Orbiculoidea baini and Orbiculoidea excentrica (Brachiopoda, Discinidae) from the Middle Devonian (Alto Garças Sub-basin, Paraná Basin) of Caiapônia, Goiás (Brazil)

Abstract

The Devonian brachiopods from Goiás (Alto Garças Sub-basin, Paraná Basin) present records in the cities of Caiapônia, Amorinópolis, and Doverlândia. However, most of the papers only mention the presence of these fossils in these areas, without any taxonomic description. Thus, our aim was to describe the discinoids Orbiculoidea baini, Orbiculoidea excentrica, and Orbiculoidea sp. found in Caiapônia city. These discinoids were preserved in assemblage, instigating a simplified taphonomic approach. The fossils were found parallel to bedding planes in a poorly package assemblage. Most of them are entire and unarticulated. Although in smaller numbers, several fragmented individuals were also found (some quite fragmented). Therefore, the material was transported configuring a parautochthonous to allochthonous taphocenosis. Another interesting aspect is the decreased size of the brachiopods, which were preserved in sandstone lens on the top of a siltstone layer that overlap black shales of the Early Givetian age. These features can be related to the Lilliput Effect, due to the preserved discinoids present both in adult and juvenile forms. The Lilliput Effect resulted from a biotic crisis (KAČÁK Event) that occurred in the Eifelian-Givetian. This is the first piece of evidence of this effect in the Devonian of Goiás (Alto Garças Sub-basin, Paraná Basin).

Keywords

• Chapada Group Unit 4
• Early Givetian
• Invertebrates
• KAČÁK Event
• Malvinokaffric fauna