Functional morphology and palaeobiology of the Pliocene rodent Actenomys (Caviomorpha: Octodontidae): the evolution to a subterranean mode of life

FERNANDEZ, MARÍA HELENA; VASSALLO, ALDO IVÁN; ZÁRATE, MARCELO

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2000 vol. 71 p. 71 - 90

0024-4066

The Pliocenc caviomorph rodent Actenomys has long becn recognized as an early fossorial representative of the subfamily CtenomJ-inae (Octodontidae), which includes one living genus, C´tenomys (tuco-tucos), and several species widely distributed in South America. To assess the degree of specialization for digging in Artenomys, we performed morphological comparisons with other octodontid genera (Octodon, Spa/acopus, and Ctenomts) of known mode of life and behaiiour. As a whole, our results indicate that, in terms of morphological specializations for digging, Bctenomys occupies an intermediate position between Octodon, a generalized semi- fossorial rodent which forages above ground, and Ctenomy.c-Spalucopu.c, two highly spccialized subterranean forms. The position of the deltoid process (humerus) and the length of the olecranon process (ulna)-two traits which affect the out-forces exerted by sc-cral forelimb muscles-were in Actenomys intermediate between non-subterranean and subterranean taxa. The skull, particularly the rostrum, appears to be strong, and sagittal and nuchal crests are well marked. The zygomatic arches are as flared as those of the generalized Octodon. Notably, the upper and lower incisors of Actenomys were extremely procumbent, as in many highly specialized chisel-tooth digging species. Based upon thc stratigraphic and sedimentological analysis of the palaeosoils containing its fossil remains, we suggest that Actenomys lived in an environment of moderate to hig primary productivity. The texture of the palaeosoils indicate that theywere hard and highly cohesive. This situation, which contrasts with that observed in living Ctenomyinae, has relevant implications for burrowing cost. The integration of morphological and palaeoenvironmental data allowed testing of hypotheses about the palaeobiological attributes of this ancestral ctenomyine.