re: Nyctosaurus pectoral girdle

[David Peters <davidrpeters@earthlink.net>]

Chris Bennett wrote:

May I respectfully suggest that if you understood the differences
between
Pteranodon and Nyctosaurus, then you would not be perplexed by my
statement.

The word articulation refers to a joint between two bones.  Joints may
be of
three basic types:  1) synovial joints with each bone bearing an
articular
cartilage, which move on one another within a synovial sac; 2) cartilage

joints, in which the bones are connected by a single cartilage, as in
the
costal cartilages between the ribs and sternum in humans; and 3) fibrous

joints, in which the two bones are joined by fibrous connective tissues,
as
in the distal tibiofibular joint in humans.  In Nyctosaurus there is no
evidence of any sort of joint between the scapula and notarium, hence my

statement: "the scapula did not articulate with the notarium."

Chris


>>>>

:  )

Why the long-winded lesson in bone joints before getting to the answer?

Here's my long-winded point:

In pterosaur ancestors, the disc-like scapulae don't even ride half way
up the ribs.

In Longisquama and early pteros the strap-shaped scapulae run roughly
parallel to the spine, perhaps a scapula width away.

In certain pteros the scapulae shorten and reorient themselves like a V
as seen dorsally. Even in Pterodactylus kochi one can see the scapulae
touching the neural spines.

In Nyctosaurus the proximal scapulae touch the neural spines. I don't
think we know enough about pterosaur soft tissue to determine what sort
of synovial sac might have developed in that area, if any. In my opinion
it might have been similar to the sliding joint between sternum and
coracoid in lepidosaurs. Certainly the bone in Nyctosaurus would not be
allowed to rub on bone without an intervening agent.

Help me think of an example of two moving bones touching without a joint
between them.

Sure there is no ball and socket connection, as in Pteranodon, and other
giant pterosaurs. That doesn't mean there is no articulation in the soft
tissue. It's just different.

David Peters
St. Louis