Meet Callichimaera perplexa, the platypus of crabs

The crab family has just had a group of new cousins, including a 95-million-year-old species of chimera that will force scientists to rethink the definition of crab.

An international team of researchers led by Yale paleontologist Javier Luque has announced the discovery of hundreds of exceptionally well preserved specimens from Colombia and the United States dating back to the Middle Cretaceous period from 90 to 95 million years ago. . The cache includes hundreds of tiny fossils of shrimp, several true shrimp and a brand new branch of the crab evolutionary tree.

The most intriguing discovery, according to the researchers, 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. The name derives from a chimera, a mythological creature whose body features come from more than one animal. Callichimaera Her full name translates as "beautiful perplexed chimera".

Luque noted that CallichimaeraIts "unusual and cute" appearance, including its small size – about the size of a quarter – large compound eyes with no dimples, no crooked claws, with the leg-shaped mouth parts, the apparent tail and long bodies are typical characteristics of pelagic crab larvae. This suggests that many of the larval traits observed in this "perplexed chimera" could have been preserved and amplified in miniaturized adults through changes in timing and rates of development. This is a process called "heterochrony" that can lead to the evolution of new body plans.

"Callichimaera perplexa is so unique and strange that it can be considered the platypus of the crab world, "said Luque. This suggests how new forms evolve and become 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 characteristics "crabby" and forces us to rethink our definition of what makes a crab a crab. "

<li data-thumb = "https://3c1703fe8d.site.internapcdn.net/newman/csz/news/tmb/2019/meetcallichi.jpg" data-src = "https://3c1703fe8d.site.internapcdn.net/ newman / gfx / news / hires / 2019 / meetcallichi.jpg "data-sub-html =" Artistic reconstruction of Callichimaera perplexa, the strangest crab that has ever lived. Credit: Elissa Martin, Yale Peabody Museum of Natural History ">



<li data-thumb = "https://3c1703fe8d.site.internapcdn.net/newman/csz/news/tmb/2019/1-meetcallichi.jpg" data-src = "https: //3c1703fe8d.site.internapcdn. net / newman / gfx / news / hires / 2019/1-meetcallichi.jpg "data-sub-html =" The diversity of body shapes in crabs, including enigmatic Callichimaera perplexa (center). Credit: Photos, Arthur Anker & Javier Luque; figure, Javier Luque, Yale University ">



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A study on discovery appears in the newspaper's online edition on April 24 Progress of science.

"It is very exciting to see today that we find in the tree of life all new branches of the distant past, especially regions like the tropics, which, despite their great diversity, are places we know least in terms of past diversity, "said Luque.