The Cretapsara athanata true crab as seen by the artist. Credit: Javier Luque et al. / Science Advances, 2021

A Crab Trapped in Amber Offers Clues on Evolution of Life

This is the first-ever crab specimen discovered in Burmese amber.

Scientists discovered the oldest crab fossil in 100 million-year-old Burmese amber. The tiny crustacean, called Cretapsara athanata, lived in brackish or freshwater bodies at the edge of the forest. As noted in an article for the journal Science Advances, the find indicates that true crabs began to colonize non-marine habitats as early as about a hundred million years ago.


True Crabs

Although crabs are associated with seashores, in reality, these crustaceans are much more widespread: they are found from the ocean depths to coral reefs. And true crabs from the Eubrachyura group have repeatedly and independently populated brackish and fresh water bodies, as well as colonized land – for example, tropical forests.

Ancestry and fossil evidence

Based on phylogenetic reconstructions, the first brackish water, fresh water, and terrestrial crabs descended from marine ancestors in the Early Cretaceous, about 125 million years ago. However, the oldest fossil remains of crabs that left the sea began to appear in the fossil record 50 million years later, at the end of the Cretaceous. This gap prevents specialists from understanding how exactly crustaceans mastered new environments.

A crab in amber

A team of paleontologists led by Javier Luque of Harvard University has gained new insights into the evolution of freshwater and terrestrial crabs. Their focus was on a 99 million-year-old piece of Burmese amber from a museum in China’s Yunnan province. Inside it, scientists have discovered a miniature crab from the Eubrachyura group with a carapace length and width of about two millimeters and a leg span of five millimeters.

Cretapsara athanata in a piece of amber. Credit: Javier Luque et al. / Science Advances, 2021
Cretapsara athanata in a piece of amber. Credit: Javier Luque et al. / Science Advances, 2021

The oldest specimen in history

This is the oldest true crab found in amber (the previous finds of crabs from Mexican amber are about 15 million years old, which corresponds to the early Miocene), as well as the first crab from Burmese amber. The specimen was so well preserved that microcomputer tomography made it possible to reconstruct the smallest details of its structure, including its compound eyes, mouth apparatus, and gills.

Name

The ancient crab was named Cretapsara athanata. The generic name, which refers to the female genus, is composed of two words: the Latin “Creta” indicates the Cretaceous period when this species lived, and “apsara” refers to the apsaras – the demi goddesses of water and clouds from Hindu mythology. The specific name in translation from ancient Greek means “immortal” (this is a hint at the excellent preservation of the sample).

Anatomy

Since from the anatomical point of view, C. athanata was very different from all modern and extinct crabs (in its structure, primitive and advanced characters were uniquely combined), it was singled out as a separate family, Cretapsaridae, consisting of a single species.

Smaller than most species

The authors note that C. athanata is much smaller than most known crab species. Perhaps this species was not large in size – or the specimen found is a young individual that did not have time to grow.

Close-up of the crab in amber. Credit: Javier Luque et al. / Science Advances, 2021
Close-up of the crab in amber. Credit: Javier Luque et al. / Science Advances, 2021

Environment

After analyzing plant particles and other inclusions in a piece of amber, the authors assumed that it formed in a fresh or brackish water body at the border of the forest. It is here, most likely, that the ancient crab lived. Probably, he spent most of the time underwater, but from time to time he went on land and fed on the forest floor. Theoretically, C. athanata could even be terrestrial, but land crabs usually have smaller gills (to make room for the development of spongy tissue that functions as lungs), while in this species they were large.

What else do we know about the crab in amber?

The life cycle of a cretapsara remains a mystery. Perhaps, like in modern freshwater crabs, the larval development of this species took place inside the eggs, from which individuals hatched, differing from adults only in small sizes. On the other hand, it is possible that the larvae of the ancient crab developed in the sea and then returned to fresh or brackish water bodies.

New facts about the evolution of crabs

The discovery of C. athanata indicates that already about a hundred million years ago, real crabs from the group Eubrachyura achieved a high diversity and mastered a variety of environments, including brackish and fresh water. Until now, it has been assumed that at least three evolutionary lines of crabs have independently mastered the non-marine habitat. Thanks to the discovery of a crab in Burmese amber, the number of such lines has increased to four.


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Sources:

EurekAlert! (n.d.). Crab found in 100-million-year-old amber is oldest modern-looking crab ever found.
Koumoundouros, T. (n.d.). Adorable crab encased in amber is among the oldest true crabs ever found. ScienceAlert.
Luque, J., Xing, L., & Briggs, D. E. G. (2021, October 20). Crab in amber reveals an early colonization of nonmarine environments during the cretaceous. Science Advances.
Sci-News. (n.d.). 99-Million-Year-Old Modern-Looking Crab Found in Burmese Amber.
Siliezar, J. (2021, October 22). Rare crab in amber offers evolution clues. Harvard Gazette.

Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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