The orbitotemporal region and the mandibular joint in the skull of shrews (Soricidae, Mammalia)

Abstract

Modern phylogenetics place the Soricidae (shrews) into the order Lipotyphla, which belongs to the relatively new superorder clade Laurasiatheria. Their most derived skull feature is the unusual position and shape of the jaw articulation: Whereas in all other mammals the glenoid region of the squamosum is more or less tightly attached to the otic capsule or petrosal, respectively, in the soricids it is attached to the nasal capsule. This new position of the jaw articulation becomes possible by the posterior extension of the nasal capsule and the rostral shift of the glenoid fossa. By the study of dated postnatal ontogenetic stages of Crocidura russula and Sorex araneus, we show that the glenoid part of the squamosal becomes fixed to the nasal capsule by the ossified alae orbitalis and temporalis. The ala orbitalis is displaced laterally by the expanded cupula nasi posterior; this posterior expansion is well documented by the lamina terminalis, which incorporates parts of the palatinum and alisphenoid. Both alae consist largely of ‘Zuwachsknochen’ (‘appositional bone’) and are then named orbitosphenoid and alisphenoid. By the forward move of the pars glenoidea and of the alisphenoid, the foramen lacerum medium (‘fenestra piriformis’) also expands rostrally. Functionally, the forward shift of the jaw joint helps to keep the incisal biting force high. Biomechanically the jaws can be considered as a tweezer, and the rostral position of the jaw joints makes the interorbital pillar and the shell-like walls of the facial skull a lever for the highly specialized incisal dentition.

A Cybertaxonomic Revision of the “Crocidura pergrisea” Species Complex with a Special Focus on Endemic Rocky Shrews: Crocidura armenica and Crocidura arispa (Soricidae)

“…The dental nomenclature follows that of Reumer [ 61 ], Dannelid [ 62 ], and Lopatin [ 63 ]. Cranial terms follow those of Wible [ 64 ] and Maier et al [ 65 ]. The endodontic nomenclature of the upper teeth follows that of Voyta et al [ 66 ]; the endodontic nomenclature of the lower teeth is provided here for the first time.…”

“…Key: An/an, upper/lower antemolars (unicuspid teeth); cond. facet, upper and lower facets of the mandibular condyle; cnp, cupula nasi posterior (by [ 65 ]); cp, cribriform plate of the ethmoid; ett1, ethmoturbinal 1; I1/i1, first upper/lower incisor; Mn/mn, upper/lower molars; P4/p4, fourth upper/lower premolar; pd, palatum durum (hard palate); pr., process; sn, septum nasi (nasal septum). …”

Evolution of the temporal skull openings in land vertebrates: A hypothetical framework on the basis of biomechanics

“…This is particularly relevant in mammals, which show a tube-like cranium that distributes bite forces very different (Preuschoft & Witzel, 2002) from what we explained for most other amniotes before. As a side note: This tubeshaped condition is developed in its extreme in soricid skulls, which even lost their jugal arches (Maier et al, 2022). Despite that extreme example, the howsoever still persisting jugal arch in most mammals could evolutionarily be explained by plesiomorphic shaking behavior invoking the formation of a supporting jugal arch (cf.…”