Discovery of a 100-million-year-old crab fossilized in amber

“The main challenge is changes in osmoregulation,” explains Heather Bracken-Grissom, “which is the way the body manages the exchange of water and electrolytes, such as salt, in its body. Another problem to take into account: new predators ready to devour them.

Despite this, crabs have repeatedly left the oceans to reach the mainland. Modern crabs live not only on beaches, among coral reefs and in the depths of the ocean. They also inhabit estuaries, rivers and lakes. Some species, such as the Caribbean purple land crab, spend most of their time on land. Others choose a unique way of life, such as the coconut crab; this huge arthropod, the weight of which can reach 4 kg, climbs the trees of the islands of the Indian and Pacific oceans.

Researchers who specialize in creating family trees based on biomolecules such as genes believe that non-marine crabs first evolved around 130 million years BC, during the Early Cretaceous. The oldest known crab fossils were only 70 million years old before the discovery of the new Burmese fossils, which makes more sense compared to genetic estimates.

A WINDOW IS OPENED INTO THE PAST

Although the fossil is the oldest non-marine crab, it is probably not the first (or last) crustacean to venture out of the oceans. “We believe that true crabs have adapted to a predominantly freshwater lifestyle at least six times and to terrestrial and brackish water environments at least twelve times,” describes Javier Luque.

And these crustaceans are not the only organisms that have undergone such transformations when leaving the oceans. For example, the ancestors of the rainbow trout that inhabit Lake Michigan originally lived in saltwater before adapting to life in fresh water less than 120 years ago. Several species of whales and dolphins have also invaded freshwater habitats, such as the boto in the Amazon.

No set of standard adaptations allows an animal to transition from a marine environment to a freshwater one. This is what makes this iterative evolutionary process so remarkable. Thanks to this fossil crab Cretapsara in a state of complete transition, scientists now have a new perspective on this mysterious evolution.

However, even if amber fossils are a window into the past, their study raises ethical questions. Aside from the amber trade dilemma, the fossil belongs to the Amber Museum in Longin, far from Burma. Paleontologists are increasingly afraid of the repatriation of fossils in order to preserve the natural heritage of countries.

As the researchers note, Burma’s laws regarding the export of fossils caught in amber contradict each other. In a letter to magazines Ecology of nature and evolution in June, Zin Maung Maung Thein of the University of Mandalay and Khin Zaw of the University of Tasmania called for paleontologists to report amber finds to the authorities or Burmese scientists to avoid spreading the precious fossils to the four corners of the world.

“In this way, the standards of scientific research will improve within the country, and the people of Burma will better understand the importance and scientific value of their own natural heritage, rather than being deprived of it.”

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