We shall appreciate this difficulty more clearly by looking to certain existing faunas and floras.
We thus see how hopelessly difficult it is to compare with perfect fairness, under such extremely complex relations, the standard of organisation of the imperfectly-known faunas of successive periods.
Along the whole west coast, which is inhabited by a peculiar marine fauna, tertiary beds are so poorly developed that no record of several successive and peculiar marine faunaswill probably be preserved to a distant age.
First, in regard to continental extension, if these straits could form such a barrier, it would seem as if nothing short of a land communication could do much towards fusing together two distinct faunas and floras.
The pocket gopher fauna known from the late Pliocene was more varied than the faunas known from any earlier time.
The Miocene faunas from the Wounded Knee area of western North Dakota.
Local faunas in Maryland and Florida of Rancholabrean age include Thomomys, in every instance referable to the subgenus Pleisothomomys on the basis of unconstricted molars.
Dalquest reported Geomys bursarius from two Sangamon faunasin northern Texas.
A survey of various Late Cenozoic vertebrate faunas of the Panhandle of Texas, Part I.
The genus Geomys has been identified in several faunas of Illinoian age, all from the Great Plains.
The Cudahy and Tobin local faunas are of approximately the same age, and presently both are included in one unit, the Cudahy fauna.
Geomys of the Cudahy and Tobin local faunas of Irvingtonian provincial age.
All the actual classes of the animal and vegetable kingdoms were represented in the tertiary faunas and floras, and in nearly the same proportions and the same diversities as at present.
Hence we can understand why the faunas of insular mountain-summits are, as in the case of Teneriffe, eminently peculiar.
On the mountain-summits of islands, characterised by peculiar faunas and floras, the plants are often eminently peculiar.
Moreover, the great similarity between the faunasof Southern Spain and North-western Africa indicate that the formation of the Straits of Gibraltar is of very recent date.
A knowledge of the past faunas is a most important factor in tracing the original home of the European animals.
The faunas of North-west Africa and the south-western portion of our continent are so closely related, that an uninterrupted intercourse by land must have existed for a very long period.
Many other authors have pointed out the close similarity existing between the faunas of Southern Europe and North Africa.
Before investigating more minutely the problems suggested by the composition of the faunas of these insular and also of some continental areas, it is necessary that we should thoroughly understand all about the migrations of animals.
In this way the similarity between the Alpine and Scandinavian faunas and floras is assumed to have been brought about.
He acknowledges indeed, just as I do, three distinct faunas in the British Islands, with the addition of the group of generally distributed species of undetermined origin.
By the more recent theory of Nehring, the Siberian animals which invaded our continent from the east, and then spread northward to Scandinavia and southward to the Alps, formed the nucleus of the faunas of these two areas.
Nevertheless, I feel that his theories regarding the origin of the faunas of oceanic islands require revision.
In this same class, but less remote from the mainland, and in their faunas and floras showing a nearer relationship to South than to North America, belong the Caribbees.
Ancient and modern continental islands have also been recognised, their age being indicated by the degree of similarity between their faunas and the fauna of the continent with which they were formerly connected.
Wallace, The Geographical Distribution of Animals, with a study of the Relations of Living and Extinct Faunas as elucidating the Past Changes of the Earth's Surface, 2 vols.
If it does not, the two faunas show no greater resemblance than the similarity of physical conditions on the two sides would lead us to expect.
We may first note that a continuous shore-line produces a mingling of fish faunas only when not interrupted by barriers due to climate.
The interlocking of the fish faunas of Asia and North America presents, however, a number of interesting problems, for migrations in both directions have doubtless taken place.
He would, however, insist that the theory of such changes must be confirmed by geological evidence, and evidence from groups other than fishes, and that likeness in separated fish faunas may not be conclusive.
To the same extent that likeness in faunas is produced by continuity of means of dispersion is it true that unlikeness is due to breaks in continuity.
The differences in the present faunas of Lake Tahoe and Utah Lake must be chiefly due to influences which have acted since the Glacial Epoch, when the whole Utah Basin was part of the drainage of the Columbia.
We may, therefore, consider the age and nature of the Isthmus of Suez and the character of the faunas it separates.
This discrepancy arises from the comparatively limited representation of the two faunas at the disposal of Dr.
If the fish faunas of different regions have mingled in recent times, the fact would be shown by the presence of the same species in each region.
Such a break in continuity of coast-line, in the present case, is the Isthmus of Suez, and the unlikeness in the faunas is about what we might conceive that such a barrier should produce.
The general modern type of the fish-faunas being determined in the latter Eocene and the Miocene, the changes which bring us to recent times have largely concerned the abundance and variety of the individual species.
It is probably true that the faunas of no two distinct hydrographic basins are wholly identical, while on the other hand there are very few species confined to a single one.
Along the whole west coast, which is inhabited by a peculiar marine fauna, tertiary beds are so poorly developed, that no record of several {291} successive and peculiar marine faunas will probably be preserved to a distant age.
For example: It has been stated, and that on the very best authority, that the marine faunas of the two coasts of the Isthmus of Panama, which joins the two continents of North and South America, have but thirty per cent.
But this difference between the marine faunas of the two coasts of the Isthmus of Panama not only proves its long duration as a barrier of dry land, but some other deductions follow naturally enough.
Now we have seen that the difference between the marine faunas of the two sides of the isthmus proves its long duration.
A further study of the lower Eocene mammalian faunas of southwestern Wyoming.
Gazin's work has demonstrated this fauna to be intermediate in composition between similarly agedfaunas recovered from sites to the north and south.
In some of the heterocerous families several species are common to Ceylon and to Australasia, and in various cases the faunas of Ceylon and of Australasia seem to be more similar than those of Ceylon and of Hindustan.
Many insects, however, can readily extend their range, and a careful study of their distribution leads us to discriminate between faunas rather than definitely to map regions.
Mayr and others, while Scudder has studied the rich Oligocene faunas of Colorado (Florissant) and Wyoming (Green River).
All observations concur in showing that the fossil floras and faunas differ from the present animal and vegetable forms the more widely in proportion as the sedimentary beds to which they belong are lower, or more ancient.
In the fossiliferous strata are inhumed the remains of the floras and faunas of past ages.
Whence came that primordial organism whose transmuted descendants make up the existing faunas and floras of the globe?
He thought it likely that the successive faunas which palæontology discloses have originated from one another by descent.
In any event these continuous shiftings of faunas at the present day enable us to form some idea of the changes which must have occurred on innumerable occasions during man's history on this planet.
Toward the close of the Tertiary land bridges connected the two Americas, and an interchange of faunas followed.
All the beast faunas and all the human cultures from the eras of the chinless Heidelberg and Piltdown men to our own time will seem in that remote perspective practically contemporaneous.
Of the general paleontological facts, of the general aspects of the various faunas in various parts of the world, during some roughly indicated period of geologic time, we may be reasonably sure.
Their conformable systems are so closely related, and the change in their faunas is so gradual, that geologists are not agreed as to the precise horizon which divides them.
During the Lower Cretaceous alone there were no less than six successive changes in the faunaswhich inhabited the limestone-making sea which then covered Texas.
In fact," he continues, "the relationship between this southern fauna and the faunas of Europe and North America is so great as to practically amount to identity.
Yet, notwithstanding such facilities for migration, and the consequent similarity of facies I have referred to, the Palaeozoic faunas of different regions have usually certain distinctive characters.
The movements of upheaval, which caused the Cretaceous seas to disappear from such broad areas of the continental plateau, induced many changes in the floras and faunas of the globe.
We know that arctic and temperate faunas and floras flourished during interglacial times, and a like succession of life-forms followed the final disappearance of glacial conditions.
Surely the occurrence of a few forms, which are common to the Forest-bed and the underlying Crag, does not necessarily prove that the two faunasoccupied adjacent districts.
He thinks, therefore, that we may fairly conclude that the two faunas occupied adjacent areas.
Descending to the Mesozoic era, we find that the character and distribution of marine faunas are still indicative of uniformity.
But, instead of this, the affinities of these two sets of faunas are with those of their respective continents--as of course they ought to be on the theory of evolution.
Since then a great deal of attention has been paid to the fauna of this Mammoth cave, and also to the faunas of other dark caverns, not only in the New, but also in the Old World.
But as it would take too long to consider, even cursorily, the faunas and floras of these immense islands, I here allude to them only for the sake of illustration.
It may be only a few miles wide; yet it exercises a greater influence on the diversification of specific types, where fresh-water faunas are concerned, than almost any other.
Even as thus restricted, however, our subject-matter would be too extensive to be dealt with on the present occasion, were we to attempt an exhaustive analysis of the floras and faunas of all oceanic islands upon the face of the globe.
Besides, even if it were, we should have no right further to assume that the faunas of widely separated geographical areas were identical during the time represented by the intermediate formation.
Morphology); and, without waiting to go into details, it is notorious that the faunas of Australia and New Zealand are not only highly peculiar, but also suggestively archaic.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "faunas" in a variety of sentences. We hope that you will now be able to make sentences using this word.
