Earth’s first animals were very picky about where they lived

For the first time, new research has revealed that some of Earth’s earliest animals, despite lacking body parts that allowed for movement, were selective about where they lived. 

These creatures, which date back to the Ediacaran Period around 550 million years ago, were soft-bodied, strangely shaped sea-dwelling animals that have long puzzled scientists.

Studying these enigmatic animals is a unique challenge for researchers, as they have no modern descendants. 

“It’s not like studying dinosaurs, which are related to birds that we can observe today,” said Phillip C. Boan, a paleontology graduate student at UC Riverside and lead author of the study. “With these animals, because they have no modern descendants, we’re still working out basic questions about how they lived, such as how they reproduced and what they ate.”

How the research was done

To better understand these early creatures, the research team focused on determining where in the sea these animals spent their lives. The ancient sea during the Ediacaran Period was a largely foreign environment compared to today’s marine ecosystems, featuring a sea floor covered by a mat of bacteria and layers of other organic materials, and a noticeable scarcity of predatory creatures.

In light of the alien nature of Ediacaran Earth, researchers were surprised to discover an animal that exhibited living habits similar to those of modern barnacles. 

Detailed in a new paper published in Paleobiology, the study reveals how Obamus coronatus, named in honor of former U.S. President Barack Obama, preferred to live on specific areas of the sea floor and in the company of other Obamus specimens.

Described by Boan as “shaped like a French cruller donut with ribbons on top,” the animal had an average diameter of about half an inch. It did not move on its own and likely spent its entire life embedded in its preferred spot on the sea floor.

Considering the antiquity of these organisms, the selectivity of Obamus is rather unexpected. “We think about the very oldest animals and maybe you wouldn’t expect them to be so picky. But Obamus only occurs where there is a thick mat, and it’s a pretty sophisticated way of making a living for something so very old,” said Mary Droser, UCR distinguished professor of paleontology and study co-author.

Named in honor of Barack Obama

In 2018, a laboratory led by Droser named a newly discovered fossil Obamus in honor of former U.S. President Barack Obama’s passion for science. The well-preserved fossil was found at an extraordinary site in the Australian Outback, now known as Nilpena Ediacara National Park.

A series of storms during the Ediacaran Period buried the sea floor at Nilpena in layers of sediment, preserving sandstone impressions of entire animal communities that lived together in that ancient ecosystem. “This way, we’re able to piece together whole ecosystems,” Droser said. “Looking at them is like snorkeling around on the ancient sea floor, instead of looking at a single animal in a fish tank.”

For their research project, the team selected three animals found in relatively large numbers at Nilpena, including Obamus, and examined their geographical distribution. The other two animals, Tribrachidium and Rugoconites, were also immobile creatures with no modern descendants. 

According to Phillip C. Boan, the lead author of the study, these animals were “tri-radially symmetrical, like the Mercedes Benz logo,” and lived their entire lives embedded in the sea floor, just like Obamus.

The distribution patterns of Tribrachidium and Rugoconites were varied; sometimes they could be found living with other organisms of their kind, but not always. However, Obamus exhibited a distinct preference for specific habitats. 

“This is really the first example of a habitat-selective Ediacaran creature, the first example of a macroscopic animal doing this,” Boan said. “But how did they get where they wanted to go? This is a question we don’t yet know the answer to.”

What the researchers learned

The research team theorizes that the habitat preference of Obamus was likely motivated by the need to reproduce. “There are a limited number of reproductive strategies, especially for animals like these,” Droser explained. “There are more strategies today, and they’re more elaborate now. But the same ones used today were still being used 550 million years ago.”

Obamus likely propagated itself through selective larvae that preferred locations with thick microbial mats and close proximity to other Obamus individuals. “We don’t entirely understand how Obamus offspring spread out, but we know that when they picked a place to live, it was very specific,” Boan said.

A deeper understanding of how life on Earth developed over time can provide researchers with valuable insights into how life could evolve on other planets. For this reason, Droser’s lab is funded by NASA’s Exobiology program.

“This is our window into how a complex ecosystem forms,” Boan said. “We only have Earth, and we need to use every part of its history when thinking about life, even way off in the cosmos.”

This study not only provides valuable insights into the lives of these early animals but also challenges long-held assumptions about the behavior and living conditions of Earth’s most ancient creatures. As scientists continue to uncover the secrets of the Ediacaran Period, we can expect further revelations about the diverse and enigmatic organisms that populated our planet over half a billion years ago.

More about Earth’s first animals

Earth’s first animals emerged during the Ediacaran Period, approximately 635 to 541 million years ago. This period preceded the Cambrian Explosion, which marked a rapid diversification of lifeforms on Earth. The Ediacaran Period is named after the Ediacara Hills in South Australia, where the first fossils of this age were discovered.

Ediacaran fauna were primarily soft-bodied, marine-dwelling organisms that displayed a wide range of sizes and morphologies. The majority of these early animals were immobile or had limited mobility, as they lacked specialized body parts for movement. Many of them were likely filter feeders, relying on organic matter and microscopic organisms in the water for nourishment. Some of the most well-known Ediacaran organisms include:

Dickinsonia

A flat, oval-shaped creature with a segmented body that could grow up to 1 meter in length. Recent research suggests that Dickinsonia might be one of the earliest known animals, possibly belonging to the group of animals called bilaterians.

Charnia

A frond-like organism anchored to the sea floor, with a branched structure that could reach up to several feet in height. Charnia is considered a sessile organism, meaning it was immobile and remained attached to one location throughout its life.

Spriggina

A small, oval-shaped organism with a segmented body and a unique head structure. It is thought to have been an early ancestor of arthropods, a group that includes insects, spiders, and crustaceans.

Rangea

Another frond-like organism similar to Charnia, characterized by its unique branching patterns and fan-like shape.

The Ediacaran biota represents a critical step in the evolution of life on Earth, as these early animals laid the foundation for the diverse and complex ecosystems that emerged during the Cambrian Explosion and beyond. 

The study of Ediacaran fossils provides valuable insights into the origins of multicellular life, the development of early ecosystems, and the evolutionary history of various animal groups.

Image Credit: Nobu Tamura

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