Helicerina, Bronnimann and Masse, 1968

Kietzmann, Diego A., Blau, Joachim, Fernández, Diana E. & Palma, Ricardo M., 2010, Crustacean microcoprolites from the Upper Jurassic- Lower Cretaceous of the Neuquén Basin, Argentina: Systematics and biostratigraphic implications, Acta Palaeontologica Polonica 55 (2), pp. 277-284 : 281

Helicerina ? isp. A aff. Helicerina siciliana Senowbari−Daryan, Schäfer , and Catalano 1979

Fig. 2C .

Material.— Four poorly preserved specimens of thin section CPBA−N ° 20675, 20676, Rahue creek ( Fig. 1 , 36 ° 01.762'S, 69 ° 59.393'W) .

Description.—Microcoprolite with circular outline and a cross section of 900 µm in diameter. The specimen is characterised by one canal which lies in the symmetry plane. This canal can be compared with the canal developed in Helicerina siciliana Senowbari−Daryan, Schäfer , and Catalano, 1979. In contrast to Helicerina siciliana the canal in Helicerina ? isp. A is not clearly separated in distinct canals (in Helicerina siciliana : a dorsal diamond shaped and a ventral triangular shaped canal) but seems to form one “unit”.

Contrary to all other known Helicerina ichnospecies the canal shows no connection to the “outside of the coprolite” (terminology according to Senowbari−Daryan and Bernecker 2005). However, this connection is very thin and can be clossed. If additional findings will confirm the lack of connection, our specimen belongs to a new ichnogenus and −species.

Stratigraphic and geographic range.— Helicerina isp. A aff. Helicerina siciliana was recognised in levels corresponding to the Lissonia riveroi and Olcostephanus (Olcostephanus) atherstoni zones (early Valanginian) of the Vaca Muerta Formation.

Figures

Fig. 2. Transversal section of crustacean microcoprolites from the Vaca Muerta Formation. A. Palaxius azulensis Kietzmann isp. nov. (CPBA−N° 20675, early Valanginian, Rahue creek). B. Palaxius caracuraensis Kietzmann isp. nov. (CPBA−N° 20689, late Tithonian, Cara Cura range). C. Helicerina? isp. A aff. Helicerina siciliana Senowbari−Daryan, Schäfer, and Catalano, 1979 (CPBA−N° 20675, early Valanginian, Rahue creek). D. Helicerina isp. B (CPBA−N° 20675, early Valanginian, Rahue creek).

Fig. 1. A. Location map of the Neuquén Basin with study localities and a stratigraphic chart of the Mendoza Group. 1, Tres Esquinas; 2, Loncoche creek; 3–4, Bardas Blancas; 5, Rahue creek; 6, Yeso creek; 7, Cara Cura range. B. Microcoprolites distribution in the Vaca Muerta Formation. Ammonite Zonation according to Aguirre−Urreta et al. (2008) and Riccardi (2008).