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his 1959 work. Figures 13-19 of Russell (1964) have been frequently relied upon as a
reference for the cranial anatomy of P. tricuspidens (Gingerich, 1976; Bloch and Silcox,
2006). Russell (1964) was the only researcher to document the sutural and foraminal
patterns in P. tricuspidens with original illustrations, although he provided no
photographs. Due to the diagramatic form of the illustrations and controversy concerning
sutural patters that followed, the lack of photographic evidence has become problematic.
In fact, none of the cranial sutures, or foramina of the orbital region, have ever been
adequately photographed. In Russell’s (1964) figures 14 and 19, the orbitotemporal
region is reconstructed as preserving a human- or tupaiid treeshrew-like pattern of
foramina for cranial nerves with separate foramina for ophthalmic (t.d.r.) and maxillary
(t.r.) branches of the trigeminal nerve. Although Russell also documented most major
sutures in his figures 14 and 19, the alisphenoid/orbitosphenoid suture and the posterior
termination of the orbitosphenoid/frontal suture were not illustrated, or discussed.
Russell (1964) changed some of the interpretations he made in his original note in 1959.
For instance, he reconsidered the stapedial artery to have been reduced relative to the
promontorial branch, or absent.
Szalay (1971) concluded that the skull of P. tricuspidens had been incorrectly
reconstructed in lateral view by Simons (1960) and Russell (1964), in which the tips of
the upper and lower incisors were shown to meet one another while the cheek teeth were
occluded. Szalay further suggested that the premaxillae did not contact the frontal and
provided a photographic dorsal view of the skull (fig. 2) showing transverse cracks (as
interpreted by other authors) in the premaxillae looking very much like symmetrical
sutures, intersecting the nasals before reaching the maxillae.
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