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Re: Spinosaurus



In a message dated 96-11-26 13:42:26 EST,
T.Williams@cclru.randwick.unsw.edu.au (Tim Williams) writes:

<< But the spiny ridge of _Spinosaurus_ is so HUGE.  (The spines of
 _Becklespinax_ are not too far behind.) >>

There are quite a few differences between _Spinosaurus_ and _Becklespinax_ in
the structure of the dorsal vertebrae. I studed the type specimens some time
ago (in the case of _Spinosaurus_, this simply meant reviewing the published
papers). In _Spinosaurus_ many of the dorsal vertebrae--particularly toward
the front end of the animal (cranial dorsals)--articulate like ball and
socket joints (opisthocoely), indicating a certain amount of mobility: the
dinosaur was probably able to arch its back to some degree, spreading the
elongate neural spines something like the ribs of a fan. This is consistent
with the neural spines supporting a web of skin that would open up (for
display, thermoregulation, whatever) as needed, but is not consistent with
the neural spines being imbedded in a huge mass of flesh. A few of the spines
seem to show injury or abnormalities that suggest intraspecific combat.

Unfortunately, there are no known cranial dorsals for _Becklespinax_, so we
cannot say whether the spine was particularly flexible there, but the three
caudal dorsals that are preserved are firmly locked together in three places
per vertebra and thus quite immobile. Furthermore, the neural spines are
textured and rough, especially at their tops, which does suggest imbedding in
muscular flesh. So it's likely that _Becklespinax_ sported a ridgeback,
whereas _Spinosaurus_ had some kind of sail.