Oldest Predatory Representative of Strange Arthropod Group Discovered

Scientists have uncovered a series of fossils which may just be the oldest representatives of a weird arthropod group. The 435-million-year-old fossils, in fact, represent a new genus of predatory arthropods.

These arthropods once roamed the Silurian seas, preying on other small creatures. They possessed a bivalve carapace and multiple abdominal limbs and were part of a now-extinct class of arthropods known as Thylacocephala.

Where exactly the thylacocephalans belong among the arthropods is still a matter of debate among scientists. Yet this latest finding sheds a bit more light on this group of animals.

"The main reason why it has been so difficult to work out the precise systematic position of thylacocephalans is that their morphology is so bizarre," said Carolin Haug, one of the researchers, in a news release. "For a long time, researchers couldn't even agree which end was anterior and which posterior."

Certain aspects of the anatomy of Thylacares brandonensis, the name for the new specimens, support the idea that the thylocephalans belong among the crustaceans. In addition, the anatomy of their posterior appendages and an analysis of the organization of their muscles suggest that they can be interpreted as a sister group of the Remipedia, which are blind crustaceans that can be found in flooded limestone caves in the tropics.

It's likely that T. brandonensis earned its living as a predator. Yet it probably was less highly specialized than later forms. Consequently, the morphological specializations seen in latter forms probably emerged in the course of further evolution of the class.

"It is quite possible that the extreme degree of specialization seen in specimens from the Jurassic proved to be an evolutionary dead end, for at the close of the Cretaceous, at a time when many other groups of animals disappeared from the fossil record, Thylacocephala also became extinct."

The findings are published in the journal BMC Evolutionary Biology.