Using an innovative "digital fossil-mining" approach, researchers have uncovered hundreds of previously hidden fossil squid beaks, revealing a record that squids originated and became ecologically dominant roughly 100 million years ago – well before the end-Cretaceous extinction. Squids are the most diverse and globally distributed group of marine cephalopods in the modern ocean, where they play a vital role in ocean ecosystems as both predators and prey. Their evolutionary success is widely considered to be related to the loss of a rigid external shell, which was a key trait of their cephalopod ancestors. However, their evolutionary origins remain obscure due to the rarity of fossils from soft-bodied organisms. The fossil record of squids begins only around 45 million years ago, with most specimens consisting of just fossilized statoliths – tiny calcium carbonite structures involved in balance. The lack of early fossils has led to speculation that squids diversified after the end-Cretaceous mass extinction 66 million years ago. While molecular analyses of living species have offered estimates of squid divergence times, the absence of earlier fossils has made these estimates highly uncertain.
Here, Shin Ikegami and colleagues address these gaps using a novel approach – "digital fossil-mining" – which uses high-resolution grinding tomography and advanced image processing to digitally scan entire rocks as stacked cross-sectional images to reveal hidden fossils as detailed 3D models. Ikegami et al. applied this technique to Cretaceous-age carbonate rocks from Japan, uncovering 263 fossilized squid beaks, with specimens spanning 40 species across 23 genera and five families. The findings show that squids originated roughly 100 million years ago, near the boundary between the Early and Late Cretaceous, and rapidly diversified thereafter. According to the authors, the previously hidden fossil record greatly extends the known origins of both major squid groups – Oegopsida by ~15 million years and Myopsida by ~55 million years. Early Oegopsids displayed distinct anatomical traits that disappeared in later species, suggesting swift morphological evolution, while Myopsids already resembled modern forms. What's more, the study suggests that Late Cretaceous squids were more abundant and often larger than coexisting ammonites and bony fishes, an ecological dominance that predates the radiation of bony fishes and marine mammals by over 30 million years, making them among the first intelligent, fast swimmers to shape modern ocean ecosystems.
For reporters interested in research integrity issues co-author Yasuhiro Iba notes, "accessibility and reproducibility in fossil-based studies have been strongly restricted by the fixation on studying physical specimens. In contrast, we performed all processes from fossil hunting to analysis in cyberspace and digitally released all specimens to the public. I believe that this breakthrough is critical to ensuring research integrity and will facilitate groundbreaking discoveries worldwide."
