Gigantic marine scorpions, some larger than humans, hunted in ancient oceans

Let’s go back the hands of time. Before the extinction knocked dinosaurs off their pillar, before the extinction “Great Death” wiped out 95 percent of all organisms, we had the Paleozoic Era.

During this age in Earth’s history, between 541 million and 252 million years ago, arthropods (animals with exoskeletons like insects, crustaceans, scorpions, and horseshoe crabs) explored extremes of size, from small to enormous.

In fact, some Paleozoic arthropods represent the largest animals on Earth at the time. If you were to swim in the Paleozoic oceans, you might have been lucky enough (or unlucky) to find one of the most fearsome extinct arthropods – the marine scorpion, Eurypterida.

Our new research, published in Gondwana Research, is the most comprehensive collection of information on these fascinating creatures that ever roamed Australian waters.

400 million years old A. Eurypterus fossil remipes.  (H. Zell / Wikipedia / CC BY-SA)400 million years Eurypterus remipes fossil. (H. Zell / Wikimedia / CC BY-SA)

A sight to behold

Although Eurypterida closely resembled scorpions (with a similar body shape, although built for swimming), they were not. They were more like the cousins ​​of modern scorpions.

An exceptional part of the evolutionary history of the marine scorpion is how they fit into the narrative of Paleozoic gigantism.

Marine scorpions include the largest marine predators to have emerged in the fossil record, including a species believed to be more than 2.5 meters long (8 feet long), Jaekelopterus rhenaniae. Back then, some of these giants were effectively in the same place in your food web as the modern great white shark.

These nimble swimmers probably would have used their large, claw-armed forelimbs to grab their prey, which they would then crush between the tooth-like structures in their legs (called gnathobasic spines).

While we’re not sure exactly what these large animals ate, it’s likely that smaller fish and arthropods would have been on the menu. And if humans had been swimming in the sea, maybe we did too!

The size of the largest extinct marine scorpions, relative to a human.  (Slate Weasel / Wikimedia / Modified)The size of the largest extinct marine scorpions, relative to a human. (Slate Weasel / Wikimedia / Modified)

A fascinating (but murky) story

Australia is famous for its wide variety of curious animals, including unique modern species like the platypus. And this uniqueness extends far beyond the fossil record, with marine scorpions being a good example.

But the scientific record and study of Australian marine scorpions has been spotty. The first documented specimen, published in 1899, consisted of a fragmented exoskeleton section found in Melbourne.

Before our new investigation examining group integrity in Australia, there were about ten records, and just another attempt to group it all together. As such, the diversity and spread of these fossils was quite uncertain.

For us, revisiting these incredible fossils resulted in some trips to different Australian museums. They also sent us specimens at the University of New England to examine them in person.

This paleontological journey of discovery uncovered many fossils of marine scorpions that had not previously been observed. As a result, we now have evidence of six different possible groups that existed in Australia.

Collecting these specimens in our most recent publication, we illustrate that Pterygotidae (the family of marine scorpions that reached 2.5 meters in length) dominated the group’s Australian fossil record. Although this has been observed previously, the abundance of material from different places and time periods, especially from Victoria, was unexpected.

Timeline of Pterygotidae (blue) and Adelophthalmidae (orange) sea scorpions. (<span style=Examples and chronology of marine scorpions Pterygotidae in blue and Adelophthalmidae in orange. (Bricknell et al., Gondwana Researcher, 2020)

Back to the source

In addition to showing the largest number of Australian marine scorpions, our document also describes the general lack of information on these animals.

Even though there is a lot of fragmented material, there is only one (mostly) complete sample, Adelophthalmus waterstoni, which is only 5.7cm long.

Future research will involve revisiting the sites where these specimens were originally collected, in hopes of finding more complete specimens. This will not only help to better document Australian marine scorpion species, but will also allow for a more complete understanding of the environments in which they lived.

Ultimately one thing is clear: Much remains to be discovered about these Titans that swam across Australia’s prehistoric oceans.

The authors thank Natalie Schroeder Geoscience Australia for her help with this project.The conversation

Russell Dean Christopher Bicknell, Postdoctoral Fellow in Paleobiology, University of New England and Patrick Mark Smith, Technical Officer – Paleontology, Australian Museum.

This article is republished from The Conversation under a Creative Commons license. Read the original article.