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Fossil stuck in 100 million-year-old amber is oldest "true crab" ever discovered

In 2015, two researchers stumbled across a piece of amber jewelry in a market in Tengchong, China, that was found by miners in Myanmar. The piece has a young, five-millimeter-long crab embedded in it. 

That crab would be a major discovery in the study of crab evolution. A research team dedicated to the little crab released their findings Wednesday after years of studying the fossil. The newly discovered species is named  Cretapsara athanata, "the immortal Cretaceous spirit of the clouds and waters," after spirits from South and Southeast Asian mythology. 

Before this discovery, scientists faced a conundrum: the known fossil record, consisting of just a few claws and carapaces, showed that crabs that lived on land and in fresh water split from their marine relatives between 50 to 75 million years ago. But the molecular record, which compares differences in DNA and RNA, said that the crab families split more than 125 million years ago.

That's why scientist Javier Luque, a Research Associate at Harvard University and co-author of the research team, was so surprised to discover the crab, that looks similar to other marine crabs, in amber, which is solidified tree sap. 

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ARTISTIC RECONSTRUCTION OF CRETAPSARA ATHANATA: THE IMMORTAL CRETACEOUS SPIRIT OF THE CLOUDS AND WATERS ARTWORK BY FRANZ ANTHONY, COURTESY OF JAVIER LUQUE (HARVARD UNIVERSITY).

"In a way, it's like finding a shrimp in amber," said Luque in a press release, "Talk about wrong place, wrong time."

Using micro-CT scans, the team was able to capture tiny appendages like the crab's antennae, legs, the hairs on its mandible, compound eyes and even its gills that had all been perfectly preserved by the amber. 

"This spectacular crab looks modern, like something you might find on the [British Columbia] B.C. coast flipping rocks, but it is actually quite old and different from anything seen before, fossil or alive," Luque says. 

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CRETAPSARA ATHANATA: THE FIRST CRAB IN AMBER FROM THE DINOSAUR ERA. LIDA XING (CHINA UNIVERSITY OF GEOSCIENCES, BEIJING)

The amber, dated to the dinosaur era, or 100 million years ago, bridges the gap between the two previously-known family splits and is, to this date, the oldest example of a "true crab" venturing onto land and the most complete fossil crab ever discovered, and indicates that crabs became terrestrial or amphibious around that time, much earlier than previously thought. 

True crabs, or the traditional crab, are contrasted with "false crabs" like hermit crabs or king crabs. Those species are considered crustaceans but not crabs — they're in the same family as shrimp and lobster.

The discovery of the crab has led the researchers to believe that a type of event called the Cretaceous Crab Revolution, when both true and false crabs diversify worldwide, happened at least 12 separate times. 

"It seems like evolution loves making crabs," Luque explained. "Crabs are doing something well, so nature is sorting them out and selecting for those forms over the less crabby relatives." 

Describing his excitement at the discovery, Luque added, "Crabs in general are fascinating, and some are so bizarre looking… and right now people are excited to learn more about such a fascinating group that are not dinosaurs. This is a big moment for crabs."

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