WASHINGTON, June 26 (Xinhua) -- An ancient reef formed almost 550 million years ago has been found on what is now dry land in the southwestern African country of Namibia, a group of researchers said Thursday.
The fossilized reef, the oldest of its kind in the world, was formed by the first animals known to have hard shells. It suggested that these aquatic organisms had been building reefs even before the so-called Cambrian explosion about 542 million years ago, when life suddenly became more complex and diverse.
The oldest animal-built reef was discovered in southern Namibia, in a region known
for its ancient sediments.
Previously, the oldest reefs on record were dated to about 530 million years ago.
In a study in the U.S. journal Science, the researchers said the tiny aquatic creatures, known as Cloudina, attached themselves to fixed surfaces and to each other by producing natural cement composed of calcium carbonate, to form rigid structures.
Cloudina were tiny, filter-feeding creatures that lived on the seabed during the Ediacaran Period, which ended 541 million years ago. Fossil evidence indicated that animals had soft bodies until the emergence of Cloudina.
The study, led by scientists at the University of Edinburgh, believed the animals may have developed the ability to build reefs to protect themselves against increased threats from predators.
Reefs also provided access to nutrient-rich currents at a time when there was growing competition for food and living space.
Scientists said the development of hard biological structures, through a process called biomineralisation, sparked a dramatic increase in the biodiversity of marine ecosystems.
"Modern reefs are major centers of biodiversity with sophisticated ecosystems. Animals like corals build reefs to defend against predators and competitors," said Rachel Wood, professor at the University of Edinburgh, who led the study. "We have found that animals were building reefs even before the evolution of complex animal life, suggesting that there must have been selective pressures in the Precambrian Period that we have yet to understand."
The study was carried out in collaboration with University College London and the Geological Survey of Namibia.