Giant sea scorpion discovered

This beast is not only the largest of its kind found to date, but also the oldest, roaming the oceans 460 million years ago...
07 September 2015

Interview with 

Dr James Lamsdell, Yale University


An artist's impression of the world's oldest sea scorpion, Pentecopterus decorahensis


Now here's a story with a sting in the tail - scientists are claiming to have found the remains of the biggest and the oldest fossilised scorpion. It was more than 1.5 metres tall, but it didn't live on land; it inhabited the deep ocean and lived 460 million years ago. It's a distant relative of the horseshoe crabs that are still around today. Joanna Kerr spoke to Yale scientist James Lamsdell. He had the painstaking task of piecing together the remains of the creature, which were found in a meteor crater that sat on the floor of an ocean in what is now the state of Iowa in the USA...

James:: I tend to work very closely on various arthropod groups and Eurypterids or sea scorpions are sort of the primary group I work on. And so, what we’ve done is found the earliest known representative of this group which means that we know these things were occurring earlier than we previously thought. We also found out that this thing was a large a predator and this means that these things were very important members of these early ecosystems.

Joanna:: When you say ‘a large predator’, what sort of size are we talking about?

James:: So, the biggest ones we’ve found, bear in mind that these are moults so this probably would have got bigger than this – 1.7 metres long.

Joanna:: What does that look like? I mean, when I'm imagining a 1.7-metre long scorpion, I imagine something out of the film, out of like Jurassic Park.

James:: This thing would’ve been obviously a very aggressive animal. The first thing we noticed were this big appendages with these long spines coming off the head. These things sort of have been used to grab prey. The body would’ve been vaguely unusual. I mean, this thing was just a really bizarre animal. It was really strange-looking. We named it Penteconter which is named after the Greek Penteconter which is early warship. The reason we did that is not only is this an early large predator, but the outline from above kind of looks like these Greek warships. It was very sleek and the head is projected into this strange prow-like structure that just looks like the front of the ship. And then there are paddles coming off the back of the head which would’ve helped it swim.

Joanna:: When you found the fossil, was it a whole fossil? Was it something that you had to piece together like a jigsaw? What did you actually discover?

James:: The initial discovery are made by researchers at the Iowa Geological Survey. And so, they found these sheets of black material that was kind of paper-like and you could sort of peel it off the rock. And so, they did this excavation where they dammed the river and dug out 8 metres of this rock and then I got all these material to look through. This stuff is fragmented exoskeleton and it really does look sometimes, like this animal has just moulted. And so, what I have to do then was first of all, get this exoskeleton out of the rock which was easier than it could’ve been because the rock thankfully became very soft when got it wet again, so I could sort of peel this off. But then I essentially had a jigsaw puzzle where somebody had removed some of the pieces and then dumped a bunch of other jigsaw puzzle in with it. And so, I had to sort of workout which belonged to which animal, what went where and just basically, place this meter and a half long animal together from fragments that were no bigger than 10 centimetres each.

Joanna:: That sounds really tricky. This is the first example of this sort of fossil. Why do you think this was so well-preserved so that it allowed you to actually tell what the fossil was?

James:: A lot of it has to do with the environment of where this thing was found. So, these things seem to have (concreated) into this old meteorite crater to shed their skins. The first is the fact that these are shed skins, meant that scavengers will not have been interested in them. So, we wouldn’t have had to deal with animals picking up corpses which is what you would normally have when you're trying to have something fossilised. This environment was very deep, very calm. There was not a lot of wave action. There was also lower levels of oxygen in the environment than usual. And so, this meant that decay probably was really supressed. And so, there was really not much around to break down these fossils. And so, we’re really lucky that this meteorite crater was here for the duration, so that we can get this exceptional preservation. The preservation really is exceptional. I've never seen anything like this before and we can see things like patterns of the hairs on the legs which is fantastic...


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