A Crab Trapped in Amber Provides Insights on the Evolution of Life

By: April Carson



The oldest crab fossil has been found in Burmese amber, which is 100 million years old. The diminutive crustacean known as Cretapsara athanata dwelled in brackish or freshwater areas near the forest's edge. According to a Science Advances article, the discovery suggests that real crabs established themselves in non-marine habitats before colonizing saltwater environments. The crab is one of the most ancient ever found, along with a 100-million-year-old spider and a 50-million-year-old wasp also found in Burmese amber.


In reality, crabs are much more prevalent than people realize: they may be found from the deep seas to coral reefs. True crabs from the Eubrachyura genus have also inhabited brackish and fresh water areas as well as land - for example, tropical rainforests.


The first brackish water, fresh water, and terrestrial crabs descended from marine ancestors in the Early Cretaceous some 125 million years ago, according to phylogenetic reconstructions. However, the earliest crab fossils reveal that they left the sea 50 million years later, at the end of the Cretaceous. This gap prevents experts from understanding how crustaceans adapted to their new environment, and why they emerged from the water at a much later time than expected.


Javier Luque of Harvard University's paleontological team has made significant new discoveries into the evolution of freshwater and terrestrial crabs. Their attention was on a Burmese amber sample from China's Yunnan province, which is around 99 million years old. Inside, scientists discovered a tiny crab from the Eubrachyura genus with a carapace length of just under one centimeter.


This is the first crab ever discovered in Burmese amber, as well as the oldest genuine crab found in amber (previous finds of crabs from Mexican amber are about 15 million years old, which corresponds to the early Miocene). Microcomputer tomography allowed us to reconstruct the structure of the smallest parts of its body, including its compound eyes, antennae, mouthparts, and abdomen.


Cretapsara athanata was the ancient crab's name. The genus name, which refers to the female species, is made up of two words: the Latin "Creta" alludes to the Cretaceous period when this creature thrived, and "apsara" is from Hindu mythology and refers to demi goddesses of the clouds and the sky. The species name "athanata" is from Greek and means "immortal", in reference to the fact that scientists were not aware of this crab's existence until relatively recently.

Anatomy


From an anatomical standpoint, C. athanata was distinct from all later and lost crabs (in its structure, primitive and advanced features were uniquely intermixed), so it was classified as a separate family, Cretapsaridae, made up of a single species.


The authors point out that C. athanata is considerably less massive than other recognized crab species. Perhaps the specie was not big in size or the specimen found is a juvenile that did not have time to develop.


Environment


The authors suggest that the piece of amber formed in a fresh or brackish water environment at the boundary of the forest. It's likely that the ancient crab lived here, feeding on underwater vegetation and breathing through his big gills. C. athanata could exist on land, although land crabs typically have smaller gills (to make room for their legs) and cannot survive in water.


What else can we learn about the ancient crab?


The life cycle of a cretapsara is still unknown. It's possible that, like today's freshwater crabs, the larval development of this species happened inside the eggs from which individuals subsequently emerged in minor sizes. On the other hand, it's conceivable that ancient crab larvae developed in salt or brackish water before returning to fresh or brackish water to molt.


The team hasn't found any other Cretapsara specimens in the deposit where the first one was discovered, although soft-sediment habitats are commonly under-sampled during field work. And because no sediment coring has been done at this site, there's no way of knowing whether these animals were more widespread in the Tethys, says David Siveter of Leicester University.


New facts about the evolution of crabs


The discovery of C. athanata suggests that some 100 million years ago, actual crabs from the Eubrachyura group already had a high variety and mastered a wide range of habitats, including brackish and fresh water. Until now, it was thought that at least three crab evolutionary paths had developed independently in non-marine areas. The new species, C. athanata, belongs to a wide-spread family of crabs, the Polychelida. The genus Carcinoscorpius is included in the same superfamily and is represented by only one living species from South Africa.





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About the Blogger:


April Carson is the daughter of Billy Carson. She received her bachelor's degree in Social Sciences from Jacksonville University, where she was also on the Women's Basketball team. She now has a successful clothing company that specializes in organic baby clothes and other items. Take a look at their most popular fall fashions on bossbabymav.com


To read more of April's blogs, check out her website! She publishes new blogs on a daily basis, including the most helpful mommy advice and baby care tips! Follow on IG @bossbabymav


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