In a study published last month in the journal iScience, a group of paleontologists have shown that the eye gave Callichimaera extremely sharp vision and the possibility of living as a free-swimming predator. The species Callichimaera perplexa, looks like a spider, with flat feet for paddles and a sturdy body.
In contrast to modern adult crabs, the ability to swim or vision is not very good. The crab traverses the silent seabed and barely relies on its tiny eyes for scavenging or grazing.
The species Callichimaera perplexa was originally discovered in 2005 by Javier Luque, a paleontologist from Colombia and now a researcher at Harvard University. Later as a scholar, he explored the fossil-rich rocks of the Boyacá department of Colombia, as the country’s province is called, and found very detailed arthropod fossils.
Callichimaera, found in Boyacá, Colombia measuring about a quarter of a meter in size, featured large compound eyes without cavities, hooked claws, foot-like mouthparts, an exposed tail, and a long tail. Previous research has shown that it is the earliest example of a swimming arthropod with paddle-like legs since the extinction of the sea scorpion more than 250 million years ago.
Seven of the specimens are preserved with eye detail. But this poses a conundrum, as crabs usually have tiny compound eyes, at the ends of the stalks and covered by protective orbits. The compound eyes of Callichimaera are large, without stalks or orbits. To that end, Dr Luque pointed out that Callichimaera was a predator.
For the study, the researchers analyzed nearly 1,000 live and fossil crabs, including crabs at various stages of development, representing 15 crab species. The researchers compared the size of the crabs’ eyes and how fast they grew. Callichimaera topped the list in both categories and has eyes that make up about 16% of its body size.
“If anyone had eyes this big, they must be very visual. This is in stark contrast to crabs with tiny eyes, and perhaps only 1 to 3% of the animal’s body size,” said Kelsey Jenkins, a graduate student in Earth & planetary sciences at Yale. .