Researchers from Hokkaido University in Japan have uncovered fossil evidence suggesting that squids originated around 100 million years ago and rapidly diversified, becoming dominant predators in ancient oceans. Most known squid families evolved within only six million years after their appearance, according to Phys.org.
Using a fossil discovery technique called "digital fossil-mining," the team digitally scanned entire rocks from Cretaceous deposits in Japan to reveal hidden fossils. The researchers uncovered 263 fossilized squid beaks, including about 40 species that had never been seen before, spanning 23 genera and five families.
"These findings change everything we thought we knew about marine ecosystems in the past," said Associate Professor Yasuhiro Iba of Hokkaido University, according to Phys.org. "Squids were probably the pioneers of fast and intelligent swimmers that dominate the modern ocean."
The lead author of the research, paleobiologist Dr. Shin Ikegami from Hokkaido University, emphasized the importance of the discovery. "Their body sizes were as large as fish and even bigger than the ammonites we found alongside them," he said. The fossilized beaks suggest that ancient squids were not only abundant but also played a crucial role in the marine food chain.
Fossilization is usually possible with structures that do not decay for a long time, such as bones, teeth, and shells. However, squids are mostly composed of soft tissues, making their fossils quite rare. The beaks of squids stand out as an exception; they are hard, chitinous structures that have been found in large numbers and are important for studying squid evolution.
The team's use of "digital fossil-mining," which involves high-resolution grinding tomography and image processing, enabled them to digitally extract small squid beaks from the rocks as detailed 3D models. This approach allowed the researchers to overcome the challenges posed by the scarcity of squid fossils.
"The origin and early evolution of squids are the biggest questions in the 500 million-year history of cephalopods," said Ikegami. "This shows us that squids were thriving as the most abundant swimmers in the ancient ocean."
The research revealed that the two main groups of modern squids, Myopsida (coastal squids) and Oegopsida (open-ocean squids), were already present about 100 million years ago. The origin of the Myopsida group is extended by approximately 55 million years, while the origin of the Oegopsida group is extended by about 15 million years. This suggests swift morphological evolution among squids.
One of the study's discoveries was how common squids were in ancient oceans. The researchers found that squid fossils far outnumbered those of ammonites and bony fishes, indicating that squids likely outnumbered ammonites in ancient oceans. Ammonites, extinct shelled relatives of squids, have been considered among the most successful swimmers of the Mesozoic era.
Fossilization of squid remains has been a rare occurrence due to their soft-bodied nature. Most squid fossil specimens consist of just fossilized statoliths, tiny calcium carbonate structures involved in balance. However, the beak fragments are the only part that can leave a trace in the fossil record.
By combining imaging with careful analysis of ancient rocks, the study has filled a gap in the story of squid evolution. "The ancient squids did not just live in the Cretaceous ocean; they dominated it," the team suggested. This challenges previous assumptions and could help rewrite the paleoecology of marine environments.
The findings, published in the journal Science, have implications for our understanding of marine ecosystems in the past. The new study demonstrates that squids had already originated and diversified exponentially long before the mass extinction event at the end of the Cretaceous period.
Squids are diverse and globally distributed marine cephalopods and are among the smartest and most agile animals in today's oceans. With their eight arms and two feeding tentacles, squids can seize their prey with lightning speed. Their slender, streamlined bodies make squids agile swimmers.
The study's findings suggest that their evolutionary success dates back much further than previously believed. The absence of earlier fossils has made molecular estimates of squid divergence times highly uncertain. The new fossil record greatly extends the known origins of both major squid groups.
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