An Early Silurian (Aeronian) cephalopod fauna from Kopet-Dagh, north-eastern Iran: including the earliest records of non-orthocerid cephalopods from the Silurian of Northern Gondwana

Abstract

The cephalopod fauna from the Aeronian Qarebil Limestone of north-eastern Iran comprises the first comprehensive record of early Silurian cephalopods from peri-Gondwana. Although consisting of relatively few taxa, the assemblage includes members of the orders Oncocerida, Discosorida, Barrandeocerida and Orthocerida. Coeval records of several of these taxa are from low palaeolatitude locations that include Laurentia, Siberia, Baltica and Avalonia, and are otherwise unknown from peri-Gondwana until later in the Silurian. The cephalopod assemblage occurs in cephalopod limestones that currently represent the oldest record of such limestones in the Silurian of the peri-Gondwana margin. The appearance of these cephalopods, together with the development of cephalopod limestones may be attributed to the relatively low latitudinal position of central Iran and Kopet-Dagh compared with that of the west Mediterranean sector during the Aeronian. This, combined with the continued post-glacial warming after the Hirnantian glaciation, facilitated the initiation of carbonate deposition and conditions suitable for the development of the cephalopod limestones whilst permitting the migration of cephalopod taxa, many of which were previously restricted to lower latitudes. •

Silurian tarphyceridDiscoceras(Cephalopoda, Nautiloidea): systematics, embryonic development and paleoecology

“…The earlier Silurian anoxic episode restricted almost all fauna except graptolites in peri-Gondwanan basins. Nautiloid immigration from low latitudes into peri-Gondwanan basins with isolated elevated submarine regions is linked with a decline in early Silurian anoxia, and activation of currents beginning in the middle Llandovery to Wenlock (Stridsberg, 1988b; Manda, 2008b; Histon, 2012; Evans et al, 2015; Fig. 11).…”

First record of a nonpaleotropical intejocerid cephalopod from Darriwilian (Middle Ordovician) strata of central Spain

“…The absence of critical internal structures in many of these specimens does not allow for a taxonomic identification at genus or species level and many taxa are in need of a revision. Hopefully, the recent reappraisal of early Paleozoic peri-Gondwanan cephalopod faunas from elsewhere (e. g. Kröger et al, 2012;Evans et al, 2013Evans et al, , 2015Bogolepova et al, 2014;Sone, 2014, 2015;Aubrechtová, 2015;Cichowolski et al, 2015Cichowolski et al, , 2018Ghavidel-Syooki et al, 2015;Rolet and Plusquellec, 2016;Aubrechtová and Turek, 2018;Manda and Turek, 2018;Ebbestad et al, 2019;Fang et al, 2019) will stimulate future research on the Iberian cephalopods. specimen MGM-8187O, lateral view.…”