Animals roamed Earth 600m years ago
Print Edition
ANIMALS have been on Earth for at least 600 million years, research led by Chinese scientists has confirmed.
The study, published in the US journal Proceedings of the National Academy of Sciences, described a well-preserved, rice grain-sized primitive sponge fossil recovered from 600-million-year rocks in southwest China’s Guizhou Province.
“It’s the world’s earliest and most credible fossil record of primitive animal bodies,” said lead author Zhu Maoyan 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 emerged on Earth 600 million years ago.”
The fossilized animal displays multiple independent characteristics seen in modern adult sponges. 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.
Flat tile-like features on the fossil’s external surface, punctuated with small pores, resemble modern sponges.
In addition, it has a simple canal system for water inflow and outflow.
“These features show 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 said.
Sponges are the most primitive living animals. They have only differentiated cells, but no real organs or tissues. The prior oldest known sponge fossil only dated to 530 million years ago, in early Cambrian period.
There are other isolated objects claiming to be pre-Cambrian fossilized sponges, including a 760-million-year-old fossil from Namibia, but Zhu said they left aside other discoveries because those objects “did not preserve typical structural characteristics of modern sponges.”
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