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This primeval worm may be the ancestor of all animals

An artist's rendering of Ikaria wariootia and its 555-million-year-old burrow.
An artist's rendering of Ikaria wariootia and its 555-million-year-old burrow.
(Image: © Sohail Wasif/UCR)

Humans, it's been said, are like donuts. They have an opening at each end, and a single continuous hole running through their middle. (Note: This theory has yet to appear in a peer-reviewed journal.)

It's a crude simplification of our species, sure, but look far enough back on the animal family tree and you'll find an ancestor organism that's little more than a digestive tract with some meat wrapped around it. Limbless and hungry like a sentient macaroni, this ancient creepy-crawler was the first bilaterian — an organism with two symmetrical sides, a distinct front and back end, and a continuous gut connecting them. 

While bilaterians run rampant today (insects, humans and most other animals among them), the identity of that progenitor organism has long eluded discovery. Now, researchers believe they've found it in the fossil record for the first time. 

In a study published March 23 in the journal Proceedings of the National Academy of Sciences, a team of scientists analyzed a chunk of rock containing an ancient undersea burrow found deep below Australia. They found several fossil organisms preserved near the burrows, each creature about the size and shape of a grain of rice and dating to roughly 555 million years ago. 

Related: This 500-million-year-old 'social network' may have helped animals clone themselves

Ikaria impressions in stone. The largest is roughly the size of a grain of rice. (Image credit: Droser Lab/UCR)

The burrows were clearly made by wriggling creatures with distinct front and back sides, but to get a more detailed picture of those ancient burrowers the researchers analyzed the fossils with a 3D laser scanner. They found that the tiny animals not only had a clear head and tail, but also had a bilaterally symmetrical body and faintly grooved musculature, similar to a worm. The researchers named this worm-like creature Ikaria wariootia, and dubbed it the oldest known example of a bilaterian — aka, the oldest shared ancestor of all living animals.

"Burrows of Ikaria occur lower than anything else," study co-author Mary Droser, a professor of geology at University of California, Riverside, said in a statement. "It’s the oldest fossil we get with this type of complexity."

Ikaria wariootia lived during the Ediacaran period (571 million to 539 million years ago), when the first non-microscopic multicellular creatures emerged. At the time, the world was chiefly populated by amorphous undersea blobs (see, for example, the shape-shifting, bottom-feeding rangeomorphs). Most Ediacaran animals died in a mass extinction event, leaving no links to modern animals. Ikaria wariootia, however, is an exception — trace fossils of their burrows persist into the Cambrian period (541 million to 485.4 million years ago), suggesting they survived long enough to evolve bilaterian descendants, the researchers wrote. 

In other words, perhaps you can thank this ancient rice-shaped worm for making you into a donut.

A 3D laser scan of an Ikaria wariootia impression. (Image credit: Droser Lab/UCR)

Originally published on Live Science.

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  • kamikrazee
    A mouth, a digestive tract, and a back passage. Charming. Reminds me of a well known chief executive.
    Reply
  • snowyphile
    Convergent evolution.
    Reply
  • Gracehartsoe
    I love his writing style! This boring information was written in a comical way that made the information more interesting and exciting to read! I actually laughed out loud-and I’m a teenager so that’s saying something if I think your funny-any way please write more in a comical way I love it.:love:
    Reply
  • Broadlands
    It is obviously not the ancestor of ALL animals, but only the bilatera. The title is very misleading.
    Reply
  • createdworld
    Oh, the assumptions! Are we still using the circular reasoning of dating rocks by the fossils and the fossils by the rocks? To state this as science (observable, testable, repeatable) is really a leap in the dark.
    Reply
  • Broadlands
    createdworld said:
    Oh, the assumptions! Are we still using the circular reasoning of dating rocks by the fossils and the fossils by the rocks? To state this as science (observable, testable, repeatable) is really a leap in the dark.

    No... they are not. Take a trip down the Grand Canyon, going back through time. There are no vertebrates, no dinosaurs. The fossils become more and more primitive. When you get to the bottom there are only microbes. That's evolution over geological time...observable and testable...and repeatable.
    Reply
  • createdworld
    Not really a good example, I think. Latest science on the Grand Canyon is rapid deposition of strata with formation being as little as 40,000 years ago, others see 6-7 mya. Lessons from Mt St Helens indicate catastrophic layering in very short order - not to mention the great unconformity stretching thought the canyon and much of the world, or the planation so obvious in the region. Fact is, the age of the canyon has been debated for years on end. Scientists of every bias have interpreted the actual evidence with incredible diverse conclusions, but it still seems that the issue is not a little water over vast eons of time, but a whole lot of water in a much shorter period of time. The so-called geologic column then would not be "a trip though time" but the burial order of billions of dead things buried in rock laid down by water all over the earth. Still, since no one was there, I have to question "observation" and "testable" - certainly not repeatable except in the sense of other catastrophic phenomena, like Mt. St Helens.
    Reply
  • Broadlands
    createdworld said:
    Not really a good example, I think. Latest science on the Grand Canyon is rapid deposition of strata with formation being as little as 40,000 years ago, others see 6-7 mya. Lessons from Mt St Helens indicate catastrophic layering in very short order - not to mention the great unconformity stretching thought the canyon and much of the world, or the planation so obvious in the region. Fact is, the age of the canyon has been debated for years on end. Scientists of every bias have interpreted the actual evidence with incredible diverse conclusions, but it still seems that the issue is not a little water over vast eons of time, but a whole lot of water in a much shorter period of time. The so-called geologic column then would not be "a trip though time" but the burial order of billions of dead things buried in rock laid down by water all over the earth. Still, since no one was there, I have to question "observation" and "testable" - certainly not repeatable except in the sense of other catastrophic phenomena, like Mt. St Helens.

    You are not paying attention? The age of the Grand Canyon is not the point. The rocks are deposited is horizontal layers. The oldest at the bottom, the youngest at the top. The most primitive fossil organisms are at the bottom, the most advanced (evolved!) at the top. This is repeatable in other parts of the world in similar layered rocks. Obviously impossible if it all was a flood. The same thing happens today in local garbage dumps. The oldest newpapers, radios, TVs, telephones are toward the bottom, Yesterday's newspapers and garbage at the top. Repeatable from dump to dump.
    Reply
  • createdworld
    To the last comment on this thread: I think I see what you are saying. Again, we are looking at the same data (strata, in this case) and coming up with different interpretations. If I understand you correctly, you are saying that the time of the formation of the canyon is not the important point, but the layering of rock strata with fossils. I'm thinking of the canyon as the rock cut out by an incredible amount of water. It is, after all, sedimentary rock until you get to the great unconformity. As we see from Mt St Helen, the layering is caused by water, or mud flow, laid down in very finely defined strata - just like the Grand Canyon (only a 40th of size). So, from my worldview (which does not include billions of years), the strata was laid from a major flood, and then the canyon of sedimentary (by definition) rock was carved by incredible water flow as the flood receded (or, as some scientists posit, a major break in the Missoula glacier lake). I base this "belief" on actual observations - particularly the lack of erosion between layers, the planation of buttes in the area (a really good geological study there!), the lack of millions-of-years kind of erosion in the canyon itself, and a number of other factors. (Actually, I became convinced by an aerial survey - obviously a whole lot of water! It seemed to fit. ) Since fossils are 95% marine fossils anyway (found in also in higher elevations, including Mt Everest), is shouldn't surprise anyone that some are found in many various rock layers. A study of the pre-Cambrian explosion should raise questions as well, with the trilobites and the nautilus obviously NOT primitive organisms. So, your view of time really does matter and provides a bias in interpreting the data - from either worldview.
    Reply
  • Broadlands
    "So, from my worldview (which does not include billions of years), the strata was laid from a major flood,"

    Not possible to lay all that sediment in one global flood event and have the included fossils be from the most primitive at the bottom and the most evolved at the top. And it's observable, testable and repeatable in other parts of the world. And, I believe you have seriously misread the Cambrian explosion of fossils by referring to it as the Pre-Cambrian explosion. The Pre-Cambrian goes back billions of years to those microbes that are found as fossils at the base of the Grand Canyon...unaccompanied by any more advanced life...trilobites, dinosaurs, horses or even people.
    Reply