Abstract
The taxonomic study of brachiopods (Family Discinidae) from the upper part of the Manacapuru Formation (Lochkovian), south border of the Amazonas Basin, Brazil, allowed to recognize’ five species of Orbiculoidea: O. baini, O. bodenbenderi, O. excentrica, and two new species described herein: O. xinguensis sp. nov. and O. katzeri sp. nov. Besides, O. baini, O. bodenbenderi, and O. excentrica are recorded for the first time in the Manacapuru Formation, and in Northern Brazil, being the oldest records (Lochkovian) of these species in South America too. Their presence in the region can be explained by two reasons: the proximity of the Amazonas Basin, located in northwest Gondwana, during the Early Devonian to the continent of Laurasia (where are recorded most occurrences of Orbiculoidea during the Silurian), favoring the specific interchange between these two geographic regions; and the global sea level rise during this time, which flooded a large part of northwestern Gondwana, resulting in the presence of shallow seas in the Amazonas Basin, represented by marine sediments in the upper part of the Manacapuru Formation. These conditions promoted the colonization of inarticulate brachiopods during the Early Devonian in the north of Brazil. The discinoids identified in the strata of the Manacapuru Formation are typical of shallow marine environments, supporting previous interpretations for the upper part of this unit.
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