Researchers have identified the heart and blood vessels of early Cambrian shrimp-like creatures from southwest China. The 520-million-year-old fossilized remains of the Chengjiang arthropod (Fuxianhuia protensa) reveal an exceptionally well-preserved organ system that’s surprisingly sophisticated. For something with such a simple body plan, its complexity rivals the vascular system of today’s arthropods, such as scorpions and horseshoe crabs.
These fossil deposits -- considered the “invertebrate version of Pompeii” -- have previously yielded the digestive system, as well as the brain and ganglia of F. protensa. About 50 of these 3-inch-long creatures were trapped by an ancient storm under many layers of fine, dust-like particles (now preserved as mudstone) in the seabed that once covered the Yunnan province. They were squashed flat during the catastrophic event and were permeated by chemicals in the water half a billion years ago.
An international team led by Xianguang Hou of Yunnan University and Nicholas Strausfeld of University of Arizona analyzed the fossilized cardiovascular system of one of the specimens, using an imaging technique that selectively reveals various structures based on their chemical composition. In this dorsal view, parts of the gut are visible as dark stains along the animal's midline:
"The animal looks simple, but its internal organization is quite elaborate,” Strausfeld says in a news release. “For example, the brain received many arteries, a pattern that appears very much like a modern crustacean."
A simple, tube-like heart extended along the main part of the body, from the thorax (belly area) to the brain, and its lateral blood vessels supplied the 20 or so segments of the body. The arteries gave rise to long channels, which presumably delivered blood to limbs and other organs.
X-ray scans revealed intricate channels in the head and neck. The brain was well supplied with looping blood vessels that extended branches into the creature’s eyes and antennae. Those external morphological features were outlined in the surrounding mineralized remains. Complete cardiovascular system below:
"It appears to be the ground pattern from which others have evolved," Strausfeld says. "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 adds: “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."
With the creature’s complete internal organization resolved, the scientists were able to speculate that it did a fair amount of thinking. "Because of well-supplied blood vessels to its brain," Strausfeld explains, "we can assume this was a very active animal capable of making many different behavioral choices."
The work was published in Nature Communications this week.
Images: reconstruction by Nicholas Strausfeld, dorsal view and whole cardiovascular system photos by Xiaoya Ma