Top 10 Open Access Fossil Taxa of 2017: Websteroprion armstrongi

We listened to your feedback from last year’s Top 10 OA Fossil Vertebrates contest, and we agreed. Non-vertebrates needed representation, too! So of the 45 nominees we included in the contest this year, 1/3rd represented various plants, algae, insects, crustaceans, etc.

And as we continue the countdown of the winners of the PLOS Paleontology Top 10 Open Access Fossil Taxa of 2017, I am pleased to feature our first representative of an invertebrate taxon. Coming in at #8 is the fossil bobbit worm Websteroprion armstrongi, from the Devonian Kwataboahegan Formation of Ontario Canada. Described by authors Mats Eriksson, Luke Parry, and Dave Rudkin and published in the Open Access journal Scientific Reports, Websteroprion represents the oldest bobbit worm (about 400 million years old), and a giant bobbit worm at that!

Now if you are unfamiliar with bobbit worms, then you are in for a terrifying treat. These unusual polychaete worms are still living today and are vicious predators, laying in wait buried in the ocean sediment, their jaws poised like a bear trap, springing to life the minute a hapless fish swims idly by, only to be sucked into the sediment, becoming a meal for an unusual creature. Just watch this video below, courtesy the Smithsonian Channel on Youtube, to see a living bobbit worm in action.

These organisms are mostly soft-bodied, with the exception of their mouthparts, known as scolerodonts. So in the fossil record, often only the scolerodonts are preserved, and they usually aren’t that big. It was the size of the scolerodonts of Websteroprion that caught the eye of the authors. Mats Eriksson, lead author on the study, described to me the discovery of the specimens in the collection of the Royal Ontario Museum (ROM):

“Luke Parry [second author and then a PhD student at the University of Bristol, UK] was doing guest research on full-body polychaete fossils at the ROM back in 2014, and Dave Rudkin [third author on this study and now-retired museum curator at the ROM] showed him the specimens. So, Luke took a quick photograph and sent it to me, knowing that I am an expert on this fossil group.”

Dr. Eriksson continues, “I was quite disappointed when I first laid eyes on the photographs. The state of preservation was far from exceptional and mainly representing negative casts, or imprints, in the rocks. At first I even concluded that it was not worthwhile pursuing since it was ‘just another’ new species without any exciting story to unveil. That is until I asked about the size! Since the original image did not come with a scale bar I had simply assumed that the specimen was of “standard” millimetre size. I did ask Luke, who said that they were in fact pretty big, and provided the scale. That is when I strongly suspected that these must be by far the largest fossil jaws ever reported in the published literature, and a hunch which subsequent research confirmed. Now, this certainly wet my wormy appetite!”

For bobbit worms, these are pretty massive, and for a polychaete worm in the Devonian, even more impressive. With the jaws wide open, they would have spanned about 2 cm across. The body, though not preserved, is estimated by the authors to be over 1 m (3 feet) in length, compared to the body proportions of extant bobbit worms. “I would not say they are necessary bigger than the jaws of extant bobbit worms,” Dr. Eriksson explains to me, “but it was surprising to find such large specimens in 400 million-year-old rocks!”

As Eriksson explains further, “Gigantism in animals is an alluring and ecologically important trait, usually associated with advantages and competitive dominance. It is, however, a poorly understood phenomenon among marine worms and has never before been demonstrated in deep time based on fossil material in this group of animals. The new species demonstrates a unique case of polychaete gigantism in the Palaeozoic, some 400 million years ago.

“Our study also shows that gigantism in jaw-bearing polychaetes was restricted to one particular evolutionary branch within the Eunicida, but has evolved many times in different species in this order of worms. However, while representing an ancient ‘Bobbit worm’ and a case of primordial eunicidan worm gigantism, the specific driving mechanism/s for W. armstrongi to reach such a size remains ambiguous.”

Would Websteroprion have been an ambush predator like its modern-day relatives? “We have little (in fact no) empirical evidence of its diet,” Dr. Eriksson explains. “As we are lacking soft parts we do not have access to preserved gut contents. And there are no coprolites found that can be directly linked to the animal. Inferring the diet of extinct worms (even jaw-bearing ones) is difficult. Especially considering that there are jaw-bearing extant forms that, despite looking like ‘fierce’ carnivorous predators, have proven to have a wide range of feeding habits. With that being said, given its size and compared to its closest modern relatives, I would assume that W. armstrongi had a similar mode of life and feeding habit as the modern bobbit worms. So, perhaps the Devonian fish and cephalopods were not safe from this critter.”

As mentioned previously, Websteroprion specimens caught the eyes of the authors in the collection of the ROM, but were actually collected over 20 years ago.

“The fossil specimens were collected over the course of a few hours in a single day in June 1994, when Derek K. Armstrong of the Ontario Geological Survey was dropped by helicopter to investigate the rocks and fossils at a remote and temporary exposure in Ontario,” Eriksson explains. “Sample materials, from what proved to belong to the Devonian so-called Kwataboahegan Formation, were brought back to the Royal Ontario Museum in Toronto, Canada, where they were stored until they caught the eyes of us authors.”

He adds, “Our study is an excellent example of the importance of looking in remote and unexplored areas for finding new exciting things, but also the importance of scrutinising museum collections for overlooked gems.”

And Websteroprion being a large and possibly terrifying creature wasn’t badass enough, it has a pretty stellar namesake as well. Lead author Mats Eriksson, in addition to being a professor at Lund University, moonlights as a Metal musician, complete with a paleo metal band Primoridal Rigor Mortis. In naming Websteroprion, Eriksson chose to honor a fellow metal musician, Alex Webster, bassist for Cannibal Corpse. And in true Metal fashion, Eriksson recently commissioned an iconic painter for Metal albums, Joe Petagno, to fashion Websteroprion in a dark and fantastical scene worthy of a album cover. The art, which can be seen here, will be part of an upcoming exhibition, Rock Fossils, which will be in Luxembourg in June 2018.

Congratulations to Websteroprion and the team that described it for making the PLOS Paleo Top 10 OA Fossil Taxa of 2017

Reference:

Eriksson ME, Parry LA, Rudkin DM (2017) Earth’s oldest ‘Bobbit worm’ – gigantism in a Devonian eunicidan polychaete. Scientific Reports 7:43061. DOI: 10.1038/srep43061