Plesiosaur Day, 18 November 2004 - Some notes on the meeting
Mark Evans
was unable to present the talk he had planned for the meeting. Arthur Cruickshank stepped in and presented Mark's data. This included the latest work on the new Pliensbachian specimen discovered by Pete Blake and on reconstructing the skull of Muraenosaurus. The Pliensbachian animal is enigmatic, and when included in cladistic analyses not only does it appear in various places on the cladogram, but it can cause significant reordering of the structure of the tree depending on which characters are used and how they are weighted. The skull has been painstakingly reconstructed (by Mark) from numerous tiny fragments.
The newest reconstruction of the Muraenosaurus specimen shows that this animal was equipped with a fairly tall, robust skull quite unlike the shallow, gracile skull as reconstructed by Andrews (1913). A prominent ridge on the frontals may have strengthened the skull and the jugal, rather than being the large subrectangular block reconstructed by Andrews, was a small element.
Dennis Parsons
of Somerset County Museum gave an account of what might be the best plesiosaur specimen ever discovered. Found at the Bridgwater Bay National Nature Reserve (a SSSI), the museum was informed of the specimen in October 2003 by Nick Collard, a local fisherman, and a rescue excavation carried out. The fossil was exposed on the beach surface, which was being actively eroded and whole layers of shale were being lifted and removed by wave action. Time really was of the essence. Three joints running through the specimen made excavation precarious, especially given that one joint ran through the forelimbs perpendicular to the specimen's long axis, but things did go as planned and the entire specimen (together with associated ammonites and other samples) was successfully collected. It was transported to the museum where it was washed in fresh water for two weeks before being taken to the NHM and carefully dried under controlled conditions. At an early stage, it was realised that there was a shortage of both geological conservators and plesiosaur specialists. Fortunately, Dennis contacted Mark Evans and Richard Forrest, and a good working relationship soon emerged. While a lot of money is needed to prepare, conserve and display the specimen (c. £21,000), its preparation has been arranged and is due to start in January 2005.
Richard Forrest
discussed the different mechanisms plesiosaurs use to stiffen the neck, the variability seen in the shape and number of cervical vertebrae, and the different 'zones' seen in the necks of assorted taxa. There is a consensus in the community that plesiosaurs kept their necks rather stiff: they did not coil, bend or lift their necks to a great degree. Employing a few of his famous 'forrestograms', Richard reinforced his earlier work on E-type and M-type necks. M-types (the 'M' stands for Muraenosaurus and/or Mauisaurus) have zygapophyses that are raised dorsally on the neural arch relative to those of other plesiosaurs while E-types (E = elasmosaurid) have interlocking neural spines and low zygapophyses in contact with the centra.
He also introduced a specimen collected in 1906 and held at Lincoln Museum which may be a new species of Microcleidus. It includes a nearly complete neck, a partial pectoral girdle and forelimb, and dorsal vertebrae that exhibit some very unusual taphonomy. The cervical series is very well preserved and substantially complete, and shows detail of structures such as the lateral keels on the centra which may indicate patterns of muscle distribution in the neck. It shows how the centra of such long-necked taxa were very closely fitting, with hardly any room for intervertebral discs. This is not the case in rhomaleosaurs where there is room for substantial intervertebral structures.