An extinct species of brachyuran crab called Callichimaera perplexa was a highly visual predator inhabiting well-lit environments, according to new research led by Yale University paleontologists.
Callichimaera perplexa lived approximately 95 million years ago during the mid-Cretaceous period.
First described in 2019, its fossilized remains were found in Boyacá, Colombia, and Wyoming, the United States.
Callichimaera perplexa was about the size of a quarter, featuring large compound eyes with no sockets, bent claws, leg-like mouth parts, an exposed tail, and a long body.
Previous research indicated that it was the earliest example of a swimming arthropod with paddle-like legs since the extinction of sea scorpions more than 250 million years ago.
“The specimens we have of the unusual Cretaceous crab Callichimaera perplexa preserve some very delicate eye tissues that don’t normally preserve,” said Kelsey Jenkins, a graduate student at Yale University.
“This includes things like facets and internal optical tissues. This kind of excellent preservation is rare.”
For the study, Jenkins and colleagues analyzed nearly 1,000 living crabs and fossils, including crabs at different stages of development, representing 15 crab species.
They compared the size of the crabs’ eyes and how fast they grew. Callichimaera perplexa topped the list in both categories. Its eyes were about 16% of its body size.
“If something has eyes this big, they’re definitely very highly visual,” Jenkins said.
“This is in stark contrast to crabs with tiny, vestigial eyes where they may only be 1 to 3% of the animal’s body size.”
Likewise, Callichimaera perplexa’s optical growth rate was faster than any other crab the researchers studied.
“Crabs whose eyes are growing very quickly are more visually inclined — likely they’re very good predators who use their eyes when hunting — whereas slow-growing eyes tend to be found in scavenger crabs that are less visually reliant,” said Professor Derek Briggs, a paleontologist at Yale University and Peabody Museum of Natural History.
The results were published in the journal iScience.
Kelsey M. Jenkins et al. 2022. The remarkable visual system of a Cretaceous crab. iScience 25 (1): 103579; doi: 10.1016/j.isci.2021.103579
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