Historic Specimens and Plesiosaur Relationships

One of the frustrations of research not only into plesiosaurs but also many other extinct animals is that large collections were built up in the 19th century which but have very limited record of where or in which geological stratum the specimens were found. Fortunately the Lincoln specimen is recorded as coming from Fosters Brick Pit, and although it was donated to the museum in 1906 we can be confident that it came from a small area which we can date geologically. One of the blocks containing some of the bones also contains ammonites which are Pliensbachian in age - about 10 million years older than the Toarcian.

Our understanding of the relationships of plesiosaurs has been undergoing a drastic revision over recent years. Plesiosaurs occur in two forms, the short-necked, large-headed forms and the long-necked, popularly known as pliosaurs, and the small headed forms of the popular imagination. We used to think that these two distinctly different body plans were different families of plesiosaurs, and only relatively distantly related. We now think that they are morphotypes, and that similar body types evolved independently in several lineages. Some 'pliosaurs' might be more closely related to long-necked forms than other 'pliosaurs', and long necks seem to have evolved more or less independently in several distinctly different lineages.

Microcleidus is a representative of a small family of plesiosaurs which are in the early stages of developing the extreme elongation of the neck. Specimens found in England, France and Germany share a number of characters, in particular elongated neck vertebrae. The Lincoln plesiosaur is part of this early radiation and is the oldest representative of the family.