Sunday, 20 May 2012

A tail

 Within the collections on display at the Sedwick Museum, Cambridge is a specimen of a Dimorphodon macronyx tail.  This is catalogue number J.61175 and is part of the Whinborne Collection.  The fossil is from Lyme Regis in Dorset and may have been collected by Mary Anning from the Lower Lias of the Undercliff.  The tail is in a state of dissociation and may be the rotting offcast from a predators meal.
Removing the bones photographically from the matrix shows the caudal vertebrae and the stiffening rods that would have kept the tail rigid in life.  There is also some material on this slab that looks like a sternum fragment.  It is not easily defined from a photograph.  If there was a cartilage running from the sternum to the tail, this would not be an unusual association.

The only other tail of Dimorphodon macronyx is in the Natural History Museum, London.  Specimen number 41349 is a complete and rigid tail with all of the stiffening rods in their natural place close to the vertebrae.  The arrangement of rods is similar to that seen in Rhamphorhynchus.

The long tail of this type of pterosaur would have been used as a balancing organ and would most probably have had a vertical sail at the tip to give the animal directional stability when flying. The sail is only seen in some Rhamphorhynchus specimens where wing membrain is preserved.  Dimorphodon does not show this degree of preservation.

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