Cambrian Fossil Pushes Back Evolution of Complex Brains
This picture shows a nearly intact fossil of Fuxianhuia protensa. The inset shows the fossilized brain in the head of another specimen. The brain structures are visible as dark outlines. (Photo: Xiaoya Ma; inset: Nicholas Strausfeld)
Complex brains evolved much earlier than previously thought, as evidenced by a 520-million-year-old fossilized arthropod with remarkably well-preserved brain structures.
The remarkably well-preserved fossil of an extinct arthropod shows that anatomically complex brains evolved earlier than previously thought and have changed little over the course of evolution. According to University of Arizona neurobiologist Nicholas Strausfeld, who co-authored the study describing the specimen, the fossil is the earliest known to show a brain.
The discovery will be published in the Oct. 11 issue of the journal Nature.
“No one expected such an advanced brain would have evolved so early in the history of multicellular animals,” said Strausfeld, a Regents Professor in the UA department of neuroscience.
“There has been a very long debate about the origin of insects,” Strausfeld said, adding that until now, scientists have favored one of two scenarios.
“There have been all sorts of implications why branchiopods shouldn’t be the ancestors of insects,” he said. “Many of us thought the proof in the pudding would be a fossil that would show a malacostracan-like brain in a creature that lived long before the origin of the branchiopods; and bingo! – this is what this is.”
“I spent a frenetic five hours at the dissecting microscope, the last hours of my visit there, photographing, photographing, photographing,” he said. “And I realized that this brain actually comprises three successive neuropils in the optic regions, which is a trait of malacostracans, not branchiopods.”
“In branchiopods, there are always only two visual neuropils and they are not linked by crossing fibers,” Strausfeld said. “In principle, Fuxianhuia’s is a very modern brain in an ancient animal.”
“It is remarkable how constant the ground pattern of the nervous system has remained for probably more than 550 million years,” Strausfeld added. “The basic organization of the computational circuitry that deals, say, with smelling, appears to be the same as the one that deals with vision, or mechanical sensation.”