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of the suture (AS). Landmark 9 is the midpoint along the posterior margin of the glenoid
fossa (GL). Landmark 10 is the anteriormost point of the foramen ovale (FO). Landmark
11 is the most lateral point on the presphenoid
basisphenoid suture where it intersects
the sphenopalatine vacuity in the photographic plane (SB). Landmark 12 is the most lateral
point on the basisphenoid
basioccipital suture (BO). Landmark 13 is the hypoglossal fora-
men (HG). Landmark 14 is the juncture between the paraoccipital process and mastoid
portion of the temporal bone (OC). Landmark 15 is where the premaxilla-maxilla suture
intersects the midline (PMI). Landmark 16 is the posterior palatine foramen (PF).
Several landmarks were added to these in the later study, designed to compare S. fulviventer
to M. m. domesticus (
Zelditch et al., 2003b
). These additional landmarks (see
Figure 2.10B
)
include the juncture between the incisors on the premaxillary bone (IJ), the midpoint of the
basisphenoid
basioccipital suture along the sagittal axis (BOM), the midpoint of foramen
magnum (FM), the juncture of mastoid, squamosal and bullae (MB) and the juncture
between the mastoid and the medial end of the auditory tube (AM). The landmarks of
M. m. domesticus include a subset of the original Sigmodon landmarks, plus the newly added
ones, and a point at the interior corner formed by the intersection of the zygomatic arch
with the braincase (ZA) (see
Figure 2.10C
).
Three-Dimensional Landmarks on a Marmot Skull
As stressed in the previous example, the mammalian skull is obviously not a two-dimen-
sional structure. Like many structures of interest to biologists, the marmot skull is not only
three-dimensional (
Figure 2.11A
) but also has relatively few landmarks (
Figure 2.11B
). The
marmot skull is strongly curved anteroposteriorly and mediolaterally, so features on the
same bone may be as far apart in the dorsoventral dimension as they are in the mediolateral
or anteroposterior dimensions. In addition, the skull is composed of a small number of rela-
tively large bony plates, so points that can be used as landmarks are sparsely distributed,
occurring primarily at locations where at least three bones meet.
Landmarks on a Squirrel Mandible
The landmarks on the eastern fox squirrel mandible (Sciurus niger,
Figure 2.12
) are a
general scheme for analyzing mandibular development, modularity, and evolution. The
rodent mandible has become one of the favorite model systems for studies of complex
morphologies, especially for studies of developmental and evolutionary modularity
(e.g.
Atchley and Hall, 1991; Cheverud et al., 1991; Mezey et al., 2000; Ehrich et al., 2003;
Klingenberg et al., 2003; Monteiro et al., 2005; Marquez, 2008
;
Zelditch et al., 2008, 2009
;
Monteiro and Nogueira, 2009; Willmore et al., 2009
). The attraction of this model system
lies partly in the contrast between its developmental complexity and its structural and
functional integration (
Atchley et al., 1985
;
Atchley and Hall, 1991
). How that integration
could be achieved developmentally, and how it facilitates and/or constrains mandibular
evolution are questions long motivating studies of rodent mandibles. One of the reasons
for selecting the mandible as the model system for these studies is that its development
is relatively well understood, although much remains to be explained. The mandible is
also interesting from a functional perspective because it is obviously crucial for feeding
