When Javier Luque looked at this 100 million-year-old piece of amber, the first thing that came to mind wasn't whether the crustaceans trapped inside helped fill a key gap in crab evolution. He just kind of wondered how it got stuck in the resin that had now turned into a fossil?
The researchers say this is the most complete crab fossil ever found
"In a way, it's like finding a fish in amber," he said of Luke, a postdoctoral fellow in Harvard's Department of Biology and Evolutionary Biology. "Say the wrong place, say the wrong time."
However, this was a stroke of luck for Luke and his team, as the amber found in the jungles of Southeast Asia gave researchers the opportunity to study a particularly complete specimen that is believed to be the oldest modern-looking crab ever found. The discovery provides new insights wednesday in scientific progress on the evolution of these crustaceans and their spread around the world.
The crab, which is about the width of a pencil eraser, is the first to be found in amber during the dinosaur eras, and researchers believe it represents the oldest evidence of "real crabs" invading non-marine environments.
Previous fossil records of crabs consisted mainly of fragments of claws, suggesting that non-marine crabs came to land and entered fresh water about 75 to 50 million years ago.
The new discovery pushes the phenomenon back at least 100 million years, answers Luke's original question about what this crab does in the jungle and aligns the fossil record with long-standing theories about crabs' genetic history.
"If we were to reconstruct the crabs' tree of life — putting together a pedigree — and do some molecular DNA analysis, the prediction would be that non-marine crabs split off from their marine ancestors more than 125 million years ago," Luque said. But there's a problem, because the actual fossil record is something we can touch, so this new fossil and its mid-Cretaceous age allow us to bridge the gap between the predicted molecular differences and the actual fossil record of crabs. ”
Researchers now believe that the so-called Cretaceous crabs evolved and began to evolve their characteristic, grumpy-looking body forms, which were not a one-time event as previously thought.
The new study recorded at least 12 times when different crab species evolved independently to live outside of marine habitats.
The new fossil was named Cretapsara athanata, "Immortal Cretaceous Spirit of Clouds and Water." "The name commemorates its time and the mythological spirit of South and Southeast Asia.
The creature suspended in amber was quickly identified as a real crab, which makes sense, as the researchers say it is the most complete crab fossil ever found.
Using microcomputer tomography, the team was able to see clearly and in detail vulnerable tissues like crabs' antennae, legs and hairy mouthparts, large compound eyes and even gills. The researchers were surprised to find that the crab did not have even a single tentacle.
The study was a collaboration between Harvard University and the Chinese University of Geosciences from 10 institutions, including Yale University, the Smithsonian Tropical Research Institute Panama, the University of Alberta, the University of California, Berkeley, Yunnan University, and the Royal Saskatchewan Museum.
Fossil amber specimens are preserved at the Longyin Amber Museum in China. The piece was collected by local miners in Myanmar and legally purchased in 2015.
Luque, who has studied crab evolution for more than a decade, said he first became aware of the specimen in 2018 and has been fascinated by it ever since. He hopes the discovery will make people think that crabs deserve to be in the spotlight again.
"Crabs are all over the world, they're great aquarium pets, and for those of us who eat them, they're a great food on the table, and they even have their own zodiac signs," Luke said.
Overall, the crabs are fascinating, and some look weird — from tiny pea-shaped crabs to giant coconut crabs and emperor crabs. The diversity of crab morphology has captured the imagination of the scientific and non-scientific public, and there is now excitement to learn more about this fascinating group of non-dinosaurs. It was a big moment for crabs. ”