New York: The first animals to have complex skeletons existed about 550 million years ago, the fossil of a tiny marine creature unearthed in Namibia suggests.


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The finding is the first to suggest the earliest complex animals on the Earth -- which may be related to many of today's animal species -- lived millions of years earlier than was previously known.


Till now, the oldest evidence of complex animals -- which succeeded more primitive creatures that often resembled sponges or coral -- came from the Cambrian period, which began around 541 million years ago.


Scientists had long suspected that complex animals existed before then but till now they had no proof.


Genetic family tree data suggested that complex animals -- known as bilaterians -- evolved prior to the Cambrian Period.


"The new finding suggests that bilaterians may have lived as early as 550 million years ago, during the late Ediacaran Period," said lead researcher Rachel Wood, professor at the University of Edinburgh in Scotland.


"This fossil has been known for a long time, and was assumed to have been a primitive animal, such as a sponge or coral. This study suggests that it was, in fact, more advanced," Wood noted.


"We have suspected that these complex animals were present in the Ediacaran, but this study provides the first proof," Wood pointed out.


The team studied fossils of an extinct marine animal -- known as Namacalathus hermanastes -- which was widespread during the Ediacaran Period.


The fossils are remarkably well preserved and reveal that the species possessed a rigid skeleton made of calcium carbonate -- a hard material from which the shells of marine animals are made.


The complex skeletal structures are similar to those of living creatures that dwell at the bottom of the sea, the team said.


The study was published in the journal Proceedings of the Royal Society B.