Upper Silurian and Devonian heterostracan pteraspidomorphs (Vertebrata) from Severnaya Zemlya (Russia): a preliminary report with biogeographical and biostratigraphical implications

Severnaya Zemlya (Kara-Tajmyr palaeocontinent) is a key-zone in understanding the palaeogeographical relationships of the Old Red Sandstone Continent and Siberia in Mid-Palaeozoic times. Its Upper Silurian-Devonian sedimentary sequence bears a rich fauna of heterostracans which allows biostratigraphical correlation to be made with Spitsbergen (on the Barentsian palaeocontinent), but also with the Canadian Arctic (on the Old Red Sandstone Continent) and Central Tajmyr-NW Siberia (Siberian palaeocontinent). This fauna is composed of various assemblages from the Ludlow (Upper Silurian) to the Frasnian (Upper Devonian), with the richest assemblages in the upper Lochkovian, and a gap in the Emsian (Lower Devonian).