1 INTRODUCTIONDroser et al. (1997) proposed four paleoecological levels to assess major ecological changes throughout the Phanerozoic. These changes refer to ecosystems and communities, and consequently include all the components of the biota, except for the fourth level, in which taxonomic changes at clade level are considered.This approach applies to the understanding of major events of life and provides a mean to scale paleoecological changes through time, even though it obscures innovations that are critical in the evolution of a particular clade.Recently, evidence supporting bivalve colonization of low-saline waters in the Mid Ordovician (Darriwilian) of Northwestern Argentina was presented (Sánchez and Benedetto, in press).
展开▼
