Boyer diss 2009 1046..

Lower premolar molarization
As indicated in the description, P. cookei has a more molarized P 4 than previously
described, which is substantially more molariform than the condition seen in P.
tricuspidens (Fig. 3.13D-F). Molarization of premolars is a known correlate of
specialization for a more folivorous diet among extant taxa (Gingerich, 1976; Van Valen,
1982; Jernvall et al., 2008). In fact, a molariform P 4 is one of the features cited as
reflecting a leafy diet for Pl. daubrei (Gingerich, 1976). As noted above, the
molarization of P 4 seems likely to have initiated and progressed in the same way in the
lineages leading to P. cookei and Pl. daubrei.
Incisor simplification
Jepsen (1930) recognized that the lower incisors of P. cookei and Pl. daubrei are
similar in lacking a margoconid (Fig. 3.12). However, this is also true of P. tricuspidens.
The shared feature of “margoconid absense” by the three taxa has thus been taken as
evidence of a close relationship. Gingerich (1976) noted additional similarities between
the upper incisors of P. cookei, Pl. russelli, and Pl. daubrei. His points are reiterated
here: P. cookei is uniquely similar to Pl. russelli and Pl. daubrei, to the exclusion of P.
tricuspidens in its upper central incisor morphology. Specifically, the posteroconid is
often (but not always) very reduced in P. cookei, and the apical morphology is much
simplified compared to that of P. tricuspidens. Whereas P. tricuspidens has a large
anterocone and laterocone, and retains a distinctive mediocone and centroconule, P.
cookei has a reduced anterocone and laterocone, and lacks the mediocone and
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