Javier Luque, a postdoctoral researcher at Harvard’s Department of Organismic and Evolutionary Biology, was extremely surprised when he found a crab trapped in fossilized tree resin: “It’s like finding a shrimp in amber: the wrong place at the wrong time.” Now, after three years trying to solve the puzzle, the researcher and his team have published their findings in the journal Science Advances .
They say that the hundred-million-year-old piece of amber, recovered from the jungles of Southeast Asia, contains what is believed to be the oldest modern-looking crab ever found. The discovery provides new insights into the evolution of these crustaceans and when they spread around the world. The five-millimeter crab is the first to be found in amber from the age of dinosaurs, and researchers believe it represents the oldest evidence of incursions into non-marine environments by so-called “true crabs” (of the infraorder Brachyurans ).
Until now, known fossils of crabs, and generally consisting of fragments of their claws, suggested that non-marine crabs would have reached land and freshwater some 70-75 million years ago. This discovery advances the date, and hence the surprise of the researchers when they discovered it.
“If we reconstruct the crab’s tree of life – in the form of a family tree – and do a molecular DNA analysis, the prediction is that non-marine crabs separated from their marine ancestors more than 125 million years ago,” explains Luque. . “But there is a problem because the actual fossil record, the one that we can touch, is very young, between 75 and 50 million years old … So this new fossil and its Middle Cretaceous age allows us to bridge the gap between the divergence. Predicted molecular and actual fossil record of crabs “.
Researchers believe that an event known as the Cretaceous Crab Revolution, when crabs (true or not) diversified around the world and began to develop their characteristic body shapes, happened more times than previously thought. According to this research, the different species of crabs evolved independently to live outside their marine habitat at at least twelve different times.
The new fossil was called Cretapsara athanata , “the immortal Cretaceous spirit of the clouds and waters.” The name honors his age and the mythological spirits of South and Southeast Asia. The creature suspended in amber is instantly recognizable as a true crab, which makes sense as researchers say it is the most complete fossilized crab ever discovered. The team, using micro-CT scanners, were able to see in clear detail delicate tissues such as the crab’s antennae, legs and mouthparts covered with fine hairs, large compound eyes and even its gills. Not a single hair was missing, they said. The diversity of shape among crabs is captivating the imagination of scientific and non-scientific audiences alike, and people want to learn more about such a fascinating group that are not dinosaurs. This is a great time for crabs, ”concludes Luque.
