Oldest human ancestor identified
A study in China that involved an international team of researchers from the UK, China and Germany has uncovered "exquisitely well preserved" 540-million year old fossilised traces of the earliest known ancestor of humans.
The species, named Saccorhytus, is the earliest example of a category of animals called "deuterostomes" which are common ancestors of a broad range of species, including vertebrates. Saccorhytus was covered with a thin, flexible skin and muscles and is believed to have lived between grains of sand on the ocean floor, moving itself around by wriggling. It has only one orifice by which to intake and excrete food.
Professor Simon Conway Morris, from the University of Cambridge, who was part of the international team that made the discovery had this to say: "To the naked eye, the fossils we studied look like tiny black grains, but under the microscope the level of detail is jaw-dropping. We think that as an early deuterostome this may represent the primitive beginnings of a very diverse range of species, including ourselves. All deuterostomes had a common ancestor, and we think that is what we are looking at here."
Degan Shu, from Northwest University in Xi'An, Shaanxi Province, where the fossils were found, said: "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." Shu further added that the team has previously made many important discoveries, such as the earliest known fish.
Prior to this latest discovery the oldest deuterostome traces to be found came from between 510 to 520 million years ago. By that time in history they had already begun to evolve and diversify, giving rise to vertebrates, sea squirts, starfish, sea urchins and small sea-worms, and that incredible level of diversity from one common species meant that until now it has been very hard for researchers to establish what an earlier common ancestor may have looked like. This latest study suggests that like humans and many of its other descendants, Saccorhytus' body was symmetrical. In addition it had a strikingly large mouth in relation to the overall size of its body. Also interesting are the conical structures on its body, which may have allowed the water that it swallowed to escape. If this is the case they would be in essence a very early version of the gills that are commonly found on fish.
Saccorhytus got its name because of the sack-like nature of its elliptical body and large mouth. It is so far the earliest step discovered on the evolutionary path that eventually led to humans all these hundreds of millions of years later.
The scientists worked by isolating the fossils from the surrounding rock and then studying them both under an electron microscope and using a CT scan, and this let them build up an accurate idea of how Saccorhytus might have looked and lived. Dr Jian Han, also of Northwest University, said: "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."
