Huncalotis, an enigmatic new pectinoid genus (Bivalvia, Late Jurassic) from South America

DAMBORENEA, S.E.; LEANZA, H.A.

PALAEONTOLOGISCHE ZEITSCHRIFT

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2016 vol. 90 p. 449 - 468

0031-0220

The extensive outcrops of the Late Jurassic-Early Cretaceous Vaca Muerta Formation black shales and marls in the Neuquén Basin have yielded very few bivalves, and these are not well-known. The material described here was collected in central Neuquén, from late Tithonian calcareous levels within the black shales, between beds with Substeueroceras sp. and with Argentiniceras noduliferum (Steuer). The material is referred to the new genus Huncalotis and to the new species H. millaini. The strongly inequivalve shells, the ligamental area with a triangular slightly prosocline resilifer, the right valve with ctenolium and a very deep byssal notch, and the lack of radial ornamentation, make the shell of this new genus strikingly similar to the Triassic pectinid Pleuronectites.This resemblance may be due to either phylogenetic relationships or convergence. Obliquipecten peruanum Rivera from central Peru is tentatively referred to Huncalotis. The Neuquén specimens are found in two main preservation types. Most of the material occurs in shell pavements, with equally abundant right and left valves and a wide size range, within beef or sandwich concretions. These specimens are commonly complete but disarticulated, and show radial fractures orientated at right angles to the shell margins. A few specimens were found on the outside of large calcareous concretions within black shales; these are often articulated, complete shells,which preserve the original convexity of the valves. In some cases these articulated shells seem to be associated with large ammonite shells, suggesting an epibyssate (possibly also pseudoplanktonic) life style.