Boyer diss 2009 1046..
Boyer diss 2009 1046.. Boyer diss 2009 1046..
Thus, despite the presence of suture-like morphologies on the medial tympanic process of plesiadapid specimens described here, there is still no solid morphological evidence for an entotympanic or ectotympanic bulla. There are, however, some surprisingly detailed similarities in bullar wall construction among existing plesiadapid specimens and some euprimates. In this context it is worth considering the morphology of various paromomyid plesiadapiforms, in which evidence for a suture (squamous) between promontorium and bulla is generally accepted (Bloch and Silcox, 2001). This suture is quite unique in that the hypothesized entotympanic has an edge that inserts dorsal to the medial tympanic process of the petrosal, opposite of the condition in treeshrews and rodents (as well as carnivorans [e.g., Vander Klaauw, 1931], pholidotans [Gaudin, 1999], and macroscelideans [Novacek, 1977; MacPhee, 1981]) (Fig. 2.38A-B’). Interestingly, there are several features of the paromomyid “medial tympanic process” which would seem to indicate that even the medial tympanic process is not petrosally-derived. Specifically, there are a series of distinct, ventrally raised ridges on the medial process, which continue laterally onto the promontorium and then stop abruptly along an anteroposteriorly running boundary (Fig. 2.38C-F:bs). This boundary appears to be a sutural edge: lateral to it, the ridges are nonexistent and the promontorium is smooth. Second, the dorsal surface of the promontorium seems to show the other side of this same suture (Fig. 2.38B: bs?). Finally, an HRxCT scan (8 m resolution) of a juvenile individual of the paromomyid Acidomomys hebeticus (UM 108207) reveals that the bone forming the cochlea is distinct in its density and porosity from the bone forming the medial tympanic process as well as other contiguous regions (Fig. 2.39). The hazy boundary between bone forming the promontorium itself and its medial tympanic process 74
seen on the HRxCT scan is expressed as a distinctly visible discontinuiiy on the medial aspect of the promontorium under a light microscope. However, the HRxCT image also shows that bones on either side of the apparent dorsal expression of this suture (bs?) are two separate processes of the same bone. DISCUSSION Presence and position of a posterior carotid foramen and canal The evidence for an internal carotid plexus going through the middle ear has recently been considered limited (MacPhee et al., 1983; Bloch and Silcox, 2001, 2006). However, as shown in descriptions above, all specimens but one, that are preserved well enough, show a posterior carotid foramen, and/or the remnants of its canal on the posterior septum. In all of these specimens the posterior carotid foramen and/or the remnants of its canal show it to have had a posterolateral entrance into the tympanic cavity. This differs from the interpretation used by some recent authors (e.g., MacPhee et al., 1983; Silcox, 2001; Bloch and Silcox, 2006). On the other hand this finding agrees with Wible (1993), who considered both plesiadapids and paromomyids to exhibit a “posterolateral” entrance. The morphology of Nannodectes gidleyi AMNH 17388 is clearly different from that of other plesiadapid taxa preserving this region, in that the internal carotid plexus route, although still adjacent to the stylomastoid foramen, was not intratympanic. It seems likely that this difference is the result of a more dorsal location of the internal carotid plexus route. Even if this is incorrect, the earlier occurring more basal N. intermedius (Gingerich, 1976) has morphology like that of other plesiadapiforms 75
- Page 51 and 52: 9c, Gingerich (1976) labeled a groo
- Page 53 and 54: portion of the bulla medial to the
- Page 55 and 56: Bloch and Silcox (2006) described t
- Page 57 and 58: MATERIALS AND METHODS Material exam
- Page 59 and 60: whitening, dark and light areas on
- Page 61 and 62: SYSTEMATIC PALEONTOLOGY Class MAMMA
- Page 63 and 64: efore meeting a large, anteroposter
- Page 65 and 66: The canine is a simple, single-root
- Page 67 and 68: existence and/or nature of contacts
- Page 69 and 70: outlined. This includes description
- Page 71 and 72: eneath it while also extending post
- Page 73 and 74: y a pair of parallel grooves (Fig.
- Page 75 and 76: the skull (Fig. 2.1). The length of
- Page 77 and 78: margin clearly had a posteriorly pr
- Page 79 and 80: groove measures about 0.29 mm in di
- Page 81 and 82: 2.13: 50). The suture with the supr
- Page 83 and 84: preserved (Fig. 2.15: 55). In fact,
- Page 85 and 86: the posterior septum, a deeply inci
- Page 87 and 88: Plesiadapis tricuspidens MNHN CR 12
- Page 89 and 90: is roughly 2.8 mm long. Medial to t
- Page 91 and 92: is not convoluted like many other s
- Page 93 and 94: 110) and the only squamosal/alisphe
- Page 95 and 96: two regions for the internal jugula
- Page 97 and 98: ventral to the sinuous suture (132)
- Page 99 and 100: provides measurements of these and
- Page 101: of the promontorium of the Pellouin
- Page 105 and 106: primates, as well as treeshrews and
- Page 107 and 108: canaliculus are present on the sept
- Page 109 and 110: it is missing from the other side o
- Page 111 and 112: observations and interpretations ma
- Page 113 and 114: REFERENCES Beard, K.C., 1993. Phylo
- Page 115 and 116: Russell, D.E., 1959. Le crâne de P
- Page 117 and 118: TABLES Table 2.1. Numerical list of
- Page 119 and 120: 81 - Occipital/petrosal suture (Fig
- Page 121 and 122: Table 2.2. Abbreviations for crania
- Page 123 and 124: Table 2.3a. Petrosal features of pl
- Page 125 and 126: Table 2.4. List of cranial measurem
- Page 127 and 128: Shape variables (Table 2.6) ac/GM -
- Page 129 and 130: Table 2.5. continued Specimen MNHN
- Page 131 and 132: Appendix Table 2.1. Specimens scann
- Page 133 and 134: Fig. 2.39 - bs, Ptr, rtp, s1, s2 Fi
- Page 135 and 136: Figure 2.1. UALVP 46685 Pronothodec
- Page 137 and 138: Figure 2.2. UALVP 46685 Pronothodec
- Page 139 and 140: Figure 2.3. UALVP 46685 Pronothodec
- Page 141 and 142: Figure 2.4. UALVP 46685 Pronothodec
- Page 143 and 144: Figure 2.5. UALVP 46685 Pronothodec
- Page 145 and 146: Figure 2.6. UALVP 49105 Pronothodec
- Page 147 and 148: Figure 2.7. UALVP 46687 Pronothodec
- Page 149 and 150: Figure 2.8. USNM 309902 Nannodectes
- Page 151 and 152: Figure 2.9. USNM 309902 Nannodectes
Thus, despite the presence of suture-like morphologies on the medial tympanic<br />
process of plesiadapid specimens described here, there is still no solid morphological<br />
evidence for an entotympanic or ectotympanic bulla. There are, however, some<br />
surprisingly detailed similarities in bullar wall construction among existing plesiadapid<br />
specimens and some euprimates. In this context it is worth considering the morphology<br />
of various paromomyid plesiadapiforms, in which evidence for a suture (squamous)<br />
between promontorium and bulla is generally accepted (Bloch and Silcox, 2001). This<br />
suture is quite unique in that the hypothesized entotympanic has an edge that inserts<br />
dorsal to the medial tympanic process of the petrosal, opposite of the condition in<br />
treeshrews and rodents (as well as carnivorans [e.g., Vander Klaauw, 1931], pholidotans<br />
[Gaudin, 1999], and macroscelideans [Novacek, 1977; MacPhee, 1981]) (Fig. 2.38A-B’).<br />
Interestingly, there are several features of the paromomyid “medial tympanic<br />
process” which would seem to indicate that even the medial tympanic process is not<br />
petrosally-derived. Specifically, there are a series of distinct, ventrally raised ridges on<br />
the medial process, which continue laterally onto the promontorium and then stop<br />
abruptly along an anteroposteriorly running boundary (Fig. 2.38C-F:bs). This boundary<br />
appears to be a sutural edge: lateral to it, the ridges are nonexistent and the promontorium<br />
is smooth. Second, the dorsal surface of the promontorium seems to show the other side<br />
of this same suture (Fig. 2.38B: bs?). Finally, an HRxCT scan (8 m resolution) of a<br />
juvenile individual of the paromomyid Acidomomys hebeticus (UM 108207) reveals that<br />
the bone forming the cochlea is distinct in its density and porosity from the bone forming<br />
the medial tympanic process as well as other contiguous regions (Fig. 2.39). The hazy<br />
boundary between bone forming the promontorium itself and its medial tympanic process<br />
74
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