An ancient cache of fossils described as the "invertebrate version of Pompeii," has revealed the cardiovascular systems of prehistoric shrimp-like creatures to be remarkably "modern."

Writing in the journal Nature Communications, an international team of researchers describe what they say is the earliest known cardiovascular system in the fossil record, a 520-million-year-old specimen complete with a heart and blood vessels.

What's more, these ancient creatures' cardiovascular systems were organized such that they strongly resemble those found in their modern descendants, the researchers said.

Nicholas Strausfeld, a professor of neuroscience at the University of Arizona who helped analyze the fossils, said the specimen is first preserved vascular system known to science.

The fossil was created when during the Cambrian Period, when a three-inch creature known as Fuxianhuia protensa was buried in earth in what is now Yunnan province in China.

"Fuxianhuia is relatively abundant, but only extremely few specimens provide evidence of even a small part of an organ system, not even to speak of an entire organ system," said Strausfeld, who is one of the world's foremost experts in arthropod morphology and neuroanatomy. "The animal looks simple, but its internal organization is quite elaborate. For example, the brain received many arteries, a pattern that appears very much like a modern crustacean."

According to Strausfeld, the cardiovascular system of this ancient creature is in fact more complex that what is found in many modern crustaceans.

"It appears to be the ground pattern from which others have evolved. Different groups of crustaceans have vascular systems that have evolved into a variety of arrangements but they all refer back to what we see in Fuxianhuia," he said. "Over the course of evolution, certain segments of the animals' body became specialized for certain things, while others became less important and, correspondingly, certain parts of the vascular system became less elaborate."

Finding such a well-preserved specimen is not any everyday occurrence, and the researchers are still puzzling over how exactly the Fuxianhuia became fossilized.

"Presumably the conditions had to be just right," Strausfeld said. "We believe that these animals were preserved because they were entombed quickly under very fine-grained deposits during some kind of catastrophic event, and were then permeated by certain chemicals in the water while they were squashed flat. It is an invertebrate version of Pompeii."