Ikaria wariootia is an early example of a wormlike, bilaterian organism. Its fossils are found in rocks in South Australia that are estimated to be about 555 million years old. That falls within the Ediacaran period, about 14 million years before the Cambrian, when the Cambrian explosion happened, with the bilaterians becoming very widespread.
The generic name is taken from the Adnyamathanha word for "meeting place" in recognition of the local indigenous people who originally lived in the region where the fossils were collected. The specific name refers to Warioota Creek, the type locality.
Features
Over 100 Ikaria fossils have been found. This is a simple imprints in the form of a small grain of rice, slightly thickening to one end. The "anterior"/"posterior" differentiation may indicate that Ikaria was bilaterally symmetrical animal. No any other details of Ikaria anatomy were found on its fossils. On the same sandstone bed there are numerous trace fossils Helminthoidichnites. The animal that produced such traces moved or burrowed through thin layers of well-oxygenated sand on the ocean floor as it sought sustenance and it had some volition, turning as it moved. It is thought to have moved by constricting muscles and should have a coelom, mouth, anus, and through-gut, in a similar way to a worm. The authors of the Ikaria description find that the size and morphology of Ikaria match predictions for the producer of the trace fossilHelminthoidichnites. However, they note that they are not aware of examples of the connection of Ikaria with these trace fossils. Therefore, the assumptions that Ikaria is the producer of these traces as well as the reasoning about Ikaria behavior, anatomy and taxonomy are speculative and may be erroneous.
Significance
This discovery is notable because while it has been long suspected that bilaterians evolved in the Ediacaran, for example Temnoxa and Kimberella, yet the vast majority of Ediacaran biota are very different from the animals that came to dominate the life on Earth in the Cambrian and until present day. Charles Darwin originally brought up the problem that most multicellular life, especially complex life, evolved at the beginning of the Cambrian period, 541 million years ago. This fossil appears to solve this problem.
