Dawsonoceras fenestratum Eichwald, 1860

Kröger, Björn, 2007, Concentrations of juvenile and small adult cephalopods in the Hirnantian cherts (Late Ordovician) of Porkuni, Estonia, Acta Palaeontologica Polonica 52 (3), pp. 591-608 : 597

Dawsonoceras fenestratum Eichwald, 1860

1860 Cycloceras fenestratum sp. nov.; Eichwald 1860: 1231, 1232, pl. 48: 14a, b.

2006 Dawsonoceras fenestratum (Eichwald) ; Kröger and Isakar 2006: 156, figs. 8B, 10B, 12C, F, G (cum syn).

Material.— Eight specimens of different growth stages from the Siuge Member (Porkuni Regional Stage) of north Estonia at TUG and NMB .

Diagnosis.— Dawsonoceras with angle of expansion of less than ten degrees in juvenile stages. Tubular adult body chamber has diameter of approximately 25 mm. Five−six annulations occur at distance similar to shell diameter. Approximately 20 longitudinal striae occur around shell circumference, approximately fifteen growth lines or transverse striae occur per cycle of annulations. Septal necks are achoanitic. Siphuncle is subcentral, expanded within the chambers (after Kröger and Isakar 2006).

Remarks.—The species was described by Kröger and Isakar (2006) in detail. It is listed herein in order to document the entire cephalopod fauna of Porkuni.

Stratigraphic and geographic range.—Dolomitic limestones of the Siuge Member, Porkuni Regional Stage, Estonia; erratics of the same lithology, northern Germany; type specimen from Saunja Formation , Nabala Regional Stage−Kõrgessaare Formation , Vormsi Regional Stage (questionable), Late Ordovician, Mõnuste (Kirna), Estonia .