The Oldest Skeleton On Earth

Up to 600 million years ago, animals had no symmetry. They were simple, soft-bodied creatures which developed in a similar fashion to the roots of a tree, branching outwards in a random fashion in order to gain surface area. It proved to be a very ineffective design as it did not allow for the development of complex systems and organs. This all changed around 600 million years ago, however, when the first animals evolved with bilateral symmetry.

The fossils of Coronacollina acula. The white and black scale bars indicate
 a centimeter and the arrows point to the positions of the spicules

They were able to develop heads, internal organs and limbs, making them the first truly complex animals on Earth. These creatures are commonly referred to as the Ediacara biota, showing traces of the first ever limbs, the first ever teeth and hard shells.

For a long time, it has been thought that the first internal skeletons evolved with the worm-like creature Pikaia gracilens, a late Cambrian organism with the first ever backbone.

Palaeontologists studying fossils from the home of the enigmatic biota, the Ediacara Hills in Australia, believe that they have found evidence of the first organism on Earth with a skeleton. 550 million years ago, this area was once part of a shallow tropical sea which encircled the globe. It was inhabited by many bizarre creatures, including the ancestors of the trilobites, the molluscs, the crustaceans and many other members of early animal groups.

Hundreds of species have been discovered. One such creature, Coronacollina acula, is well known from a number of different specimens. Yet its true importance has only now been revealed. The palaeontologists, led by Dr Mary Droser from the University of California, examined top quality specimens of Coronacollina. They discovered the presence of a series of spindly lines running through the fossil outwards from a central point in the shape of a star.

Around 20 to 40 centimeters in length, the mineralisation of the lines revealed them to have once been a part of the creature. The researchers concluded that they were the remains of a primitive yet effective skeletal system running through the body of Coronacollina. As the nature of the lines, properly called spicules, was shown through painstaking measurements of micro-features within the fossil, the researchers were able to use the data to investigate the animal as a whole.

They now believe that Coronacollina was a primitive sponge, perhaps the first ever on Earth. The spicules running through the cellular structure would have provided support whilst giving it the ability to move and actively feed. As a significant number of specimens have been found within close proximity to each other, the researchers think that they lived a gregarious lifestyle, living in small colonies.

'We often associate skeletons with predation since skeletons greatly assist animals in their fight against predators,' Droser said. 'But Coronacollina acula used its skeleton only for support, there being no predators in the Ediacaran.' The Ediacara biota is one of the most important animal groups on Earth. Yet study of different species will provide evidence on the origins of many modern animal groups on the planet.