Advances in Angiocardiography

Abstract

There is a certain ambiguity in the taxonomy of Amphicytherura Butler & Jones, Aracajuia Krömmelbein and Sondagella Dingle. Recent publications have addressed the separation of these three genera, but a deeper taxonomic analysis is still needed. Aracajuia benderi Krömmelbein, type-species of Aracajuia and an index fossil for the upper Aptian–Albian of the Sergipe–Alagoas Basin, northeastern Brazil, was previously attributed to Amphicytherura, but this replacement is nowadays considered debatable. To approach this problem, the type-species Aracajuia benderi is re-described herein. Sexual dimorphism and some of its instars are illustrated for the first time using scanning electron microscopy. At the generic level, emended diagnoses of Amphicytherura and Aracajuia are proposed in an effort to consolidate the validity of both. Sondagella, which was originally proposed as a subgenus of Amphicytherura and later elevated to the generic level, is here considered to be a synonym of Aracajuia. A new genus, Dinglecythere, is created to group certain species previously identified as Amphicytherura. Because Aracajuia benderi is an index fossil for the Zone Amphicytherura benderi and a homonymous subzone, the nomenclature of both is changed to Aracajuia benderi, based on the results of this taxonomic revision. Additional palaeozoogeographic studies make it possible to trace the evolutionary history of Amphicytherura, Aracajuia and Dinglecythere. Aracajuia and Dinglecythere were found from tropical to warm-temperate marine environments, mostly restricted to Gondwana, but the first occurred mostly during the Early Cretaceous, while the second was a Late Cretaceous genus. Amphicytherura occurred throughout Laurasia in warm-temperate and “paratropical” waters, reaching great diversity in the Late Cretaceous.