Prehistoric Tank: Aegirocassis benmoulae Edition

by Ariana McCumber

In homage to the classic Jurassic Park movies and the recent theater debut of Jurassic World, I’d like to introduce the first piece of an article series called Prehistoric Tank. This series of articles will discuss different sea creatures –extinct or still among us…  

So, let’s talk about the newest creature that should be added to the Jurassic Park Aquarium (if there was one): The human-sized (possibly larger) docile, lobster-like creature would swim freely while filtering water and dinner (probably plankton) through its’ net-like mouth. Like a school of fish, people would swarm to the entrance to get a glimpse of Jurassic Park’s latest clone– Aegirocassis benmoulae.



The Discovery and Naming

Bubbling to the surface in March 2015, the research report published in NatureAnomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps and the unearthed Aegirocassis benmoulae fossils had begun to catch attention. Located off the southeastern coast of Morocco the fossils of a new creature dubbed Aegirocassis benmoulae was discovered in 2011 by Mohamed Ben Moula, a Moroccan collector and fossil hunter (Duhaime-Ross; Geggel; “Human-sized lobster-like animal”). The second part of the creature’s name was dedicated to the discoverer (Duhaime-Ross; Shelton; “Human-sized lobster-like animal”), while the first portion can be translated to “Aegir’s Helmet” (“Aegirocassis”). “Aegir” is translated to ‘sea’ in Old Norse and is commonly known as a giant of the ocean in Norse mythology. On the other hand, “cassis” is translated to ‘helmet’ in Latin, probably chosen to mimic the elongated structure of the Aegirocassis benmoulae’s head. Scientifically speaking, Aegirocassis is the genus, or subfamily, of the extinct clade, or organisms classified based on a common ancestor, anomalocaridids; and thus identifies Aegirocassis benmoulae under the invertebrate animal group, arthropoda (; Shelton; “Human-sized lobster-like animal”). Aside from this ancient creature, there are several arthropods that are still among us including: spiders, butterflies, ants (among other insects), scorpions, and lobsters (Shelton; “Human-sized lobster-like animal”).


Bare Bones Bio

The excavation team –Peter Van Roy, Derek Briggs, and Allison Daley– were able to draw various conclusions based on the analysis of the fossils. So, here are some basics about our friend, Aegirocassis benmoulae:

*The Aegirocassis benmoulae fossil dates back to approximately 480 million years ago (Shelton; “Human-sized lobster-like animal”); thus, gaining membership as a tenant of the Palaeozoic era, or the time millions of years ago –542 to 251 million years to be exact (Worland). However, if details are your thing, Aegirocassis benmoulae was specific to the second period of the Paleozoic Era known as the Ordovician Period.

*The Aegirocassis benmoulae was a whopping 2 meters long, which is just a few inches shy of 7 feet (Shelton; “Human-sized lobster-like animal”). According to Peter Van Roy, a paleontologist at Yale University and an excavator of the new species: “It would have dwarfed anything else at the time, being twice as big as the next biggest animal — at the very least” (Duhaime-Ross). Until we uncover new fossils, Aegirocassis benmoulae is considered to be one of the largest animals around at the time of its’ existence. But even then, Aegirocassis benmoulae is considered to be one of “the biggest arthropods that ever lived” (Shelton).

*The Aegirocassis benmoulae was a filter feeder, unlike previously found anomalocaridid fossils which were primarily apex predators (Duhaime-Ross; Shelton; “Human-sized lobster-like animal”). This basically means that the Aegirocassis benmoulae filtered water through its mouth in order to obtain food. Modern filter feeders include whales and corals. The researchers believe that the ‘filter feeding’ quality of Aegirocassis benmoulae demonstrates the adaptability of arthropods to the environment, causing a shift from hunting to filter feeding (Shelton; “Human-sized lobster-like animal”).


Scientific Implications

 When the excavation team set out to unearth this mysterious creature, they ended up extracting a little more information than expected. The fossil was well preserved, 3D if you will, allowing the research team to notice a feature that may have been overlooked or unnoticed in other anomalocaridid fossils (Shelton; “Human-sized lobster-like animal”). Previous anomalocaridid fossils were thought to have only one pair of swimming flaps for each segment of the creature’s body; however, Aegirocassis benmoulae has two sets of swimming flaps corresponding to the each upper and lower segment of the creature’s body (Shelton; “Human-sized lobster-like animal”). This discovery clarified the anatomy of anomalocaridids –which had puzzled paleontologists– providing evidence for this clade to be classified among the arthropoda family (Geggel; Shelton; “Human-sized lobster-like animal”).   


Imagine…Aegirocassis benmoulae, today?

Despite the gentle nature of Aegirocassis benmoulae (Worland), it would be terrifying (at least for me) to come across one of this creature in the ocean. Thankfully, our modern day lobsters are usually half the size of our friend Aegirocassis benmoulae (“Lobster: Nephropidae”). At least that’s one this thing to worry about at the beach!


Thanks for reading! If you have any thoughts or have any suggestions for the new Prehistoric Tank series, please comment below!



“Aegirocassis.”, n.d. Web. 16 Jun. 2015. <>., LLC, 2015. Web. 15 Jun. 2015.

Duhaime-Ross, Arielle. “This giant lobster ancestor was once the biggest animal on Earth.” The Verge. Vox Media, Inc, 11 Mar. 2015. Web. 15 Jun. 2015. <>.

Geggel, Laura. “Prehistoric ‘Sea Monster’ Had More Legs Than Thought.”Livescience. Purch, 11 Mar. 2015. Web. 16 Jun. 2015. <>.

“Lobster: Nephropidae.” National Geographic. National Geographic Society, n.d. Web. 15 Jun. 2015. <>.

Shelton, Jim. “Giant sea creature hints at early arthropod evolution.” Yale News. Yale University, 11 Mar. 2015. Web. 15 Jun. 2015. <>.

“Human-sized lobster-like animal roamed ancient seas.” University of Oxford: News & Events. University of Oxford, n.d. Web. 15 Jun. 2015. <>.

Worland, Justin. “This Giant Sea Creature Was Once Earth’s Largest Animal.” Time. Time INC, 16 Mar. 2015. Web. 16 Jun. 2015. <>.


Feature Photo: Photo courtesy of Martin Cathrae on (2009). <>