Geologists Have Discovered Humanity’s Earliest Ancestor, And It’s A Worm

RIVERSIDE, Calif. — A new discovery is putting the term respect your elders to the test. Prepare to meet your mega great grandparent; a tiny, wormlike creature. Geologists from the University of California, Riverside have discovered the earliest known ancestor to most animals alive on this planet today, including humans.

The creature, named Ikaria wariootia, is believed to have lived over 555 million years ago. That time frame makes it the earliest bilaterian, or organism with a front and back, two symmetrical sides, and openings on both ends of its body connected by a gut.

Ikaria Wariootia
Artist’s rendering of Ikaria wariootia. (Image credit: Sohail Wasif/UCR)

Evidence of its existence was found within fossilized burrows discovered in Nilpena, South Australia.

Now, there are known multicellular organisms that date back even further than 555 million years ago, such as sponges, but these little beings came in a variety of shapes. As fascinating as sponge fossils are to examine, these creatures are not the ancestors of modern day humans or animals.

The development of bilateral symmetry, or an evenly proportioned body, was a major development for the evolution of life on Earth. From insects to dogs and ultimately humans, virtually all animals on Earth today feature a bilaterian body plan.

Evolutionary biologists have long theorized that the first bilaterian had to be very small, and relatively simple in its design and organ composition. Of course, these were just theories because it was always thought to be impossible to uncover actual proof of such an organisms existence.

Roughly 15 years ago, fossilized burrows were discovered in Ediacaran Period deposits in Australia. These burrows suggested that a bilaterian had existed 555 million years ago, but there was no actual sign of the creature.

Ikaria wariootia fossil
These are Ikaria wariootia impressions in stone. (Photo credit: Droser Lab/UCR)

Recently, however, oval impressions were discovered near some of the burrows. Using a three-dimensional laser scanner, the team at UC Riverside were able to construct the body of whatever left those impressions. They created a creature with a consistent, cylindrical body featuring a head, tail, and even some grooved musculature. This worm-like animal is estimated to have been between 2 and 7 millimeters long and about 1 and 2.5 millimeters wide. That would make it about the size of a grain of rice, or smaller.

“We thought these animals should have existed during this interval, but always understood they would be difficult to recognize,” comments Scott Evans, a recent doctoral graduate from UC Riverside, in a release. “Once we had the 3D scans, we knew that we had made an important discovery.”

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Ikaria Wariootia
A 3D laser scan that showing the regular, consistent shape of a cylindrical body with a distinct head and tail and faintly grooved musculature. (Image credit: Droser Lab/UCR)

“Burrows of Ikaria occur lower than anything else. It’s the oldest fossil we get with this type of complexity,” adds Mary Droser, professor of geology. “Dickinsonia and other big things were probably evolutionary dead ends. We knew that we also had lots of little things and thought these might have been the early bilaterians that we were looking for.”

This worm creature may sound terribly simple in comparison to modern day animals, but for its time it was very advanced. Researchers believe it burrowed under sand in the ocean in search of nutrients, and may have even had some sensory abilities.

“This is what evolutionary biologists predicted,” she concludes. “It’s really exciting that what we have found lines up so neatly with their prediction.”

The study is published in the Proceedings of the National Academy of Sciences.

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