Observations on the Burrowing Rodent Spalax in Iraq

Abstract

In many parts of Eurasia and extending into northeastern Africa, Spalax (the single living genus of the muroid family Spalacidae) is the commonest burrowing rodent. Unlike most fossorial mammals, its feet are not the primary dirt-dislodging tools; instead, Spalax uses the incisor teeth almost entirely for loosening soil. In correlation with this use of the teeth in burrowing, the jaw articulation has become particularly specialized, the typical antero-posterior sliding arrangement of the rodent condyle in the glenoid fossa being greatly accentuated. The lower jaw can be pulled further posteriorly than in other rodents; a special flange of the squamous portion of the temporal has been evolved to check this backward movement and the external auditory meatus has become displaced somewhat posteriorly, also. Vinogradov (1927) has discussed this masticatory situation in Spalax in somewhat greater detail, but I find his description of the presence of a secondary, or false, mandibular fossa, indented in part into the typmanic bulla, to be misleading. I also find his drawing to be misleading in the implication that something new is formed. Actually, the whole arrangement seems merely to be a further specialization of the already specialized rodent jaw mechanism; whether the bursa in Spalax does or does not involve any surface of the tympanic bulla can only be determined by dissection.