What Is That Body?

Jaekelopterus rhenaniae

We have made mention many times this week of the general morphology of eurypterids. These sea scorpions are what they sound like they are, in all honesty. Like other arthropods eurypterids are thought to have moulted a carapace that was probably chitin based. These insect-like creatures were segmented, having three main body segments composed of a head, body, and tail. The tail is hypothesized to have been able to inject venom into prey items in a similar fashion to the way that extant scorpions perform that function. Unlike modern arachnids eurypterids possessed three pairs of legs like extant insects with at least one pair better suited to swimming than walking. Eurypterids are considered one of the first potential terrestrial animals because of their ability to use their legs both in and out of the water. Possibly helping to adjust to the air after leaving the water, eurypterids possessed two pairs of eyes with the smaller ocelli residing between the larger compound eyes. As the first animals hypothesized to reach land, Protichnites being the first of the first, eurypterids were also uninhibited when it came to growth. This applies to growth in the water as much as it does to growth on land without any competition or natural predators initially following them out. To that end, they could grow to be quite enormous and the largest on record, Jaekelopterus rhenaniae, was a monster. The largest claws that have been discovered to date measure approximately 46 cm (18 in). The smallest eurypterid on record was about a quarter of the size of the claw!