Scientists have discovered the world's oldest primitive animal fossil in China, suggesting that animals have been on Earth for at least 600 million years.
A new study described a well-preserved, rice grain-sized primitive sponge fossil recovered from 600-million-year old rocks in southwest China's Guizhou Province.
The prior oldest known primitive sponge fossil only dated to 530 million years ago, in early Cambrian period.
"It's the world's earliest and most credible fossil record of primitive animal bodies," said lead author Maoyan Zhu of the Nanjing Institute of Geology and Palaeontology, which is part of Chinese Academy of Sciences.
"The discovery will help remove doubts as to whether animals have emerged on Earth 600 million years ago," said Zhu.
An analysis found that the fossilised animal, slightly more than 1.2 mm wide and 1.1 mm tall, displays multiple independent characters of modern adult sponges, Xinhua News agency reported.
The analysis was based on advanced imaging techniques including scanning electron microscope and synchrotron X-ray tomography.
Researchers said the specimen is composed of hundreds of thousands of cells, and has a gross structure consisting of three adjacent hollow tubes sharing a common base.
"These features showed it's a primitive animal very similar to modern sponges and could have lived a filter-feeding life through its simple water canal system on the shallow sea floor," Zhu added.
Sponges are the most primitive living animals. They have only differentiated cells, but no real organs or tissues.
The study was published in the journal PNAS.
