Morphology and systematics of Late Palaeozoic syringothyrid brachiopods from West-Central Argentina

CISTERNA, G.A.

Memoirs of the Association of Australasian Palaeontologists

Association of Australasian Palaeontologists, Canberra

Año: 2011 vol. 41 p. 315 - 325

0810-8889

Late Palaeozoic syringothyrid brachiopods from the central western Argentinian basins, have been studied for the small changes in the ventral interior features (i.e. syrinx, delthyrial plate, median septum), considered critical for the generic diagnoses of this group. Argentinian species previously described are also reviewed and, with the new collections obtained for the present study, some are considered synonyms. Three time intervals are studied. Early Carboniferous (Tournaisian-Visean) syringothyrids are not abundant and are characterised by the presence of a delthyrial plate, an incomplete wedge-shaped syrinx and a median septum, the latter suggesting a possible new (?) Septosyringothyridine genus. Late Carboniferous (late Serpukhovian-Bashkirian) syringothyrids have a delthyrial plate, syrinx and median septum, all typical of Septosyringothyris Vandercammen. This genus is well known in the Argentine Precordillera with two species: Septosyringothyris keideli (Harrington) and Septosyringothyris sp. aff. S. keideli. These species are found in the Levispustula fauna that is usually associated with glaciomarine deposits related to the late Carboniferous glacial events in southwestern Gondwana. Early Permian syringothyrids (Asselian-Sakmarian) are very abundant and are characterised by a large syrinx (which is partially enclosed by the delthyrial plate unlike the genus Septosyringothyris), a very short delthyrial plate and a distinctive median septum. These features suggest that species previously described as Septosyringothyris jaguelensis Lech, Septosyringothyris sp. aff. S. jaguelensis, Septosyringothyris globosa Lech, Septosyringothyris feruglioi (Amos) and Septosyringothyris sp. aff. S. feruglioi (Amos), can be included in a new subgenus of Septosyringothyris Vandercammen, here named Septosyringothyris (Precosyringothyris) subgen. nov. The new subgenus and its constituent species appear in the Tivertonia jachalensis-Streptorhynchus inaequiornatus and Costatumulus amosi faunas, of basal Permian age, and are associated with an important climatic amelioration recorded in the central western Argentinian basins.