scapular facet intercoracoid facet
ntercoracoid facet
scapular facet anterior notch
glenoid contribution
intercoracoid facet
Fig. 57. Left coracoid of Ichthyosaurus communis (BMNH R1191). A) dorsal, B) ventral, C) medial, D) distal, and E) posterior
views. Scale equals 40 mm.
vertical, and the two surfaces extend parallel to one another
(Fig. 57E). Thus, when the two coracoids are articulated,
with their lateral margins elevated, the articular surface of
the glenoid is vertical. All articular surfaces are rugose. The
coracoid has a prominent emargination on its leading
edge, immediately medial to the scapular facet. There is
often a second emargination in a corresponding position
on the posterior margin of the bone.
The scapula is an elongated element with a strongly
curved, strap-like shaft that becomes flared and thickened
proximally (Fig. 58). This proximal margin is rugose throughout,
and although there is no obvious discontinuity, the
thinner and shorter anterior portion is set off at an obtuse
angle from the thicker segment. The anterior area appears
to be for articulation with the coracoid, whereas the other
appears to be entirely the scapular contribution to the
glenoid. Ophthalmosaurus has a similar scapula in that the
anterior portion of the proximal end is thinner and set off
Fig. 58. Right scapula of Ichthyosaurus communis (BMNH R1779). A) ventrolateral and B) medial views. Scale equals 50 mm.
scapula
Fig. 59. Right coracoid and scapula of Ophthalmosaurus icenicus
100 mm.
from the thickened posterior portion. However, the anterior
half of the latter thickened portion is indented, and this
excavated area articulates with the scapular facet of the
coracoid (Fig. 59). Thus articulated, the thin anterior portion
of the proximal end of the scapula has no contact with
the coracoid, helping, instead, to continue the curvature of
the anterior emargination of the coracoid. The rugosity in
(BMNH R2137), in natural articulation, dorsal view. Scale equals
this region, and the absence of a well-defined glenoid, are
indicative of an extensive covering of cartilage (Kirton,
1983). A similar situation pertains for Ichthyosaurus. The
distal end of the scapula is hollowed in Ichthyosaurus, indicating
a cartilaginous continuity, and the same is true for
Ophthalmosaurus. In large ichthyosaurs, such as T. platyo-
don (exemplified by BMNH 46563), the distal end is rugose.
Pelvic Girdle
As noted earlier, there is no sacrum, and therefore no sacral
rib, so the pelvic girdle is not attached to the vertebral
column. As a consequence of this lack of osseous connection,
the pelvic girdle, and its associated fin, commonly
undergo some degree of displacement during fossilization.
Consequently, the original orientation of the pelvic girdle
and limb are usually lost, making it difficult to distinguish
left from right and dorsal from ventral. The pelvic girdle
and limb are also less often preserved than the pectoral
ones, so they tend not to be used for taxonomic purposes.
The ilium is a gently curved rod, slightly flattened
dorsally, and inflated ventrally where it articulates with
the pubis and ischium (Fig. 60). The curvature is directed
posteriorly, such that the dorsal end lies posterior to the
ventral end. The pubis and ischium are probably always
fused proximally, as evidenced by the occurrence of isolated
associations of the pubis and ischium. Fusion often
.'{-M r
Fig. 60. Pelvic girdle of Ichthyosaurus communis (BMNH 41849),
viewed from the left side. Scale equals 50 mm.