The Ancient Sea Scorpion Might Have Been Earth's Largest Insect

Imagine sitting by a serene lake on a perfect day. The sky is an astonishing shade of blue, clearer than anything you've witnessed before. The air feels refreshing and pure, making every breath a delight. As you step into the lake, the cool water soothes your skin. Venturing further, your foot brushes against what seems like a submerged rock or log. Upon closer inspection, you notice a branch-like structure with a tapered, crescent-shaped end adorned with sharp spikes.

Without warning, the "log" shifts, revealing its true nature. The crescent-shaped part is actually a massive claw, which latches onto your leg, dragging you underwater. Another claw seizes your torso. You've just come face-to-face with a colossal sea scorpion, and your odds of escaping alive are alarmingly low.

Thankfully, this scenario would require a journey back approximately 400 million years to the Devonian period of the Paleozoic Era. This era was marked by the prevalence of gigantic creatures roaming both land and sea. Imagine dragonflies with wingspans stretching two-and-a-half feet and millipedes measuring six feet in length. However, the most dominant species of all were the pterygotid eurypterids, commonly referred to as the giant sea scorpion.

What are Eurypterids?

Eurypterids belong to an extinct group of arthropods thought to be the predecessors of modern scorpions and possibly all arachnids, which include creatures like spiders and other eight-legged arthropods. While their scientific name is rarely used, they are more commonly known as sea scorpions.

For 27 million years, giant sea scorpions reigned supreme at the top of the food chain, flourishing without natural enemies. These formidable predators were among the most fearsome on Earth, preying on large fish and even each other. Eurypterids were cannibalistic, battling and consuming one another for resources, food, and mates. They evolved to colossal sizes, though recent discoveries have altered our understanding of just how massive they could grow [source: Braddy, et al].

A Close Relative

Although giant sea scorpions are no longer around, we can study their close relatives, such as the horseshoe crab. Sadly, only four species of horseshoe crabs remain today, but the earliest group, now extinct, dates back 450 million years according to fossil records. These ancient arthropods, the giant sea scorpions, were among the first of their kind [source: Science Daily].

To visualize their appearance, we can examine the modern horseshoe crab (Limulidae). Research indicates they share the same eye structure as the extinct sea scorpion [source: Astrobiology].

How Scientists Estimate Their Size

Several years ago, paleontologist Markus Poschmann was excavating fossils in a German quarry. Alongside his team, he uncovered siltstone slabs that had formed in an ancient lake or lagoon millions of years ago. This prehistoric lake bed was the habitat of the largest arthropod ever recorded [source: University of Bristol].

Poschmann spotted a dark organic patch on one of the siltstone slabs, which turned out to be part of a claw from Jaekelopterus rhenaniae, a sea scorpion species. The fossil revealed a claw fragment measuring over 18 inches (46 centimeters). By extrapolating the proportions to the rest of the body, researchers estimated the scorpion's length at more than eight feet, surpassing previous estimates by nearly a foot and a half.

What Caused Sea Scorpions to Reach Such Enormous Sizes?

Paleontologists have varying theories about the massive size of giant sea scorpions. During the Devonian period, the atmosphere contained significantly more oxygen (35 percent compared to today's 21 percent). Some experts argue that this high oxygen level contributed to the gigantism seen in creatures of that era.

Another theory suggests that sea scorpions grew large out of necessity. To penetrate the increasingly tough armor of their fish prey, their claws and bodies had to evolve to enormous proportions. However, the researchers behind Poschmann's discovery argue that multiple factors, including the reduced gravity underwater, played a role in their gigantic size.

Forced From Water and Onto Land

Despite their size, most eurypterids were eventually outmatched by large, powerful fish with strong jaws and teeth. These predators drove sea scorpions onto land, where they evolved into smaller forms. The fossils they left behind serve as a testament to their dominance during their reign on Earth.

To explore further details about evolution, arachnids, and related subjects, proceed to the following page.