A 100 million year old crab could explain when these animals came out of the water, and refine our evolutionary timeline.
Crabs may seem like animals of little scientific interest. Known for millennia by researchers, they are in fact one of the fundamental proofs of Charles Darwin’s theory of evolution. In fact, crabs, like all species, have evolved over the millennia. Originally a marine species, they gradually got used to dry land, to the point that some species living on Earth today are unable to live in water and prefer to stay on beaches.
The big question is therefore to know when this change took place. A complex question, as the evolution has taken place over a long period. Until today, there were two theories about when crabs left seawater for the sand of beaches and freshwater rivers. The first was based on fossil dating, which indicated that this change had taken place at the end of the Upper Cretaceous, about 73 million years ago.
But other studies, based on molecular analyzes found a very different result, with a tipping point in the early Lower Cretaceous, 125 million years ago. Two dates for the same event, it was therefore necessary at all costs to bring them together, in order to find the exact time of this change. Scientists then began to search for older fossils on the one hand, and on the other for better calculation methods for molecular dating, in order to refine the results.
A fossil much younger than the others
Finally, it is an international team of researchers who published the beginning of a response in the journal Science Advances. They have indeed found a crab fossil, 100 million years old, which has the distinction of having left its original marine environment. This discovery makes it possible to immediately advance by nearly 25 million years, at least, the evolutionary history of crabs, thus proving the molecular dating that had been done until then right.
This fossil, extremely well preserved in amber, was enclosed with particles of wood and insect droppings, validating the idea that this crab was capable of living on earth. If the study prefers to speak here of an amphibic crab, living in nearby fresh waters, the researchers recognize that species must have already left the marine world to reach land. According to the first analyzes carried out on the specimen, amber would have covered it while it was still alive.
This discovery helps to clarify our knowledge of the evolutionary history of life on our planet. If crabs left their marine world 100 million years ago, it is surely not the only species to have done so. Scientists will therefore look into this question, but also seek to know what prompted these crabs to leave their habitat for an unknown world.