Humans' common ancestors may have had tentacles around 600m years ago

A new study has revealed that humans' common ancestors reportedly had tentacles around 600 million years ago.

The famous Vitruvian Man, which was drawn by Leonardo da Vinci, pictures the canon of human's proportions. However, humans have become bilaterally symmetric not at once. There are two main points of view on the last common bilaterian ancestor, its appearance and the course of evolution.

It was likely 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, which lived in the Vendian sea, were mostly radially symmetrical creatures. Some of them were floating in the water, while others were crawling along the bottom or leading sessile benthic life.

There 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. Proponents of this theory are sure that in addition to the lack of the coelom the last common bilaterian ancestor was devoid of any appendages and had simple nervous system.

According to the first view, which tends to researchers outside Russia, the coelom appeared independently in different groups of bilaterally symmetrical animals.

The second point of view, which adheres to the Russian zoological school, suggests that the last common bilaterian ancestor was a complicated coelomic creature and had both and appendages for movement and food collection and a complex nervous system.

According to this view the coelom in different groups underwent reduction for various reasons related to the peculiarities of development, anatomy, and lifestyle.

The hypothesis, proposing that the last common bilaterian ancestordescended from a common coelenterates ancestor, which had radial symmetry and multiple chambers in the gastric cavity related to formation of the coelom, was originally created by the British zoologist Adam Sedgwick.

Elena Temereva said that she has managed to prove otherwise through research conducted by immunocytochemistry techniques, laser confocal microscopy, 3D-reconstruction and transmission electron microscopy.

It meant tha that the group of the Lophophore animals does exist and that it descended from a common ancestor, which had both the lophophore and the tentacles. It was confirmed by the similar structure of the nervous system of the lophophore in different groups of the Lophophore animals.

The study is published in PLOS ONE.