Plesiosaur Day, 18 November 2004 - Some notes on the meeting
Some unanswered questions and potential areas for research.
Plesiosaur ancestry
There is 30 million year ghost lineage before the first plesiosaurs are recorded in the Rhaetian of Southern Britain.
Comment from Colin McHenry: There's an extensive series of Mesozoic marine sediments, all the way from Saudi Arabia, through Iraq and Iran, and into Afganistan. Tony Thulborn and Tom Rich looked at the Saudi Arabian stuff back in the 70's - early Upper Triassic - they stopped at 6 places on a four day drive an found stuff in every location. Lots of 'nothosaur indet' stuff. It's crying out for some decent work..
European Cretaceous plesiosaurs
Fragmentary plesiosaur specimens are held in museum collections such as the Booth Museum, Brighton, the Natural History Museum, the Yorkshire Museum, Dorking Museum and others. Apart from Andrews (1922) account of Leptocleidus superstes no papers have been published on this material since the 19th century and although fragmentary, these specimens may help clarify the taxonomic relationships.
Kimmeridge Clay plesiosaurs
Although the Callovian Oxford Clay contains perhaps the best known of all plesiosaur faunas, that of the slightly more recent Kimmeridge Clay is sparsely studied. Specimens from this formation have been assigned to Callovian taxa, but usually on the basis of fragmentary material and inadequate taxonomic analysis. Inspection of collections both in public and private hands suggests that the diversity of this fauna was greater than that of the Oxford Clay.
Leslie Noè is working on the clarification of the taxonomic and nomenclatural issues for the pliosaurs from this fauna (Noè, Smith & Walton 2004).
The status of genus Kimmerosaurus (Brown 1981), needs to be resolved. It has been suggested (Brown, Milner & Taylor, 1986) that it is synonymous with Colymbosaurus, and this suggestion is supported by Adam Smith's cladistic analysis (above).
Lower Cretaceous plesiosaurs
Brancasaurus brancai (Wegener 1914) is of uncertain phylogenetic status, and much in need of detailed revision. Little material from the Lower Cretaceous has been described, though it is known from the marine Aptian/Albian in Colombia and other parts of South America, Madagascar and the marine Albian in Alberta and Montana . Pat Druckenmiller is working on the north American material.
General
Comment from Colin McHenry: Can we cook up a standard methodology of anatomical description? An anatomical model for the Plesiosauria doesn't exist. We need a model that we can use as a reference point for descriptions, including anatomical nomenclature. We don't have one. You say pectoral, I say prothoracic. After nearly 200 years, the anatomical nomenclature of plesiosaurs is just about as messy as the taxonomy. It needs standardising.
Taxonomy
The degree of homoplasy we find in the cladistic analyses is so high that we need to think very carefully about what they are telling us. An understanding of biomechanics in plesiosaurs is needed to resolve some taxonomic issued. There is also the need for development of a more robust character set including better post-cranial characters, and a better understanding of ontogenetic variation.
Behaviour
Comment from Mike Everhart: What were they eating? Let's pay special attention to stomach contents and a possible change in habits from the Jurassic through the Cretaceous.
Gastroliths
Comment from Mike Everhart An old, yet unanswered question: What was the role of gastroliths? Do they occur regularly in any group besides elasmosaurs? What is their earliest occurrence? What can we say regarding the range / mobility of elasmosaurs from the probable source of their gastroliths versus where their remains are found? (Elasmosaurs found in western Kansas are several hundred kilometers from the nearest sources of such stones)
Comment from Mike Taylor: And someone might want to point out that nobody has quite successfully (in my view) refuted my argument of gastroliths used in ballast (whether for trimming or overall buoyancy or for enabling an increased lung volume is perhaps debatable). A related problem seems to be that that some- but not all! - people confuse weight in air (in which gastros make a relatively small contribution) with weight in water (where they make a very large contribution as most of the animal is effectively the density of water and so weightless).
Having said that, Don Henderson's buoyancy-sceptical croc buoyancy paper (Canadian Journal of Zoology 2004) is very interesting and must be taken seriously, although he focuses on what to me is the limiting condition of surface swimming, and vice versa. I'd also draw attention to Oliver Wings's papers and website, and Mike Everhart's Oceans of Kansas site. And Mike's point about the distribution of gastroliths in plesiosaurs is also crucial, if it helps point to fundamentally different lifestyles for the subgroups. More widely than gastroliths: given the convergence in lifestyle in other groups (e.g. penguin/otariid), can we not expect convergence and parallelism within plesiosaurs - which also ties in with what others here are saying?