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CT renderings of the bony labyrinth (and surrounding petrosal, upper images) of AMNH 53323. (A) Medial (endocranial) view. (B) Rostral view. (C) Ventrolateral view. https://doi.org/10.1371/journal.pone.0251832.g003
Source publication
Protoceratids are an extinct family of endemic North American artiodactyls. The phylogenetic position of protoceratids in relation to camelids and ruminants has been contentious for over a century. The petrosal morphology of basal (Leptotragulus) and derived (Syndyoceras) protoceratids has suggested that protoceratids are closely related to ruminan...
Contexts in source publication
Context 1
... tegmen tympani is pierced rostrally by a slit-like hiatus Fallopii (Figs 2B and 3B). The path of the greater petrosal nerve can be traced from where it enters the foramen acusticum superius with the rest of the facial nerve to where it exits though the hiatus Fallopii (Fig 3). The exact point at which the greater petrosal nerve diverges from the rest of the facial nerve cannot be located because the facial canal is incomplete. ...
Context 2
... of both the left and right bony labyrinths are preserved in AMNH-VP 53523. The left bony labyrinth is more complete and will be the basis of this description (Fig 3). The cochlear canal makes approximately 2.75 turns (rotation of 990˚), but the exact termination point of the apex cannot be identified. ...
Context 3
... utricle sits between the saccule and the anterior ampulla of the anterior semicircular canal. The anterior semicircular canal is the only semicircular canal fully preserved in the left bony labyrinth (Fig 3). The posterolateral base of the lateral semicircular canal is present, but the path of the canal cannot be traced. ...
Context 4
... identify this exit as the supraglenoid foramen based on AMNH-VP 1229. A similar foramen could not be identified on the surface of AMNH-VP 53523, but the internal canal is clearly visible in CT cross-sections ( Fig 3A). The canal appears to terminate caudally around the rostral margin of the ectotympanic, but the exact point of termination is indistinct. ...
Citations
... Norris (2000) described the basicranium of Leptotragulus and agreed with Joeckel and Stavas (1996) that protoceratids resemble ruminants. Robson et al. (2021) recently described the basicranium of Protoceras celer, a protoceratid phylogenetically intermediate between Leptotragulus and Syndyoceras ( Fig. 1). They concluded that many aspects of the basicranial morphology of protoceratids-such as a shallow subarcuate fossa and an endocranial ridge-is relatively conserved, but they identified some differences among Protoceras, Leptotragulus, and Syndyoceras (Robson et al. 2021). ...
... Robson et al. (2021) recently described the basicranium of Protoceras celer, a protoceratid phylogenetically intermediate between Leptotragulus and Syndyoceras ( Fig. 1). They concluded that many aspects of the basicranial morphology of protoceratids-such as a shallow subarcuate fossa and an endocranial ridge-is relatively conserved, but they identified some differences among Protoceras, Leptotragulus, and Syndyoceras (Robson et al. 2021). For example, Protoceras and Syndyoceras lack the rostral tympanic process of the petrosal found in Leptotragulus, but Protoceras retains a ventrally directed fenestra cochleae (Robson et al. 2021). ...
... They concluded that many aspects of the basicranial morphology of protoceratids-such as a shallow subarcuate fossa and an endocranial ridge-is relatively conserved, but they identified some differences among Protoceras, Leptotragulus, and Syndyoceras (Robson et al. 2021). For example, Protoceras and Syndyoceras lack the rostral tympanic process of the petrosal found in Leptotragulus, but Protoceras retains a ventrally directed fenestra cochleae (Robson et al. 2021). These differences suggest that Protoceras represents a transitional morphology between basal and highly derived protoceratids (Robson et al. 2021). ...
Leptoreodon is a basal member of the Protoceratidae, an extinct group of artiodactyls variably allied with the Camelidae and the Ruminantia. The basicranial morphology of other protoceratids (Leptotragulus, Protoceras, Syndyoceras) is similar to that of ruminants, supporting the hypothesis that the two clades are closely related. However, study of the basicranium of Leptoreodon major has revealed that protoceratid basicranial morphology is more variable than previously thought. Leptoreodon does share morphological features with some, if not all, other protoceratids, but the taxon also has some features not previously documented in the family. These previously undocumented features resemble the basicranial morphology of camelids rather than ruminants, suggesting that previous hypotheses of protoceratid relationships need to be reexamined.
