A bizarre night hunting crab forces scientists to reconsider the evolution of modern species

With enormous eyes, large claws, paddle-shaped legs and lobster-shaped shells, scientists have describes a recently discovered species as "the strangest crab that has ever lived".

FOres discovered in Colombia revealed the new evolutionary branch of the crab swimmer, who lived about 95 million years ago.

Small creatures would have reminded carillon palaeontologistsras – monsters of Greek mythology with a lion's head, a goat's body and a snake's tail – because of their mixed features that are very similar to those of other marine arthropods.

Appointed Callichimaera perplexa, which means "beautiful puzzled chimera", after its unusual mix of features, it is the oldest example of an arthropod – shaped paddle – legged swimmer since the extinction of sea scorpions more than 250 million years ago.

It was discovered by an international team of researchers led by paleontologist Javier Luque of the prestigious American University of Yale.

"Callichimaera perplexa is so unique and strange that it can be considered the platypus of the crab world, "said Dr. Luque. "It suggests how new forms evolve and become so disparate over time."

He added: "We generally 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. "

Fossilized creatures, found in the Andes in Colombia, once lived in a shallow coastal sea during the Cretaceous.

Researchers have recovered more than 70 specimens in soft clay, as well as hundreds of other crustaceans such as shrimp and lobsters.

L & # 39; single Callichimaera perplexa the crab had wing-like legs that allowed it to swim and large eyes allowing it to hunt at night (Oksana Vernygora, University of Alberta)

Although the fossils are no bigger than a coin, Mr. Luque explained that their exceptional degree of preservation allows researchers to select specific details, including their paddle-shaped legs and large eyes, suggesting that crabs spent their lives swimming, rather than crawling like modern crabs. to do today.

Dr. Luque said Callichimaera An "unusual and cute" appearance, including its small size, large compound eyes without cavities, curved claws, leg-shaped limbs, apparent tail and long body are typical characteristics of pelagic crab larvae.

He added that this suggests that many of the larval traits observed in the species may have been conserved and amplified in miniaturized adults through changes in timing and rates of development.

This process is called "heterochrony" and it is thought that it leads to the evolution of new body parts.

"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 Dr. Luque. "It's an incredible amount of detail and we were able to reconstruct them as if they lived yesterday."

The high quality of fossils has even allowed researchers to create a detailed 3D model of crab.

"It is common to find new body shapes in ancient rocks, such as those of the Paleozoic, as life exploded in many new forms," ​​said Dr. Luque. "This discovery, since the Middle Cretaceous, shows that there are still surprising discoveries of newer and more strange organisms waiting to be discovered, especially in the tropics. One wonders then "what else is there to discover?"

The study appears in the newspaper Progress of science.