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

Carames, A., Martinez, M., Concheyro, A., Remirez, M. & Adamonis, S., XX 2019. Holothuroidea: new records from the Lower Cretaceous of the Agrio Formation, Neuquen Basin, Argentina. An integrated study with foraminifers and calcareous nannofossils. Alcheringa XX, xx-xx. ISSN 0311-5518 New records of holothurian ossicles (Echinodermata) from the Lower Cretaceous Agrio Formation, Mendoza Group, in the northern Neuquen Basin, west-central Argentina, represent, excepting some general mention of ossicles, the first collection from the Lower Cretaceous of South America. The discovery is one of the few worldwide records of holothurian remains from this age. The analysed skeletal elements are associated with 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 Epistomina loncochensis, suggesting quiet marine environments and low levels of dissolved oxygen in the bottom/water interface. A late Valanginian age is confirmed by the nannofossil assemblage found together with the holothurian ossicles. Analysis of ossicle shapes allows their attribution to molpadiids (Molpadida: Molpadiidae): one two-armed racquet-like single ossicle that remains as an indeterminate molpadiid and a new genus and species proposed for the abundant cross-shaped and star-shaped ossicles. The latter, owing to the presence of four holes and the lack of a spire 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. Andrea Carames [carames@gl.fcen.uba.ar], IDEAN-Instituto de Estudios Geologicos Andinos 'Don Pablo Groeber', CONICET, Ciudad Universitaria Pabellon II, Intendente Guiraldes 2160-C1428EHA Buenos Aires, Argentina; Mariano Martinez [mmartinez@macn.gov.ar], Museo Argentino de Ciencias Naturales 'Bernardino Rivadavia', CONICET, A. Gallardo 470-C1405DJR Buenos Aires, Argentina; Andrea Concheyro [andrea@gl.fcen.uba.ar], IDEAN-Instituto de Estudios Geologicos Andinos 'Don Pablo Groeber', CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria Pabellon II, Intendente Guiraldes 2160-C1428EHA Buenos Aires, Argentina, and Instituto Antartico Argentino, Argentina; Mariano Remirez [mremirez@cig.museo.unlp.edu.ar], CIG-Centro de Investigaciones Geologicas, CONICET, Universidad Nacional de La Plata, Diagonal 113 N degrees 275-B1904DPK, La Plata, Argentina; Susana Adamonis [suad@gl.fcen.uba.ar], Departamento de Ciencias Geologicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, IDEAN. Ciudad Universitaria Pabellon II, Intendente Guiraldes 2160-C1428EHA Buenos Aires, Argentina.