Boyer diss 2009 1046..

process appears as solid bone. Admittedly, the resolution of the scan may simply be too
coarse to allow visualization of such a suture. Even if there is no evidence of such a
feature at any resolution, the foramina could still represent a suture that is almost
completely fused through internal remodeling. For instance, the tympanic canaliculus
foramen is among the many other tiny foramina that form this boundary. If the entrance
point for these nerves corresponds to the boundary between bulla-forming bone and a
separate petrosal, then the morphological pattern would be extremely similar to that of
the extant rodents Marmota (Fig. 2.34) and especially Lagostomus (Figs. 2.35, 36).
However, these nerves are perfectly capable of obtaining access to the intratympanic
cavity via “intrapetrous” canals, as discussed by MacPhee (1981) for Microcebus, and in
specimens of Eulemur (SBU efr-3562: pers. observ.). Given observations on Indri and
paromomyid plesiadapiforms (Figs. 2.37-39), the line of foramina cannot be regarded as
evidence of a non-petrosal bulla even if it is a suture or boundary between different bony
laminae. It is perhaps also relevant to note that UM 87990 was apparently
ontogenetically younger than other specimens whose skulls were discussed in Chapter 2
(as reflected by its pristine teeth), and is the only one to exhibit this line of foramina.
Consideration of the ectoympanic bulla of rodents such as Marmota and
Lagostomus raises the question of the medial extent of ectotympanic-derived bone in P.
cookei. No visible suture exists anywhere on the bulla or external auditory meatus
delimiting the boundary between ectotympanic from bulla-forming bone. Nor is such
morphology convincingly well preserved in other plesiadapids or plesiadapiforms (see
Chapter 2).
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