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

CARATELLI, MARTINA; CITTON, PAOLO; ARCHUBY, FERNANDO M; PIGNATTI, JOHANNES

Congreso; 3rd Palaeontological Virtual Congress; 2021

Fish skeletal debris, composed ofminute-sized teeth and dermal scales highly resistant to dissolution, occurs inmarine and non-marine palaeoenvironments, especially in the deep-sea. Althoughparataxonomically classified and generally rare, ichthyoliths have been used tointerpret abundance and diversity of fish communities, and as biostratigraphicmarkers in otherwise barren, muddy sediments. Here we describe three teleostteeth from marly shales (Crioceratites schlagintweiti Zone) andcalcareous shales (Crioceratites diamantensis and Paraspiticerasgroeberi zones) of the Lower Cretaceous Agua de la Mula Member (AgrioFormation), which formed in a mixed siliciclastic-carbonate marine homoclinalramp system, under low energy and dysoxic conditions. Specimens were picked upfrom three washing residues (90 g total weight) that yield foraminiferalassemblages with low abundance and species richness. The specimens are between0.5 and 1.5 mm long, triangular in outline, and have a smooth external surfacewith straight margins. Adopting the system of morphological descriptors forichthyoliths, the specimen with flattened cusp and circular section in occlusalview can be referred to type a8/b1/c1/d1, while two teeth showing acute cuspsand with sub-oval and acute laterally section can be referred to typesa9/b1/c5/d2/e1/f1/g1/h0 and a9/b2/c5/d2/e4/f3/g1/h0, respectively. The newmaterial enriches the poor vertebrate fossil record of the marine members ofthe Agrio Formation, to date composed of scattered remains referred to marine?reptiles?, pycnodontiform fishes, hybodont and lamniform sharks, and addsfurther faunal components exploiting different, as yet unrecorded, niches.