A three-inch long, 520-million-year old fossil from China has the oldest preserved cardiovascular system in the world. The fossil, Fuxianhuia protensa was an arthropod, belonging to the same group of animals that contains modern spiders, crabs and shrimp.
Unlike most fossils from this time period, the internal structure of this ancient arthropod was beautifully preserved, with researchers able to distinguish arteries and blood vessels connecting the heart to the brain and other areas of the body.
From the Los Angeles Times:
Fossils are typically made of mineralized shell or bone, or are the rocky imprints left by those hard skeletal elements. Soft tissue like skin, muscle or arteries quickly decompose without a chance to leave an impression in the surrounding rock. But in a Pompeii-like natural disaster, this animal was trapped, killed and flattened in fine-grained soil in a relative flash, giving it a better shot at preservation.
Pompeii, in this case, doesn’t necessarily mean a volcanic eruption. The fossil was found preserved in a fine, dusty sediment, possibly the remnant of another kind of natural disaster that isn’t seen on Earth today. Without plants to hold down the soil, sandstorms would have been fierce: "The habitats of these creatures must have been inundated with massive fallouts from huge storms," the lead author, Nicholas Strausfeld, said in a press release. He also suggested that the creature could have been entombed in mud after a tsunami.