Description

Jaekelopterus is a predatory eurypterid genus, an extinct group of aquatic arthropods. Fossils of Jaekelopterus have been found in Early Devonian deposits, specifically in the Pragian and Emsian stages. Two distinct species are known: the type species J. rhenaniae discovered in brackish to fresh water strata in the Rhineland, and J. howelli found in estuarine strata in Wyoming. The genus name is a fusion of German paleontologist Otto Jaekel's name, who described the type species, and the Greek word (pteron) signifying "wing."

Based on isolated fossil evidence of a large chelicera (claw) from Germany's Klerf Formation, J. rhenaniae is estimated to have attained a size of roughly 2.3–2.6 meters (7.5–8.5 ft), marking it as the largest arthropod ever unearthed.

Jaekelopterus stood as an apex predator of the ancient seas, with an astonishing size that sets it apart from its contemporaries. It was one of the largest arthropods to ever inhabit Earth. Its formidable appearance was characterized by a robust exoskeleton, a pair of large, grasping appendages, and a long, paddle-like telson at the rear for locomotion. As fully matured creatures, Jaekelopterus would have held the position of top predators within their ecosystems, likely preying on smaller arthropods (potentially engaging in cannibalism) as well as early vertebrates.

Predatory vision

Jaekelopterus possessed forwardly overlapping vision, a characteristic feature of predatory creatures, indicating stereoscopic vision. Morphologically, the eyes of eurypterids closely resembled those of horseshoe crabs. While the square-like arrangement of receptor cells in Jaekelopterus' compound eyes bears resemblance to that of horseshoe crabs, it displays some distinct differences, suggesting a specialized visual system. Notably, the photoreceptors in Jaekelopterus are remarkably large, measuring approximately 70 µm. This size greatly exceeds that of humans (1-2 µm) and most other arthropods (also 1-2 µm), but aligns with the dimensions of contemporary horseshoe crabs.

The distinct eyes of modern horseshoe crabs stand apart from those of other present-day arthropods. They confer heightened edge-perception and enhanced contrast sensitivity, qualities vital for creatures navigating low and diffused light conditions. Given the similarity of Jaekelopterus' eyes, it is reasonable to assume it possessed similar adaptations. The highly specialized eyes of Jaekelopterus would have provided it with optimal adaptations for its predatory way of life.

Bitemarks that last

The chelicerae of Jaekelopterus are enlarged, robust, and feature a curved free ramus, alongside denticles of varying lengths and sizes. These adaptations closely parallel the robust puncturing and grasping capabilities observed in modern scorpions and crustaceans. Fossil evidence also suggests that Jaekelopterus howelli might have been responsible for puncture wounds found on the poraspid agnathan fish Lechriaspis patula, recovered from Utah's Devonian deposits.

Exoskeleton

Jaekelopterus' exoskeleton, composed of a chitinous material, provided protection against predators and supported its massive body. Its segmented body and flexible exoskeleton enabled efficient swimming and maneuverability, allowing it to navigate the complex underwater environment in pursuit of prey.