The Serrialis Bone, Interparietals, “X” Elements, Entotympanics, and the Composition of the Notoungulate Caudal Cranium

Supplemental Material for 'Exceptional skull of Huayqueriana (Mammalia, Litopterna, Macraucheniidae) from the late Miocene of Argentina : anatomy, systematics, and paleobiological implications. (Bulletin of the American Museum of Natural History, no. 404)'

“…antiquua, and M. patachonica MACN-PV 2. As in other SANUs (MacPhee, 2014), the posttemporal canal, a primitive feature that transmits the arteria diploëtica magna in a diverse array of mammals (Wible, 1987), is confluent with the transverse sinus, which is mostly enclosed by bone and very large in Huayqueriana (figs. 11, 17A).…”

“…Anatomical terminology generally conforms to, or is adapted from, nomina recognized in Terminologia Anatomica (e.g., Schaller, 1992); for more specialized terms, we utilized MacPhee (1981MacPhee ( , 2014 for the caudal cranium, Soria (2001) for the dentition, and Macrini et al (2007aMacrini et al ( , 2007b for the cerebral endocast. The description of the inner ear assumes that the lateral semicircular canal is oriented horizontally and centrally within the surrounding array of anatomical structures (Graf and Klam, 2006;Ekdale, 2013).…”

“…In all probability the canal transmitted both an artery and a vein. It may be briefly noted that, although the posttemporal canal is located much more laterally and ventrally in macraucheniines than in notoungulates (MacPhee, 2014), in the latter group it has the same relationship with the petrosal and occipital, and connects with the transverse sinus in the same way. Thus, we see no reason to question the homology of these openings in the different SANU orders.…”

“…Although a separate opening for the internal carotid was not identifiable, the vessel may well have been present judging from comparative data on a variety of SANUs (Billet and Muizon, 2013;MacPhee, 2014; but for conditions in extant perissodactyls see Du Boulay, 1991). If present in the adult stage, it presumably passed into the endocranium through the piriform fenestra.…”

“…If present in the adult stage, it presumably passed into the endocranium through the piriform fenestra. However, no specific osteological features could be identified in CT scans that might support such an inference (MacPhee, 2014;Billet et al, 2015; see also Petrosal), although it is important to note that a certain amount of bone was lost during preparation in the relevant region.…”