alans biogeography black sea bulgars caspian sea catacomb culture caucasus cenozoic cimmerians classical antiquity cossacks crimean khanate crimean submediterranean forest complex cumans dagestan eurasian avars eurasian steppe golden horde goths huns indo-iranians kazakh steppe kazakhstan khazars kipchaks kurgan hypothesis mesozoic moldova nogais novocherkassk culture oghuz languages onogurs paratethys pechenegs romania russia russian empire sarmatians scythia scythians sea of azov southern federal district soviet union sredny stog culture srubna culture steppe taiga temperate broadleaf and mixed forests turgai sea turkic peoples ukraine ukrainian lgm refuge ural mountains ural river volga federal district volga tatars west siberian plain