The first fossil isopod from Argentina: a new species of Cirolanidae (Crustacea: Peracarida) from the Miocene of Patagonia

Abstract

Cirolana centinelensis, a new species of fossil cirolanid isopod from the early Miocene of Argentina is described, and the fossil record of South American isopods is briefly reviewed. Few fossil isopods are known from South America, and none were previously known from Argentina. The new taxon is represented by a single specimen collected from the Estancia 25 de Mayo Formation, formerly known as the Centinela Formation, in the Calafate region of southern Patagonia. It is preserved in a concretion that was formed in a glass-rich volcanic ash deposited into a shallow epicontinental seaway. The high reactivity of the enclosing volcanic ash set the stage for unique and variable taphonomic conditions with some skeletal elements being preserved in high resolution, whereas others were completely obliterated by the formation of large crystals of secondary zeolites. Because mouthparts that are usually used to make familial and generic assignments are not preserved, traditional systematic methods are combined with a multivariate principal coordinate analysis, as well as ecological and paleontological considerations to evaluate the most likely affinity of the fossil isopod.