The record of the terebratulid brachiopod Septothyris in the Lower Devonian of the Argentine Precordillera, and the biogeographic affinities of its Lochkovian faunas

Abstract

The terebratulid brachiopod Septotyhys is documented for the first time in the Lower Devonian ofthe Precordillera basin. The material comes from the uppermost part of the los Espejos Formation(reddish-purple interval) of well constrained early Lochkovian age. This is not only the earliestrecord of the genus Septothyris but also is one of the oldest records of the Order Terebratulidaworldwide. The early Lochkovian brachiopod fauna of the Precordillera developed during the shorttime interval that mediates between the extinction that decimated the Silurian Afro-SouthAmerican fauna and the first appearance of the typical Devonian Malvinoxhosan fauna. Thebrachiopod assemblage containing Septothyris sulcata sp. nov. consists of genera and speciesthat evolved from local Silurian ancestors, as well as taxa introduced in the Precordillera basin fromlow-latitude temperate oceans. It seems likely that the faunal turnover at the Silurian/Devoniantransition was linked to the significant environmental change from a storm-dominated platform torestricted quiet marine waters that took place in the Precordillera basin at that time.