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
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.