The History of the European Fauna

by R. F. Scharff

A great number of the species belonging to the South-western British element seem to have originated in South-western Europe, or at any rate to have spread over our continent from that part. Their home lay therefore probably in a warm, damp climate, and it seems a reasonable inference to suppose that they spread north at a time when the temperature over the British Islands was much higher than what it is now. Any one familiar with our Bristle fern, or Killarney fern, as it is called in Ireland (Trichomanes radicans), will readily admit that it must have come to us at such an epoch. It at once suggests some shady waterfall in a tropical forest, and indeed the home of the genus is South America. It is one of those plants which have evidently migrated to us from South-western Europe, a mere remnant of a once luxuriant flora.

Sir Archibald Geikie tells us (p. 837), and in the main every one agrees with him, that at the beginning of the Tertiary era in which we now live, the climate was of a tropical and subtropical character in Europe. Gradually it became more temperate, and eventually it passed into a phase of extreme cold, but since that time the cold has again gradually diminished. It is quite evident, therefore, that from a purely geological point of view our south-western flora must have migrated northward before the cold came on, and survived in sheltered localities under the influence of the mild coast climate. Some, however, suppose that there occurred a phase of extreme mildness immediately after the Glacial period, and that it was during that time that the Lusitanian fauna and flora became established in the British Islands. To this Professor James Geikie replies (b, p. 169), "there are few points we can be more sure of than this, that since the close of the Glacial epoch—since the deposition of the clays with Arctic shells and the Saxicava sands—there have been no great oscillations, but only a gradual amelioration of climate. It is quite impossible to believe that any warm period could have intervened between the last Arctic and the present temperate conditions without leaving some notable evidence in the superficial deposits of Scotland, Scandinavia, and North America." Thus it appears that on the whole the assumption that the Lusitanian fauna and flora are very ancient and pre-glacial is also supported on geological evidence.

Fig. 5.—Map of Europe, with arrows indicating approximately the course taken by the different streams of migration towards the British Islands.

The course of events in the origin of the British fauna might have been therefore somewhat as follows:—In early Tertiary times, when the climate all over Western Europe was moist and semi-tropical, a migration proceeded northward from the south-western corner of Europe. This was strengthened by Oriental migrants which had moved westward along the Mediterranean basin ([Fig. 5], No. 1). Owing to geographical changes supervening, the Alpine fauna (No. 2) was then enabled to colonise the British Islands, and subsequently another migration had begun to come in from the south-east (No. 3). The climate had meanwhile gradually become more temperate and drier. About the same time, or even earlier, an Arctic migration commenced to pass southward (No. 4), and finally the Siberian animals (No. 5) poured into our continent. The arrows in the map indicate the directions followed by the different migrants as they travelled to the British Islands. The arrows are not meant to represent the whole nor the full extent of the migrations from any particular centre, but only in so far as they affect our islands. Moreover, it would be impossible to indicate on one map the geographical conditions which obtained during the several migrations. It must be remembered that during the time which elapsed while they passed into the British Islands, these were joined in the north to Scandinavia and in the south to Belgium and France. The various phases of geographical evolution of Europe will be studied in the subsequent chapters, and maps will then be given to show as far as possible in a general way the leading characteristics of these great changes.

I have now given some reasons for the belief that several different migrations of animals entered the British Islands in later Tertiary times. I have also shown why some of them must be looked upon as being older than others, and in so far we have come to a decision as to their relative ages. It still remains for us, however, to examine how their geological ages can be approximately determined. We require for this purpose palæontological aid.

In the fifth chapter will be found the history of the Siberian migration. And since we possess most valuable records of it in the numerous fossil remains discovered in Central and Western Europe, we are able to trace their progress from the east to the west in a very complete and satisfactory manner. In England their first appearance dates from the Forest-Bed, for here we find remains of the Glutton (Gulo luscus), Musk-Ox (Ovibos moschatus), and others (see p. [204]). It seems reasonable to suppose, therefore, that the first entry of these Siberian mammals into Europe took place at or just before the Forest-Bed period. But Professor Nehring tells us in his remarkable work on the Tundra and Steppes (p. 222), that in Germany the remains of the same mammals occur in deposits which are certainly more recent than the lower continental boulder clay; and he is inclined to the belief that they migrated into Europe during the inter-glacial phase which is supposed to have separated the earlier from the later stage of the Glacial period. It is evident that in this case the inter-glacial period in Germany would have corresponded to, and be contemporaneous with, our Forest-Bed period. The deposits immediately preceding the Forest-Bed would also be contemporaneous with the lower continental boulder clay. Although this may seem rather a startling statement to make, from the evidence which will be brought forward in the fourth and fifth chapters I am inclined to the belief that such is probably the case.

Having once arrived at a determination of the exact geological period during which the Siberian mammals invaded our continent, and having also previously determined the relative ages of the various other migrations, we have advanced another step in the direction we are aiming at. Let us suppose that the Siberian migration actually reached the British Islands during the Forest-Bed period. Since the Siberian migration is the most recent of those which entered the British Islands, the others must have commenced their march before the Forest-Bed period. Now it was Professor Boyd Dawkins who first indicated to us, as I have remarked before, the method of research to be adopted in an attempt to determine the geological age of the different migrations in so far as they affected the British Islands. I may be excused, therefore, for again quoting the following important passage in one of his works. "The absence," he says (b, p. xxix), "of the beaver and the dormouse from Ireland must be due to the existence of some barrier to their westward migration from the adjacent mainland, and the fact that the Alpine hare is indigenous, while the common hare is absent, implies that, so far as relates to the former animal, the barrier did not exist." The Beaver, Dormouse, and Common Hare are either Siberians or later migrants from elsewhere, and there can be no doubt that at the Forest-Bed period Ireland was already, or was just being, separated from England. All the southern species, that is to say all the Lusitanian, Alpine, and Oriental forms occurring in Ireland, must therefore be older than that period. I have advocated similar views in a former essay on this subject. Mr. Carpenter recently advanced some interesting and valuable criticisms on these views, which we may examine a little more closely (p. 385). "While, then," he remarks, "I find myself in almost complete agreement with Dr. Scharff with regard to the older sections of our fauna, I think that those widespread species which survived the Glacial period must have been confined to the more southern parts of our area, and have only subsequently spread northwards and westwards to Scotland and Ireland." He suggests, in fact, that the widespread British species belong to a younger or newer section of our fauna than the local ones. In many cases this may be quite true, but we possess also a large number of common and widely-spread forms which bear the impress of antiquity upon them. We have the most positive proof of the antiquity of the very common small circular Snail (Helix rotundata), since it was found in miocene freshwater deposits near Bordeaux. Many other examples might be mentioned to show that, though discontinuous range is generally a proof of antiquity, continuous range is not always a sign of the opposite. Some species, in fact, appear to be short-lived and disinclined to spread, whilst others multiply rapidly even under a change of temperature and climate, and are to be found almost everywhere. But even if we supposed, with Mr. Carpenter, that these widely-ranging species must have been confined during the Glacial period to the more southern parts of England, the idea that they afterwards made their way northwards along the eastern shore of the Irish Sea and then passed into Ireland, does not appeal to me. Southern England was occupied at that very same time by an assemblage of Siberian mammals. Mr. Carpenter thinks these might have been kept out of Ireland by an arm of the sea until the land-connection with North-western England had broken down. But if an arm of the sea could keep out the Siberian mammals it would also keep out the widely-spread British species of the general fauna. On the other hand, I quite admit that my view of the survival in Ireland of the pre-glacial fauna is somewhat difficult to accept, considering that we have such undoubted evidence of a very extensive submergence. The case of Isle of Man, quoted by Mr. Carpenter, can be met, I think, by the supposition that it was connected with Cumberland until quite recently, and quite independently of any connection between England and Ireland; that the Isle of Man, in fact, was always a cape or peninsula of the mainland, and only recently became separated by local subsidences or by the action of the sea.

Part of the history of the British fauna will be referred to again in the next chapter, which deals with the Arctic migration. We need not therefore dwell any longer on this subject here. There is one matter, however, which is of importance in connection with the geographical conditions of the British Islands at the time when the greater portion of our fauna arrived from abroad.