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Artistic reconstruction of Callichimaera perplexa: The strangest crab that has ever existed. (Image credit: Elissa Martin, Yale Peabody Museum of Natural History)
The crab family has just received a group of new cousins, including a 95-million-year-old species, which will force scientists to rethink the definition of crab – and perhaps the different ways that animals evolve with the weather.
An international team of researchers led by Yale Paleontologist Javier Luque has announced the discovery of hundreds of exceptionally well-preserved specimens from rock formations in Colombia and the United States, dating from the 90th to the Cretaceous 90 million years ago. 39; years. The cache contains hundreds of tiny shrimp fossils, with their indicative curve. several caridians, which are the "true" shrimp widespread; and an entirely new branch of the evolutionary tree for crabs.
The most intriguing discovery, according to the researchers, is Callichimaera perplexa, the oldest example of an arthropod swimmer with paddle-shaped legs since the extinction of sea scorpions there are more than 250 million of them. 39; years. The name derives from the chimera, a mythological creature that features the body features of more than one animal. The full name of Callichimaera translates as "a beautiful perplexed chimera".
Video credit: Images by Daniel Ocampo R., Vencejo Films and Javier Luque, Yale University / Animation and 3D reconstruction by Alex Duque.
Callichimaera is about the size of a quarter. His "unusual and cute" appearance, Luque notes – large compound eyes without cavities, bent claws, leg-like mouthparts, an open tail, and a long body – are typical features of offshore 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," Luque said. "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 will force scientists to rethink the definition of crab. (Photo credit: Daniel Ocampo R., Vencejo Films.)
Luque also stressed the importance of making this discovery in a tropical region of the world. There are fewer researchers actively looking for fossils in the tropics, he said, and the amount of vegetation cover and dense vegetation in tropical forests makes 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.
The Luque team included researchers from the University of Alberta, Kent State University, the University of Montreal, the Smithsonian Tropical Research Institute in Panama, the Canadian Society parks and nature, the National Autonomous University of Mexico, the University of Nevada and the College of Communication and Design in Boca Raton, Florida.
Publication: J. Luque, et al., "Exceptional conservation of Middle Cretaceous marine arthropods and evolution of new forms via heterochrony", Science Advances, April 24, 2019: vol. 5, no. 4, eaav3875; DOI: 10.1126 / sciadv.aav3875
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