Scientists have found microfossils in China of a weird bag-like sea creature from 540 million years ago that may have been our earliest known ancestor. Saccorhytus resembles an alien species more than it does a human, and the creature is just a millimeter long and probably lived in the mood in the seabed, according to the study published in the journal Nature.

The fossils are found on what is now land but during the time it lived would have been a shallow sea. It is part of a category of creatures that are known as deuterostomes, which then evolved into many branches including vertebrates like humans as well as animals like starfish and sea urchins.

While deuterostomes were a natural place to look for the earliest ancestor to humans, as they are the ancestors to many species that exist today, it was tough to figure out exactly which one. However, researchers in England and China were able to dial into the saccorhytus and create a profile of the species that could tell us a lot about our own evolution.

Simon Conway Morris, Professor of Evolutionary Palaeobiology and a Fellow of St John’s College, University of Cambridge, said in a statement: “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. All deuterostomes had a common ancestor, and we think that is what we are looking at here.”

Degan Shu, from Northwest University, added: “Our team has notched up some important discoveries in the past, including the earliest fish and a remarkable variety of other early deuterostomes. Saccorhytus now gives us remarkable insights into the very first stages of the evolution of a group that led to the fish, and ultimately, to us.”