Taxonomy and palaeobiogeography of the Silurian cephalopods from Severnaya Zemlya, Russian Arctic

Cephalopods are common in the Silurian carbonate platform succession of the Severnaya Zemlya Archipelago, Arctic Russia. Hitherto, these fossils were not sufficiently collected and studied. We present the first study of the nautiloid fauna from this area. The preliminary identification list includes the following taxa: Elrodoceras sp., Ephippiorthoceras sp., Mixosiphonoceras beimapoense, Nothoceratidae gen. et sp. indet, Orthoceratida gen. et sp. indet, Pentameroceras heshuiense, Protophragmoceras cf. butovitcense, Sichuanoceras sp., Shuranoceras sp. and Stenogomphoceras inflatum.

In terms of paleobiogeographic relationships, comparison between cephalopod assemblages worldwide is difficult due to lack of modern revisions and often poorly described and illustrated taxa from some areas. The reported assemblage from Severnaya Zemlya appears to be mixed, as it contains genera and species known from Baltica (Elrodoceras sp., Protophragmoceras cf. butovitcense), Laurentia (Elrodoceras sp., Stenogomphoceras inflatum), South China (Ephippiorthoceras sp., Mixosiphonoceras beimapoense, Pentameroceras heshuiense, Sichuanoceras sp.) and Kazakhstan (Shuranoceras sp.).

During the Silurian, Severnaya Zemlya was located in tropical to subtropical latitudes between the nearby palaeocontinents of Laurentia and Siberia (Metelkin et al. 2005). Apparent affinity to South China, located at similar latitudes, but distant is interesting. One more example of this similarity can be shown with regard to the benthonic ostracod Entomozoe, which occurs in the Early Silurian strata of Severnaya Zemlya (Siveter & Bogolepova 2006), together with the cephalopods Ephippiorthoceras sp., Pentameroceras heshuiense, Protophragmoceras cf. butovitcense and Stenogomphoceras inflatum, and South China. Similarities to Siberia are very weak and are represented only by the specimens preliminarily defined as Ephippiorthoceras sp. They resemble the species Geisonoceras kureikense, known from the Early Silurian of East Siberia (Myagkova 1967). There is no evidence found so far for any faunal exchange between Severnaya Zemlya and the peri-Gondwana areas.