Boyer diss 2009 1046..
Boyer diss 2009 1046.. Boyer diss 2009 1046..
MNHN CR 125 does not express the g2-3 grooves. However, the g4-5 grooves are present (Fig. 2.21). Plesiadapis tricuspidens MNHN CR 965 This specimen appears frustratingly incomplete on preliminary inspection, being represented by only sphenoids, palatine and parts of maxillae with teeth; however, it provides the most solid evidence available for deducing the pattern of cranial foramina in P. tricuspidens. In fact, reconstructions of cranial foraminal patterns by other authors have been based primarily on MNHN CR 965 (Russell, 1964; Kay et al., 1992). Little of the dorsal aspect of the orbitosphenoid or alisphenoid remains: only the ventral portions are intact, but this is helpful in some ways (Fig. 2.22). Cranial sutures.— For the most part the sutural patterns in the orbitotemporal region depicted by Russell (1964: fig. 19) are based on this specimen and can easily be observed: they are illustrated here with photographs for the first time (Figs. 2.23, 24: 96- 99). There are two particular sutures that were not previously discussed or illustrated by Russell (1964). The dorsal margin of the orbitosphenoid actually appears to be an intact sutural edge, and would represent the dorsal boundary with the frontal bone. This suture appears to be preserved in a consistent position in MNHN CR 125 as well (Figs. 2.23, 24A: 100). Additionally, the alisphenoid/orbitosphenoid suture is evident (Fig. 2.24: 101). It passes through, or just above, the sphenorbital fissure, such that the medial aspect of the foramen is probably formed of orbitosphenoid, while the lateral aspect is alisphenoid. On superficial inspection this boundary looks more like a crack, because it 62
is not convoluted like many other sutures; however, the contact between these particular bones frequently looks this way in various other taxa (e.g., tenrecs). Furthermore, two features (only one could be photo-documented) of this contact strongly suggest it is a suture: (1) the form of the discontinuity between the alisphenoid and orbitosphenoid is revealed by the absence (i.e., broken condition) of the orbitosphenoid in the region of interest. Instead of appearing “crack-like” and planar, the discontinuity is dished like a sutural contact (Fig. 2.24: 102). (2) Even though the discontinuity is not convoluted like other sutures, it is still more complex than would be expected for a crack created by brittle deformation. Identification of this final suture helps interpret cranial foraminal patterns. Having recognized this suture on MNHN CR 965, it becomes apparent that it has a slightly different course than that preserved on the left side of MNHN CR 125 connecting foramina 90 and 93 (Fig. 2.20D’). The latter suture would likely have resulted in the orbitosphenoid forming most of the medial wall of the sphenorbital fissure. Cranial foramina.— Foramina for the trigeminal nerve’s mandibular division (Figs. 2.22, 25: 103), for its combined maxillary and ophthalmic divisions (Figs. 2.22-25: 104), and for the optic nerve (Figs. 2.22, 24-25: 105) are clearly visible and traceable to endocranial space. There are a number of small foramina representing sinus drainage from the lateral aspects of the alisphenoid and the lateral aspect of the orbitosphenoid (Fig. 2.23, 24: 106). These cannot be mistaken for cranial nerve foramina because they are not bilaterally present in some cases or do not lead to the endocranium in other cases. This is also true for the “suboptic foramen” located posteroventral to the optic foramen (Figs. 2.22, 24: 107). It appears to lead into the trabecular space of the orbitosphenoid and probably communicates directly with the blood sinus foramina on the opposite side. 63
- Page 39 and 40: Szalay, F.S., 1972. Cranial morphol
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- Page 69 and 70: outlined. This includes description
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- Page 83 and 84: preserved (Fig. 2.15: 55). In fact,
- Page 85 and 86: the posterior septum, a deeply inci
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MNHN CR 125 does not express the g2-3 grooves. However, the g4-5 grooves are<br />
present (Fig. 2.21).<br />
Plesiadapis tricuspidens MNHN CR 965<br />
This specimen appears frustratingly incomplete on preliminary inspection, being<br />
represented by only sphenoids, palatine and parts of maxillae with teeth; however, it<br />
provides the most solid evidence available for deducing the pattern of cranial foramina in<br />
P. tricuspidens. In fact, reconstructions of cranial foraminal patterns by other authors<br />
have been based primarily on MNHN CR 965 (Russell, 1964; Kay et al., 1992). Little of<br />
the dorsal aspect of the orbitosphenoid or alisphenoid remains: only the ventral portions<br />
are intact, but this is helpful in some ways (Fig. 2.22).<br />
Cranial sutures.— For the most part the sutural patterns in the orbitotemporal<br />
region depicted by Russell (1964: fig. 19) are based on this specimen and can easily be<br />
observed: they are illustrated here with photographs for the first time (Figs. 2.23, 24: 96-<br />
99).<br />
There are two particular sutures that were not previously discussed or illustrated<br />
by Russell (1964). The dorsal margin of the orbitosphenoid actually appears to be an<br />
intact sutural edge, and would represent the dorsal boundary with the frontal bone. This<br />
suture appears to be preserved in a consistent position in MNHN CR 125 as well (Figs.<br />
2.23, 24A: 100). Additionally, the alisphenoid/orbitosphenoid suture is evident (Fig. 2.24:<br />
101). It passes through, or just above, the sphenorbital fissure, such that the medial<br />
aspect of the foramen is probably formed of orbitosphenoid, while the lateral aspect is<br />
alisphenoid. On superficial inspection this boundary looks more like a crack, because it<br />
62
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