Proterocameroceratidae Kobayashi, 1937

Cichowolski, Marcela, 2009, A review of the endocerid cephalopod Protocyptendoceras from the Floian (Lower Ordovician) of the Eastern Cordillera, Argentina, Acta Palaeontologica Polonica 54 (1), pp. 99-109 : 102-103

Family Proterocameroceratidae Kobayashi, 1937 Genus Protocyptendoceras Cecioni, 1965

Type species: Protocyptendoceras fuenzalidae Cecioni, 1965 , by original designation. Floian Stage. La Ciénaga , about 5 km west of Purmamarca, Jujuy Province, Eastern Cordillera of Argentina .

Emended diagnosis.—Straight and longiconic shell with circular to subcircular section. Almost straight suture line, with a narrow ventral lobe. Growth lines on the surface, ornamentation absent. Moderate to large size circular siphuncle, in contact with ventral shell wall. Subholochoanitic septal necks combined with thick connecting rings. Endocones generally droplet shaped in cross section, but sometimes simply rounded.

Remarks.—In his original definition, Cecioni (1965) did not explicitly indicate the presence of endocones, but he observed secondary calcite in an adapical position in the siphuncles, which could correspond to recrystallised endosiphuncular deposits. These are well preserved in the new collected material studied here. The presence of endocones is a key feature permitting assignment of the genus to the Endocerida . Furthermore, the “layered” connecting rings noted by Cecioni (1965) are probably a diagenetic structure, as Mutvei (1997) noted when studying endocerid material using SEM. Cecioni (1965) compared his new genus Protocyptendoceras with others that do not belong to the same family, or even to the same order, such as Cyptendoceras Ulrich and Foerste, 1936 , Clarkoceras Ruedemann, 1905 , and Quebecoceras Foerste, 1925 . Based on the present studies of betterpreserved new material, other comparisons can be made

Puncoviscana Fm.

(Precambrian)

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LIMESTONES

SEPULTURAS

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SHALES

CIENEGUILLAS

“ m

50

shale bioturbated siltstone and mudstone fine grained sandstone shell concentrations Yacoraite cephalopod occurrences (Cretaceous which help in the identification of this western Gondwanan genus.

Protocyptendoceras is very similar to Anthoceras Teichert and Glenister, 1954 , from the Lower Ordovician of North America, NW Australia, Baltica, and Siberia, in the general conch shape and the siphuncle structure; however, Anthoceras is distinguished by having an annulated shell. Furthermore, some species of Anthoceras have larger dimensions at mature stage than Protocyptendoceras , such as A. vaginatum ( Schlotheim, 1820) (see Mutvei 1997). Protocyptendoceras differs from Proterocameroceras Ruedemann, 1905 , from the Lower Ordovician of North America, Greenland, Siberia, and NW Australia, mainly in having longer septal necks and in the structure of the endosiphuncular deposits ( Proterocameroceras has three endosiphuncular blades) ( Teichert 1964). Protocyptendoceras is usually smaller than Lobendoceras Teichert and Glenister, 1954 , from the Lower Ordovician of NW Australia and Siberia, and has an elliptical cross section in later ontogenetic stages, rather than circular as in Lobendoceras . Proendoceras Flower, 1955 , from the Lower Ordovician of North America and China, has a smaller siphuncle and a wider range of variability in the length of the septal necks compared with the genus studied here. Protocyptendoceras differs from Paraendoceras Ulrich and Foerste, 1936 from the Lower Ordovician of North America and Siberia in having longer septal necks and a lower angle of expansion. Cotteroceras Ulrich and Foerste, 1936 , from the Lower Ordovician of the USA and Siberia, has a compressed cross section instead of a depressed one. Protocyptendoceras differs from Ventroloboceras Teichert and Glenister, 1954 , from the Lower Ordovician of Western Australia, in having a larger siphuncle and shorter septal necks. Catoraphiceras Ulrich and Foerste, 1936 , from the Lower Ordovician of the USA, Canada, Estonia, and Australia, differs from Protocyptendoceras mainly in having an annulated shell.