A team of researchers have determined the earliest known prehistoric ancestor of humans. As stated in the journal Nature, the human ancestor is called Saccorhytus, a one-millimeter small bag-like sea creature that lived 540 million years ago.

The human’s oldest ancestor, which is the most primitive example of deuterostome, has an elliptical body and large mouth. The species was found in microfossils in China. The scientists, including researchers from the University of Cambridge in the UK and Northwest University in Xi’an China and Germany, believe that Saccorhytus is the ancestor of different species. Hundreds of millions of years later, this creature eventually evolved to humans.

The human’s oldest ancestor is believed to have lived between the grains of sand on the seabed. Apparently, it did not have an anus so Saccorhytus probably excreted its waste through its mouth.

“We think that as an early deuterostome this may represent the primitive beginnings of a very diverse range of species, including ourselves. To the naked eye, the fossils we studied look like tiny black grains, but under the microscope the level of detail is jaw-dropping,” adds Simon Conway Morris, Professor of Evolutionary Palaeobiology and a Fellow of St John’s College, University of Cambridge. “All deuterostomes had a common ancestor, and we think that is what we are looking at here.”

The team believes that humans inherited the bilaterally symmetrical characteristic of its body. The creature is also said to have been covered in skin and moved by wriggling. It also ate by engulfing creatures and other food particles. The small conical structures on its body could have let the water to escape, which probably evolved into gills of fish.

The evidence was found in Shaanxi Province, in central China. It pre-date all known deuterostome, which have been dated back at 510 to 520 million years ago. “We had to process enormous volumes of limestone — about three tonnes — to get to the fossils, but a steady stream of new finds allowed us to tackle some key questions: was this a very early echinoderm, or something even more primitive? The latter now seems to be the correct answer,” said Jian Han of Northwest University.