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Researchers have discovered new branches of the crab family, including a 95-million-year-old species called the "weirdest crab that has ever existed" and that helps shed light on the evolution of "crabs". crab".
A team of international researchers, led by paleontologist Yale University, Javier Luque, has uncovered hundreds of exceptionally well-preserved specimens in rock formations in Colombia and the United States dating back to the Cretaceous period average of 90 to 95 million years.
The discovery, described in the newspaper Progress of science, includes hundreds of tiny shrimp fossils, with their comma-shaped indicator curve; several caridians, which are the "true" shrimp widespread; and an entirely new branch of the evolutionary tree for crabs.
But the most intriguing discovery is Callichimaera perplexa, the oldest example of an arthropod – shaped paddle – legged swimmer since the extinction of sea scorpions there are more than 250 million years. About the size of a quarter, the Callichimaera has "unusual and cute" features – large compound eyes without cavities, curved claws, leg-like mouthparts, exposed tail and long body – typical of deep sea crab larvae.
This suggests that some ancient crabs may have retained some of their larval traits in adulthood, amplified them, and developed a new body architecture. It is an evolutionary process called "heterochrony".
"Callichimaera perplexa is so unique and strange that it can be considered the platypus of the crab world, "said Luque. "This suggests that new forms are evolving and becoming so disparate over time. Usually, we think that crabs are large animals with large shells, strong claws, small eyes in long locks, and a small tail folded under the body. Well, Callichimaera defies all these "crabby" characteristics and forces us to rethink our definition of what makes a crab a crab. "
Javier Luque poses with Callichimaera perplexa, a 95 million year old species that illuminates the evolution of crustaceans. (Photo credit: Daniel Ocampo R., Vencejo Films)
Luque also emphasized the importance of making the discovery in a tropical region of the world, where there are fewer researchers in search of fossils in the tropics, and where the amount of land cover and thick vegetation make the # Access to exposed rocks more difficult.
"It's very exciting that today, we found in the tree of life all new branches of the distant past, especially regions like the tropics, which, despite their great diversity, are places that we know the least in terms of the past. diversity, "said Luque.
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