Name: Microcleidus ‭(‬Small collarbone‭)‬.
Phonetic: Mi-cro-clie-dus.
Named By: Watson‭ ‬-‭ ‬1909.
Synonyms: Plesiosaurus homalospondylus,‭ ‬Plesiosaurus macropterus.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Sauropterygia,‭ ‬Plesisauria,‭ ‬Plesiosauridea.
Species: M.‭ ‬homalospondylus,‭ ‬M.‭ ‬macropterus, M. melusinae.
Diet: Piscivore.
Size: Roughly about 3 meters long.
Known locations: England.
Time period: Toarcian of the Jurassic.
Fossil representation: At least one almost complete specimen.

       With up to forty cervical vertebrae,‭ ‬Microcleidus had a proportionately longer neck than other plesiosaurs.‭ ‬This‭ ‬longer neck has in the past seen Microcleidus treated as an elasmosaurid‭ (‬the group of long necked plesiosaurs like Elasmosaurus‭)‬,‭ ‬although Microcleidus has also been considered to be a‭ ‬cryptoclidid‭ (‬the group established around Cryptoclidus).‭ ‬On top of this some researchers consider Microcleidus to actually be intermediate in form,‭ ‬and so should be placed between these two groups.
       As a living animal,‭ ‬Microcleidus would have been a more specialised hunter of fish than its shorter necked brethren.‭ ‬This would seem to be the trend taken by the piscivorous plesiosaurs as they progressed through the Jurassic,‭ ‬something that was in stark contrast to the shorter necked,‭ ‬large skulled pliosaurs like Liopleurodon that were distantly related but evolving to hunt marine reptiles like plesiosaurs.

Further reading
- A preliminary note on two new genera of upper Liassic plesiosaurs. - Memoirs and Proceedings of the Manchester Literary and Philosophical Society 54(4):1-28. - D. M. S. Watson - 1909.


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