This Tiny Crustacean Trapped in Amber Tells a Different Story About Crab Evolution

A team of scientists has discovered the oldest aquatic animal preserved in amber. The tiny crab encased in tree resin is over 100 million years old, dating back to the Cretaceous era, according to the study published this week in Science Advances. The find—the most complete fossilized crab ever seen—is helping researchers piece together when the crustaceans began to migrate away from the sea.

Scientists can piece together what life was like millions of years ago from preserved specimens like amber fossils and bones. Insects, plants, feathers and microorganisms are specimens most likely to be found entrapped in amber. However, finding an aquatic critter fossilized in resin is extremely rare. "Finding a crab in amber is like finding a needle in a haystack," Heather Bracken-Grissom, a biologist from Florida International University, not involved with the study, told Riley Black for National Geographic.

The animal is so well preserved that its compound eyes, claws, jointed legs and gills are visible in full detail, reports National Geographic. Using micro-CT scans, the international team visualized the crab's body in 3D and even imaged its mouthparts lined with fine hairs. It is unknown if the five-millimeter-long crab is a full-grown adult, a juvenile or a baby, reports Gizmodo's George Dvorsky.

The crab also has well-developed gills, which suggests it was an aquatic to semi-aquatic animal, according to a statement.

Based on the crab's anatomy, the research team determined that the tiny crustacean was a new species and dubbed it, Cretapsara athanata. The scientific name references the dinosaur era the crab lived in and Apsara, a spirit belonging to South and Southeast Asian mythology, reports Katie Hunt for CNN. The new species belongs to a group of still-living crustaceans called Eubrachyura. C. athanata is part of a new branch in the crab family tree, per a statement.

The absence of sand in the fossil and the way in which the sap flowed over the crab suggest the animal lived away from the beach and in either fresh or brackish water, National Geographic reports. It is also possible that the crab may have migrated like red Christmas Island crabs do to release their offspring into the ocean and then go back to land, CNN reports.

The crab's evolutionary move out of ocean water was a huge side-step. It meant that the animal had to adapt to living in brackish or fresh water by changing the way it regulated water, breathed and kept from drying out, Javier Luque, a paleontologist at Yale University and the study's first author, told National Geographic.

Evidence proves that crabs mastered dwelling on land and in brackish and fresh water at least twelve times since the dinosaur era. Because of this, their gills evolved to have lung-like tissue that allows them to breathe in and out of water. C. athanata did not have any lung tissue and instead had well-developed gills, suggesting it did not wholly live on land, per a statement.

"Now we were dealing with an animal that is likely not marine, but also not fully terrestrial," Luque said in a statement. "In the fossil record, nonmarine crabs evolved 50 million years ago, but this animal is twice that age."

The researchers say that the new fossil evidence moves this split between marine and nonmarine crabs from the mammal era, also known as the Cenozoic, back to the dinosaur era, CNN reports. The crabs began side-stepping on land when dinosaurs roamed the Earth and not after dinosaurs went extinct. 

The amber was found in Myanmar, where most of the world's amber fossils are sourced, and currently resides at the Longyin Amber Museum in China. In recent years, ethical concerns about collecting, studying and buying highly prized amber in areas of conflict as well as the repatriation of fossils to preserve the country's natural history have been raised, National Geographic reports. In their paper, the authors write, "Conducting research on specimens collected before the conflict and acknowledging the situation in the Kachin State will serve to raise awareness of the current conflict in Myanmar and the human cost behind it," per CNN.

 

Elizabeth Gamillo | | READ MORE

Elizabeth Gamillo is a correspondent for Smithsonian and a science journalist based in Milwaukee, Wisconsin. She has written for Science magazine as their 2018 AAAS Diverse Voices in Science Journalism Intern.