Earth’s first animals had particular taste in real estate

Newswise — Despite lacking appendages for mobility, recent findings indicate that certain of the earliest creatures on Earth were able to exhibit selectivity in their choice of habitat. This represents a novel discovery.

The soft-bodied organisms that inhabited the sea during the Ediacaran Era, approximately 550 million years ago, are characterized by peculiar shapes and have always been a mystery to researchers.

Phillip C. Boan, a graduate student of paleontology at UC Riverside and the primary author of the recent study, remarked, "Unlike the study of dinosaurs, which have avian descendants that we can observe today, investigating these creatures presents a different challenge. As they have no living descendants, we are still grappling with fundamental inquiries concerning their way of life, such as their mode of reproduction and diet."

The scientists, in this specific research undertaking, directed their attention towards comprehending the specific location in the sea where these creatures dwelled.

Compared to present-day marine ecosystems, the ancient sea was vastly dissimilar and unfamiliar. The seafloor was primarily covered by a bacterial mat intermixed with layers of other organic substances. Moreover, the existence of predatory animals was rare.

As the Ediacaran world was so alien, the discovery of an organism that lived similarly to present-day barnacles caught the researchers off-guard. The new Paleobiology publication describes Obamus coronatus, named after a former U.S. president, and how it favored living in particular regions of the seafloor alongside its counterparts.

The creature had an average diameter of around half an inch and was described by Boan as resembling a French cruller donut with ribbons on top. It lacked self-propulsion and probably remained affixed to its favored location on the seafloor for its entire life.

Mary Droser, a co-author of the study and distinguished professor of paleontology at UCR, stated, "When we consider the earliest animals, we may not anticipate such discerning behavior. However, Obamus only inhabited areas with a dense mat, and it's an incredibly sophisticated way of earning a living for an organism so ancient."

Back in 2018, Mary Droser's research team named the Obamus after Barack Obama due to his ardent support for science. The researchers uncovered the specimen in an exceptionally well-preserved fossil location situated in the Australian Outback, which is currently recognized as the Nilpena Ediacara National Park.

A sequence of storms caused sediment to cover the Ediacaran seafloor at Nilpena, resulting in the conservation of sandstone impressions that captured complete animal communities that lived in that region. "This technique enables us to reconstruct entire ecosystems," Droser remarked. "Examining them is akin to snorkeling in the ancient seabed instead of observing a solitary animal in an aquarium."

The scientific team, for this investigation, handpicked three animals that were present in sizable quantities at Nilpena and examined their geographical distribution.

The two additional organisms, Tribrachidium and Rugoconites, were also immobile organisms that lack any present-day descendants. "They possess a tri-radial symmetry, akin to the Mercedes Benz logo," Boan explained. "Moreover, like Obamus, they would have remained embedded in the seafloor for the duration of their lives."

The distribution of the other two organisms was quite diverse. They could occasionally be discovered residing alongside other similar creatures, but it was not always the case. On the other hand, Obamus demonstrated a distinct preference for a particular habitat.

"This is actually the initial example of an Ediacaran animal that selects its habitat, and the first instance of a macroscopic creature exhibiting this behavior," Boan explained. "However, the means by which they got to their preferred location remains unknown. This is a query for which we currently lack an answer."

The research team theorizes that Obamus were likely motivated by the need to reproduce. 

Droser stated that "there is a finite number of reproductive approaches, particularly for creatures like these. There are presently more intricate and varied strategies than before. But the same methods that exist now were also employed 550 million years ago."

It is probable that Obamus disseminated itself via selective larvae that favored locations with a dense microbial mat and were in close proximity to other Obamus. Boan stated that "although we don't have a complete understanding of how Obamus offspring spread, we do know that when they chose a habitat, it was extremely precise."

Gaining a more profound comprehension of how life evolved on Earth can provide scientists with knowledge about how life may emerge on other planets. Therefore, NASA's Exobiology program finances Droser's lab.

Boan highlights that studying the formation of complex ecosystems is crucial to understanding how life evolves. He emphasizes the importance of using every part of Earth's history to consider life, including when examining extraterrestrial life. In essence, Earth's past can serve as a window into the potential development of life on other planets.