Ancient "Monster" Sea Scorpions Were Gentle Giants

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Justine Alford

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1463 Ancient "Monster" Sea Scorpions Were Gentle Giants
A fossil of A. cummingsi. Photograph by Division of Invertebrate Paleontology, Peabody Museum of Natural History, Yale University

A few years back, scientists discovered the fossil of a giant marine scorpion (Acutiramus cummingsi) that lived some 400 million years ago. This two meter long monster was thought to be a top predator of the seas, capable of tracking down prey and tearing it to shreds with claws the size of tennis rackets. Sounds pretty terrifying, right? Well, much to our disappointment, new research carried out by scientists at Yale and University College Cork has suggested that this beast was more of a gentle giant than the Kraken in disguise.

Members of the Pterygotidae family, which includes A. cummingsi, roamed the seas some 436-402 million years ago and were the largest arthropods that ever lived, reaching lengths of over two meters. These now extinct animals possessed huge claws (lined with sharp teeth, no less) and forward-facing compound eyes, which led scientists to believe that they were formidable predators that could hunt down armored cephalopods, big or small, and crush their hard shells. Now, for the second time, a study has suggested that this assumption may have been a little hasty.


A few years back, research carried out on Acutiramus’s pincers found that they were too weak to be able to crack open hard shells. Furthermore, the restricted mobility of the claws meant that they were more suited to grasping prey on the seafloor than catching fast swimming organisms. In the latest study, which has been published in Biology Letters, researchers add to the notion that these creatures were more likely to be scavengers than top predators with the finding that they had very poor eyesight.

The researchers made this discovery by investigating the eyes of several A. cummingsi specimens with the help of an electron microscope. They made estimates of eye size and lens angle and then compared this information with data obtained from smaller relatives and modern arthropods. They concluded that A. cummingsi would have had poor visual acuity and therefore wouldn’t have been able to catch fast moving prey. This giant creature would have therefore been more suited to feeding on soft-bodied animals such as sea slugs, or perhaps even plants. However, the researchers note that it is difficult to make assertions about behavior from fossils, so it remains a possibility that they were still pretty feisty. 

[Via Phys.orgNational Geographic, Biology Letters and Live Science]