Vertebrate micro-remains from the Lower Cretaceous Agrio Formation (Neuquén Basin, Argentina)

MARTINA CARATELLI; PAOLO CITTON; ARCHUBY FERNANDO; PIGNATTI JOHANNES

Virtual

Congreso; 3rd Palaeontological Virtual Congress; 2021

3rd Palaeontological Virtual Congress

Fish skeletal debris, composed of minute-sized teeth and dermal scales highly resistant to dissolution, occurs in marine and non-marine palaeoenvironments, especially in the deep-sea. Although parataxonomically classified and generally rare, ichthyoliths have been used to interpret abundance and diversity of fish communities, and as biostratigraphic markers in otherwise barren, muddy sediments. Here we describe three teleost teeth from marly shales (Crioceratites schlagintweiti Zone) and calcareous shales (Crioceratites diamantensis and Paraspiticeras groeberi zones) of the Lower Cretaceous (Hauterivian) Agua de la Mula Member (Agrio Formation), which formed in a mixed siliciclastic-carbonate marine homoclinal ramp system, under low energy and dysoxic conditions. Specimens were picked from three washing residues (90 g total weight) that yield foraminiferal assemblages with low abundance and species richness. The specimens are between 0.5 and 1.5 mm long, triangular in outline, and have a smooth external surface with straight margins. Adopting the system of morphological descriptors for ichthyoliths, the specimen with flattened cusp and circular section in occlusal view can be referred to type a8/b1/c1/d1, while two teeth showing acute cusps and with sub-oval and acute laterally section can be referred to types a9/b1/c5/d2/e1/f1/g1/h0 and a9/b2/c5/d2/e4/f3/g1/h0, respectively. The new material enriches the poor vertebrate fossil record of the marine members of the Agrio Formation, to date composed of scattered remains of marine ?reptiles?, pycnodontiform fishes, hybodont and lamniform sharks, and adds further faunal components exploiting different, as yet unrecorded, niches.