A tiny crab is the first to be found trapped in amber from the dinosaur era. It lived in a forest area of South-East Asia 99 million years ago.
Remarkably similar to modern crabs, the 5-millimetre-long crustacean is fully preserved, making it “the most complete crab [fossil] ever discovered”, says at Harvard University.
“We are talking about pristine preservation, as in, not missing a single hair,” Luque says. “And even though it’s so small, we were able to see so many details so exquisitely, including the gills. That’s just mind-boggling.”
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żěè¶ĚĘÓƵs have already studied a few crabs in 15-million-year-old amber from Mexico, but this new specimen, which came from amber mined recently in Myanmar, fills important knowledge gaps about how crabs – including those that can walk on land or live in freshwater – evolved.
Although molecular estimates set the origins of non-marine crabs at approximately 130 million years ago, we hadn’t found any evidence of such crabs beyond 75 million years ago. Because the fossil appears to be a freshwater crab, it potentially extends the record of the group back almost 25 million years.
The “exciting” discovery represents a new genus that the team has named Cretapsara: “Creta” for the Cretaceous period and “Apsara” meaning the cloud and water spirit in South-East Asian mythology, to honour the local culture and heritage. The species itself is C. athanata.
Luque and his colleagues analysed the specimen under a standard microscope and X-ray micro-CT scanner. They clearly identified the animal’s eyes, antennae, pincers, mouthparts, fine hairs and all eight legs – including one that had separated from the body, probably as the crab struggled to free itself from the tree resin that engulfed it “like a time capsule”, says Luque.
Despite its small size – its body measures a mere 2 millimetres wide – the ancient crab, which might be a juvenile, shares many common features with today’s crabs. “You have this roundish carapace [upper shell] and the very well-developed walking legs, the big eyes, the small tail tucked under the body,” he says. “All these features are modern-like.”
Yet it also has distinct differences that connect it to its primitive origins, says Luque. In particular, it has deep grooves on its carapace, unlike the smooth tops of current crabs. And its chest is much narrower, more like that of a shrimp or lobster than a modern-day crab’s broad chest. “It’s not a missing link, but more like a distant cousin to modern crabs,” he says.
The crab’s gills suggest it mostly lived in water, unlike current land-dwelling crabs which have lung-like air pockets sharing the body space for the gills. “This was a really puzzling and exciting point,” Luque says. “How does an aquatic animal get into the sap of a tree in a forest? It gives some food for thought.”
One plausible explanation is that the crab was taking a brief land-based journey between two bodies of water when it got trapped, says Luque. Its misfortune, however, has led to an “invaluable” scientific treasure: resin consolidates quickly in water – “like super glue”, he says – so it almost never creates fossils. “It was sad for the animal, but it was basically the only opportunity we have to know that it existed.”
Science Advances
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