Deep Sea Origins and Mass Extinction Triggered 100 Million Year Evolutionary Fuse for Modern Squid

OIST researchers map the evolutionary "long fuse" of squid and cuttlefish, tracing their survival through mass extinction in deep-sea refugia.

By: AXL Media

Published: Mar 30, 2026, 6:34 AM EDT

Source: Information for this report was sourced from Okinawa Institute of Science and Technology (OIST) Graduate University

The Genomic Resolution of a Cephalopod Mystery

The enigmatic history of squid and cuttlefish, known for their jet-propelled movement and adaptive camouflage, has long remained obscured by a fragmented fossil record. Scientists at the Okinawa Institute of Science and Technology (OIST) have utilized state-of-the-art sequencing to resolve decades of conflicting hypotheses regarding decapodiform ancestry. By combining global databases with three newly sequenced genomes, the research team successfully ordered the evolution of these ten-limbed creatures. Dr. Gustavo Sanchez, a lead scientist on the project, noted that whole-genome data now provides a significantly clearer and more consistent picture of how these complex marine animals evolved over millions of years.

The Enigma of the Internal Shell

One of the primary challenges in tracing cephalopod lineage has been the diverse and often contradictory forms of their internal shells. From the buoyant, rounded bone of the cuttlefish to the thin, gladius structure of coastal squid, these physical traits previously led researchers toward inaccurate evolutionary conclusions. The study highlighted the ram’s horn squid as a pivotal example, whose unique spiral shell once caused scientists to incorrectly group it with cuttlefishes. According to Dr. Fernando Á. Fernández-Álvarez, the genomic potential of this rare species was essential in closing a major data gap and clarifying the broader relationships between distinct cephalopod families.

Mid-Cretaceous Origins in the Abyss

The new evolutionary mapping indicates that the ancestors of modern squid and cuttlefish first split into distinct orders approximately 100 million years ago. This initial divergence occurred in the deep ocean, a habitat that still serves as a home for ancestral-style species like the ram’s horn squid. During this mid-Cretaceous period, the deep sea provided a stable environment that allowed the foundational lineages of decapodiformes to establish themselves. This finding challenges previous assumptions that these animals originated in shallower coastal regions, suggesting instead that the deep ocean acted as the original laboratory for ten-limbed cephalopod biology.