The Permian brachiopod genus Trigonotreta Koenig 1825 and its occurrence in Argentina

CISTERNA, G.A.; ARCHBOLD. N.W.; SIMANAUSKAS, T.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2002 vol. 39 p. 213 - 220

0002-7014

Abstract. A review of the Permian an spiriferid brachiopod genus Trigonotreta and its occurrence in the Early Permian of Argentina is provided herein. Severa! species are known from the Late Palaeozoic sequences of the Argentinean Precordillera. These include Trigonotreta sp. and Trigonotreta riojanensis (Lech and Aceñolaza), from the Río del Peñón Formation (Río Blanco Basin), Trigonotreta pericoensis (Leanza), from the Tupe Formation at the La Herradura creek locality (Paganzo Basin) and Trigonotreta sanjuanensis (Lech and Aceñolaza), from Del Salto Formation (Calingasta-Uspallata Basin). These species are characterised by being snall to medium sized, relatively transverse, with cardinal extremities often strongly angular. Costae are weakly bifurcated and superim­posed on weakly developed lateral flank plications adjacent to the fastigium and sulcus. The Argentinean species are clase to the oldest known Indian species of the genus, Trigonotreta hesdoensis (Sahni and Dutt), particularly with respect to the nature of its weakly fasciculated costae. Further study will refine the details of the relation­ship of the South American species with those from elsewhere in Gondwana and may permit the recognition of a distinctive lineage. The presence of the genus in Argentina in the earliest Permian is an important palaeobio­geographical observation that raises questions about the probable migration routes of the genus from the west­ern Gondwanan South American margin to eastern Australia and India. The Precordilleran region appears to be the likely site of the first appearance of Trigonotreta. Species with relatively simple costae appeared first. These gave rise to more complex species with a more elaborate costal pattern indicating an evolutionary progression through time.