Holothuroidea: new records from the Lower Cretaceous of the Agrio Formation, Neuquén Basin, Argentina. An integrated study with foraminifers and calcareous nannofossils

Abstract

New records of holothurian ossicles (Echinodermata) from the Lower Cretaceous Agrio Formation, Mendoza Group, in the northern NeuquenBasin, west-central Argentina, represent, excepting some general mention of ossicles, the first collection from the Lower Cretaceous of SouthAmerica. The discovery is one of the few worldwide records of holothurian remains from this age. The analysed skeletal elements are associatedwith other microfauna and nannoflora retrieved from washed residues of claystones and marlstones of the lower strata of the Pilmatue Member,in Area 3000 and Puerta Curaco sections. The calcareous microfossil assemblage is composed almost exclusively of the foraminifera Epistominaloncochensis, suggesting quiet marine environments and low levels of dissolved oxygen in the bottom/water interface. A late Valanginian age isconfirmed by the nannofossil assemblage found together with the holothurian ossicles. Analysis of ossicle shapes allows their attribution tomolpadiids (Molpadida: Molpadiidae): one two-armed racquet-like single ossicle that remains as an indeterminate molpadiid and a new genusand species proposed for the abundant cross-shaped and star-shaped ossicles. The latter, owing to the presence of four holes and the lack of aspire or some elevation projecting well out from surface in the centre of the plates, resemble two known species of the genus Cruxopadia Reich,but they differ in their arm morphology.