A 520 million-year-old fossil shows complex brains evolved much earlier than previously thought with little change anatomically since then, U.S. scientists say. The fossilized arthropod, representing the earliest specimen to show a brain, shows remarkably well-preserved brain structures, the University of Arizona reported Wednesday. Found in China\'s Yunnan province, the approximately 3-inch fossil, which belongs to the species Fuxianhuia protensa, represents an extinct lineage of arthropods combining an advanced brain anatomy with a primitive body plan, researchers said. The fossil provides a \"missing link\" that sheds light on the evolutionary history of arthropods, the group that contains crustaceans, arachnids and insects. \"No one expected such an advanced brain would have evolved so early in the history of multicellular animals,\" Nicholas Strausfeld of the university\'s department of neuroscience said. The fossil supports the idea that once a basic brain design had evolved, it changed little over time, he said. Instead, he said, peripheral components such as the eyes, the antennae and other appendages and sensory organs underwent considerable diversification and specialized in different tasks, but all remained plugged into the same basic brain circuitry. \"It is remarkable how constant the ground pattern of the nervous system has remained for probably more than 550 million years,\" Strausfeld said.