A new study suggests that common ancestors of the humans had tentacles around 600 million years ago.
The famous Vitruvian Man was drawn by Leonardo da Vinci and it pictures the canon of proportions of the humans. But the humans did not become bilaterally symmetric not at once. However, there are two main points of view on the last common bilaterian ancestor, its appearance and the course of evolution.
Some theories suggest that the ancestor of Bilateria appeared at the end of the Vendian period which is the last geological period of the Neoproterozoic Era preceding the Cambrian Period. It lasted from approximately 635 to 541plus-minus1 million years ago.
The organisms in the Vendian sea were mostly radially symmetrical creatures. Some of them used to float in the water, while others used to crawl along the bottom or leading sessile benthic life.
The first point of view on the last common bilaterian ancestor suggested that it was a worm without a coelom what means the second body cavity. The backers of this theory suggest that beside the addition to the lack of the coelom the last common bilaterian ancestor was devoid of any appendages and had simple nervous system.
The first view tends to researchers outside Russia and according to this, the coelom appeared independently in different groups of bilaterally symmetrical animals.
The second point of view adheres to the Russian zoological school and according to this theory the last common bilaterian ancestor was a complicated coelomic creature and had both and appendages for movement and food collection. It had a complex nervous system.
The study is published in PLOS ONE.