Siberia—long spells of still weather, with intense frost, interrupted now and again (especially at the changes of the seasons) by fierce snowstorms, in which the wild animals could hardly fail occasionally to perish in large numbers.
How long these tundra conditions obtained we can not tell. All we know is that eventually they gradually passed away and the climate became less arctic. This is shown by the well-ascertained fact that both in the loss and the contemporaneous cave accumulations remains of the arctic animals are confined to the lowest beds, becoming gradually less numerous as we trace them upward, until they finally disappear. But before the last of the tundra forms has vanished remains of a steppe fauna begin to occur. In a word, there was no sudden dying out of one fauna and precipitate appearance of another, but a gradual replacement, consequent, doubtless, upon changing climatic conditions.
All the animals already mentioned as most characteristic of the subarctic steppes are represented in the caves and alluvial deposits of west and middle Europe. Jerboas, pouched marmots, bobacs, and true marmots, tailless hares and others, all formerly flourished in those latitudes. Besides these most characteristic steppe animals occurred many other forms which were not restricted to steppe lands, such as mammoth and woolly rhinoceros, marsh lynx, cave lion, hyena, wolf, common fox, ermine, weasel, badger, reindeer, urus, bison, etc. Many birds also were present—all of them species which in our own day frequent the steppes of southeast Russia. Land shells are also very often found in less or greater abundance along with the relics of the steppe animals just mentioned, most of the shells representing forms that now live in dry steppes, while some are denizens of wooded regions.
The plant remains associated with relics of the steppe fauna are quite in keeping with the latter, but are upon the whole seldom met with, the conditions not being favorable to their preservation. Trunks and branches of trees occur very rarely, the most common remains being a few thin layers and seams of peaty matter, apparently consisting chiefly of grasses. Nevertheless, we need have no doubt that a steppe flora formerly flourished in middle Europe, for (as Engler, Ascherson, Petry, and other botanists have shown) many well-known steppe plants survive in the existing flora of that region.
Among the animals associated with the true steppe forms were some which, as we have seen, had already invaded central Europe in tundra times. Of these, perhaps the most notable are the mammoth and the woolly rhinoceros. Probably they were only summer visitors, but in the subsequent steppe epoch they became truly indigenous and very abundant. The broad valleys and open spaces of central Europe were at that time treeless plains, although woods seem to have existed here and there, especially along the margins of lakes and streams. The climate, we need not doubt, was much like that of the subarctic steppes
