Re: sauropod arm articulations

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

David Marjanovic wrote-

> At the moment I can't find the SVP meeting abstract (2002 or 2001, IIRC)
> which claims to have found a groove on sauropod ribcages into which the
> scapula fits -- in a position that is a bit more horizontal than
"normally"
> thought. Can someone help me...?

RIB ANGULATION, SCAPULAR POSITION, AND BODY PROFILES IN SAUROPOD
DINOSAURS
PARRISH, J. Michael, Dept. of Biological Sciences, Northern Illinois Univ,
DeKalb, IL
60115; STEVENS, Kent A., University of Oregon, Eugene OR 97403.
Ribs are one of the most ignored parts of the skeletons of fossil
vertebrates. In dinosaurs generally
and sauropods in particular, the neutral position of the dorsal ribs has a
significant
impact on calculations of body mass and of the positioning of the shoulder
girdle. Rib articulation
is reconstructed by analysis of the joint articular surfaces in sauropods,
and of the normal
neutral orientation and range of mobility of the ribs in extant archosaurs.
A rib is raked
when the distal end of the rib is posterior to the proximal head as viewed
laterally relative to
the long axis of the centrum. In dorsal view the rib may also be swept, such
that the plane containing
the rib's curvature is not perpendicular to the long axis of the centrum.
The relative
rake and sweep of the ribs of Apatosaurus and Camarasaurus are compared, and
used as the
basis for their ribcage reconstructions. A digital model of the sauropod
ribcage is animated to
examine the role of rake and sweep in the volumetric changes associated with
lung ventilation.
Aflattened area on the lateral surface of dorsal ribs 2-5 in Apatosaurus
indicates the likely
position of attachment of the scapula to the trunk. If these contours indeed
reflect the position
of the scapula to the trunk, this would favor a subhorizontal orientation of
the shoulder
girdle, with the glenoid opening almost directly ventrally. The more nearly
continuous curvature
of the ribs in Camarasaurus precludes the use of similar landmarks to
position the scapulae,
but similarities in shape and medial curvature of the scapula suggests a
shoulder girdle
orientation similar to that in Apatosaurus. A reconstruction of the
curvature of the dorsal column
along with the dimensions of the ribcage and the position of the
scapulocoracoid permits
a geometrically constrained skeleton which can then form the basis of an
estimation of body
profile and derivative volume and mass estimates.

Mickey Mortimer