Boyer diss 2009 1046..

outlined. This includes description of any bulla-forming bones and bony bulla-butressing
septa extending from the promontorium. The description of the promontorium will be
followed by comments on the pars canalicularis of the petrosal and finally the
ectotympanic bone. Table 2.3 provides a summary of morphology exhibited/preserved
by each specimen, including other plesiadapid taxa to be discussed later.
On UALVP 46685, crushing and shifting of the skull has obliterated most of the
sutures between the petrosals and other elements (Fig. 2.2). The left petrosal is best
exposed ventromedially (Figs. 2.2, 4). The pars cochlearis is visible as a fairly smooth,
bulging piece of bone. It is marked by two major sets of grooves. One emerges from the
posterolateral aspect, crosses the promontorium and disappears at the anteromedial aspect
of the element. A groove with this particular course is recognizeable in most plesiadapid
specimens (see below). It is termed the “g3” groove in further descriptions and
discussions (Table 2.3; Fig. 2.4: g3). More specifically, this groove (1) stems from the
area that is anterolateral to the oval window, (2) is often connected to the other set of
grooves (termed “g4” here - see below) visible in this specimen and (3) leads towards a
consistently present septum termed “s2” here (see below). Admittedly, to where this
groove leads and how it terminates are unknown because this part of the course is not
preserved in any plesiadapid specimen.
The other groove marks the medial side of the promontorium and has a
ventrolateral course that brings it into close proximity with the posterolateral beginning
of g3, although they do not visibly meet in this particular specimen. Many other
plesiadapid specimens also frequently display sets of grooves with a course similar to that
just described and are referred to as “g4” grooves from here on out (Fig. 2.4: g4). In
41