An article published in “Journal of Systematic Palaeontology” reports the identification of a new species of trilobites that lived about 500 million years ago, in the Cambrian period. A team of researchers examined fossils discovered in the Emu Bay Shale, on Kangaroo Island, Australia, finding in some specimens characteristics that were different from the majority identified in the species Redlichia takooensis. Due to their size considerable for trilobites, with lengths that could reach 30 cm, and due to their predator characteristics, they decided to name the new species Redlichia rex, similarly to T.rex.

Trilobite fossils have been discovered in abundance all over the world but generally they’re exoskeletons while only in rare cases soft parts got preserved at least partially. The Emu Bay Shale is one of the deposits in which soft tissues such as antennae and legs have been preserved thanks to the lack of oxygen on the seabed where the dead animals ended, with the consequence that their decomposition was blocked and soft tissues could fossilize together with the exoskeletons.

So far the trilobites discovered in the Emu Bay Shale were classified as Redlichia takooensis, a species first identified in the 1950s by examining fossils discovered in southern China. Morphological differences were already detected among the discovered specimens but were attributed to ontogeny. Now a team of researchers led by James Holmes, a PhD student from the Australian University of Adelaide, examined those differences and concluded that some specimens belong to a different species, the largest among Australian trilobites.

The top image (Cortesia Holmes et al. All rights reserved) shows a fossil specimen of Redlichia rex. The bottom image (Courtesy Katrina Kenny. All rights reserved) shows an artist’s concept of Redlichia rex in their marine environment.

This species was not only large by trilobite standards but also had legs with spines used to crush their prey, which is why the researchers decided to name that species Redlichia rex by analogy with T. rex. Some specimens show traces of wounds that suggest that they had fights with other animals capable of breaking their exoskeletons. Perhaps even these trilobites were prey to other animals such as Anomalocaris, which could reach almost a meter in length, but it’s possible that they were cannibals and fought each other.

According to James Holmes, Redlichia rex’s size and the strong legs are the consequence of a sort of arms race that took place in the Cambrian period, when natural selection rewarded more powerful predators and prey that were able to escape their hunt.

This research offers new information on the diversification of trilobites, a very successful group of arthropods since it existed between about 520 and 250 million years ago. Redlichia rex is added to the thousands of species of trilobites already known and is interesting because it dates back to the first phase of their diversification, which occurred during what was called the Cambrian explosion, the greatest diversification of the history of life on Earth. Each new discovery about organisms of that era can provide important information on that extraordinary event that influenced the entire subsequent history with common ancestors evolving into the current big groups of organisms.