Using an innovative digital fossil-mining approach, paleontologists analyzed more than 250 fossil beaks from 40 ancient squid species. Their results suggest that the radical shift from heavily shelled, slowly moving cephalopods to soft-bodied forms did not result from the end-Cretaceous mass extinction, around 66 million years ago; early squids had already formed large populations, and their biomass exceeded that of ammonites and fishes; they pioneered the modern-type marine ecosystem as intelligent, fast swimmers.
This lithograph shows Loligo forbesii, a species of squid in the order Myopsida. Image credit: Comingio Merculiano.
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.
In the new study, Hokkaido University paleontologist Shin Ikegami and colleagues addressed these gaps using 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.
They 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 about 15 million years and Myopsida by about 55 million years.
Early Oegopsids displayed distinct anatomical traits that disappeared in later species, suggesting swift morphological evolution, while Myopsids already resembled modern forms.
The study also 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.
“In both number and size, these ancient squids clearly prevailed the seas,” Dr. Ikegami said.
“Their body sizes were as large as fish and even bigger than the ammonites we found alongside them.”
“This shows us that squids were thriving as the most abundant swimmers in the ancient ocean.”
“These findings change everything we thought we knew about marine ecosystems in the past,” said Dr. Yasuhiro Iba, also from Hokkaido University.
“Squids were probably the pioneers of fast and intelligent swimmers that dominate the modern ocean.”
The study was published in the journal Science.
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Shin Ikegami et al. 2025. Origin and radiation of squids revealed by digital fossil-mining. Science 388 (6754): 1406-1409; doi: 10.1126/science.adu6248