The science of the Weymouth Bay pliosaur.
The announcement of the discovery of this spectacular specimen created a media frenzy in October of 2009 and was followed by another significant media event when the prepared skull was put on display and formally unveiled by Sir David Attenborough in June 2011.
In many ways, this is when the hard work of the scientific investigation began
A problem which occurs far too often with significant specimens like this is that a single researcher claims it as their own, and then delays publication of their analysis until they have the time to dedicate to detailed investigation. This can cause delays of many years, even decades as work pressures eat into available time. To avoid this problem, it was decided that a team of researchers would prepare a joint paper. This “dream team” consists of Roger Benson, Mark Evans, Hilary Ketchum, Judyth Sassoon, Adam Stuart Smith and myself (Richard Forrest). Most of the team were able to get to Dorchester for one or more days, in particular in April 2012. The underside of the skull, the palatal view is normally obscured by the mount and is an important source of information, so the specimen was demounted so that all aspects could be examined, drawn and photographed.
Also present on those days was a team from Bristol University, who have been working with the scans of the skull made on the University of Southampton’s recently acquired high-resolution CAT scanner by Mark Mavrogordato and Ian Sinclair.(Link). Extremely detailed work by Davide Foffa, under the supervision of Judyth Sassoon, Andrew Cuff, Emily Rayfield and Mike Benton, has revealed a complex network of vascular channels within the snout suggesting the presence of a sensory system. Finite Element Analysis, an engineering tool which allows the stresses within complex shapes to be analysed, has been applied to the skull and demonstrates an enormously powerful bite force. A preliminary account of this work was presented by Davide at the SVPCA conference in Oxford in 2012. (Link)
Having a specimen of such high quality can give considerable insight into other, less well-preserved specimens. It can help to resolve confusion about the identity of bones where they are crushed or distorted elsewhere, and provide information on missing elements. The study of the skull has taken about a year to complete, as most of us are juggling the pressures of work with time set aside for research. Roger took the lead in writing the paper and by his ability to write the description quickly and accurately drove the process forward, to some extent dragging the rest of the team along with him! The paper was published on PLOS1, an open-access journal, on 31st May 2013. Link
The conclusion reached by the team is that the Weymouth Bay pliosaur is significantly different from other known specimens, and is therefore a previously unknown species. However, it is similar to other specimens identified with the next taxonomic rank as genus Pliosaurus. It has been named at the request of the finder, Kevan Sheehan as Pliosaurus kevani – in tribute to the underestimated and undervalued Kevans of this world. Insights gained from studying this specimen also led to the naming of two other new species, Pliosaurus carpenteri and Pliosaurus westburyensi, the former named after its finder Simon Carpenter, the latter after the town of Westbury near which it was found.
It may seem a fairly mundane matter to name a new species – after all, a name is just a label, which makes the process look more like stamp collecting than hard science – but it is something fundamental to the science of biology. Naming a species requires a detailed description from a painstaking and systematic study of the specimen itself, and a comparison to other known species. In the case of P.kevani we went over the skull millimetre by millimetre, measuring and recording every tiny detail and combining those data to write the full description. Unless we can identify species, we cannot investigate issues such as the interaction of ecological systems, extinctions and extinction rates, the impact of new organisms into an area or many other aspects of biological systems. Taxonomy, the scientific identification of species, is the nuts and bolts of biology.
Research into pliosaurs has become a very active field over the past few years. In addition to the Weymouth Bay pliosaur, finds of very large specimens have been made in a number of localities all over the world such as the Svalbard Archipelago, Mexico and Australia. The Svalbard pliosaurs, publicised as “Predator X”, were formally published in 2012 as Pliosaurus funkei. (Link) An interesting picture which has emerged from this recent research is that these very large pliosaurs were closely related, and the only top predators in the late Jurassic seas. In addition to Pliosaurus kevani and P.funkei, we have P.carpenteri, P.westburyensis, P. brachydeirus, P. macromerus and P. rossicus. This may be because top predators form a small proportion of the total number of organisms in a system and our data does not give a full picture of diversity, but if valid is an unusual situation. It seems that for a few million years, a single genus dominated the marine ecosystem and wiped out all competitors.
The most dramatic aspect of these predators is their sheer size. The Weymouth Bay pliosaur is one of those specimens which impresses even if you are not particularly interested in fossils, and even more if you have a detailed knowledge. Other specimens on public display, such as those in Bristol Museum and Art Gallery, are also very impressive if rather smaller. P.funkei is about the same size as P.kevani. Unfortunately, much of the material of funkei is badly shattered by the permafrost from which it was excavated making comparison difficult.
The FEA analysis showed also that the bite of P.kevani was enormously powerful. It estimates biting force towards the back of the jaw of around 40 tons. It was almost certainly greater than this: a recently published paper comparing computer models of bite forces with measured forces in lizards showed that the methodology used underestimates the force by 20%. In addition, the analysis was not carried out on the more recent reconstructions of the skull which increase the depth at the back and therefore increase the power of the bite by increasing the size of the muscles. Taking this into account, it can be reasonably argued that a force of over 50 tons is realistic. To put this into perspective, the ‘jaws of life’ – the device used by emergency services to cut to roofs off cars in a couple of minutes – exert a force of 50 to 150 tons depending on the model.
If there was no competition, why did they become so huge and powerful? We know that they preyed on smaller marine reptiles such as ichthyosaurs and long-necked plesiosaurs because we find their bite marks on the bones. However, smaller pliosaurs such a Liopleurodon were effective predators on equally large prey a few million years previously and being bigger doesn’t necessarily make you more effective. A possible explanation comes from the evidence for injury on the pliosaurs themselves. P.kevani has marks on the right side of the skull which look like bite marks from a very large predator. The tip of the upper jaw of P.westburyensis, on display in Bristol, has been bitten off and healed. Other pliosaur specimens show extensive evidence for injury, including healed wounds. The most likely explanation is that these injuries were caused by other large pliosaurs. Evolution is usually driven by competition between species, but in this case it seems that evolution was driven by competition within species.
There is still a lot to be learned from the Weymouth Bay pliosaur. So far, we have done some of the basis science, but there in doing so have opened up new potential areas of research. The taphonomic study, the investigation what happened to the animal between the time when it died and sank to the sea floor and when Kevan started to find huge chunks of bone on the sea shore still needs to be done. The initial findings beg a whole set of questions. Why were these animals so big? How did they hunt? What did they hunt? How did they fit into the ecosystems of their time? Why were they driven to extinction?
So watch this space: this is only the beginning of a long journey.