Digital fossil-mining finally reveals origin of squids

Squids are some of the smartest and most agile animals in today’s oceans, but their evolutionary history has been hard to figure out because their soft bodies don’t fossilise well.

A new study has changed this using a method called digital fossil-mining to uncover fossils that were hidden inside rocks.

Instead of using traditional tools like chisels and acid baths, which often damage fragile rocks, scientists from Japan created a machine that slowly grinds a rock while taking detailed photographs of each layer. These images were stitched together to form a 3D model of everything inside the rock, including fossils.

The method enabled the team to detect and digitally extract small squid beaks, the hard, chitin-based mouthparts all squids have.

By combining cutting-edge imaging with careful analysis of ancient rocks, the study has filled a big gap in the story of squid evolution. It was published in Science on June 26.

The team collected hard, round carbonate concretions from Cretaceous-era deposits in Japan dated 110-70 million years ago. These rocks were already known to preserve fossils well. From there, the team scanned and reconstructed 263 lower beaks from squids for further analysis.

The team found that the fossil beaks came from at least 40 squid species, divided among 23 genera and five families. This is a major discovery because previously only one fossil squid beak was known. The newfound squids belonged to two modern groups: deep-sea squids (Oegopsida) and coastal squids (Myopsida). It meant both groups existed as early as 100 million years ago, which is about 30 million years  earlier than previously thought.

The earliest squids already had many different forms. Within only 6 million years, most known squid families had evolved, suggesting squids diversified very quickly once they appeared. By the Late Cretaceous, squids had become so abundant that their fossils outnumbered those of  ammonites and bony fish.

The findings suggest squids became important players in marine ecosystems long before the mass extinction 66 million years ago that wiped out dinosaurs and many marine species. In fact, squids were already replacing shelled cephalopods like belemnites and ammonites by then.

The authors have also suggested that thanks to their rise before marine mammals, squids were early pioneers of contemporary ocean life: composed of fast, intelligent animals like modern fish, whales, and dolphins.