An international team of researchers from institutions such as the University of Cambridge in the U.K. and Northwest University in China has found the "oldest human ancestor." The scientists were able to uncover well-preserved, fossilized traces of the creature.

BBC reported that the microscopic sea animal is 540 million years old. It is believed to be the starting point that led to fish and eventually formed the first humans.

The discovery was made in central China. Details of the study have been published in the journal "Nature."

The international team of researchers explained that Saccorhytus is the earliest known example of a category of animals named "deuterostomes." These are said to be common ancestors of a wide range of species, which includes vertebrates.

Saccorhytus has a size of about a millimeter. It is believed to have lived between grains of sand on the sea bed. Moreover, it may have consumed food and excreted it from the same opening since researchers were not able to find any evidence of an anus.

Professor Simon Conway Morris, from the University of Cambridge and one of the researchers, said that the fossils just looked like tiny black grains. However, when they studied it under the microscope, it revealed details that point to it being the ancestor of deuterostomes.

Degan Shu, from China's Northwest University, added that Saccorhytus has given new insights to the earliest stages of evolution of a group that led to the fish. The creature's body was symmetrical, which has been inherited by its evolutionary descendants.

According to Phys.org, it was also covered in a thin, flexible skin and muscles. This suggests that it moved around through contractile movements such as wriggling.

The Los Angeles Times added that, with the creature's age of about 540 million years old, it lived around the time of the "Cambrian explosion." This was an evolutionary turning point where small, single-celled organisms quickly transformed to complex multicellular life.