Micromammals (Mammal: Rodentia) from Pilauco: Identification and Environmental Considerations

Abstract

Rodents are small-sized animals that form one of the most extensive groups of mammals. They share highly specialized masticatory organs and very unique molar shapes allowing some species to be identified based on a single tooth. Additionally, rodents share some biological characteristics with other groups of small mammals (micromammals) making them particularly informative species in terms of their chronological occurrence and environmental conditions, which explains their extensive study in paleontological and archaeological sites. There are two groups of rodents in Chile—Caviomorpha and Myomorpha—with most of the related species represented in the fossil record. At Pilauco, representatives from both groups have been recorded and assigned to the species Myocastor cf. coypus and Loxodontomys micropus. Both species currently inhabit southern South America and their ecological demands suggest humid environments and temperate climate for the period of deposition of the fossil-bearing layer PB-7. The inferred habitat of M. coipus corresponds to a wetland landscape with slow water currents and abundant hydrophilic vegetation, whereas open lands with dense shrub vegetation cover or brushwood would provide shelter for L. micropus. A transition zone (e.g., an ecotone wetland-forest), covering the necessities of the two species, might also explain their common occurrence at Pilauco.