About 100 million years ago, a young crab died, preserved in amber.
Fast forward to today, and that crab has found itself at the centre of a new study by researchers out of the University of Alberta (U of A), who argue the crustacean, which is the most complete fossil of its kind ever found, is helping to fill in an evolutionary gap.
“This crab is telling us a very interesting story about the tree of life of crabs,” Javier Luque, a research associate at Harvard University who began working with the encased crab while a U of A Ph.D. student, said in a statement.
“There is a lot of excitement about crab evolution because evolution has produced crab-like forms, known as carcinization, many times independently.”
So far, scientists have used the molecular record – built by comparing similarities and differences in DNA and RNA – to determine that non-marine crabs split from marine crabs about 125 million years ago.
But the fossil records are sparse, especially for non-marine crabs. Scientists believe marine crabs moved on land and into freshwater between 75 and 50 million years ago, but that leaves behind a significant time gap.
“So we’ve had this gap between the predicted molecular time of split of non-marine crabs and the known fossil record of about 50 million years,” Luque said.
Using micro CT scans of the fossil, scientists constructed a 3D representation of what the ancient crab may have looked like. In addition to being the most complete crab fossil found to date, it is also the oldest non-marine crab ever described.
This will allow researchers to compare the ancient crab with other species to understand how they evolved.
Luque says it isn’t an ancestor to modern crabs but rather, “a distant cousin.”
The two-millimetre-long fossil of the ancient crab was found encased in a piece of amber jewelry at a market in Tengchong, China. (Lida Xing/University of Alberta)
FOUND IN A MARKET
The crab involved in the study was not found in an expedition or buried in a museum’s archives.
According to U of A, researchers “came across” the 2-millimetre-long crab embedded in a piece of amber jewelry in a Tengchong, China market back in 2015.
“When I saw it for the first time I could not believe my eyes,” Luque said.
“This spectacular crab looks so modern, like something you may find in B.C. flipping rocks, but it is actually quite old and different from anything seen before, fossil or alive.”