First Clarkeia and Heterorthella (Brachiopoda; Lower Silurian) occurrence from the Paraná Basin in eastern Paraguay

The existence of the Malvinokaffric Realm during the Silurian (Boucot, 1990) is based on the presence of three endemic brachiopod genera (Anabaia, Clarkeia, Heterorthella), and their absence in the coeval North Silurian Realm, where roughly 100 other brachiopod genera Aegiria to Zygospiraella are present. Within the Malvinokaffric Realm the vast reaches of the Paraná Basin, covering an area almost equivalent to the United States east of the Mississippi River, has previously yielded only Anabaia, and that from a single area. In light of this, the recognition of both Clarkeia and Heterorthella within the confines of the Paraná Basin is noteworthy.