The fossils were discovered near Waukesha, Wisconsin, with the new species, Thylacares brandonesis, named after the Brandon Bridge Formation where it was found. It is the oldest known example of the Thylacocephala group — shrimp-like creatures, mostly from the Jurassic period, known for their bulbous eyes and multiple limbs. The muscle structure and leg morphology of the new species suggests that it used its long, claw-like appendages to catch prey in a similar way to modern remipedes, blind crustaceans still found in salt water-filled caves.

Jurassic thylacocephalan Clausocaris lithographica.
Credit: Haug et al. 2014

Derek Briggs, Yale University, says: “This new research extends the range of this enigmatic group of fossil arthropods back to the Silurian, some 435 million years ago, and provides evidence that they belong among the crustaceans, the modern group that includes lobsters, shrimps and crabs.”

Carolin Haug, LMU Munich, said: “T. brandonensis was probably an actively hunting predator, which caught the prey with its front claws and crushed it into smaller pieces with the protrusions nearer its mouthparts.”

“This early, Silurian, example of Thylacocephala is in many ways much less extreme than the more recent Jurassic species. It still has normal-sized eyes in contrast to the very enlarged ones that came later, and shorter front claws in T. brandonensis compared to the extremely elongated ones in more recent Jurassic representatives.”

The description of the new Silurian species was part of a wider investigation into this group of fossils, including several new Jurassic specimens. Modern imaging techniques allowed the scientists to visualise new features, such as the tiny details of the T. brandonensis muscle structure. Based on these images, they created 3D models of the new species, which help us to understand the creature’s life habits.