Boyer diss 2009 1046..

Bloch and Silcox (2006) argued that communicating suboptic foramina are not expected
in a taxon with such broad interorbital spacing; however, despite broad interorbital
spacing, the postorbital constriction of the neurocranium in Plesiadapis is extreme and
results in a sphenoid region as narrow as that of many euprimates. It thus seems unlikely
that previous interpretations of the suboptic foramen as the “t.d.a.” are correct. It is
acknowledged that there is some distortion, which prevents complete confidence in the
interpretation: the left side of the orbitosphenoid has been displaced substantially.
However, the right side is more intact and the remnants of the optic canal can be traced to
the dorsal (endocranial) aspect of the orbitosphenoid (Fig. 2.23: 108). There is no
comparable canal that could represent the ophthalmic branch of the trigeminal running
ventrolateral to this. Moreover, given the identification of the orbitosphenoid/alisphenoid
suture above, Russell’s (1964) “t.d.a.” and ophthalmic canal would have run within the
orbitosphenoid, which would be an unusual pattern for a eutherian mammal, as discussed
above.
Morphology of cranial bones.—The only previously unmentioned aspect of this
specimen is the existence of pneumatization of the alisphenoid (Figs. 2.22A, 2.23C, 2.25:
109). This is consistent with observation by MacPhee and Cartmill (1986) that the
Pellouin skull is enervated by empty “celluoles.”
Plesiadapis tricuspidens Pellouin skull
Cranial sutures.— The Pellouin skull does not add an incredible amount of new
information regarding position of cranial sutures. However, it does preserve perhaps the
best example of a remnant of the palatine/alisphenoid suture (Figs. 2.26C-C’, 2.29B-B’:
64