Researchers have discovered a fossil of the oldest ancestor of almost all animals to date. Ikaria wariootia was the size of a grain of rice and for the first time had a front and a back.
Admittedly, the similarity is not exactly obvious. But this being, about the size of a grain of rice, is the oldest known ancestor of many animals, including humans. A team of paleontologists and geologists from the University of California found several animal fossils in Nilpena, South Australia, in rock strata that are estimated to be at least 555 million years old (PNAS).
The special thing about the being, called Ikaria wariootia, is that it is bilaterally structured. So it has a left and a right half of the body, which – at least in the early stage of development – are mirror images. Most animals living today, whether earthworm, butterfly, shrimp, dog or human, are such “bilateria” or two-sided animals. Other features include a front and a back end and a casing with two open ends. It is estimated that this type of body organization developed in the Ediacarium, a period in earth’s history that ended about 541 million years ago.
The researchers are certain that Ikaria wariootia is a two-sided animal, among other things it has a thick and a thin end, i.e. a front and a back. In the course of evolution, the head of the species existing today has developed from the front; about the tails from the back. Ikaria most likely had a mouth in the front and an anus in the back – both connected by an intestine, the authors of the current study write.
In the evolution of animals, the emergence of bilateral symmetry was a crucial step. Among other things, it is the prerequisite for being able to move in a specific direction.