Prehistoric crab found perfectly preserved in amber after 100 million years

CAMBRIDGE, Mass. — The oldest ever crab, trapped in amber for 100 million years, has been unearthed by scientists. Researchers at Harvard University say the fossil dates back to the age of the dinosaurs and may be a “missing link” in evolution.

Study authors believe the tiny crustacean is the ancestor of today’s red crabs, which migrate by the millions to the oceans during breeding season. The fossil’s body is perfectly preserved, including its claws, shell, bulging eyes, and even gills. Like fish, crabs use their respiratory organs to absorb oxygen from water.

“The specimen is spectacular, it is one of a kind. It’s absolutely complete and is not missing a single hair on the body, which is remarkable,” says lead author Dr. Javier Luque in a university release.

Prehistoric crab in amber
Fig. 1. Cretapsara athanata Luque gen. et sp. nov., a modern-looking eubrachyuran crab in Burmese amber.(A to D) Holotype LYAM-9. (A) Whole amber sample with crab inclusion in ventral view. (B) Close-up of ventral carapace. (C) Whole amber sample with crab inclusion in dorsal view. (D) Close-up of dorsal carapace. White arrows in (B) and (D) indicate the detached left fifth leg or pereopod. (Credit: Lida Xing, Javier Luque)

Scientists have named it Cretapsara athanata, which translates to “immortal spirit of the clouds and waters.”

It is the most intact crab fossil to date and researchers believe it lived on both the land and in the sea. Finding crabs in amber is extremely rare.

“The more we studied the fossil, the more we realized that this animal was very special in many ways,” Dr. Luque adds.

Prehistoric crabs lived on both land and sea?

Cretapsara is remarkably modern-looking, superficially resembling some shore descendants living today. Its entombment in the sticky tree resin sheds fresh light on the evolution of crabs. Most during the mid-Cretaceous era looked quite different.

The well-developed gills indicate an aquatic or semi-aquatic lifestyle. They have conquered land and sea-living at least 12 times since the dinosaurs disappeared 66 million years ago. In doing so, their gills evolved to include lung-like tissue allowing them to breathe both in and out of the water.

Researchers note Cretapsara had no lung tissue, indicating the animal was not completely land-dwelling.

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

Family tree modeling showed true crab-looking forms emerged in the most recent common ancestor more than 100 million years ago. Cretapsara bridges the gap and confirms they actually invaded land and fresh water during the dinosaur era rather than the mammal era.

Rewriting the evolution timeline

The finding pushes the evolution of non-marine crabs much further back in time. Measuring just a fifth of an inch wide, Cretapsara was a juvenile freshwater or amphibious species. It may have been a semi-terrestrial animal migrating onto land from water.

Study authors compare this behavior to modern red crabs, where land-dwelling mother crabs release their babies into the ocean. They later swarm out of the water, back onto land at Christmas Island in the Indian Ocean.

The findings in the journal Science Advances note that Cretapsara could also have been a tree climber, similar to a living group of tropical land descendants. Known as Sesarmidae, they first appeared 15 million years ago during the Miocene period.

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“These Miocene crabs are truly modern looking crabs and, as their extant relatives, they live in trees in little ponds of water,” Luque explains. “These arboreal crabs can get trapped in tree resin today, but would it explain why Cretapsara is preserved in amber?”

Amber provides a window to the past

The fossilized crab was among a batch of dull and unpolished amber pieces collected by local miners and sold as jewelry in China six years ago. Scientists are calling it a new branch in the crab “tree of life.” Its perfect preservation in amber rivals the completeness of the mysterious 95 million-year-old Callichimaera perplexa fossil. This very distant relative is nicknamed the “platypus of the crab world.”

Callichimaera’s stunning preservation as a stone fossil included soft tissues and delicate parts that rarely fossilize. Study authors note that both the Cretapsara and Callichimaera lived during a point in history they call the “Cretaceous Crab Revolution.”

It was a period when crabs diversified worldwide and the first modern groups originated while many others disappeared. They first appear in the fossil record more than 200 million years ago. Amber has a unique ability to entomb ancient plants and animals thanks to its transparency, opening a window into the past.

Cretapsara joins a list of specimens, including feathered tails of dinosaurs, that have been invaluable to finding out about the story of life on Earth.

South West News Service writer Mark Waghorn contributed to this report.

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