FIG. 8 in The Serrialis Bone, Interparietals, "X" Elements, Entotympanics, And The Composition Of The Notoungulate Caudal Cranium

FIG. 8. (Continued.) Precise positions of sutures on caudal aspect of skull notably vary among Paedotherium specimens because overgrowths (alae) from surrounding elements may develop in such a way that they produce internal or self-sutures, thereby falsely suggesting presence of separate elements (e.g., "mastoideo-posttympanic suture" between theca and petrosal in Hegetotherium mirabile AMNH-VP 9223; Sinclair [1909: 71, text-fig. 14]). In this specimen, probable position of lines of fusion among elements indicated by question marks. Externally, aperture of posttemporal canal actually lies at junction of three bone territories (petrosal, squamosal, and exoccipital), but how the aperture is framed in the adult varies. Petrosal also produces alae, which may overgrow the posttemporal dehiscence in such a way that in some specimens (as here) the aperture appears to be wholly encased by petrosal material. In pachyrukhines the paroccipital process is a broad flange that incorporates not only exoccipital material but also ectotympanic and petrosal. Size of individual contributions also varies (cf. figs. 9B, 12F, G). In AMNH-VP 45914, both ectotympanic and petrosal appear on lateral side. As usual there is no sutural or other identifiable boundary between supraoccipital and exoccipital. Key to D: 1, supraoccipito-thecal suture; 2, parieto-thecal suture (along squamosal bar); asterisk,?lateral interparietal (see text).