, especially for animals like this,” Drosser said. “There are more strategies today, and they are more detailed now. But the same strategies used today were still used 550 million years ago.”
Obamus likely spread via selective larvae that prefer sites with thick germ mats and close proximity to other Obamus. “We don’t fully understand how the Obamus offspring spread, but we do know that when they chose a place to live, it was very specific,” Boan said.
A deeper understanding of how life on Earth has evolved over time could give researchers insight into how life might have evolved on another planet. For this reason, Droser’s lab is funded by NASA’s Exobiology Program.
“This is our window into how a complex ecosystem forms,” Puan said. “We only have Earth, and we need to use every bit of its history when thinking about life, even far out in the universe.”