You may want to plan to get a second Mother’s Day and Father’s Day card this year – scientists have discovered the single living creature that all living creatures on Earth descended from. And, in case you’re just filling out your U.S. census form, your original nationality is Australian, mate!
“This organism is consistent with predictions based on modern animal phylogenetics that the last ancestor of all bilaterians was simple and small and represents a rare link between the Ediacaran and the subsequent record of animal life.”
In a paper published this week in the Proceedings of the National Academy of Sciences (PNAS), Scott Evans, a recent doctoral graduate from University of California, Riverside, and Professor Mary Droser, a professor of geology at the school, describe leading a team of researchers to Nilpena, South Australia, where fossilized burrows found in 555 million-year-old Ediacaran Period deposits were believed to have been made by bilaterians – animals whose bodies have a bilateral symmetry -- a left and a right side that are mirror images of each other – as well as a front, a back, a head and a gut. If this looks familiar, you’re probably looking in a mirror. Scientists believe bilaterians are the ancestors of all living creatures and this Ediacara Biota– the oldest known complex animal community -- should contain the oldest evidence of them. The problem is, no one has found bilaterian fossils there.
Until Evans and Droser found Ikaria wariootia.
With funding from NASA, the team studied the burrows with a 3-D laser scanner and saw tiny grooves that would match a tiny (2-7 mm (.08-.27 in) long, 1-2.5 mm (.04-.1 in) wide – about the size of a grain of rice) cylindrical body with a distinct head and tail. The burrows showed that the creatures moved by contracting muscles like a worm (peristaltic locomotion) and contained evidence that they fed on buried organic matter with a mouth, digested it with a gut and excreted it out an anus. (TMI?) All of that adds up to this:
“Together, these suggest that Ikaria represents one of the oldest total group bilaterians identified from South Australia, with little deviation from the characters predicted for their last common ancestor.”
They named the creature Ikaria wariootia – Ikara means “meeting place” in the Adnyamathanha language, and warioota comes from the nearby Warioota Creek – to signify they are the original custodians of this land. More significantly, since this is the oldest known burrow of bilaterians, they are the “last common ancestor” of every symmetrical creature – basically all animals except sponges, jellyfish, anemones and some tiny multicell organisms. That includes the group at the other end of the bilaterians – humans … or at least those who believe in evolution.
There is significance to this discovery besides the obvious “last common ancestor” … which is why NASA was involved.
“We can also see that Ikaria specifically sought out oxygen rich environments and avoided oxygen poor ones. These indicate that having an appreciable amount of oxygen was really important for the evolution and success of these types of organisms and that we should be looking for exoplanets with similar, well-oxygenated conditions.”
NASA’s exobiology program gave Evans and his team a grant, and the investment paid off. The search for signs of oxygen on exoplanets should lead to signs of life resembling Ikaria wariootia – and its descendants.
If you can’t find an appropriate Mother’s Day or Father’s Day card for Ikaria wariootia, just draw a picture (here’s a photo) and sign your name. it’s the thought that counts.