Boyer diss 2009 1046..

is that the internal carotid plexus had the same course as in other plesiadapids in which
the groove is visible. Variance in other structures such as the g3 groove, may actually
reflect real variability in soft anatomy, because it is interpreted to represent a vein.
Generally speaking the observation of tympanic cavity morphological variability is
important because it demonstrates that intraspecific variation must be carefully
considered when interpreting detailed aspects of cranial morphology, just as it must when
interpreting postcranial and dental characters.
Absence of the foramen rotundum in Plesiadapis tricuspidens
New observations of the specimens of interest show that Russell’s (1964) “t.d.a.”
is clearly formed within the orbitosphenoid on MNHN CR 125 (Fig. 20B’,20D’: 91). On
MNHN CR 965 it appears to have been present only on the left side, and, as for MNHN
CR 125, contained within the orbitosphenoid (Fig. 2.24C shows a ridge of the alisphenoid
positioned where the posterior rim of the foramen should be, but this appears to be an
artifact of breakage). Furthermore, in MNHN CR 965 it seems clear that this foramen
simply did not connect to the endocranium through any sort of canal (Figs. 2.23, 25).
What Russell (1964) identified as the foramen rotundum (“t.r.”) appears to be formed at
the boundary between the alisphenoid and orbitosphenoid, instead of within the
alisphenoid. This interpretation is based on observation of an apparent suture that spans
from this foramen (Fig. 2.20B’, 20D’: 90) to a tiny foramen located ventral to the
suboptic foramen (Fig. 2.20B’, 20D’: 93) in MNHN CR 125. The question of why
foramen 93 is not a candidate for a superior orbital fissure (t.d.a.) could be posed. I
would argue that it is not the superior orbital fissure because (1) it is so miniscule and (2)
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