XI'AN, Jan. 31 (Xinhua) -- Scientists have discovered a tiny creature that dates back 535 million years and believe it may be the oldest known ancestor of a vast group of species, including humans.
The research was conducted by China's Northwest University, Cambridge University, and other institutions. The finding was published by "Nature" online Monday.
The animal is probably the oldest example of a category of creatures named deuterostomes that includes vertebrates.
Saccorhytus, about a millimeter in size, was found in Cambrian fossils from northwest China's Shaanxi Province. Its bag-like body has a prominent mouth but no anus. Several lateral openings probably served to expel water and waste materials.
The finding suggests that a key step in deuterostome evolution was the development of these lateral openings that subsequently became gills.
Shu Degan, an academician of the Chinese Academy of Sciences and an author of the paper, said deuterostomes dating back 520 million years were around a centimeter in size, so must had evolved from smaller ancestors.
"There were the tiny creatures first, then came primitive fish, and eventually humans," Shu said.