Oldest Known Human Ancestor Found in China

In January this year, the fossil of a “bag-like” sea creature was discovered in China. The fossilised organism existed 540 million years ago, and was named Saccorhytus.

The Saccorhytus is a deuterostome, a broad group of animals that develop anus first as an embryo. Within this group is the subphylum Vertebrata, which contains vertebrate organisms such as humans. This therefore means that this newly discovered ancient animal is the ancestor of all vertebrate life, and thus also humans.

Although the Saccorhytus looks vastly different to humans, it is a missing organism in the tree of life that links all vertebrates together. All vertebrates, both alive and extinct, are related to this fossilised animal.

Due to the vast diversity of appearance displayed in deuterostomes, it has been incredibly difficult for scientists to predict what the missing link would look like. Now, we can see that this link is a bilaterally symmetrical organism, with a large mouth, and thin, flexible skin. These characteristics are shared with many of the Saccorhytus’s ancestors to this day, including humans who are also bilaterally symmetrical organisms.

Appearance alone, however, is not a good basis for species identification, and is an extremely poor method for deciding relationships between species. In order to be certain of their conclusion, the scientists who discovered the Saccorhytus fossil looked at biomolecular data which allowed them to estimate when two species diverged. This unfortunately was an estimate, so the scientists had to carry out more research to confirm their discovery.

Most organisms present 540 million years ago were much like the Saccrohytus, in which that they were microscopic. This means that discovery of the fossilised remains from this time period is rather difficult to say the least. But thanks to knowledge of how deuterostomes develop and from comparison of the biomolecular data, scientists are confident in their conclusion that the Saccorhytusis the missing link that is the common ancestor to all deuterostome life, making it the oldest known human ancestor to date.

Reference

Jian Han, Simon Conway Morris, Qiang Ou, Degan Shu and Hai Huang. Meiofaunal deuterostomes from the basal Cambrian of Shaanxi, China.