Seed-sized crustacean fossils have revealed that seafloor species crossed the North Pacific five million years ago along active cold-water routes.
That discovery reframes how ocean circulation linked Asia and North America during a warmer phase of Earth’s climate.
Shells that tracked currents
The evidence comes from microscopic shells preserved in marine sediments in northern Japan, where ancient seafloor life recorded the paths available to cold-adapted species.
By documenting those shells and tracing their relationships, researchers at Kumamoto University showed that the same lineage once occupied distant edges of the Pacific.
The finding demonstrates long-range movement rather than isolated survival.
The fossils place that movement in the Early Pliocene, when global temperatures were higher yet northern…