Nowadays, bilateral symmetry is the norm among species that grow and evolve on our planet. Most humans, insects and animals have a body that is split into two identical halves down an axis. However, the identity of the first organism to adopt this symmetry has long been a mystery to scientists… until just a few weeks ago in August, when a certain study was published in the Proceedings of the National Academy of Sciences magazine.
Ikaria wariootia, a worm like no other
To discover this organism, researchers from the University of California, Riverside in the United States, examined a piece of ancient rock that had been found in South Australia. The rock had fossils of underwater burrows which had been created by creatures no bigger than a grain of sand… more than 555 million years ago. In order to form a more complete picture of what this creature was, the research team analysed these fossils by performing 3D laser scans on them.
From these scans, they finally managed to get a better idea of what these little burrowers could have been and looked like: a sort of soft, slightly grooved worm with a distinct head and tail connected by a bilaterally symmetrical, cylindrical body. Scientists called these creatures Ikaria wariootia. The genus name comes from Ikara, which is the Adnyamathanha name for a grouping of mountains that, in English, is known as Wilpena Pound and the species name comes from Warioota Creek, which is a landmark close to where this fossil was originally discovered.
‘The oldest bilateral yet recognised in the fossil record’
With this left-right symmetry and the presence of an intestine, this worm could be the oldest known ancestor of all bilaterians - which most modern animals are part of. But that’s not all. Their research also shows that the Ikaria wariootia had rudimentary sensory abilities since they used to burrow into thin layers of well-oxygenated sand on the ocean floor in search of organic matter.
'The major finding of the paper is that this is possibly the oldest bilateral yet recognised in the fossil record,’ confirmed Doctor Scott Evans, of the Smithsonian National Museum of Natural History and co-author of this study, to the Guardian.
‘Because humans are bilaterians, we can say that this was a very early relative and possibly one of the first on the diverse bilaterian tree of life.’
Between 541 and 485.4 million years ago
The Ikaria warioota is said to have lived on Earth during the Ediacaran period (around 635 to 541 million years ago) when all non-microscopic multicellular creatures started to emerge. Before this period, the world was mainly populated by amorphous marine organisms such as rangeomorphs for example. Most of these species died out in mass extinction.
However, this study suggests that this new worm-like creature could be an exception since traces of these burrows have also been found that date back to the Cambrian period (between 541 and 485.4 million years ago) which was the transitional period between simple microscopic creatures and more complex animal life. But scientists have nevertheless confirmed that this creature could have lived long enough to be the origin of the evolution of all other bilateral descendants.