Roedores Subterraneos

El rol de la vizcacha (Lagostomus maximus) en los procesos de formación de los sitios arqueológicos de la llanura Interserrana argentina The role of the vizcacha (Lagostomus maximus) in the formation processes of archaeological sites from the Argentinian interhill plains Resumen El movimiento de sedimentos que generan los mamíferos cavadores constituye uno de los principales procesos de formación que sufren los sitios arqueológicos de la región pampeana. En este trabajo se presentan los resultados de un estudio actualista realizado sobre una colonia de vizcachas ubicada en la localidad arqueológica El Trebolar, provincia de Buenos Aires. El objetivo principal fue describir el impacto que estos roedores generan sobre el paisaje, con el fin de identificar su accionar en los sitios arqueológicos de la región. A partir del relevamiento de 21 vizcacheras se pudo establecer que las vizcachas afectan al registro arqueológico de diferentes maneras. Por un lado, su actividad cavadora altera las secuencias estratigráficas y genera asociaciones de materiales de distinta cronología. Por otra parte, las vizcacheras son ocupadas por otros animales, dando lugar a conjuntos faunísticos con alta riqueza taxonómica. Además, estos roedores acarrean a sus madrigueras objetos disponibles localmente. Por último, un alto porcentaje de especímenes óseos presentan surcos que generan las vizcachas para mantener funcionales sus incisivos. En conclusión, las distintas evidencias presentadas permitirían reconocer el accionar de este roedor en el registro fósil, diferenciándolo de otros animales fosoriales que habitan la región pampeana.
The movement of sediments generated by digging animals/burrowing mammals is one of the main formation processes affecting the archaeological sites in the Pampas region. In this article, we present/report the results of an actualistic study conducted on a vizcacha colony, in the archaeological locality El Trebolar, province of Buenos Aires. The main objective was to describe the impact that these rodents generate on the landscape in order to identify their action on the archaeological sites of the region. The analysis of 21 vizcacheras showed that the vizcachas affect the archaeological record in different ways. Firstly, their digging activity alters stratigraphic sequences and generates associations of material of different chronology. Secondly, the vizcacheras are occupied by other animals, producing/giving rise to taxonomically rich faunal assemblages. In addition, these rodents carry locally available objects to their burrows. Finally, a high percentage of bone specimens present/shows grooves generated by vizcachas to keep their incisors functional. In conclusion, evidence would allow recognizing the action of this rodent in the fossil record, distinguishing it from other fossorial animals that inhabit the Pampas region.

ABSTRACT Burrow construction in the subterranean Ctenomys talarum (Rodentia: Ctenomyidae) primarily occurs by scratch-digging. In this study, we compared the limbs of an ontogenetic series of C. talarum to identify variation in bony elements related to fossorial habits using a morphometrical and biomechanical approach.Diameters and functional lengths of long bones were
measured and 10 functional indices were constructed. We
found that limb proportions of C. talarum undergo significant changes throughout postnatal ontogeny, and no significant differences between sexes were observed. Five of six forelimb indices and two of four hindlimb indices showed differences between ages. According to discriminant analysis, the indices that contributed most to discrimination among age groups were robustness of the humerus and ulna, relative epicondylar width, crural and brachial indices, and index of fossorial ability (IFA).
Particularly, pups could be differentiated from juveniles and adults by more robust humeri and ulnae, wider epicondyles, longer middle limb elements, and a proportionally shorter olecranon. Greater robustness indicated a possible compensation for lower bone stiffness while wider epicondyles may be associated to improved effective forces in those muscles that originate onto them, compensating the lower muscular development. The gradual increase in the IFA suggested a gradual enhancement in the scratch-digging performance due to an improvement in the mechanical advantage of forearm extensors. Middle limb indices were higher in pups than in juveniles–adults, reflecting relatively more gracile limbs in their middle segments, which is in accordance with their incipient fossorial ability. In sum, our results show that in C. talarum some scratch-digging adaptations are already present during early postnatal ontogeny, which suggests that they are prenatally shaped, and other traits develop progressively. The role of early digging behavior as a factor influencing on morphology development is discussed.

Activity patterns are a fundamental aspect of the biology of many species, with important implications for survival and reproduction. Typically, such patterns of activity are thought to be entrained by light cues, raising intriguing questions about the nature of circadian rhythms in subterranean species, members of which spend virtually their entire lives in dark, underground burrows. As part of ongoing studies of the behavioural biology of the Rio Negro tuco-tuco (Ctenomys rionegrensis), we used data from free-living animals to characterize daily patterns of activity in this subterranean species of rodent. The locations of 5 radiocollared adults were recorded hourly for 72 consecutive hours during November, 2005. Analyses of 5 measures of activity based on these data revealed that individuals changed locations more often and moved greater distances between successive radio fixes during daylight hours. These data are consistent with studies of other ctenomyid rodents in suggesting that C. rionegrensis tends toward diurnality. Comparisons with other lineages of subterranean rodents indicate that activity patterns vary markedly among these burrow-dwelling mammals, with substantial intra-as well as inter-specific differences in activity reported. RESUMEN. Patrones de actividad diaria en libertad de los tuco-tucos de Río Negro (Ctenomys rionegrensis). Los patrones de actividad son un aspecto fundamental de la biología de muchas especies, con gran impacto en su sobrevivencia y reproducción. Típicamente, se considera que los patrones de actividad, aun siendo endó-genos, se sincronizan con la luz, lo cual plantea interrogantes sobre la expresión de los ritmos circadianos en las especies subterráneas, cuyos miembros pasan virtualmente toda su vida en oscuras cuevas subterráneas. Como parte del estudio de la biología del comportamiento del tuco-tuco de Río Negro (Ctenomys rionegrensis), colectamos datos de animales en condiciones naturales para caracterizar el patrón diario de actividad en esta especie de roedor subterráneo. Se registró la localización de 5 individuos cada hora durante 72 horas consecu-tivas en noviembre 2005. El análisis de 5 medidas de actividad calculadas a partir de los datos mostró que los individuos cambian de localización más frecuentemente y se mueven mayores distancias durante el día. Esta tendencia a mayor actividad diurna es consistente con estudios realizados en otras especies de ctenómidos. Las comparaciones con otros roedores subterráneos muestran que el patrón de actividad diario es un rasgo muy variable, con importantes variaciones tanto dentro como entre especies.