How squid survived Earth’s biggest extinction and took over the oceans

Science News from research organizations How squid survived Earth’s biggest extinction and took over the oceans Squid and cuttlefish evolved in the deep sea and survived Earth’s biggest extinction by hiding in oxygen-rich refuges. Date: April 1, 2026 Source: Okinawa Institute of Science and Technology (OIST) Graduate University Summary: Scientists have finally cracked a long-standing mystery about squid and cuttlefish evolution by analyzing newly sequenced genomes alongside global datasets. The research reveals that these bizarre, intelligent creatures likely originated deep in the ocean over 100 million years ago, surviving mass extinction events by retreating into oxygen-rich deep-sea refuges. For millions of years, their evolution barely changed—until a dramatic post-extinction boom sparked rapid diversification as they moved into new shallow-water habitats. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY Photo of a common cuttlefish (Sepia sp.) Credit: Keishu Asada Squid and cuttlefish are among the ocean's most fascinating animals, known for their color-changing skin and jet-like movement. For decades, scientists have tried to understand how these unusual creatures evolved. Progress has been slow because their fossil record is limited and their genomes are complex. Now, new research is finally providing clearer answers. A study published in Nature Ecology & Evolution by researchers at the Okinawa Institute of Science and Technology (OIST) combines large genomic datasets with three newly sequenced squid genomes. This work reveals a "long fuse" pattern that explains how squid and cuttlefish, together known as decapodiform (ten-limbed) cephalopods, evolved into the diverse group seen today. Dr. Gustavo Sanchez, first author on the study and Staff Scientist in OIST's Molecular Genetics Unit, says, "Squid and cuttlefish are remarkable creatures, yet their evolution has been notoriously difficult to study. The question of their ancestry has been under investigation for decades, and many research groups have proposed different evolutionary hypotheses based on different morphological characteristics and molecular datasets. With our new genomic information, we have been able to resolve some of the mysteries surrounding their origins." A Clearer Picture of Squid and Cuttlefish Evolution Squid and cuttlefish live in environments ranging from deep ocean waters to shallow coastal regions. Despite their diversity, most share one feature: an internal shell. This structure varies widely, from the rounded cuttlebone in cuttlefish to the thin, blade-like gladius in many squid, as well as the spiral shell of the ram's horn squid. Some shallow-water species have even lost the shell entirely. Understanding how these different forms are related has been challenging. Sanchez explains, "Earlier reconstructions of decapodiform evolution were built from datasets with limited resolution and were prone to biased signals, obscuring the true relationshi