Myoskeletal specializations for digging in the rodent Lagostomus maximus (Caviomorpha, Chinchillidae)

MORGAN, C.C.; OLIVARES, A.I.; ALVAREZ, A.; VERZI, D.H.

La Plata

Congreso; IX Congreso de Ciencias Morfológicas; 2007

Sociedad de Ciencias Morfológicas

The plains viscacha, Lagostomus maximus, is a South American rodent which builds extensive colonial burrow systems. We evaluated digging specializations of this species through dissection of the jaw and forelimb muscles, and quali-quantitative analysis of associated skeletal characters. Functionally significant indexes were calculated and compared with those from other caviomorphs with diverse habits, and analyzed by Principal Components Analysis (PCA). The temporalis and masseter medialis infraorbitalis muscles, linked to vertical mandibular forces, were greatly developed. M. masseter lateralis showed subhorizontal fibers. M. masseter posterior was very poorly developed. Comparatively, the subterranean Ctenomys (Ctenomyidae) showed good development of the latter muscle, as well as hypertrophied m. masseter lateralis with nearly vertical fibers. Chinchilla (Chinchillidae, epigean) showed little development of these muscles. In the arm of L. maximus, m. triceps brachii was extremely well developed; in particular, its long head presented three parts with differently-oriented fibers, which suggests great force production during forearm extension. Hand flexor muscles were less developed than those of Ctenomys. PCA segregated genera from epigean to subterranean habits, and clustered Lagostomus with other fossorial genera by its mandibular and incisor width, procumbency and orbital size. Myological features associated to postcranium agreed with the distalized deltoid process, large humeral epicondyles and well developed olecranon, which set Lagostomus apart from other chinchillids and closer to Ctenomys. These results show that L. maximus has moderate myoskeletal specializations for digging in both forelimb and head; these could be associated to a dual digging strategy, mainly scratch-digging but with some use of incisors.