The auditory region and nasal cavity of Oligocene Nimravidae (Mammalia: Carnivora)

Abstract

ABSTRACT Highly detailed microscopic preparation of both newly discovered and previously undescribed nimravine crania from the White River Group of North America reveals hitherto unreported morphological features of the basi-cranium and auditory region, particularly the composition of the auditory bulla and form of the petrosal. The monophyly of Dinictis, Hoplophoneus, and Nimravus is supported by a remarkably uniform configuration of the auditory bulla: (1) the form and placement of the entotympanics; (2) a near-vertical ectotympanic with elaborate styliform process partially enclosing the Eustachian tube; and (3) an anterior bulla wall formed by a unique overlap of the anterior entotympanic lamina by the elongate styliform process. Although an intact auditory bulla is unknown in an Eurasian nimravine, the auditory regions of the species represented by crania (Eusmilus bidentatus and Nimravus cf. intermedius from Quercy) demonstrate a definite affinity with New World genera, affirming the Holarctic distribution of the Nimravinae. In addition to identifying basicranial similarities among nimravines, we describe the first largely intact turbinate bones within the nasal cavity of a nimravid. CT (computed tomography) scanning of nimravid rostra reveals differing configurations of the maxilloturbinate in Dinictis and Hoplophoneus, the former more derived than the latter. Compared to other Carnivora, nimravid maxilloturbinates are most similar to those of living aeluroids, which are confined to the ventral part of the anterior nasal cavity. Nimravids lack the elaborately branching (dendrolamellar) maxilloturbinates of arctoid and cynoid carnivorans.