Scientists studying the brains of turtles have uncovered surprising evidence that complex visual processing mechanisms once thought to be unique to mammals may have originated hundreds of millions of years earlier in evolutionary history.
The research, published in the journal Science Advances suggests that turtles possess a visual computation ability that allows them to detect unexpected events in their environment regardless of where those stimuli fall on the retina-a capability previously attributed only to the more advanced cerebral cortices of mammals, including humans.
Researchers from the Department of Neurobiology and the Sagol School of Neuroscience at Tel Aviv University, led by Milan Becker, Nimrod Leberstein, and Dr. Mark Shein-Idelson, focused on the dorsal cortex of turtles - a brain region considered an evolutionary counterpart to the mammalian visual cortex.
By recording neural responses in awake turtles and tracking eye movements, the team found that the animal’s brain can distinguish between expected and deviant visual stimuli while remaining invariant to changes in gaze direction.
This means the turtle brain can “recognize something new” in the visual field even when the animal moves its head or eyes, an impressive form of processing given the animal’s relatively simple cortical structure.
Reptiles and mammals are believed to have diverged from a common ancestor about 320 million years ago.
Since then, the mammalian brain has expanded dramatically in size and complexity, while the reptilian brain has remained comparatively simpler and more similar to that of early amniotes - the first vertebrates to fully adapt to life on land.
Challenging traditional views of cortical evolution
The new findings challenge traditional views of cortical evolution, showing that the ability to process visual information independently of specific retinal positions likely emerged very early in vertebrate history, before the evolution of the layered, highly folded cortices seen in mammals.
According to the researchers, these invariant visual computations would have been crucial for early terrestrial animals learning to navigate and survive in changing environments, helping them distinguish between sensory changes caused by their own movements and genuinely new information that could signal danger or opportunity.
The study not only provides new insights into the functions of ancestral cortices but also raises fundamental questions about how and when key neural computations evolved during the transition from simple to complex brains.
Dr. Shein-Idelson noted that discovering such sophisticated mechanisms in turtles offers a unique window into the evolutionary past. Because both turtles and mammals share a distant common ancestor, the presence of advanced visual processing in both lineages suggests that these capabilities either date back hundreds of millions of years or evolved independently in response to similar environmental pressures.
The findings mark a significant step forward in our understanding of brain evolution, showing that even animals with relatively modest neural structures can perform computations once thought to require the large, complex brains of mammals, and hinting at deep evolutionary roots for some of the cognitive functions we associate with higher vertebrates today.