Morphometrics and functional morphology of middle ears of extant pocket gophers (Rodentia: Geomyidae)

Abstract

The 11 species of pocket gophers (Geomys bursarius, G. personatus, G. pinetis G. texensis, Thomomys bottae, T. bulbivorus, T. talpoides, Pappogeomys bulleri, P. castanops, Cratogeomys tylorhinus, Orthogeomys heterodus) that we examined exhibit a distinctive suite of auditory characters: otic capsule of thick trabecular bone, a bone-encased stapedial artery having a very narrow lumen (except in P. bulleri), absence of the stapedius muscle, and most notably a stapes with a highly convex hollow footplate that protrudes into the vestibule of the inner ear. Qualitatively, all species of pocket gophers that we examined were similar. Quantitatively, there was little intraspecific variation in meristic features with regard to sex, but ontogenetic variation was significant with most features increasing in size with increasing skull dimensions. Interspecifically, measured auditory features scaled positively with condylobasal length. For most functional auditory features (e.g., areal ratios, lever-arm ratios), intraspecific (sex or age) and interspecific variations were insignificant. The peculiar morphology of geomyid ears might serve a protective function in the noisy subterranean setting. Alternatively, novel features of the geomyid ear simply might be the result of heterochrony.