To examine the evolution of burrowing specializations in the sister families Octodontidae and Ctenomyidae (Rodentia: Caviomorpha), we produced a synt

Humeral variation associated with digging ability in the subterranean rodent Ctenomys was analyzed through 6 functionally significant indexes. The hu

A quali‐quantitative morphofunctional analysis of the craniomandibular joint in subterranean rodents of the family Ctenomyidae showed that specializations of this joint are coupled with adaptations to digging. The presence of a postglenoid articular region in the skull ofEucelophorusandCtenomysimplies a new position of the mandible in digging, different from those involved in gnawing and chewing. In this third position of the mandible, the mandibular joint is stabilized when the deeply inserted incisors attack the soil or an obstacle, preventing dislocation. The proposed new mandibular function imposes a mechanical constraint on size and shape of the auditory bullae in tooth‐digger ctenomyids, because inflated bullae preclude a satisfactory opening of the mandible when it articulates in the postglenoid region. The configuration of the craniomandibular joint and other specializations for digging ofEucelophorusare unique among all South American rodents. The presence of non‐homologous, and even more specialized, postglenoid cavities in burrowing rodents of other continents suggests a common requirement for stabilizing the mandibular joint when strong forces with incisors are developed. The less specialized postglenoid region ofEucelophorusandCtenomys, with respect to that of other rodent clades, may be related to the more recent differentiation of ctenomyids.