Origin and dispersion of the Cenozoic genera Amiantis Carpenter, 1864 and Eucallista Dall, 1902 (Veneridae, Pitarinae)

ALVAREZ, MAXIMILIANO; DEL RIO, CLAUDIA JULIA

Burgos

Congreso; XXI Reunión Bienal de la Real Sociedad Española de Historia Natural; 2015

Real Sociedad Española de Historia Natural

The confuse and difuse systematic information prevailing during almost the last 100 years, has linked the history of the pitarinae genera Amiantis to that of Eucallista, leading to misinterpretations about their origin, dispersion and phylogenetic relationships. A careful survey of the more than a dozen nominal species longely assigned to Aminatis, has allowed to provide accurate diagnostic characters that differentiate this genus from Eucallista. Moreover it has been possible to restrict the presence of Amiantis to the tropical región of Western North America, and that of Eucallista to the Argentinean and Brasilean Bioprovinces of the Southwestern Atlantic Ocean. While the Neogene record indicates that Amiantis would have originated in the California region during the Oligocene, where remained confined until nowadays, the oldest known record of Eucallista occurred in the Early Miocene of the middle latitudes of Chile. This taxon inhabited the Chilean and Peruvian coasts until Pliocene, but dispersed into Patagonia in Late Miocene times, where it remained until Recent times, migrating northwards to northern Brazil anytime during Quaternary. These findings prove that both genera are not related as previously stated, and that a probable source of confusion could have been the presence of convergent characters such as the development of rugose nimphs in both taxa. According to the present research, Eucallista purpuratus Lamarck,1818, the type species, would have originated during Pleistocene time in theSouthwestern Atlantic Ocean contrary to that supposed by previous authors who considered this species as a Miocene relict taxon. E. purpuratus has notbeen recorded in the area earlier than the Pleistocene and has been usually mixed up with E. laziarina (Ihering, 1907), the only Miocene species of the genus that has been recorded in Chile (Navidad Formation, Early Miocene)and Argentina (Puerto Madryn Formation, Late Miocene; ?Araucaense beds?,Early Pliocene). Systematic and phylogenetic analyses presently carriedout indicate that E. purpuratus could have evolved from E. laziarina during Pleistocene.This is a contribution supported by the Research Projects ANCyP PICT57 and CONICET PIP 320.