The oldest ancestor of most of the familiar life forms living on the planet today was discovered in the outback of Australia, in the form of a strange worm-like organism.
Ikaria wariootia, a ball the size of a grain of rice, may not sound like much, but scientists believe it may be the oldest organism ever discovered: an organism with a bilaterally symmetrical body (mirrored left and right) and anterior lateral and posterior side, back and mouth. Like you, in other words.
“This is what biologists predicted,” says geologist Mary Drozer of the University of California, Riverside. “It's really exciting, what we found is very close to their prediction.”
In recent years, scientists have learned a lot about the spongy, slimy multicellular organisms that make up the so-called Ediacaran biota – a mysterious group of ancient life forms that existed before the Cambrian explosion.
Ikaria wariootia footprint in stone. (Droser Lab / UCR)
In particular, one of these creatures, called Dickinsonia, has attracted a lot of research attention, which was identified a couple of years ago as the earliest known animal in the world.
However, not everything that appeared during this period is directly related to people and other animals with bilateral physiology.
“Dickinsonia and other important organisms were probably evolutionary dead ends,” explains Droser.
So where are we from? For many years, a series of fossilized footprints imprinted on stone deposits in Nilpen, South Australia have interested researchers.
The fossil footprints, called helmintoidichnites, date back to the Ediacaran period (in particular, about 551-560 million years ago), and are believed to be the legacy of an ancient two-sided life form. Thanks to new research made possible by laser scanning of stones, these assumptions are confirmed.
“We assumed we should find them during this time interval, but we always knew that there would be difficulties with recognition,” says paleontologist Scott Evans of the Smithsonian Institution's National Museum of Natural History.
3D laser scanning of the Ikaria wariootia impression. (Droser Lab / UCR)
“After we did 3D scanning, we made an important discovery.”
Scans reveal impressions made by more than a hundred ancient organisms, ranging from 2 to 7 millimeters long and about 1–2.5 millimeters wide.
“We hypothesize that Ikaria wariootia is a successor of helmintoidichnitis and possibly the oldest, definitive Bilaterian, at least as represented in the fossils of South Australia,” the researchers wrote in their article.
The morphology of Ikaria implies a potentially modular body design that would aid in the muscular organization necessary for peristalsis [contraction of the digestive system].
'Since humans are bilaterally symmetric, we can say that it was a very ancient relative and possibly one of the first on the diverse two-sided tree of life.'
The results are presented in PNAS.
Sources: Photo: (Sohail Wasif / UCR)
