Fossil Of Ancient Shrimp Reveals First Known Cardiovascular System
When the first living creatures formed about 3.7 billion years ago, they were extremely simple, single-celled organisms. Over the next few billion years, multiple-celled animals emerged with more cell functions. But it's difficult now, hundreds of millions of years later, to draw a precise evolutionary timeline.
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This week, science came closer by identifying the evolution of animal complexity. A team of scientists has identified the very first example of a closed cardiovascular system in a shrimp-like sea creature that lived 520 million years ago. Back then, life on Earth was confined to ocean-dwelling arthropods, the ancestors of modern crustaceans. Published in this week's Nature Communications, researchers explain how they discovered what may be the earliest species to have a heart and blood vessels just like those found in their modern descendants.
The key to understanding the organic system of something that's been dead for half a billion years is finding an unusually well-preserved fossil, then doing some chemical sleuthing. A fossil isn't the animal itself; it is the product of mineral buildup within the cavity of something that's long since decayed. But one University of Arizona neuroscientist named Nicholas Strausfeld has gotten pretty good at reading the chemical leftovers deposited on fossils.
Strausfeld was the guy who discovered the first arthropod brain in this same species of ancient arthropod, called Fuxianhuia protensa. It takes an extremely well-preserved specimen. The present one, found in southwestern China, was said to be frozen in a Pompeii-like death position, possibly killed by a wall of mud and preserved in place. By locating tiny traces of carbon embedded in the fossil, left there by the blood vessels, Strausfeld and his colleagues created a 3-D picture of what the system looked like. "This is another remarkable example of the preservation of an organ system that nobody would have thought could become fossilized," Strausfeld said in a statement.
Considering its great complexity, it's a good species to study. "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," Strausfeld says. "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." Taken together with Strausfeld's brain discovery and other research on its digestive system, scientists understand the internal anatomy of F. protensa better than any other ancient arthropod.
Science builds upon science: now that they know what the animal's insides looked like, they can ask better questions about why it looked the way it did. "We can now start speculating about behavior," as Strausfeld put it. With so many blood vessels snaking through its extremities, Strausfeld speculates that F. protensa was an active little bug (it was about three inches long) with a brain large enough to make behavioral choices.
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