A group of researchers has found in Xixiang County, in the Shaanxi province of central China, a body of microfossils that could reveal human’s earliest ancestor. However, the resemblance with the human body is inexistent, as the creature is a bag-like sea specimen that lived almost 550 million years ago.
The scientific name for the creature is Saccorhytus coronarius, and it measures only a few millimeters. The habitat of the specimen was between the mud and the grains of salt within the seabed. The study originally published in the journal Nature stated that the fossils were discovered on dry land. However, about half billion years ago, that area would have been located in a shallow sea.
The biological group in which the Saccorhytus is part of is called deuterostomes. According to the investigations, this group started to evolve fast into different branches about 500 million years ago. These branches include vertebrates like humans and other species like sea squirts, starfish and acorn worms.
The study showed how the deuterostomes are the common ancestors of many species. This finding explains the pathway that the human evolution went through millions of years after the existence of that group.
However, because of the large and notable diversity of the branches that had its origin in the deuterostome group, it was not easy to conclude if the human evolution began in that species. Hence, the importance of the discovery of the Saccorhytus, as the piece of evidence needed to determine the start of the human evolution.
Study conduction and findings
The search for the answer of the human evolution genesis was not easy. A team of researchers from the University of Cambridge in England and Northwest University in China had to conduct an exhaustive quest through 3 tons of limestone. Afterward, the investigation team found small black specs located in the rock studied, for then analyzing them in a microscope and have a more detailed image of the recently discovered creature.
“This is, if you like, the starting point of an evolution which led ultimately to things as different as a sea urchin, starfish and rabbit. When you look at them under the microscope they look like tiny grains of black rice, frankly – they are pretty uninteresting – but as soon as you put them under the electron microscope, the detail becomes absolutely phenomenal,” said Conway Morris, part of the research team conformed by both China and England members.
The study described the creature’s body as “elliptical with bilateral symmetry,” as those features evidence the presence of musculature and a both flexible and thin skin. However, the most impressive characteristic of this specimen is its enormous mouth. This mouth had the ability to grow and take food particles and large prey.
Another notable feature of the specimen is that it had the presence of eight structures similar to gills that functioned to remove the excess of water in the organism. Morris says that this structures could be the precursors of the small gills that are present in fish. However, he admits, some pores located through the creature’s body are still a mystery. One of the hypothesis is that these pores could have had the ability to release a kind of adhesive for the animal to secure itself in the sand. Another theory is that these pores could have functioned as sensorial receptors.
According to the study, this Saccorhytues specimen also lacks an anus, although, according to Morris, the team might not have spotted it at the first time. Anyway, he explains that other species also don’t have the orifice, like the worm-like acoels. He explains that since this kind of creatures are so small, the investigation team can “envisage something which is basically just a digestive sack with holes on the side.”
The importance of the discovery for the understanding of human evolution
According to Imran Rahman, museum research fellow at the Oxford University Museum of Natural History, the findings from the University of Oxford and the Northwest University of China are jus exciting.
“These are really interesting and to my mind surprising fossils. [They have the] potential to greatly improve our understanding of the early evolution of deuterostomes, which is the major group to which vertebrates – including humans – belong, so they are obviously going to be important going forwards for understanding our evolutionary history,” Rahman stated.
He also noticed that the fact that the specimens are so small show that many of these animals were “really microscopic,” as all the evidence found before the Saccorhytus measured centimeters.
Tom Harvey, a lecturer in geoscience at the University of Leicester, also recognizes the importance that this finding has to the scientific community, as he says that the evidence of the Saccorhytus would help to “reconstruct” the tree of life. He points out the conclusion of the researchers regarding the Saccorhytus as part of the human tree life as jokes about the incredible amount of changes a species can suffer through history adaptations.