VOA常速英语:Scientists Discover Ancient Shrimp Had Heart

Scientists have discovered the world's earliest known cardiovascular system - heart and blood vessels - in the fossil of a shrimp-like creature from more than 500 million years ago. The rare find sheds new light on the evolutionary timeline of life on Earth.

The Yunnan Province in southwestern China is known for rich fossil deposits, but researchers had not expected a fossil so exquisitely preserved as the specimen of the 520-million-year-old shrimp-like species.

Researcher Peiyun Cong with the Yunnan Laboratory for Paleobiology unearthed the fossil, which gave researchers the first detailed image of the creature's circulatory system.

“[The fossil] is a beautiful carbon trace," said University of Arizona neuroscientist and team member Nicholas Strausfeld. "It is bilaterally symmetrical. It shows the dorsal blood vessel and the lateral vascular components, the arteries, the lateral arteries and then a very, very, beautiful, system of arteries over where the brain sits in the head.”

In earlier research with fossils of the same species, the scientists on this project had identified its brain, gut and nervous system.

Strausfeld says it is common to see fossils with imprints of teeth, shell and bone, but no soft tissues because they decay first when a creature dies. He explains how the internal organs may have fossilized.

“We assume that the specimens became entombed by a very sudden event - a sudden burial, maybe an underwater landslide, maybe something to do with a tsunami, who knows, maybe a very, very heavy dust fall out from a storm," he said. "And, then this chemical preservation of the internal tissue as it was squashed flat.”

This ancient marine species dates from the Cambrian period, a time in Earth’s history when major animal groups began to appear with a huge variety of shapes and forms. Strausfeld says the organ systems detailed in this study are easily recognizable in today's crustaceans.

“It suggests that already 520 million years ago, the basic layout, what we call the ground pattern, of say a vascular system, had already evolved," he said. "And the ground pattern persists until this day in modified forms.”

If we see this ancient shrimp as modern, then, Strausfeld asks, who was the ancestor that gave rise to its sophisticated and very elaborate set of organs?

“This is not going to be easy [to answer] because we do not really have access to any older deposits," Strausfeld said. "So what we hope to find in these Chengjiang deposits in China are fossils of organisms that clearly were already ancient by that time, and that might give us a lead into how these more elaborate systems, these very recognizable elaborate systems, how these systems maybe originated.”