Researchers have admitted that the half-a-billion-old shrimp fossil that allowed them to discover the oldest form of cardiovascular system to date was an extremely rare and unusual case.

The well-preserved corpse of three-inch Fuxianhuia protensa, the ancestor to modern arthropods like crabs and lobsters, had a heart and blood vessels. The researchers found a tubular heart in the center of shrimp's fossilized body, with vessels connected with brain, legs, antennae and eyes.

Xiaoya Ma, a paleontologist at the Natural History Museum in London, said that it was an extremely rare case; however, soft tissue could also be preserved in fossils under extreme circumstances.

Speaking on the topic, Ma said, "It is an extremely rare and unusual case that such a delicate organ system can be preserved in one of the oldest fossils and in exquisite detail. However, under very exceptionally circumstances, soft tissue and anatomical organ systems can also be preserved in fossils."

Strausfeld, director of Center for Insect Science at the Arizona University, said that only extremely few specimen of Fuxianhuia offer evidence of even a tiny part of an organ system, not even to speak of a whole organ system, as provided by the half-a-billion-old fossilized shrimp.

The researchers said that the inner structures of the ancient three-inch creature helped them know more about the evolution of numerous modern species.