# 1911 Encyclopædia Britannica/Zoological Distribution

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​ZOOLOGICAL DISTRIBUTION (also known as Zoogeography), the science dealing, in the first place, with the distribution of living animals on the surface of the globe (both land and water), and secondly with that of their forerunners (both in time and in space). The science is thus a side-branch of zoology, intimately connected on the one hand with geography and on the other with geology. It is a comparatively modern science, which dates, at all events in its present form, from the second half of the 19th century.
Different parts of the land-surface of the globe are inhabited by different kinds of animals, or, in other words, by different faunas. These differences, in many cases at any rate, are not due to differences of temperature or of climate; and they do not depend on the distance of one place from another. The warm-blooded land-animals of Japan are, for example, very much more closely related to those of the British Isles than is the corresponding fauna of Africa to that of Madagascar. Again, on the hypothesis of the evolution of one species from another, in the case of land-animals unprovided with the means of flight such resemblances and differences between the faunas of different parts of the world depend in a great degree on the presence or absence of facilities for free communication by land between the areas in question. Prima facie, therefore, it is natural to suppose that the fauna of an island will differ more from that of the adjacent continent than will those of different parts of that continent from one another.
To a great extent this is the case; and if the present continents and islands had always been in statu quo, the proposition ​would, for the most part at any rate, be universally true. Geology has, however, taught us that many parts of what are now continents formed at earlier periods of the earth's history portions of the ocean-bed, while what are now islands have in some instances been connected with the adjacent mainlands, or even with land-masses the sites of which are now occupied by the open sea.
We can hope, therefore, to understand and explain the present distribution of terrestrial animal life only by taking into account what geology teaches us as to past changes in the configuration of the land-masses of the globe, accompanied by investigations into the past history of animals themselves, as revealed by their fossil remains.
Although to understand the reason of many facts in the present distribution of animals—as, for example, why tapirs are confined to the Malay countries and South America—it is essential to study fossil faunas, yet it has been found possible from the consideration of existing faunas alone to map out the land-surface of the globe into a number of zoological "regions," or provinces, more or less independent of the ordinary geographical boundaries, and severally characterized by a greater or smaller degree of distinctness in the matter of their faunas. One of the pioneers in this line of research was Dr P. L. Sclater, who in a paper on the geographical distribution of birds, published in the Journal of the Linnean Society of London for 1858, was enabled to define and name six of such zoological regions; these being mainly based on the distribution of the perching or passerine birds. Two years later Dr A. Russel Wallace, in the same journal, discussed in some detail the problems presented by the distribution of animals in the Malay Archipelago and Australasia. This preliminary essay was followed in 1876 by the appearance of the latter author's Geographical Distribution of Animals, an epoch-making work, which may be said to have first put the study of the distribution of animals generally on a thoroughly firm and scientific basis. With some slight modifications, the names proposed for the six zoological regions by Dr Sclater were adopted by Dr Wallace. Certain changes in regard to the limits and number of the zoological regions adopted by Sclater and Wallace have been proposed; but the original scheme forms the basis of all the later modifications, and these eminent naturalists are entitled to be regarded as the fathers of the study of distributional zoology. T. H. Huxley was also one of those who did much to advance the science in its early days, while among those who have proposed more or less important modifications of the original scheme special mention may be made of Dr W. T. Blanford, Dr A. Heilprin, Prof. P. Matschie and Prof. Max Weber.
The zoological regions proposed by Dr Sclater were based mainly on the distribution of the perching birds; but in the writings of Dr Wallace and of later authors mammals were very largely taken into consideration, and in later schemes there has been a similarly extensive use of the evidence afforded by mammalian distribution. That different groups of animals do not agree with another in the matter of geographical distribution will be evident when we reflect that in many instances there are very great differences in the relative ages of such groups, or, at all events, in the dates of their dispersal, or "radiation," over the surface of the earth. The radiation and dominance of reptiles, for example, greatly antedated that of either birds or mammals. Consequently, the zoological regions indicated by the present geographical distribution of the former group are very different from those suggested by the distribution of the two latter. If zoological regions are based on the evidence of the existing distribution of animals, groups with a relatively late radiation are clearly to be preferred to those the dispersal of which was earlier. Mammals and birds, therefore, are of greater value from this point of view than reptiles; while the absence of the power of flight in the great bulk of the class renders the evidence afforded by mammals superior to that derived from birds. The marked general agreement between the geographical distribution of birds on the one hand and of mammals on the other is, however, a fact of the greatest importance in regard to the value of the zoological regions established on their evidence. Further testimony in the same direction is afforded by the distribution of certain other groups, more especially spiders (Arachnida); and it is also noteworthy that the distribution of the three main divisions of the human race accords to a certain extent with the boundaries of some of the zoological regions based on the distribution of the lower animals.
With regard to the theory of the polar origin of life and the gradual dispersal of animals from the arctic regions, it may be briefly stated that the presumed series of radiations of life southward from the northern pole can have nothing to do with the present geographical distribution of animals, since we have abundant evidence that mammals have been spread over the whole of the warmer parts of the globe since, at any rate, the commencement of the Tertiary period, while the radiation of reptiles commenced at a much earlier epoch.
As regards barriers to the free dispersal of nonvolant terrestrial animals these may be grouped under two main heads, namely, climatic and geographical, of which the second is by far the more important. At the present day a certain number of animals are fitted to live respectively only in hot and in cold climates. The man-like apes and elephants among mammals, and trogons and parrots among birds, are, for example, now exclusively dwellers in tropical or subtropical climates; whereas the polar bear, the musk-ox and ptarmigan are equally characteristic of the arctic zone. To a great extent this must be regarded as a comparatively modern adaptive feature, since many of these arctic and tropical animals belong to groups the distribution of which, either in the past or the present, is more or less independent of climate. Elephants, for instance, formerly inhabited Siberia at a time when the climate, although probably less cold than at present, was certainly not tropical; while the polar bear is a specialized member of a group some of the representatives of which are denizens of the tropics.
It is true, indeed, that within the limits of the different zoological regions temperature-control has had an important influence on the distribution of animals, and has resulted in certain cases in the formation of life-zones, as in North America. As remarked, however, by H. A. Pilsbry and J. H. Ferriss in connexion with, the distribution of land-molluscs, "the life- zones of the United States as mapped by Dr C. H. Merriam emphasize the secondary and not the primary facts of distribution. The laws of temperature-control do not define transcontinental zones of primary import zoologically. These zones are secondary divisions of vertical life-areas of which the molluscan faunas were evolved in large part independently." And what is true of molluscs will hold good in the case of several other groups.
​There is also the phenomenon of vertical temperature-control. On this subject Dr A. R. Wallace has written (Ency. Brit., 9th ed., art. "Distribution"): "As we ascend lofty mountains, the forms of life change in a manner somewhat analogous to the changes observed in passing from a warm to a cold country. This change is, however, far less observable in animals than in plants; and it is so unequal in its action, and can so frequently be traced to mere change of climate and deficiency of food, that it must rank as a phenomenon of secondary importance. Vertical distribution among animals will be found in most cases to affect species rather than generic or family groups, and to involve in each case a mass of local details.… The same remarks apply to the bathymetrical zones of marine life. Many groups are confined to tidal, or shallow, or deeper waters; but these differences of habit are hardly geographical, but involve details, suited rather to the special study of individual groups." Temperature-control is therefore mainly a factor which has acted independently in the different zoological regions of the globe, and as such demands little or no further mention in a general sketch of the present nature.
The same remark will apply in the case of the influence of humidity on distribution, and also as regards "station." To illustrate the latter we may take the instances of the European squirrel and the chamois, the former of which is found only in wooded districts and is entirely absent from the open plains, while the latter occurs only in the isolated mountain ranges of the Pyrenees, the Alps, the Apennines and the Caucasus. The distributional area of both may, however, be regarded as including Europe generally, so that these local restrictions of range have nothing to do with the wider problems of distribution.
Very different is the case with regard to geographical barriers to the free dispersal of terrestrial animals. It should be observed, however, that even these act with different degrees of intensity in the case of different groups. From the fact that the great majority of them are oviparous, reptiles, whose powers of dispersal in the adult state are generally as restricted as those of mammals, have an advantage over the latter in that their eggs may be carried long distances on floating timber down rivers and thence across the ocean, or may even be occasionally transported by birds. The eggs of batrachians, like those of fresh-water fishes, will in some cases at any rate withstand being frozen, and hence conceivably may be transported by floating ice. Adult insects may be carried in the same manner as the eggs of reptiles. After all, however, such unusual means of transport are probably of no great importance; and it seems most likely that the varying features in the geographical distribution of different groups of animals are due much more to differences in the dates of radiation, or dispersal of those groups, than to varying degrees of facility for overcoming natural geographical barriers to dispersal.
The greatest barriers of all are formed by the ocean and the larger rivers; and from the former factor it follows that zoological regions coincide to a considerable extent—although by no means altogether—with the main geographical (as distinct from political) divisions of the earth's surface. In the main, mammals and other nonvolant terrestrial animals are debarred from crossing anything more than comparatively narrow channels of the sea, while even these and the larger rivers form a more or less effectual barrier to the dispersal of the great majority of the species. Hence it results that oceanic islands are usually devoid of such forms of life; while it may be laid down, as a general rule, that the existence of nearly allied types of terrestrial animals in countries now separated by stretches of sea implies a former land-connexion between them. There are, however, in many cases great difficulties in determining the nature of such connexions, largely owing to the fact that we are still in the dark as to whether the dispersal of many groups of animals has taken place down the lines of the present continents from north to south or equatorially by means of belts of land long since swallowed up by the ocean. In this connexion it may be remarked, as tending against the old idea of the radiation of all the modern groups of terrestrial animals from the north towards the south, that there is decisive evidence to prove the existence during the Tertiary period (so far at least as mammals are concerned) of certain great centres of development, and in some instances, at all events, also of radiation, in the southern hemisphere; one of these developmental centres being in Africa a second in South America, and a third in Australia.
To the general law that straits and arms of the sea form an effectual barrier to the dispersal of the larger land-animals, and more especially mammals, certain exceptions may be pleaded. Jaguars have, for instance, been known to cross the Rio de la Plata, while tigers constantly swim from island to island in the delta of the Ganges and probably also in the Malay Archipelago, and a polar bear has been observed swimming twenty miles away from land in Bering Sea. Deer, certain antelopes, pigs and elephants are also good swimmers; while hippopotamuses and crocodiles—especially the latter—can cross channels of considerable width. The great tropical and subtropical rivers also carry down masses of floating soil or large trees upon which mammals and reptiles are borne, and although in many or most instances such are swept out to sea and their occupants drowned, in other instances they may be stranded upon the opposite bank or shore where their living freight can effect a landing. Such instances, however, cannot be very frequent, and they cannot affect widely sundered countries, owing to the lack of food supplies. Moreover, supposing a mammal to have reached a new land, unless it happened to be a pregnant female, or unless another individual of the opposite sex be similarly stranded, it would eventually die without progeny. Even in the case of a pregnant female, there is no certainty that the offspring, if but one, would be a male; and even supposing this to be the case, the progeny might perish from the attacks of other animals or from inbreeding. On the whole, it may be said, that instances of such methods of dispersal must be relatively few and can affect only countries not very widely sundered. The most important case that can be cited is the occurrence of a pig and an extinct hippopotamus in Madagascar, which probably reached that island by swimming from Africa. As a rule, a strait like that separating Ceylon from India may be considered an effectual barrier to the dispersal of large land-animals.
Although the Rio de la Plata has effectually prevented the amphibious carpincho from reaching Argentina, deserts form even more impassable barriers than large rivers, the Sahara having prevented the North African fauna from reaching the heart of that continent. High and continuous mountain-ranges are likewise most effective in restricting the range of animals; this being more especially the case when, like the Himalaya, their trend is equatorial instead of, as in the case of the Rocky Mountains and the Andes, from north to south in the direction of the main continental extension. Forests also present great obstacles to animal migration, although this is to a great extent of a local nature and comes, in fact, under the category of "station." Indeed, there appears to be no instance of the separation of one zoological region from another by forest alone.
Lastly it should be mentioned that ice may serve as a factor in the dispersal of animals by acting as a bridge between different land-areas; and at some period this means of communication may have aided in the great migrations of animals that have taken place between the Old and the New World by way of what is now Bering Sea.
I. Terrestrial Distribution
The zoological regions recognized by Dr A. R. Wallace in 1876, which are in the main identical with those Zoological Regions.proposed by Dr P. L. Sclater in 1858, and are chiefly based on the distribution of birds and mammals, are as follows:—
1. Palaearctic, which includes Europe to the Azores and Iceland, temperate Asia from the high Himalaya and west of the Indus, with Japan, and China from Ningpo and to the north of the watershed ​of the Yane-tse-kiang; also North Africa and Arabia, to about the line of the tropic of Cancer.
2. Ethiopian, including Africa south of the tropic of Cancer, as well as the southern part of Arabia, with Madagascar and the adjacent islands.
3. Oriental, or Indo-Malay, comprising India and Ceylon, the Indo-Chinese countries and southern China, and the Malay Archipelago as far as the Philippines, Borneo and Java.
4. Australian, composed of the remainder of the Malay Archipelago, Australia, New Zealand and all the tropical islands of the Pacific, as far east as the Marquesas and the Low Archipelago.
5. Neotropical, which comprises South America and the adjacent islands, the West Indies or Antilles, and Central America and Mexico.
6. Nearctic, consisting of temperate and arctic North America, with Greenland.
"These six regions," remarks Dr Wallace, "although all of primary importance from their extent, and well marked by their total assemblage of animal forms, vary greatly in their zoological richness, their degree of isolation and their relationship to each other. The Australian region is the most peculiar and the most isolated, but it is comparatively small and poor in the higher animals. The Neotropical region comes next in peculiarity and isolation, but it is extensive and excessively rich in all forms of life. The Ethiopian and Oriental regions are also very rich, but they have much in common. The Palaearctic and Nearctic regions being wholly temperate are less rich, and they too have many resemblances to each other; but while the Nearctic region has many groups in common with the Neotropical, the Palaearctic is closely connected with the Oriental and Ethiopian regions."
In Dr Sclater's original scheme the first four of the above regions were bracketed together under the designation of Palaeogaea, and the fifth and sixth, or those belonging to the New World, as Neogaea. T. H. Huxley, in a paper on the distribution of game-birds, published in the Proceedings of the Zoological Society of London for 1868, instead of dividing the world into an eastern and a western division, adopted a northern and a southern division, calling the former Arctogaea, and the latter (which included Australasia and the Neotropical region of Messrs Sclater and Wallace, but not the Ethiopian region) Notogaea.
In 1874 Dr Sclater, taking mammals as well as birds into consideration, adopted Huxley's Arctogaea as the major northern division to include the Nearctic, Palaearctic, Oriental and Ethiopian regions; and instead of Huxley's Notogaea recognized three primary divisions, namely, Dendrogaea for the Neotropical region, Antarctogaea for the Australian region (in a somewhat restricted sense), and Ornithogaea for New Zealand and Polynesia.
The tendency of these amendments on the original scheme of a simple division into six regions was to recognize three primary divisions of higher rank than such "regions." This view was adopted in 1890 by Dr W. T. Blanford, who proposed to designate these three major divisions of the earth's land surface respectively the Australian, the South American and the Arctogaean regions. A weak point in this scheme is that since the term "region" is likewise applied to the subdivisions of Arctogaea, there is a danger of confusion between the primary and secondary divisions. An amendment proposed anonymouslyin 1893 was to substitute the names Notogaea, Neogaea and Arctogaea for the three primary divisions of Dr Blanford. Yet another emendation, suggested by R. Lydekker and subsequently adopted by Prof. H. F. Osborn, was to designate these three primary divisions as "realms," and to reserve the name "region" for their subdivisions.
Emendations on the original scheme also included modifications in the limits of the regions themselves. In 1878, for instance, Dr A. Heilprin (in accordance with a suggestion of
Prof. A. Newton) proposed to nuite the Nearctic with the Palaearctic region under the name of Holarctic; separating at the same time from the former a "transitional" Sonoran, and from the latter a similar Mediterranean, or Tyrrhenian, region, while he also recognized a distinct Polynesian region, distinguished in the main by negative characters. The Sonoran region was subsequently adopted by Dr C. H. Merriam in 1892, and later on by Dr Blanford in the address already cited, the title being, however, changed to Medio-Columbian. A most important proposal was also embodied in Dr Blanford's scheme, namely, the separation from the Ethiopian region of Madagascar and the Comoro islands to form a separate Malagasy region. Another modification of the original scheme was to transfer the island of Celebes, together with Lombok, Flores and Timor, from the Australian to the Oriental region, or to regard them as representing a transitional region between the two. The effect of this change was practically to abolish "Wallace's line" (the deep channel between the islands of Bali and Lombok and thence northward through the Macassar Strait), the deepest channel being really situated to the eastward of Timor.
The later evolution of the scheme, as presented by Dr Max Weber, may be tabularized, with some slight alteration, as follows, the "realms" being printed in capitals, the regions and sub-regions in ordinary type, and the transitional regions in italics:—
I. Arctogaea :
| 1. Holarctic. | 1. Holarctic. | 3 . Malagasy. | 4. Oriental. |
| Nearctic Sonoran | Palaearctic Mediterranean | | Austro-Malayan |
| II. Neogaea | | III. Notogaea. | |
| 5. Neotropical. | 5. Neotropical. | | 6. Australian |
| | | | (?) 7 . Polynesian |
| | | | (?) 8. Hawaiian. |
In the accompanying map the Sonoran and Mediterranean transitional regions are represented as equivalent in value to the main regions, and the Austro-Malayan transitional region is not indicated. The recognition of a Polynesian and still more of a Hawaiian region, is provisional.
The most distinct of the three primary realms is undoubtedly Notogaea, the Australian section of which is the sole habitat of egg-laying mammals (Monotremata) and of a great Notogaea. variety of marsupials, inclusive of the whole of the diprotodonts, with the exception of the few (cuscuses) found in the Austro-Malayan transitional region. Apart from monotremes and marsupials, the only indigenous mammals found in Notogaea are rodents and bats, with perhaps a pig in New Guinea; although it is most probable that the latter is introduced, as is almost certainly the dingo, or native dog, in Australia. The rodents are all referable to the family Muridae, and are mostly of peculiar types, such as the golden water-rat (Hydromys) and the jerboa-rats (Conilurus, Notomys, &c.); they are, however, in many instances more or less nearly related to species found in Celebes, the mountains of the Philippines and Borneo, and apparently represent an ancient fauna. The mammalian fauna of Notogaea is practically limited to the Australian region, its indigenous representatives in New Zealand being only a couple of bats, The monotremes are in all probability the survivors of a group which was widely spread in Jurassic times; while marsupials, as represented by the American opossums (Didelphyidae), had a very wide range even as late as the Oligocene division of the Tertiary period. The diprotodont marsupials may not improbably have originated within the Australian region, or this region conjointly with the Austro-Malayan transitional region.
Notogaea is likewise the home of a number of peculiar types of birds, some of which range, however, into the Austro-Malayan area, that is to say, Celebes and Ceram. In the Australian region the ​peculiar avian families include the birds-of-paradise (Paradiseidae), the honeysuckers (Meliphagidae), and the lyre-birds (Menuridae) among the perching group, the cockatoos (Cacatuidae) and lories (Loriidae) among the parrots, the mound-builders, or brush-turkeys (Megapodiidae) among the game-birds, and the cassowaries and emeus (Casuariidae and Dromaeidae) in the ostrich group. The peculiarity of the region is also marked by the absence of certain widely spread family groups, such as the barbels (Megalaemidae), the otherwise cosmopolitan woodpeckers (Picidae), the trogons (Trogonidae), and the pheasant and partridge tribe (Phasianidae).
The reptiles, owing probably to tneir earlier radiation, are much less peculiar, such widely spread types as the monitors (Varanidae) and skinks, (Scincidae) being abundant, as are also crocodiles (Crocodilidae). The tortoises belong, however, exclusively to the side-necked group (Pleurodira), now restricted to the southern hemisphere; among these the most noteworthy being the giant horned tortoise (Mioiania) from the Pleistocene of Queensland, which belongs to a genus elsewhere known only from the South American Tertiary. The Australian lung-fish (Ceratodus, or Neoceratodus) is the sole survivor of a widely spread Triassic and Jurassic type. The salmon tribe (Salmonidae), however, is notable for its absence, although one peculiar form occurs in New Zealand; and the Cyprinidae, or carps, are wanting throughout 'the realm, this absence extending to Celebes, although in Borneo the group is abundantly represented.
New Zealand, here provisionally included in a separate Polynesian region, is characterized by the absence of all indigenous mammals except two bats, each representing a peculiar genus. Among birds, the Neogaeic family Meliphagidae includes several peculiar genera, as does also the widely spread starling group (Sturnidae) ; while the parrots of the genera Siringops and Nestor are likewise peculiar. Still more noteworthy is the abundance of the ostrich group, represented by the living kiwis (Apteryx), and the moas (Dinornithidae) which have been exterminated within comparatively recent times. Reptiles are scarce, but among them the tuatera lizard (Sphenodon) is especially noteworthy on account of being the sole survivor of an ordinal group (Rhynchocephalia) widely spread during Triassic and Jurassic times.
Of the Hawaiian area (whether or no rightly regarded as a distinct region), it must suffice to state that it is the sole habitat of the gorgeously coloured birds known as mamos, or sickle-bills (Drepanididae).
With regard to the origin of the modern fauna of Notogaea, and more especially the Australian region, as here restricted, we enter extremely debatable ground. Dr Wallace, who refused to admit the existence of any great inter-continental connexions in the past, was of opinion that Australia received the ancestors of its marsupials and monotremes from Asia by way of the Austro-Malayan area (as it certainly has its rodents) "far back in the Secondary period." This view has been endorsed by the present writer who suggested the early Eocene as the most probable date of immigration; and it has also received the assent of Dr Max Weber, who is of opinion that in pre-Tertiary—very likely Cretaceous—times Australia was united by land with Asia. A Euro-Asiatic fauna inhabited this land, from which during the Eocene a southern portion was cut off by partial submergence, this southern portion being the modern Australia and New Guinea, the home of monotremes, marsupials and ancient forms of other groups, such as cassowaries and birds-of-paradise, while widely distributed specialized types are wanting. Northwards extended a coral-sea, in the islands of which dwelt primitive rodents, insectivores and other ancient groups, with perhaps cuscuses. During the Miocene, great changes of level took place in the archipelago, which attained its present form in the Pleistocene. Celebes was insulated early, Java later. Intermittent land-connexions took place, which allowed of periodical immigrations of Asiatic forms from one side and of Australian types from the other. The question is left undecided whether the cuscuses of the Austro-Malayan islands are remnants of the primitive Euro-Asiatic fauna or later immigrants from Australia. The suggestion is also made that the Australian and Philippine rodents are survivors of the original pre-Tertiary fauna, although it is admitted that the specialization of Hydromys is against this. The author fails to see [any evidence in favour of a former connexion of Australasia with either South America or a former large antarctic continent (Antarctica).
While admitting that this may be the true explanation, Mr B. A. Bensley considers it possible that opossums (Didelphyidae), which he regards as the ancestral stock of the marsupials, may have effected an entrance into Neogaea by way of Antarctica. In either event, he would place the date of entry as post-Eocene; but against this view is the occurrence of remains of a diprotodont marsupial (Wynyardia) in Tasmanian strata believed to be of Eocene age. Prof. Baldwin Spencer is also of opinion that the Australian marsupials and monotremes reached their present habitat by means of a land-connexion in the south subsequent to the insulation of New Zealand. This, of course, implies the existence of an extinct southern marsupial fauna of which we have no knowledge except in the case of the Epanorthidae of Patagonia.
That Australia formed part of a great equatorial land-belt connecting the southern continents in Jurassic times appears to be demonstrated by the evidence of the "Gondwana flora." The question is whether such a connexion—either by way of Antarctica or not—persisted in the case of Neogaea long enough to admit of the ancestors of the modern fauna (supposing it all to have come by a southern route) having effected an entrance. The existence of such a land-bridge was suggested by Sir Joseph Hooker in 1847; and the idea of a late connexion between Neogaea and Notogaea has been adopted by L. Riitimeyer (1867), Captain F. W. Hutton (1873), Prof. H. O. Forbes (1803), Mr C. Hedley (1895), Dr H. von Ihering (1891 and 1900), Prof. H. F. Osborn, who takes an intermediate view of the extent of the part played by Antarctica (1900), and by Dr A. F. Ortmann (1902). On the other hand, Dr T. Gill (1875) believed in the existence of an "Epgaea" connecting the three great continents exclusive of Antarctica; and in 1884 Capt. Hutton, abandoning his former view, suggested the connexion of Australia and South America by means of a mid-Pacific continent. A summary of these views, with references, is given by Dr Ortmann in vol. xxxv. pp. 139-142 of the American Naturalist (1901).
So far as mammals are concerned, the evidence in favour of a comparatively late land-connexion is weakened by the recent view that certain supposed Patagonian Tertiary marsupials, such as Prothylacinus, are really creodont Carnivora. On the other hand (putting aside these carnivores), Mr W. J. Sinclair is of opinion that the living South American marsupial Caenolestes and its extinct relatives are annectant forms between diprotodonts and polyprotpdonts, and not far removed from the ancestral stock which gave rise to the Australian phalangers. The occurrence in the Tertiary of Patagonia of primitive opossums, which cannot be regarded as ancestral to the modern South American forms, is also an important determination. From this, coupled with the testimony afforded by the invertebrate faunas, he considers himself justified in stating that "considerable evidence is now available to show that a land-connexion between Patagonia and the Australian region existed not later than the close of the Cretaceous or the beginning of the Tertiary, and it is possible that at this time the interchange of marsupials between the two continents was effected. Whether the marsupials originated in South America and migrated thence to Australia, or the reverse, cannot at present be determined." The above-mentioned tortoises of the genus Miolania also appear to afford strong evidence of the persistence of the Jurassic connexion between Notogaea and Neogaea to a comparatively late epoch.
Again, Prof. W. B. Benham, from the evidence of earthworms, is strongly disposed to believe in a late connexion between the areas in question. From their invariable association with angiospermous plants, this author is of opinion that earthworms are a comparatively modern group, which did not attain any important development before the Cretaceous. The ancestral type would appear to have been more or less nearly related to the existing Notiodrilus, of which the headquarters, if not the birthplace, was the "Melanesian plateau." New Zealand and the neighbouring islands, which possess the most ancient worm-fauna, were separated at an early date from this plateau. From this area the primitive worms travelled in one direction into the Austro-Malayan countries, while in another, by way of Antarctica, they reached South America and Africa. With this brief summary of the chief views, this part of the subject must be dismissed without the writer being committed to any definite conclusion.
Next to Notogaea the most distinct faunistic continental area, so far at any rate as its present and later Tertiary mammals are concerned, is Neogaea, containing, as we have seen, only Neogaea.Neogaea. the Neotropical region. It is remarkable as being, with the exception of Notogaea, the only land-area which contains at the present day more than one living genus of marsupials, and also a large middle Tertiary marsupial fauna. The living marsupials include a large number of true opossums, constituting the family Didelphyidae and Caenolestes the surviving representative of the Epanorthidae of the Patagonian Tertiaries. The opossums are represented by the genera Chironectes and Didelphys; the latter divisible into a number of sub-genera of which the typical group alone ranged into North America. Whether the modern opossums belong to the endemic Neogaeic fauna, or whether they are late immigrants from the north (where they were represented in the Oligocene of both hemispheres), is a question in regard to which a definite answer can scarcely at present be given. It appears, however, that Microbiotherium and certain allied forms from the middle Tertiary of Patagonia are endemic representatives of the Didelphyidae which did not give rise to the modern types. The Epanorthidae, in the opinion of Prof. Max Weber, indicate a subordinal group by themselves; and if this be correct their evidence ​in favour of a land-connexion between Neogaea and Notogaea cannot have the weight attributed to it by Mr W. J. Sinclair.
The typical Edentata (sloths, anteaters and armadillos) are at the present day practically confined to Neogaea where they have existed from the date of the Santa Cruz beds of Patagonia (which are probably of Miocene age). A few armadillos, however, have penetrated into Texas; and in the Pleistocene epoch several representatives of the extinct ground-sloths (Megatheriidae) and a glyptodon, or giant armadillo, also ranged into North America. The group is, however, essentially Neogaeic. Among the monkeys the Cebidae, or American monkeys, and their relatives the Hapalidae, or marmosets, are likewise peculiar to Neogaea, where they date from the Santa Cruz epoch. The vampire-bats, or Phyllostomatidae, are likewise peculiar to this realm, and are doubtless also endemic. With the exception of a few shrew-mice, which have evidently entered from the north, continental Neogaea is at the present day devoid of Insectivora. It is, however, very note-worthy that one peculiar family (Solenodontidae) of the order, apparently nearly allied to the Malagasy Centetidae (tenrecs), occurs in the West Indies, while the extinct Necrolestes, believed to be near akin to the African golden moles (Chrysochloridae), is found in the Santa Cruz beds. Rodents of more or less peculiar types are highly characteristic of Neogaea and for the most part date from the Santa Cruz epoch. Among these the Caviidae, Chinchillidae and Octodontidae are peculiar to this realm, while the Capromyidae are common to the Ethiopian region of Arctogaea, but are unknown elsewhere.
Ungulates are in the main very poorly represented in Neogaea and include only the llama group (guanaco, &c.), tapirs, and certain small or medium-sized deer related to North American types. Palaeontological evidence tells us that these, like certain peculiar genera of horses now extinct (such as Hippidium) and mastodons, were comparatively recent intruders into the realm from the north. On the other hand, Neogaea at the date of the deposition of the Santa Cruz beds was the home of certain endemic groups of ungulates, such as the Toxodontia and Litopterna, some of the representatives of which (Toxodon and Macrauchenia) flourished during the Pleistocene Pampean epoch.
Of the Carnivora, the civet group (Viverridae) is absent, and the representatives of the dog tribe (Canidae), bears (Ursidae), of which there is only a single existing representative, cats (Felidae), and probably raccoons (Procyonidae), must be regarded as intruders from the north, although several genera of the last-named group are peculiar to the area. In the Santa Cruz epoch the place of these modern specialized Carnivora was taken by marsupial-like creodonts, such as Prothylacinus.
In birds Neogaea is especially rich and contains more than a score of family groups unknown elsewhere. Several of these, such as the tyrant-birds (Tyrannidae), manakins (Pipridae), chatterers (Cotingidae), ant-thrushes (Formicariidae), the oven-bird group (Dendrocolaptidae) , plant-cutters(Phytotomidae) , and wren-thrushes (Pteroptychidae), belong to a low and generalized type of the perching, or passerine, group. Among the so-called picarian birds, which are likewise a generalized type, the big-billed toucans (Rhamphasiidae), puff-birds (Bucconidae), jacamars (Galbulidae), motmots (Momotidae), and the vast assemblage of humming-birds (Trochilidae) are in the main peculiar to this realm, although some of the last- named family wander to the northward in summer. The condors (Cathartidae), form a highly characteristic Neogaeic family; while the hoatzin (Opisthocomus) represents another. Of the higher forms of perching-birds the quit-quits (Coerebidae), greenlets (Vireonidae), the hang-nests and many other representatives of the Icteridae, and the tanagers (Tanagridae) are exclusively Neogaeic ; while crows, starlings, thrushes, warblers and flycatchers are either rare or wanting, although the finches are abundant. Parrots are numerous, and represented by peculiar forms such as the macaws (Ara) and conures or ordinary South American parrots (Conurus). Very characteristic of the realm, and unknown elsewhere are the curassows and guans (Cracidae) among the game-birds, the chajas, or screamers (Palamedeidae), the trumpeters (Psophiidae), sun-bitterns (Eurypygidae), and the seriema (Cariamidae). Allied apparently to the last is Phororhachos, a giant extinct bird from the Santa Cruz beds with a skull nearly as large as that of a pony. The tinamous (Tinamidae), possibly an annectant type between game-birds and the ostrich group, and the rheas or American ostriches (Rheidae) are likewise exclusively Neogaeic. It may be added that the distribution of all the members of the ostrich group affords a strong argument in favour of a former union of the southern continents, especially as their earliest known representative is African.
Among reptiles, the tortoises, with the exception of representatives of the terrestrial genus Testudo, all belong to the Pleurodira, and include several peculiar generic types such as Chelys (matamata) and one, Podocnemis, common to Madagascar. The occurrence in the Tertiary of Patagonia of a representative of Miolania, else-where known only from the Pleistocene of Queensland, has been already mentioned. A number of snakes of the boa group (Boinae) occur in the realm, to which the genus Eunectes anacondas) is restricted; but Boa itself, like Podocnemis among the tortoises, is common to Neogaea and Madagascar. The blind burrowing-snakes of the family Glauconiidae occur throughout the warmer parts of the realm, and are also found in Africa and south-western Asia. The caimans or South American alligators (Caiman) are solely Neogaean; the iguanas (Iguanidae) are mainly peculiar to the realm, although a few inhabit North America, and there are two outlying genera in Madagascar and a third in Fiji. The tejus (Tejidae) are wholly Neogaean. The Xantusiidae are exclusively Central American and Antillean; while the Amphisbaenidae are practically restricted to Neogaea and Africa. On the other hand, Lacertidae, Varanidae and Agamidae are absent. Tailed amphibians are unknown south of Central America; but the region is the home of several peculiar types of toads, such as Pipa (Surinam toad) belonging to an otherwise Ethiopian section, and the majority of the family Cystignathidae, as exemplified by the horned toad and the escuerso (Ceratophrys), the remainder of the group being Australian.
Freshwater fishes are very abundant in Neogaea, where they are represented by a number of peculiar generic and certain family types; some of the members have developed the remarkable habit of feeding upon the floating fruits abundant in the rivers of the tropical forest-districts.
The electric eels (Gymnotidae) are peculiar to the waters of Neogaea, as are certain other groups, such as the armoured cat-fishes (Loricariidae), while true cat-fishes (Siluridae) are extremely abundant. Perhaps, however, the most remarkable feature of the fish-fauna of Neogaea is its affinity to that of the Ethiopian region. Among the lung-fishes the family Lepidosirenidae is, for example, restricted to the two areas, with one genus in each, as is also the family Characinidae. Much the same may be said of the Cichlidae, which have, however, representatives in the Malagasy and Oriental regions; and the Cyprinodontidae, which are extremely abundant in Neogaea (where certain of their representatives are separated by some naturalists as a distinct family, Poeciliidae) likewise present the same general type of distribution, although their area includes the southern fringe of the Palaearctic sub-region and a considerable portion of the Oriental region.
As regards the past history of Neogaea, Professor Carl Eigenmann, writing in the Popular Science Monthly for June 1906, observes that "in the earliest Tertiary tropical America consisted of two land-areas, Archiguiana and Archamazonia, separated by the lower valley of the Amazon, which was still submerged. There was a land-mass, Hellenis, between Africa and South America, possibly in contact with Guiana and some point in tropical Africa. This land-mass, which was inhabited, among other things, by fishes belonging to the families Lepidosirenida (lung-fishes), Poeciliidae, Characinidae, Cichlidae and Siluridae (cat-fishes), sank beneath the surface of the ocean, forcing the fauna in two directions, towards Africa and towards South America, exterminating all types not moved to the east or to the west. From these two rudiments have developed the present diverse faunas of Africa and South America, each reinforced by intrusions from the ocean and neighbouring land-areas, and by autochthonous development within its own border.… The connexion between Africa and South America existed before the origin of present genera, and even before the origin of some of the present families and sub-families, some time before the early Tertiary. There has never been any exchange between Africa and South America since that time."
This connexion between Neogaea and Africa was doubtless a continuation of the old Jurassic equatorial land-belt to which allusion has been already made; freshwater fishes being probably a group of earlier radiation than mammals. Perhaps the distribution of the reptilian genera common to Neogaea and Madagascar may be explained in the same manner, although tortoises apparently identical with Podocnemis occur in the Eocene of Europe (as well as in that of Africa and India), so that this group may have radiated from the north. Whether the evidence of the Cystignathidae among the amphibians and of the extinct Miolania among chelonians is also evidence of the persistence of the Jurassic connexion between Neogaea and Notogaea till a considerably later epoch must, for the present, be left an open question. The distribution of other families of lizards is, however, not in favour of such a connexion, the Lacertidae and Agamidae being confined to the Old World, inclusive of Australia but exclusive of Madagascar, while the cosmopolitan Scincidae, so abundant in Notogaea, are extremely scarce in Neogaea.
Reverting to the mammalian fauna, its evidence, combined with that of geology, indicates that during the greater portion of the Tertiary period South America was isolated from North America, and inhabited by its autochthonous fauna of monkeys, marmosets, sloths, ground-sloths, ant-eaters, armadillos, glyptodonts, toxodonts, macrauchenias (together with certain other peculiar ungulates), rodents, marsupials and creodonts, as well as by Phororhachos, rheas, tinamous and probably some of the other groups of birds now peculiar to the area. This state of things continued till the later Miocene or Pliocene epoch, during some portion of which a connexion was established with North America by way of the isthmus of Darien. By means of this new land-bridge a certain proportion of the autochthonous fauna of Neogaea was enabled ​to effect an entrance into North America, as is exemplified by the occurrence there of ground-sloths and glyptodonts. Simultaneously a large immigration of northern forms took place into Neogaea; these invaders from Arctogaea, including cats and sabre-toothed tigers, bears, fox-like dogs, raccoons, llamas, horses, tapirs, deer, mastodons and perhaps opossums. While representatives of most of these invaders have persisted to the present day, some groups, such as horses and mastodons, have entirely disappeared, as has also a large portion of the autochthonous fauna. Here it may be well to notice that the evidence for the Insulation of Neogaea during a large portion of the Tertiary period does not by any means rest only on that supplied by mammals. C. H. Gilbert and E. C. Starks, for instance, in a work on the fishes of the two sides of the isthmus of Darien, wrote as follows: "The ichthyological evidence is over-whelmingly in favour of the existence of a former open communication between the two oceans, which must have become closed at a period sufficiently remote from the present to have permitted the specific differentiation of a very large majority of the forms involved. ... All evidence concurs in fixing the date of that connexion at some time prior to the Pleistocene, probably in the early Miocene." This, it will be observed, agrees almost precisely with the conclusions drawn from the fossil mammalian faunas of North and South America, which indicate that land-communication between those two continents was interrupted during a considerable portion of the Tertiary epoch, and only re-established (or [?] established for the first time) either towards the close of the Miocene or the early part of the Pliocene epoch.
The South American mammalian fauna, as we now know it, is, then, a complex, consisting of an original autochthonous element and of a large foreign infusion from the north. As to the origin of the latter, there is no difficulty; but some degree of obscurity still prevails with regard to the source of the autochthonous fauna. According to Prof. Eigenmann's interpretation of the evidence of the fresh-water fishes the early Tertiary Atlantic "Hellenis" may have been in contact with Guiana on the one side and tropical Africa on the other. That such a connexion did really exist in Tertiary times is the conclusion reached by Dr C. W. Andrews, as the result of his studies of the Tertiary vertebrate fauna of the Fayum district of Egypt, as expressed in the following passage: "Speaking generally, it appears that (1) probably in Jurassic times Africa and South America formed a continuous land-mass; (2) in the Cretaceous period the sea encroached southwards over this land, forming what is now the South Atlantic. How far this depression had advanced southwards at the end of the Secondary period is not clear, but it appears certain that the final separation of the two continents did not take place till Eocene times, and that there may have been a chain of islands between the northern part of Africa and Brazil which persisted even till the Miocene."
By this route, as was suggested considerably earlier by Prof. W. B. Scott and subsequently by the present writer, Neogaea may have received a considerable portion pi its autochthonous mammal-fauna. Further reference to this point is made later; but it may be added that the evidence of the land-faunas is supplemented by that of the shallow-water marine faunas on the two sides of the Atlantic, which present a striking similarity.
In an address to the British Association at the meeting in 1905 in South Africa Mr G. A. Boulenger expressed himself, however, as by no means satisfied with the evidence of a Tertiary connexion between Africa and South America. "It is undeniable," he observed, "that the hypothesis of a South Atlantic land-communication in the Eocene has much in its favour, and when this is really established, all difficulty in explaining the distribution of the Cichlidae will have disappeared. In the meanwhile ... we must not construct bridges without being sure of our points of attachment." In this connexion it may be mentioned that those who explain the distribution of certain forms of life by the former existence of a land-connexion between the southern continents ^by way of "Antarctica," have attached some importance to the existence of fishes of the genus Galaxias in the freshwaters of New Zealand, Australia, South America and the Cape. This evidence has been shattered by Mr Boulenger's description (in a memoir of the fishes of the Congo) of a marine representative of the genus in question from the Southern Ocean.
For the zoological subregions of Neogaea the reader must refer, as in the case of most of the other regions, to special works on zoological distribution.
As Arctogaea includes the whole of the rest of the land-surface of the globe (with the exception of Antarctica) it is almost impossible to give Arctogaea. any general diagnosis even of its mammalian fauna. It may be mentioned, however, that at the present day monotremes are wholly wanting, while marsupials are represented only by one or two species 01 opossums (Didelphys) in North America and by cuscuses (Phalanger) in the Austro-Malayan subregion. The true or typical Edentata are, if we except late wanderers from Neogaea into North America, absent from this realm at the present date and during the Pleistocene; the alleged occurrence of a ground-sloth in the Pleistocene of Madagascar being probably due to a misinterpretation. On the other hand, this region, and more especially its eastern half, is the great home of the ungulate mammals. Indeed rhinoceroses may be considered absolutely characteristic of Arctogaea, since at one time or another they have ranged over the whole area, except Madagascar, and are quite unknown elsewhere. The modern land Carnivora are likewise an essentially Arctogaeic group, which only found its way into Neogaea at a comparatively recent epoch; and the realm may be said to have been the birthplace of most of the higher groups of placental mammals. The tortoises of the family Trionychidae form an exclusively Arctogaean group, once ranging all over the realm, although long since extinct in Europe.
If Madagascar be excepted, the Ethiopian region (or Ethiopia) is the most distinct of all the regions of Arctogaea. So distinct is it that, on the evidence of the distribution of moths, Ethiopian region. Dr H. S. Packard has suggested that it should be separated from Arctogaea to form a realm by itself, under the name of Apogaea. The mammalian fauna, even exclusive of the Tertiary one of Egypt, does not, however, countenance such a separation. By Sclater and Wallace, Madagascar was included in the Ethiopian region, but that island was subsequently made a region by itself by Dr Blanford. This separation of Madagascar to form a Malagasy region has met with general acceptance; but in the opinion of Mr R. I. Pocock, who bases his conclusion on the distribution of trapdoor-spiders (which in other respects accords curiously well with that of mammals), it is not justified. The mammalian evidence appears, however, to be overwhelmingly strong in its favour; and it also receives support from reptilian distribution. All are agreed that the Ethiopian region should exclude that part of Africa which lies, roughly speaking, north-ward of the tropic of Cancer. By Sclater and Wallace the region was taken to include that portion of Arabia lying to the south of the same tropic; but Mr Pocock has pointed out that this separation of Arabia into two portions is not supported by the distribution of scorpions, and he would refer the whole of it to the Mediterranean transitional region. The occurrence of a tahr-goat (Hemitragus) in Oman lends some support to this proposal since that genus has no representative in Africa, and occurs else-where only in the Himalaya and the mountains of southern India. Other writers have not accepted Mr Pocock's emendation; and the reference of the northern half of Arabia to the Mediterranean and of the southern half to the Ethiopian region is usually followed. The area is admittedly a meeting-ground of at least two faunas.
Discoveries in the Fayum district of Egypt have conclusively proved that during the early (Eocene) part of the Tertiary period Ethiopia was a great centre of development, and subsequently of dispersal, instead of having received (as was formerly supposed) the whole of its higher modern mammalian fauna from the north. In this Ethiopian centre were developed the ancestors of the elephants (Proboscidea) and of the hyraxes (Hyracoidea); the latter group being represented by species of much larger size than the existing forms, some of the former of which ranged into southern Europe during the later Tertiary. It was also the home of a peculiar subordinal group of ungulates (Barypoda), typified by Arsinoitherium, and may likewise have been the birthplace of the swine (Suidae) as the earliest known representative of that group (Geniohyus) occurs in the Fayum Eocene. The hippopotamuses (Hippopotamidae), which appear to be descended from the Tertiary Anthracotheriidae, may likewise be of Ethiopian origin, and the same may turn out to be the case with the giraffe group (Giraffidae) although definite evidence with regard to the latter point is wanting.
The occurrence of an ostrich-like flightless bird in the Fayum Eocene—the oldest known representative of that group—is suggestive that the Ratitae originated in Ethiopia, which would accord well with their distribution both in the present and the past. A giant land-tortoise (Testudo) is likewise known from the Fayum beds, and as it is allied to the species recently or still inhabiting Madagascar and the Mascarene islands, there is a strong probability that Ethiopian Africa was likewise the centre of development and dispersal of that group.
Turning to its existing mammalian fauna, Ethiopia possesses a number of peculiar family or generic groups, and is also nearly equally well characterized by the absence of others. As remarked by Wallace, one of its characteristics is the great number of species of large size. Among the Primates, it is the home of the typical group of the Negroid branch of the human species, whose northern limits coincide approximately with the boundary of the region itself, being replaced in northern Africa by races of the Caucasian stock. Gorillas and chimpanzees (Anthropopithecus) are peculiar to the region, as are also baboons (Papio and Theropithecus), if southern Arabia be included. Monkeys abound, and although in most cases nearly allied to those of the Oriental region, are generically ​distinct. The Prosimiae, or lemuroids, include the galagos (Galago) and pottos (Perodictycus), of which the latter are akin to the Oriental loriscs, while the former are quite distinct from the Malagasy lemurs. Among the Carnivora, the aard-wolf (Proteles), the hunting-dog (Lycaon) and the long-eared fox (Otocyon) are peculiar generic types, as are several forms of mungooses (Herpestinae); while the spotted hyaena forms a subgenus by itself. The bear-family (Ursidae), on the other hand, is totally absent. In the great ungulate order the African elephant is widely sundered from its Asiatic cousin, as are the two species of rhinoceros from their representatives in the Oriental region; indeed each group is sub-generically distinct. The hyraxes, forming the suborder Hyracoidea, are, with the exception of a single outlying Syrian species, confined to Ethiopia. Zebras and true wild asses are likewise peculiar to the region. More remarkable is the extraordinary number of peculiar genera of antelopes, a few of which range, however, into North Africa, Syria and Arabia; the African buffaloes are markedly different from those of Asia; and sheep and goats are absent from the region, with the exception of intruding into it to some extent in the mountains of the Sudan and Abyssinia. The giraffe-family (Giraffidae), as represented by giraffes (Griraffa) and the okapi (Ocapia), is absolutely confined to this region, from which the deer-tribe (Cervidae) is completely absent. Chevrotains, or mouse-deer, are represented by the peculiar genus Dorcatherium (or Hyomoschus); in the pigs the wart-hogs (Phacochoerus), forest-hogs (Hylochoerus), and the bush-pigs (subgenus Potamochoerus), with the exception of one Malagasy species, are now unknown elsewhere, as are also hippopotamuses. Rodents include a number of peculiar types, among which may be noticed the scaly-tailed squirrels (Anomaluridae), the jumping-hares (Pedetes), the strand-moles (Bathyergidae), the crested-rats (Lophiomys), and the cane-rats (Thryonomys, or Aulacodus); the last being nearly allied to South American forms. In the Insectivora, moles (Talpidae) are absent, the jumping-shrews (Macroscelididae) are solely African, although ranging north of the Sahara, while the golden moles (Chrysochloridae) and the Potamogalidae are exclusively Ethio pian. Lastly, the ant-bears, or aard-varks (Orycteropodidae), represent a suborder of the Edentata unknown elsewhere; while the African pangolins (Manidae) differ markedly from their Oriental kindred.
The Ethiopian birds are less peculiar. The ostrich (Struthio) ranges, in suitable localities, all over the region, thus entering the Mediterranean transition-region in the north. The guinea-fowls (Numidinae) form a subfamily confined to Ethiopia and Madagascar, where true pheasants are unknown. Other peculiar types are plantain-eaters (Musophagidae), colics (Coliidae), wood-hoopoes (Irrisoridae), barbets (Megalaemidae), ground-hornbills (Bucorvus), secretary-birds (Serpentariidae), glossy starlings (Lamprotornis), ox-peckers (Buphaga), the genera Laniarius and Telephorus, as well as a number of others, all of which are unknown in Madagascar. In addition to true pheasants, wrens (Troglodytidae) and water-ousels (Cinclidae) are unknown in the Ethiopian region.
Apart from the widespread Trionychoidea (of which there are two genera peculiar to the region), the Ethiopian fresh-water tortoises belong to the section Pleurodira; the two genera Pelomedusa and Sternothaerus being common to Africa and Madagascar, and unknown elsewhere. The Amphisbaenidae are common to Neogaea and Ethiopia, to the exclusion of Madagascar; but the Gerrnosauridae and Zonuridae, on the other hand, are restricted to the present region and Madagascar, which also form the headquarters of chameleons. In contrast to the latter community is the absence in Madagascar of Agamidae and Varanidae, which are common in Ethiopia. The absence of slow-worms and their kindred (Anguidae) is a marked negative feature of the present region. As regards batrachians, the region has no salamanders or other tailed forms, but, in common with India, possesses caecilians (Apoda); while it shares the group of tongueless toads (Aglossa) with Neogaea, its peculiar family being the Xenopodidae, in contra-distinction to the South American Pipidae. The Pelobatidae are absent, and true toads are few, but frogs are abundant.
Among fishes, Africa south of the Sahara possesses a number of peculiar types. With Neogaea it shares the possession of the typical lung-fishes (Lepidosirenidae), while it is the habitat of the species of bichir (Polypterus) and Calamoichthys, the sole survivors of the ancient group of fringe-finned ganoids (Crossopterygii). The other families peculiar to Ethiopia are the Mormyridae (proboscis-fishes), Pantodontidae, and Phractolaemidae; the two latter being represented only by a single species each. The Notopteridae, Ophiocephalidae, Anabantidae, Osphromenidae and Mastacembelidae are common to Ethiopia and the Oriental region. In addition to the Lepidosirenidae, the Characinidae are peculiar to this region and Neogaea. The Cichlidae occur in Madagascar, Ethiopia, the Oriental region and Neogaea; and the Osteoglossidae are common to the last three of these regions, as well as Australia, while the Nandidae are Ethiopian, Oriental and Neotropical. On the whole, the affinities of the fish-fauna of Ethiopia are nearest to that of the Oriental region, and, secondly, to that of South America.
Although invertebrates do not come within the scope of the present article, it may be mentioned that Ethiopia is remarkable for the total absence of fresh-water cray-fishes.
As regards its past history, Ethiopian Africa was in connexion with India during the Triassic and Jurassic periods, the two areas collectively forming "Gondwanaland," which doubtless constituted a portion of the equatorial land-belt referred to as existing during the epochs in question. Gondwanaland was the home of a large section of the anomodont reptiles from which mammals have sprung; and it is quite probable that the evolution of the latter group took place within the present area. Between the Trias and the Eocene little or nothing is known of the vertebrate palaeontology of Ethiopia; and in Egypt there is also a long gap between the lower Miocene and certain Pliocene beds in the Wadi Natrun. The Tertiary deposits of southern Europe and northern India indicate, however, that Ethiopian Africa was in free communication with these countries during the upper Miocene and Pliocene epochs. There occur, for instance, either in south-eastern Asia or southern Europe, or both, during the latter period numerous genera of antelopes now restricted to Ethiopia, as well as giraffes, okapi-like ruminants (Palaeotragus), elephants and rhinoceroses of an African type, probably zebras, hippopotamuses, baboons, chimpanzees and ostriches. Owing to imperfect knowledge of Pliocene Africa, it is impossible to say whether these types were first developed in Ethiopia or to the north-east, and consequently whether or not Professor Huxley was right in his theory that the modern higher mammalian fauna of Ethiopia came from the north. It has, however, been suggested that while the Bovidae are an autochthonous Ethiopian group, the Cervidae originated in either the Holarctic or the Oriental region; a theory which if confirmed will materially aid in explaining the absence of the latter group from Ethiopia. It is supported to some extent by the fact that we are acquainted with primitive ancestral deer in the European Tertiary, while the ancestors of the Bovidae are at present unknown. Whatever be the truth on this point, it is manifest that whether the middle Tertiary Bovidae migrated from Ethiopia to Asia or in the opposite direction, there must have been some cause which barred the entrance by the same route into the latter area of all members of the deer-tribe (as well as bears). It should be added that although the ancestral Proboscidea were Ethiopian, the passage from the mastodons into the true elephants appears to have taken place in Asia; a circumstance which would imply the Asiatic origin of the African elephant.
The evidence in favour of the continuation of the Mesozoic land-bridge between Ethiopia and Neogaea has been discussed under the heading of the latter area. If the arguments in favour of such a connexion are valid, it is to the old mammal fauna of Ethiopia that we must probably look for the progenitors of the Santa Cruz fauna of Patagonia. Very noteworthy is the alleged occurrence of remains of primitive armadillos in the Oligocene beds of southern Europe in association with those of pangolins and aard-varks; since, if these fossils be rightly determined, there at once arises the probability of Africa having been the original home of the entire Edentate order.
In the case of an island lying so close to the African continent as does Madagascar the natural expectation would be that its fauna should be intimately related to that of the former. As a matter of fact—in the case of mammals and birds, at any rate—it is much more distinct from the Ethiopian fauna than is the latter from the fauna of either the Oriental orMalagasy region. the Holarctic region. The evidence—from the above-mentioned groups—in favour of recognizing a distinct Malagasy region is in fact positively overwhelming, while it is also supported in some degree by the distribution of groups other than those named. In place of the Ethiopian assemblage of apes, monkeys, baboons, galagos and pottos, Madagascar (together with the Comoro islands) possesses an absolutely unique fauna of lemurs, constituting the family Lemuridae, which, as now understood, is confined to this island, where it is represented by the three subfamily-groups of sifakas (Indrisinae), true lemurs (Lemurinae), and aye-ayes (Chiromyinae). All these animals agree with one another in the characters of the tympanic region of the skull; thereby differing from the African and Oriental Prosimiae, but agreeing with the European Oligocene Adapis, which must apparently be regarded as the ancestral form. This is a striking confirmation of the theory advanced many years ago by Huxley that Madagascar received its lemuroid fauna from Europe at a very early date, since which time, at any rate, it has been isolated from Africa. Some of the Pleistocene Malagasy lemurs were much larger than any of the living forms, rivalling in this respect a chimpanzee. The Carnivora are represented only by a small number of species, mostly referable to peculiar genera, of Viverridae, among which the fossa (Cryptoprocta) is the largest. In the ungulates there are only two extinct species of hippopotamus and a living bush-pig, the ancestors of all three of which probably crossed the Mozambique channel by swimming; and Edentata are equally conspicuous by their absence. Insectivora, on the other hand, are represented by the tenrecs (Centetidae), with numerous generic types, whose nearest relatives ​appear to be the west Indian solenodons. The bats are likewise different from those of the mainland; a notable feature being the occurrence of flying-foxes of the Asiatic and Australian genus Pteropus. Of the countless rodents of Africa, all are wanting; while the only members of that group inhabiting the island are certain rat-like animals collectively constituting the family Nesomyidae.
The birds are scarcely less remarkable than the mammals, such common Ethiopian types as the ostrich, secretary-bird, honey-guides {Indicator), wood-hoopoes, ground-hornbills, ox-peckers, barbets and glossy starlings being entirely unknown. On the other hand, the Malagasy region, inclusive of the Mascarene islands, comprises quite a number of distinctive bird-genera, such as Mesites, Tylas, Artamia, Calicalicus, Euryceros, Philepitta, Atelornis and Leptosomus; the first of these representing a peculiar family of game-birds, while the last, including only the kirombo, forms a subfamily of rollers (Coraciidae). In the Pleistocene the ostrich group was represented by various species of Aepyornis, probably the original of the legendary roc; while within historic times Mauritius and Reunion were the respective homes of the two species of dodo (Didus), and Rodriguez was inhabited by the solitaire (Pezophaps), the three constituting the family Dididae. The guinea-fowls, on the contrary, form a group common to the Ethiopian and Malagasy regions and are unknown elsewhere.
Many of the features of the reptilian fauna are alluded to under the headings of Neogaea and the Ethiopian region. Among lizards, the absence of Agamidae, Veranidae, Lacertidae, Amphisbaenidae and Anguidae is very remarkable, since all these except the last are Ethiopian. In addition, Madagascar possesses, apart from the cosmopolitan skinks and geckos, only Gerrhosauridae, Zonuridae and chameleons (Chamaeleontidae), which are essentially African groups. Affinity with Neogaea is indicated by the presence of a few iguanas, of snakes of the boa group (especially the genus Boa), and of Podocnemis among the tortoises. The other pleurodiran tortoises are, however, of an Ethiopian type. The same may perhaps be said with regard to the giant land-tortoises of the genus Testudo, which in Pleistocene or modern times were spread over all the islands of the region, while they existed in Africa in the Eocene, as well as in India in the Pliocene. The spider-tortoise (Pyxis) is a peculiar cryptodiran Malagasy genus. In the matter of batrachians the Malagasy region lacks both coecilians (Apoda) and tongueless toads (Aglossa), while it has abundance of true frogs (Raninae), among them the Oriental genus Rhacophorus. Of fishes, the peculiar Ethiopian types are absent from the present region, although the community of the Cichlidae to Neogaea and the Ethiopian, Malagasy and Oriental regions is noteworthy. It may be added that Madagascar differs from Ethiopia in possessing one fresh-water cray-fish, the representative of a genus by itself.
The radical distinctness of the Malagasy fauna is thus demonstrated from all sides. That the island has been separated from Ethiopia during the greater portion of the Tertiary period is self-evident. The interpretation of its relationships with other regions is, however, exceedingly difficult. It is generally considered that the Comoro and Seychelle groups mark the line of a former connexion between Madagascar and India, and also with South Africa; but it is evident that this line must have been closed to the passage of mammals since a very remote date, as is exemplified by the fact that the lorises of Ceylon and southern India are quite distinct from the Malagasy lemurs, and much nearer to the African pottos. Whether the occurrence of South American types of reptiles (boas, Podocnemis, and iguanas) in Madagascar and not in Africa can be held to indicate a late connexion with Neogaea by way of the Pacific, cannot yet be decided. The occurrence of iguanas in Fiji is, however, as noteworthy as is the community of Miolania to Patagonia and Queensland. Moreover, Polynesia is evidently a subsiding area. In the opinion of Captain F. Hutton the land-shells of the genus Endodonta, which range all through Polynesia, New Zealand, eastern Australia, New Guinea and the Philippines, with an outlier in Ceylon, afford the best evidence in favour of a Polynesian continent, the Singhalese outlier pointing to the conclusion that this group of molluscs originally came from the north. The molluscan evidence will not, however, explain the South American connexion.
Zoological evidence of the latter connexion, by way of Antarctica, is afforded by the earthworms of the family Acanthodrilidae, which are unknown north of the equator, although their occurrence in Madagascar may point to a northern origin. Additional evidence of a connexion with Patagonia is afforded by the occurrence in the Tertiary strata of South America and New Zealand of a number of shallow-water marine invertebrates. Further, the occurrence of these forms in older strata in South America than in New Zealand suggests that the migration took place from the former to the latter area.
The relatively small and wholly tropical or subtropical Oriental region was originally taken to include the Punjab; but in a memoir, of which an abstract appeared in the Proceedings of the Royal Society of London for 1900 (vol. Ixvii. p. 484), Dr Stanford came to the conclusion that the Punjab differs so remarkably in its fauna from the rest of India that it cannot be included in the Oriental region, and must be assigned to the Mediterranean oriental transitional region. To the latter belongs also the Oriental region. Himalayan area above the forests, as does Tibet. India proper, together with Ceylon, is regarded as a single subdivision of the Oriental region, under the title of Cisgangetic, while the Himalaya and Burma form a second subregion, the Transgangetic, which also includes southern China, Tonquin, Siam and Cambodia. A third subregion, the Malayan, includes southern Tenasserim, the Malay Peninsula, and the Malay Archipelago exclusive of Celebes. In the map in the present article the last-named island is included in the present region, although, as stated, it is by preference referred to an Austro-Malay transitional region. Wallace drew the main line dividing the Oriental from the Australian region between the islands of Bali and Lombok, and between Borneo and Celebes: "The strait [between Bali and Lombok] is here fifteen miles wide, so that we may pass in two hours from one great division of the earth to another, differing as essentially in their animal life as Europe does from America. If we travel from Java or Borneo to Celebes or the Moluccas, the difference is still more striking." The hydrographic results obtained by the Dutch Siboga Expedition show, however, that although there exists a line of great depth separating the two areas, this line on no point corresponds to "Wallace's line." On the contrary, it passes east of Timor and through the Banda and Molucca seas, separating Sula from Buru, Obi and Halmaheira. For this line which replaces "Wallace's line," Dr A. Pelseneer has proposed the name of "Weber's line." It is this "Weber's line" which marks the real division between the Arctogaeic and the Notogaeic faunas, although it has been convenient to make Celebes the centre of an intermediate transitional region.
The Oriental region agrees with the Ethiopian in being inhabited by elephants, rhinoceroses, buffaloes, several large representatives of the Felidae (among which the lion, leopard and hunting-leopard are common to the two areas), and numerous civets and mungooses. The elephant and the three species of rhinoceros are, however, subgenerically distinct from their Ethiopian relatives, and the buffaloes are also widely different from those of Africa. Wild cattle (of the subgenus Bibos), as represented by the gaur and the bantin, are peculiar to this region; and, with the exception of gazelles, antelopes are poorly represented, although the three genera Antilope (blackbuck), Tetroceros (chousingha), and Tragocamelus (nilgai) are restricted to the area. Southern India has one tahr (Hemitragus) in its mountains, and this genus also occurs in the Himalaya, where serows (Nemorhaedus) and gorals (Urotragus)—goat-like antelopes ranging through the Malay countries—are likewise met with. Deer (Cervidae) are abundant, and include three peculiar subgenera of Cervus, namely Rusa, Hyelaphus and Rucervus, to the exclusion of the typical red deer group. The typical Tragulus represents the chevrotains; and the pigs, unlike those of Ethiopia, belong to the typical section of Sus. In addition to Neogaea, the Malay subregion is now the sole habitat of tapirs (Tapiridae). A notable distinction from Ethiopia is the presence of bears, which are, however, distinct from the typical Ursus arctus group of the north. Borneo and Sumatra form the home of the orang-utan (Simia), the sole Oriental representative of the Simiidae, while the gibbons (Hylobatidae), which range as far west as the eastern Himalaya, are restricted to the region. The monkeys are all generically distinct from those of Ethiopia. The tarsier represents a family (Tarsiidae) by itself; and the lorises a subfamily (Nycticebinae) peculiar to the forest-tracts. Fruit-bats of the genera Pteropus, Rousettus and Cynopterus help to distinguish the region from Ethiopia; while among the Insectivora the tupais, or tree-shrews (Tupaiidae), .with three genera, and the rat-shrews (Gymnurinae), also with three generic modifications, are likewise solely Oriental. The cobegos, or flying-lemurs (Galeopithecus), represent an ordinal group (Dermoptera) peculiar to this region; while there are several distinctive genera of rodents, especially in the mountains of the Philippines, where some approximate closely to the Australian type represented by Hydromys.
Pangolins, of a type different from those of Ethiopia, alone represent the Edentata. A striking feature of the mammalian fauna of the region is the presence of so many peculiar and probably archaic types in the Malay subregion, and the affinity of the fauna of this area to that of western Africa. Both districts may be said to be highly conservative in the matter of their faunas.
The birds are extremely abundant, and include a number of peculiar genera to which detailed reference is impossible. There is no representative of the ostrich group; and the place of guinea-fowls is taken by pea-fowl (Pavo) and argus-pheasants (Argusiana), while francolins (Francolinus) abound. Attention may be directed to the abundance of pheasants, pigeons, king-fishers, sunbirds, flycatchers and starlings. The babblers (Timeliidae) are especially numerous, the group allied to the hill-robin (Liothrix) being peculiar to the region, as are also the green bulbuls (Chloropsis). True ​bulbuls (Pycnonotidae) and king-crows (Dicruridae) are also more abundant than elsewhere; while the broad-bills (Eurylaemidae) are peculiar.
Among reptiles, the long-snouted crocodiles of the genera Gavialis and Tomistoma are elsewhere unknown at the present day. The river-tortoises of the family Trionychidae have three peculiar genera; while the other fresh-water tortoises differ from those of Ethiopia in belonging to the section Cryptodira, of which there are a number of peculiar generic types. The family Platysternidae is solely represented by a tortoise confined to the Malay countries. In the lizards the family Anguidae is represented by one genus; Agamidae are very abundant; and include several types peculiar to the region, among which may be noticed the flying-dragons (Draco). Chameleons are rare. The burrowing-snakes of the genus Typhlops are exceedingly numerous; the allied Ilysiidae are common to India and Neogaea; while the Uropeltidae are restricted to India and Ceylon. In the presence of pythons the region agrees with Ethiopia, as it does in possessing cobras; but it divides with Neogaea the range of the Amblycepnalidae, while it is also inhabited by pit-vipers (Crotalinae), which form an exclusively Asiatic and American group. Among the Amphibia, the region agrees with Ethiopia in possessing representatives of the limbless Apoda, but differs in the presence of frogs of the family Pelobatidae, while toads (Bufonidae) and true frogs (Raninae), especially those of the genus Rhacophorus, are abundant.
Of the fishes it must suffice to state that lung-fishes and ganoids are absent, as are also Mormyridae. But the families phiocephalidae (serpent-heads) and Rhynchobdellidae (or Mastacembelidae), which have a few African representatives, are abundant; while the Cobitidae are a group unknown in Ethiopia. Siluridae and Cyprinidae are common.
Allusion has been already made to the presence of African forms of mammals in the Tertiary deposits of northern India (some of which are, however, within the Mediterranean transition-region); and it may be added that remains of a baboon (Papio) and of a large pangolin allied to the west African species have been found in Madras.
Few words must suffice for the Malayan transitional area, which embraces Celebes, the Moluccas, &c.; and has a fauna showing a blending of that of the Oriental with that of the Australian region. While Celebes possesses a small buffalo allied Austro-Malayan transition-region to the Indian species, a monkey (Cynopithecus), and a peculiar type of pig (Babirusa), it has also cuscuses (Phalanger), while cassowaries, cockatoos and other Notogaeic types occur in the area. A notable feature is also the absence of Cyprinidae (carps) from Celebes, although they are abundant in Borneo.
The Mediterranean transition-region, the limitations of which are approximately shewn on the map, must likewise be dismissed with brief notice; its fauna at the eastern end being Mediterranean transition-region intermediate between those of the Oriental and the Holarctic region, while in the west it serves as the No-man's-land between the Holarctic and the Ethiopian faunas. The most distinct portion of the Mediterranean fauna is undoubtedly that of Tibet, where are such peculiar types among mammals as the takin (Budorcas), the chiru antelope (Pantholops), the yak, representing a subgenus of Bos, snub-nosed monkeys (Rhinopithecus), the giant panda (Aeluropus), and certain peculiar shrews (Nectogale).
Farther west the great mole-rat (Spalax), the rabbit (subgenus Oryctolagus) and the two species of fallow-deer (subgenus Dama), are very characteristic of the Mediterranean zone, which is also the home of the addax antelope (Addax),the Barbary sheep (sub-genus Ammotragus), and numerous true sheep, wild goats and gazelles. Ctenodaclylus, the gundi, is a characteristic North African genus of rodents. It is also noteworthy that with the Mediterranean zone we enter the domain of typical deer of the red deer group (Cervus), and of bears of the brown bear group (Ursus arctus). The wolf and the fox are also animals whose territory we reach on entering the Mediterranean zone, although neither of these, or the brown bear, are confined to this tract, or even to the Palaearctic section of the Holarctic region.
Reference to many other animals of the Mediterranean tract will be found under the heading of the Palaearctic subregion.
The Holarctic region, which comprises the whole of the land lying northward of the Mediterranean transitional zone in the eastern, and north of the Sonoran zone in the western hemisphere,Holarctic region is the largest of all the zoological provinces of the globe. The whole territory is extra-tropical, and it is inhabited at the present day neither by monotremes, marsupials, edentates, lemurs nor monkeys, although representatives of the three latter occur in portions of the Mediterranean transitional region. The types common to the eastern and western halves of this region are to be met with on the two sides of the northern Pacific, and it is evident that the main communication took place by way of Bering Strait, although it has been suggested that there was also a land-bridge connecting the European continent with Iceland, and thus with Greenland.
Among characteristic groups of mammals common to the two halves of the Holarctic region (or in some instances of portions of the adjacent transitional zones to the southward) the following may be mentioned: elk (Alces), reindeer (Rangifer), wapiti (Cervus canadensis and its Asiatic representatives), bison (subgenus Bison), bighorn sheep (Ovis canadensis and its representatives in north-eastern Asia), musk-ox (Ovibos), now extinct in the eastern hemisphere, glutton or wolverine (Gulo), brown bear (Ursus arctus and its representatives in north-east Asia and America), lynx (Felis lynx), wolf (Canis lupus), fox (C. vulpes), pine-marten (Mustela martes and the allied American form), ermine and weasel (Putorius), variable hare (Lepus timidus and its relatives), picas (Ochotona, or Lagomys), beavers (Castor), marmots (Arctomys), chipmunks (Tamias), susliks (Spermophilus, or Citillus), jumping-mice (Zapus), field-mice, or voles (Microtus, or Arvicola), lemmings (Lemmus and Dicrostonyx), mole-shrews (Urotrichus), and several genera of bats. To these may be added, as more exclusively arctic forms, the polar bear (Ursus maritimus), and the arctic fox (Canis lagopus). There are likewise many groups or species of birds common to the two divisions of the region. Among reptiles, the pond-tortoises of the genus Emys, it we include their Pleistocene range, are an essentially Holarctic (and Mediterranean-Sonoran) group. In regard to fishes, the whole area is characterized by the abundance of sturgeons (Acipenseridae), carps (Cyprinidae), pike (Esocidae), and the salmon group (Salmonidae), coupled with the scarcity of cat-fishes (Siluridae).
Further testimony in favour of the unity of the Holarctic region is afforded by the presence on the two sides of the Pacific (and in most cases nowhere else) of true alligators (Alligator), giant salamanders (Cryptobranchus and Megalobatrachus, really scarcely worthy of separation), and shovel-beaked sturgeons Scaphirhynchus). Again, it is highly probable that Pere David's deer of Central Asia, alone representing the genus Elaphurus, is akin to the fork-antlered deer, Mazama, of North America; and many other analogous instances might be quoted. Finally, the distribution of earth-worms affords the strongest confirmation of the view that the two halves of the Holarctic region form but a single zoological province, with the Mediterranean and Sonoran zones as transitional appendages.
In briefly reviewing some of the chief faunistic areas of the Palaearctic, as distinct from the Nearctic, subregion, it will be convenient to include some of the groups and species inhabiting the transitional Mediterranean zone, much of which is in reality only a portion of the Palaearctic sub-region.Palaearctic sub-region Distinctive of the area in this wider sense are a number of wild sheep, such as Ovis musimon, gmelini, ammon, poli, &c., which have no representatives on the other side of Bering Strait, as well as wild goats, like Capra hircusaeeaerus, C. ibex, and C. sibirica, belonging to an exclusively Old World genus. The saiga antelope (Saiga) and the chamois (Rupicapra) may also be regarded as Palaearctic (in the sense of Old World) types; as are also wild horses (Equus caballus przewalskii), and the kiang (E. hemionus) and onager (E. hemippus), the two latter being commonly termed wild asses, although widely different from the African animals properly so-called. There are also many peculiar types of deer, inclusive of the red deer (Cervus elaphus), Pere David's deer (Elaphurus), the roe-deer (Capreolus), and the musk-deer (Moschus); while the Chinese water-deer (Hydrelaphus) is one of the characteristic forms from the Mediterranean zone. Camels (Camelus) are a type quite unknown east of Bering Sea. Among the Carnivora, reference may be made to the raccoon-dog (Nyctereutes), the panda (Aelurus), now a Himalayan and Chinese type, but occurring in the later Tertiary of England and the continent, and the tiger (Felis tigris); the last being essentially a Siberian and Mongolian animal which only reached India at a comparatively recent date, and never penetrated to Ceylon. Badgers (Meles) are unknown in the Nearctic region. In the Insectivora the water-shrew (Neomys or Crossopus) is exclusively Palaearctic, as is the allied Diplomesodon, while the desmans (Myogale), although a Mediterranean type, are solely Old World. Among the rodents, reference may be made to the Old World family of the dormice (Gliridae or Myoxidae), of which the genera Glis and Muscardinus are restricted to the area; as are the hamsters (Cricetus) and zokors (Ellobius and Siphneus) in the Muridae, and Euchoreutes, Alactaga, and Platycercomys in the jerboa-group (Jaculidae, or Dipodidae). Sminthus is another characteristic Palaearctic (and Mediterranean) rodent. To continue the list would merely be wearisome, without any compensating advantage; but it may be added that there are a number of characteristic extinct forms, among the most notable of the latter of which are the aurochs or wild bull (Bos taurus primigenius) and the giant Irish deer (Cervus [Megaceros] giganteus).
Of the remaining groups of vertebrates characteristic of this subregion space admits of but scant mention. Among abundant and more or less characteristic birds, reference may be made to thrushes, warblers, jays, magpies, buntings, sparrows, and (in the eastern part of the Mediterranean zone) pheasants, pratincoles, ​coursers (Glareolidae), and bustards (Otididae), of which there are numerous genera confined to the area. The two families last named, together with that of the Panuridae (represented by the bearded tit), being solely Old World, are of themselves sufficient to distinguish the Palaearctic from the Nearctic fauna.
Of reptiles there is not much to be said, the Palaearctic subregion, in its restricted sense, being characterized by the poverty of its fauna, several of the widely spread families of the Old World, such as the Varanidae and Agamidae, stopping short of its southern limits. Among batrachians, the tailed salamanders are common in this and the Mediterranean region (as in the northern hemisphere generally), the genera Salamandra and Chioglossa, as well as the frogs and toads of the genera Alytes and Pelobates, being unknown in the Nearctic subregion, while newts (Molge) abound in the Palaearctic and are rare in the Nearctic subregion. The olm (Proteus) is a native of the Mediterranean rather than the proper Palaearctic area.
As regards fishes, the subregion differs from the Nearctic province by the absence of bony-pike (Lepidosteidae), bow-fins (Amiidae), and the family Catostomatidae, as typified by the "suckers," "red horses" and "stone-rollers" of the genus Catostomus, and the presence of loaches (Cobitidae) and barbels (Barbus).
As compared with the Palaearctic (and Mediterranean) province of the Holarctic region the Nearctic subregion (together with the Sonoran transitional zone) is characterized by the extreme poverty of its fauna of hollow-horned ruminants.Nearctic subregion. Of so region, is generically (and subgenerically) identical with its European relative, while the musk-ox can scarcely be regarded as a distinctive Nearctic type, seeing that it is only since the Pleistocene epoch that it has ceased to be a denizen of northern Europe and Asia. The only other living members of the group are the bighorn sheep (Ovis canadensis), which has representatives in Kamchatka and north-eastern Siberia, and the white, or Rocky Mountain goat (Oreamnus, or Haploceros), which is a peculiar type. All must be regarded as originally immigrants from Europe; and it is noteworthy that in the Nearctic Pleistocene are several extinct types of musk-oxen, together with certain other genera which may possibly serve to connect the white goat and the musk-ox with the serow and the takin of the Old World. The deer (Cervidae), apart from the three Old World types alluded to under the heading of the Holarctic region, are altogether peculiar types referable to the genus Mazama (subgenus Dorcelaphus, Cariacus or Odocoileus), but they may be akin to the Asiatic Elaphurus, and the group is certainly of Old World origin. The same may be said of the bears (Ursidae), in which the black bear (Ursus americanus) is a peculiar species, although probably allied to the Himalayan U. torqualus. In the brown bear group (U. arctus) it is noteworthy that while the Alaskan forms are very close to those inhabiting Kamchatka and Amurland, the Rocky Mountain grizzly, which has penetrated farther into the continent, is more distinct. The grey-fox (subgenus Urocyon) is a characteristic Nearctic type. Among other groups of mammals, the following generic groups distinguish the Nearctic from the Palaearctic subregion, although some of them enter the Sonoran area. In the Insectivora we have Blarina, Scalops and Scapanus; in the Carnivora Procyon among the raccoons, Mephitis among the skunks, and Taxidea among the badgers. Cynomys ("prairie-dog ") is a characteristic rodent; and in the same order a very important feature is the replacement of all the true rats and mice (Murinae) of the Old World by the deer-mice and their allies belonging to the subfamily Cricetinae, which is but poorly represented in the Old World. Peromyscus is a very characteristic Nearctic genus, although it has an analogue in the Old World in the form of the single representative of the Persian Calomyscus. The wood-rats of the genus Neotoma and the musquash (Fiber) are characteristic Nearctic types of the vole-group. More important is the family Haplodontidae, represented only by the sewellels (Haplodon, or Aplodon), all the members of which are exclusively North American, although some are Sonoran. The pocket-gophers (Geomyidae) and kangaroo-rats (Heteromyidae) are also solely American, though more developed in the Sonoran than in the Nearctic area; Geomys and Thomomys in the former and Perognathus in the latter family are, however, found in the Nearctic area. Lastly, among the rodents, we have the Canadian porcupine (Erithizon), typifying the New World family Erithizontidae. Among bats it must suffice to state that the genus Lasiurus (Atalapha) is solely North American.
Reference to the Tertiary mammal-faunas of North America must be of the briefest. It may be mentioned that even in the Pleistocene these display a much greater development of large forms than occurs at the present day; while a notable feature at this epoch is the mingling of Arctogaeic and Neogaeic types, as exemplified by the occurrence of elephants and mastodons alongside of ground-sloths (Megalonyx and Mylodon). In the Pliocene and Miocene, the fauna was more of an Old World type, including a great development of camels (Tylopoda), horses (Equidae), rhinoceroses (Rhinocerotidae), mastodons, &c., but also a number of peculiar types, such as the ruminating oreodonts (Oreodontidae, or Merycodidae), the perissodactyle Titanotheriidae, and the more generalized Uintatheriidae, which typify a subordinal ungulate group by themselves. It has been suggested that some of the more widely spread of these groups, such as the camels and horses, may have originated in the New World, but there seems at least an equal probability that Central Asia—or a land-area common to Asia and America—may have been their birthplace.
The earliest Tertiary North American fauna is that of the lowest, or Puerco, Eocene, which includes a number of mammals of various types, some of the largest being of the approximate dimensions of a mastiff. Evidently the Puerco epoch was a period of great development and radiation on the part of mammals; its fauna including primitive creodont Carnivora, amblypodous and condylarthrous Ungulata, and a number of smaller types, some of which were probably related to the modern Rodentia, Insectivora and Primates. As only a foreshadowing of the Puerco mammals is found in the under upper Cretaceous Laramie beds, it has been suggested that the fauna was largely of northern origin.
By the middle of the Eocene period the more generalized types of the Puerco fauna had almost disappeared, although a few creodonts survived till the Oligocene. It is surmised that the low brain-capacity of the members of this fauna rendered them unfit to cope with the irruption of more highly organized mammals which suddenly appeared on the scene in the Lower Eocene; this new fauna, it is conjectured, may have developed from a side-line of the original Puerco stock which had remained in the old northern home at the time of the earlier radiation.
"Assuming that the Puerco mammals," observes Mr Madison Grant, "were driven out of more northerly or boreal lands, where they had originally developed, by a declining temperature, it is conceivable that some animals remained behind and adjusted themselves to the changed conditions, until a still further increase of cold freed them also to follow the path of their predecessors, southward.
"Some of these Lower Eocene types of this second radiation, which are found in the Wasatch beds of Wyoming, have sent down lines of descendants, which have ultimately culminated in existing animals. At this time first appear the horses, tapirs, rhinoceroses, camels and dogs (or rather the ancestral stocks thereof). Some of these animals, such as the horses and rhinoceroses, are found contemporaneously in Europe, others, like the (ancestral) camels, are peculiar to America [some of the later types have recently been discovered in Asia].
"Being more highly organized and better adapted to their environment, these new types entirely supplanted the older fauna, and by the Oligocene this transformation was complete, and the older fauna had disappeared. This Wasatch fauna culminated, and then faded gradually away on this [American] continent, until in the Middle Pleistocene it was largely supplanted by arrivals from Asia."
The relationship of the fauna to that of South America, and the interchanges which took place between the two during the Pleistocene and Pliocene epochs, have been already sufficiently discussed when treating of Neogaea.
Of the birds of the Nearctic subregion and the adjacent Sonoran zone, there are a very large number of peculiar genera in the passerine order, a large proportion of which are referable to the finch-group (Fringillidae), and the American warblers (Mniotiltidae), the latter being solely a New World family; there are also a few stragglers from the Neogaeic family of tanagers (Tanagridae). Among game-birds the turkeys (Meleagris), the ruffed grouse (Bonasa), the prairie-grouse (Tympanuchus, or Cupidonia), the sage-cock (Centrocercus), the prairie-chicken (Pedioecetes), and several genera of the American partridges (Odontophorinae), such as Lophortyx and Ortyx ("bob-white"), may be cited as characteristic Nearctic groups, although some extend farther south. Turning to reptiles, the presence of rattlesnakes (Crotalus) is a feature broadly distinguishing the Nearctic subregion (together with America generally) from the Palaearctic; in the more southern territories we also enter the domain of iguanas; while among chelonians we have the family of snappers (Chelydridae), the "stink-pot terrapins" (Cinosternidae), and in the Testudinidae the box-tortoises (Cistudo), and the terrapins of the genera Chrysemys and Malacoclemmys are solely American, although some of them range far to the south, while during the Pliocene the snappers were represented in Europe. There are several more or less peculiar types of North American amphibians, but since these are for the most part Sonoran in range, they may be best noticed in a later paragraph.
From that of the Palaearctic (+Mediterranean) subregion the fish-fauna of the Nearctic subregion (together with that of at least much of the Sonoran area) is broadly distinguished by the presence of bony-pike (Lepidosteidae), bow-fins (Amiidae), and the members of the family Catostomatidae, for which there appears to be no collective English name, as well as by the absence of the loach family (Cobitidae), and barbels (Barbus) among the Cyprinidae.
The last of the zoological provinces into which the land-surface of the globe is divided on the evidence of the distribution of mammals and birds is the Sonoran, which, although often regarded as an ​independent region, is best ranked (on Prof. Max Weber's scheme) as a transitional zone between the Nearctic subregion of the Holarctic region of Arctogaea, on the one hand, and Neogaea on the other. Sonoran transition-zone. Its fauna is indeed essentially a mixture of Nearctic and Neotropical types (inclusive of those originally indigenous to Neogaea and such as are properly immigrants from the north) together with a few more or less wholly endemic forms. Marsupials are represented by opossums (Didelphys), and armadillos by Tatusia. Peccaries (Dicotyles, or "Tagassu") make their appearance, but the fork-antlered deer (Mazama) are mainly of the northern type. The pronghorn antelope, representing the family Antilocapndae, may be regarded as mainly a Sonoran type; and the same may be said with regard to the pocket-gophers (Geomyidae) and kangaroo-rats (Heteromyidae), some of the genera of which are peculiar to this area. Among cricetine rats, Rhithrodontomys, Sigmodon and Neofiber are characteristically Sonoran. In the Carnivora the three genera of skunks, Mephitis, Conepatus and Spilogale are represented, as are the three raccoon genera Procyon, Nasua and Bassariscus; the third in each case being mainly confined to this zone. Scalops and Notiosorex among the Insectivora are almost exclusively Sonoran, while Blarina and Scapanus here attain their maximum development.
Omitting all reference to birds, it may be mentioned that among reptiles the poisonous lizards (Helodermatidae) and the chelonian family Dermatemydidae, with two or three genera, are almost or quite exclusively Sonoran; while such southern types as iguanas become more numerous than in the north. The Mississippi alligator is also Sonoran, although with a congener in China. Among Batrachians the salamanders of the genera Cryptobranchus (if distinct from the Old World Megalobatrachus), Amphiuma, Typhlomolge, Necturus and Siren, together with Scaphiopus and certain other genera of the frog and toad groups, are exclusively American and mainly Sonoran. The axolotls, or tiger-salamanders (Amblystoma), are also a group attaining a great development in this zone, although also ranging to the northward, and likewise recurring in south-eastern Asia.
So far as birds and mammals are concerned, the Antarctic continent can scarcely represent a distinct zoological province; its fauna consisting mainly of certain peculiar generic groups of sealsAntarctica. (which are at least as much inhabitants of the pack-ice as of the continent) together with a number of species of penguins a group common to the extremities of the three great southern continents and certain other birds.
The zoological provinces already discussed are based on the present distribution of mammals and birds (see further Mammalia and Bird). The distribution of reptiles and batrachians, like that of fresh-water fishes, by no means accords with that indicated by mammals and birds, Reptilian and Amphibian regions.probably owing to the earlier radiation, or rather radiations, of the former groups, and different zoological provinces have been proposed to indicate their distribution, as is more fully recorded in the articles Batrachia and Reptiles.
From the evidence of batrachian distribution Dr H. Gadow adopts the view that the world may be divided into a northern and a southern half, for the former of which the name Arctogaea is adopted, while Notogaea is used for the latter. It would, however, be much better if entirely new terms were proposed, since the use of the former in a sense different from that in which they are now employed in the case of mammals is liable to create confusion. Notogaea, which (in this sense) includes Australia, Polynesia and the Neotropical region, is characterized by the presence of that family of frogs known as the Cystignathidae, combined with the preponderance of the section Arcifera, the representatives of which form nearly 90 per cent, of the Anura (frogs and toads) inhabiting this half of the globe. Arctogaea, on the other hand, is characterized by the absence of Cystignathidae, and is divisible into two main provinces, or regions, respectively termed Periarctic and Palaeotropical. Of these latter, the Penairtic province is characterized by the presence of salamanders and their allies (Urodela), which are indeed almost peculiar to the area. It is divisible into the (1) Western Palaearctic, (2) Eastern Palaearctic and (3) Nearctic subregions, of which the first two approximately correspond to the Palaearctic subregion plus the Mediterranean transition-zone of the mammalian scheme, while the third represents the combined Nearctic and Sonoran areas. The Palaeotropical region has few salamanders or newts; but possesses caecilians (Apoda) which are wanting in the Periarctic; and includes the Ethiopian, Oriental, Malagasy and Austro-Malayan areas of the system based on mammalian distribution, together with Melanesia. Whether the region should be broken up into the four above-named divisions, or regarded as indivisible, may be a matter of opinion; but if such divisions be adopted, they have no approach to the corresponding mammalian areas, the Oriental tract not even possessing a peculiar subfamily. It is thus evident, as might have been expected, that the zoological provinces indicated by the distribution of batrachians are in no wise comparable to those based on mammalian evidence.
As regards reptiles, Dr H. Gadow has remarked that since the various orders have come into existence at very different geological periods, and have each followed their own line of dispersal, no scheme of zoological distribution can be formulated for the class as a whole. In the case of the crocodilian order little information of importance can be gathered from its present distribution, seeing that representatives of all the principal groups occur together in the older Tertiary deposits of Europe. It is, however, of some interest to note that caimans (Caiman) are restricted to Neogaea (in the mammalian sense); while the long-snouted Gavialis and Tomistoma are equally confined to the Oriental region. An important feature in the present distribution of chelonians is the restriction of the section Pleurodira to the southern hemisphere (inclusive of all the three southern continents, as well as Madagascar), and thus in no wise corresponding to the "batrachian Notogaea." The value of this feature in chelonian distribution is to some extent discounted by the occurrence of Pleurodira in the northern hemisphere during the Eocene period.
In regard to lizards (Lacertilia), Dr Gadow remarks that their distribution does not support the division of the land-areas of the globe into a northern and a southern half; the marked distinctness of the lacertian fauna of the New from that of the Old World pointing in the same direction. On the other hand, lizards countenance the view "that the Palaeotropical region is but the tropical and therefore richer continuation of the now impoverished Palaearctic subregion."
The present distribution of snakes, according to the same naturalist, indicates that the Ophidia are a group of late radiation, while it further suggests that some of the divisions adopted in classification are not natural ones. Perhaps the most important fact is that the two families, Boidae (boas and pythons) and Typhlopidae (blind burrowing-snakes), which alone retain vestiges of hind-limbs, occur all over the tropical zone, while certain allied families are found in portions of the same. The restriction of true vipers (Viperinae) to the Palaeotropical and Periarctic areas of the batrachian distributional scheme is a noteworthy fact. The pit-vipers (Crotalinae), however, may perhaps be presumed to have originated in the Palaearctic area, whence they reached and spread all over America, although they were unable to enter either Africa or Australia. The absence of all venomous snakes (which abound in Africa and India) from Madagascar, is a fact harmonizing with mammalian distribution, so far as the peculiarity of the fauna of that island is concerned.
For a fuller account of the distribution of fishes, both fresh-water and marine, see Ichthyology; here it will suffice to refer to a zoo-geographical scheme, based on the present distribution of the freshwater families, adopted by Dr A. C. L. G. Günther. According to this scheme,the land-surface of the earth is divided into three parallel zones, the Northern, the Equatorial and the Southern. Distribution of fresh-water fishes.The Northern zone is characterized by the presence of sturgeons (Acipenseridae), the paucity of cat-fishes (Siluridae), and the abundance of carps (Cyprinidae), the salmon-tribe (Salmonidae), and pike (Esocidae). This zone falls naturally into an eastern and a western section. In the first, forming the Palaearctic, or Europe-Asiatic region, bony-pikes (Lepidosteidae) are lacking, while loaches (Cobitidae) and barbels (Barbus) abound. In the second section, constituting the Nearctic or North American region, bony-pikes, bow-fins (Amiidae), and the family Catostomatidae, all of which are unknown in the Palaearctic area, are present, while loaches and barbels are lacking.
The Equatorial zone is divisible into two provinces: an Eastern, characterized by the presence of carps and of the family (Anabantidae) typified by the well-known "climbing-perch," and a Western province, in which these two groups are wanting. The Eastern province includes an Indian (Oriental) region, in which lung-fishes (Dipnoi) are absent, while serpent-heads (Ophiocephalidae), Mastacembelidae and loaches are numerous; and an African (Ethiopian) region, distinguished by the presence of lung-fishes, bichirs (Crossopterygii), and proboscis-fishes (Mormyridae), the abundance of chromids (Chromididae) and characinids (Characinidae), and the lack of loaches. The Western Equatorial province is likewise divisible into two regions, namely, a Tropical American (Neotropical), distinguished by the possession of lung-fishes and electric eels and the abundance of chromids and characinids, and a Tropical Pacific (Australian and Hawaiian) characterized by the presence of Dipnoi (widely different, however, from those of Africa and South America, which are nearly related), and the lack of chromids and characinids.
Lastly, the Southern zone is characterized by the absence of carps and the scarcity of cat-fishes, while the salmon tribe is replaced by the Haplochitomdae and pike by the Galaxiidae (since this classification was proposed a marine Galaxias has been discovered). This zone includes only a single (Antarctic) region, embracing Tasmania and the south-eastern point of Australia, New Zealand and Patagonia and Tierra del Fuego.
It will be seen that the present distribution of fishes, although showing certain features in common, by no means accords as a whole with that of mammals. Indeed, it is suggestive of the period of the earth's history when there was an extensive and more or less continuous belt of equatorial land.
​For the distribution of invertebrate animals generally, the reader may be referred to the articles dealing with the various groups of that assemblage. An exception must, however, be made with regard to that group of spiders known as the Mygalomorphae (which includes the trap-door spiders) on account of the remarkable general similarity presented by its distribution to that of mammals. Distribution of spiders.According to Mr R. I. Pocock, the distribution of this group justifies the mapping of the world into the following zoological regions:—(1) The Holarctic, including Europe north of the southern mountain-chains, North Asia, and North America north of about the 45th parallel of latitude. (2) The Mediterranean, including South Europe, Africa north of the Sahara and the desert-regions of south-western Asia. (3) The Sonoran, comprising the United States of America south of about the 45th parallel and the plateau of Mexico. (4) The Ethiopian, embracing Africa south of the Sahara, South Arabia and Madagascar. The last-mentioned island ranks merely as a subregion of the Ethiopian. (5) The Oriental, including India, Ceylon, Burma, Siam, and all the Indo- and Austro-Malayan Islands to Australia; "Wallace's line" being non-existent so far as spiders are concerned. (6) The Australian, containing Australia and New Zealand; the latter being worthy of recognition as a subregion. (7) The Neotropical, including Central America, apart from the Mexican plateau, the West Indies and South America.
These spiders furnish, moreover, strong evidence in favour of a former union between Africa and South America, and of a connexion between the Afro-Mascarene and Austro-Zealandian continents on the one hand and Austro-Zealandia and the southern extremity of South America on the other. As regards the "regions," apart from the greater divisions, or "realms, the distribution of these spiders accords with remarkable closeness to that of mammals, if we except the more intimate connexion indicated between the faunas of Ethiopian Africa and Madagascar.
The fact that the generally accepted scheme of division of the land-surface of the globe into zoological regions is based almost entirely upon the present distribution of mammals and birds has already been emphasized. It is perhaps only fair to quote the views of Dr A. E. Ortmann (who has devoted much study to the distribution of animals), although they by no means wholly commend themselves to the present writer:—
"(1) Any division of the earth's surface into zoo-geographical regions which starts exclusively from the present distribution of animals, without considering its origin, must be unsatisfactory, since always only certain cases can be taken in, while others remain outside of this scheme. (2) Considering the geological development of the distribution of animals, we must pronounce it impossible to create any scheme whatever that covers all cases. (3) Under these circumstances, it is incorrect to regard the creation of a scheme of animal distribution as an important feature or purpose of zöo-geographical research."
Dr Ortmann adds in a later paragraph, "the chief aim of zöo-geographical study consists—as in any other branch of biology—in the demonstration of its geological development."
II. Marine Distribution
That the fauna of the ocean, apart from the influence of temperature, would be much more uniform, and therefore less susceptible of being divided into zoological provinces, or regions, will be apparent from a glance at the map of the world on Mercator's projection, in which the fact that the three great oceans the Pacific, the Atlantic and the Indian are in free communication with one another in the southern hemisphere is clearly brought out. There is, however, more than this; for there is evidence that during the early part of the Tertiary period the Pacific and the Atlantic were not separated by the isthmus of Darien; while there is a probability that the Mediterranean was at one time in communication with the Red Sea, and that other connexions of a like nature have existed.
In addition to this general community of the marine fauna of the world, there is the further important fact that such faunas may be divided into three main, and for the most part perfectly distinct, groups: namely, the littoral, or shallow water, fauna, the abyssal, or deep-sea, fauna, and the pelagic, or surface, fauna. Of these three the first alone is really susceptible of division into more or less ill-defined zoological regions, the other two being practically uniform in character. Moreover, these three faunas are for the most part perfectly welldefined; the pelagic being very sharply sundered from the abyssal, although there may in certain instances be a tendency for the littoral to merge locally into the abyssal. As regards the sharp demarcation between the pelagic and the abyssal faunas, an idea was formerly current that whales, which are essentially pelagic animals, when "sounding," descended to abyssal depths in the ocean. A moment's reflection will show the absurdity of such a supposition; for no surface-dwelling animal could possibly support the enormous pressure existing at great depths, which would crush in the body-cavities. Evidence of this is afforded by the fact that when fishes are brought to the surface from great depths their bodies are practically broken to pieces by the removal of the normal pressure, while their scales start from the skin and the eyes from their sockets. The absolute darkness prevailing at great depths would be another bar to pelagic animals descending to the ocean abysses. We may accordingly regard the pelagic and the abyssal faunas as perfectly distinct and widely sundered from one another; as widely sundered in the case of some species as are beings living in three-dimension space from these (if such there be) inhabiting space of four or more dimensions.
Modern research shows that invertebrates, and probably also fishes, live at the greatest depths that have yet been reached by the dredge, and the inference from this is that they occur everywhere. Deep-sea fauna.The general results of these explorations is indeed to show that the fauna of the ocean depths is much the same all the world over, and that identical species occur at points sundered as widely as possible from one another. The ocean floor, as has been well remarked, with its uniformity in the matter of temperature, food, station and general conditions of life, contains, in fact, no effectual barriers to the almost indefinite dispersal of species.
The following general conclusions with regard to the deep-sea fauna were arrived at after working out the material and evidence obtained during the cruise of H.M.S. "Challenger":—(1) Animal-life is present at all depths on the ocean floor. (2) At extreme depths life is not nearly so abundant as at moderate depths; but since representatives of all classes of marine invertebrates are met with at all depths, this poverty probably depends more upon certain causes affecting the composition of the bottom deposits, and the degree to which the bottom-water is provided with chemical substances necessary for animals, rather than upon conditions immediately associated with depth. (3) There is reason to believe that the fauna of "blue water" is chiefly restricted to two belts; one at or near the surface, and the other near the bottom, the intervening zone being more or less completely devoid of inhabitants. From the surface-zone a continual ram of organic debris is falling to the bottom, which, however, in the case of the greatest depths may be completely dissolved in descensu. (4) Although all the chief groups of invertebrates are represented in the abyssal fauna, their relative proportions are unequal; molluscs, crabs and annelids being, as a rule, scarce, while echinoderms and sponges predominate. (5) Depths below 500 fathoms are inhabited by a practically uniform fauna, the genera being usually cosmopolitan, although the species may differ, and be represented by allied forms in widely sundered areas. (6) The abyssal fauna, so far as invertebrates are concerned, is of an archaic type as compared with shallow-water faunas. (7) The most characteristic and archaic abyssal types seen to be most abundant and to attain their maximum dimensions in the southern ocean. (8) In general character the abyssal fauna approximates to that of shallower water in polar latitudes, doubtless owing to the fact that the conditions of temperature, on which the distribution of marine animal life mainly depends, are nearly the same.
In reference to the abundance of sponges in the deep-sea fauna, it may be mentioned that the calcareous group is absent, and that among the siliceous section, the Hexactinellidae, of which the Venus flower-basket (Euplectella) and glass-rope sponge (Hyalonema) are familiar representatives, are exceedingly abundant; this group being likewise of great geological antiquity. Corals are sparse and belong for the most part to the Turbinolidae. Echinoderms are represented by all the existing ordinal groups; some of the crinoids, or stone-lilies, belong to the family Apiocrinidae, which attained its maximum development during the Jurassic epoch; and somewhat similar relationships are exhibited by certain of the brittle-stars (Ophiuroidea). Very noteworthy is the great development of the sea-cucumber group (Holothuroidea), and likewise the bizarre forms assumed by some of its abyssal representatives. Molluscs, however, are poorly represented, and it is not improbable that cephalopods (nautilus and cuttlefish group) are wanting. Bivalves of the genera Leda and Arca have, however, been obtained from a depth of 16,000 ft. Lamp-shells (Brachiopoda) are likewise scarce.
​Considerable difficulty exists in determining from what depths fishes are dredged. Although many species display various structural peculiarities, such as a huge head, or an attenuated ribbon-like body, while special phosphorescent organs are very generally present, yet deep-sea fishes as a whole do not represent an ordinal or sectional group by themselves, but are drawn from a number of families, certain members of which have adapted themselves to an abyssal existence. A preponderance of representatives of the families Macruridae, Ophidiidae and Scorpclidae is, however, noticeable.
Whether light or temperature is the prepotent agency in regulating the limitations of the deep-sea fauna, has long been a debated question. It may be noted that reef-building corals, which require an average temperature of from 70° to 75° F. and one which never falls below 68°, are never found below a depth of 20 fathoms (120 ft.). Nevertheless, there are several areas where a temperature of from 70° to 77° obtains to depths of between 80 and 100 fathoms. It is further remarkable that well-characterized deep-sea faunas are locally met with in comparatively shallow waters, one such area occurring in the European Atlantic and a second in the Mediterranean, where they live within the 100-fathom zone. Light, which was formerly supposed not to penetrate to a greater depth than the 40 to 50 fathom-line, has also been regarded as the chief agent controlling vertical distribution. It appears, however, as Prof. Heilprin has remarked, "more than likely that not a single cause, but a combination of causes, is operative in bringing about the general results. That the deep-sea fauna is a fauna of darkness must be admitted; but this is so from the nature of the case rather than a matter of choice resting with the animals composing it."
After referring to the fact of the dissimilarity between the faunas of the two poles, Dr A. E. Ortmann, in a paper on the origin of the deep-sea fauna, observes that we have reason to believe that each of these faunas had a separate origin, "the north-polar fauna being a derivate of the old Mesozoic Mediterranean, the south-polar fauna of the old Pacific fauna. The first developed along the shores of the northern continents, while the second had its original home on the shores of the Antarctic continent. We know that there is a strange element among the littoral fauna of the southern extremities of the continents, differing entirely from the arctic fauna, and we cannot but think that this is a remnant of the old Tertiary antarctic fauna. The above considerations give us a threefold origin of the present deep-sea fauna: (1) An ancient Mesozoic (or pre-Tertiary) constituent, derived from a transformed part of the old warm-water fauna of the deep sea, adapted to the changed climatic conditions. It is clearly autochthonous. (2) A more modern, immigrant, Tertiary constituent, which came from the north-polar littoral waters, and immigrated into the deep sea together with the cool water (or after it had cooled). This element goes back to an old pre-Tertiary stock that lived in the warm littoral waters of the old Tethys (Mediterranean Sea), but as a cool-water fauna, it is not older than Tertiary. (3) Another Tertiary element, corresponding to the second one, but belonging to the south pole, which is finally to be traced back to the warm waters of the old Pacific Ocean of pre-Tertiary times."
The surface, or pelagic, fauna contains some of the smallest and actually the largest of all living animals, for among its members are included a host of so-called animalcules on the one hand and the whales on the other.The surface fauna. The essential characteristic of pelagic animals is that they pass the whole of their existence swimming at or near the surface of the ocean, and only by accident touch the shores or the bottom. Much information with regard to the smaller pelagic creatures will be found in the article Plankton. Among the groups included in the pelagic fauna may be mentioned the radiolarian animalcules, together with certain representatives of the Foraminifera; the siphon-bearing jelly-fishes, such as Physalia (Portuguese man-of-war), Velella, Porpita, &c.; all the pteropod molluscs, such as Clio, Clione and Cavolinia (Hyalaea), together with less aberrant gastropods, like Janthina (violet-snail), Atlanta and Glaucus; a few cephalopodous molluscs, such as the paper-nautilus (Argonauta) and Spirula; and a number of social ascidians, like Salpa and Pyrosoma. Crustaceans belonging to the entomostracous (shelled) and schizopod divisions abound; and there is a group of insects (Halobates), belonging to the order Hemiptera, whose home is on the ocean-surface at, practically, any distance from land. Fishes form no inconsiderable portion of the pelagic fauna, among these being the true flying-fishes, or flying-herrings (Exocoetus), herrings, mackerel, tunny, flying-gurnards (Dactyloptera), sword-fishes (Histtophorus), sea-horses (Hippocampus), pipe-fishes (Fistularia) and many of the sharks. With the exception of the comparatively few fluviatile species, the whole of the cetacean mammals—that is to say, whales, grampuses, porpoises, dolphins, &c.—claim a place among the surface-fauna of the ocean. Whether the sea-cows (Sirenia) should likewise be included is doubtful, as they hold a somewhat intermediate position in regard to habits between cetaceans and seals. While they agree with the former in never (or very rarely) landing and in bringing forth their young at sea, they come inshore to feed. Turtles certainly cannot be considered truly pelagic, since they come ashore to lay their eggs.
A large proportion of the smaller pelagic animals are more or less completely transparent, while others, such as the violet-snail, have developed an azure tint which renders them as inconspicuous as possible in the waste of waters. In the case of the larger animals, like mackerel and the finner-whales, the same result is attained by the under surface of the body being silvery white (thus rendering them invisible when looked at from below against the sky), and the upper surface olive or blackish green, sometimes, as in the mackerel, mottled to harmonize with the ripple of the waves.
The distribution of whales and dolphins has been taken by P. L. and W. L. Sclater to some extent as a basis in dividing the ocean into zoological regions. Since, however, such regions were mainly defined on the distributional evidence afforded by seals and sea-cows, they are best considered in connexion with the shallow-water fauna.
The shallow-water, or littoral, fauna includes all marine animals which belong neither to the deep-sea nor to the surface fauna, and is the most important of all three.The shallow-water fauna. In addition to the great bulk of marine invertebrates, the littoral fauna may be taken to include the reef-building corals (whose distributional limitations under the influence of temperature-control have been already mentioned) and likewise seals and sea-cows among mammals, and turtles among reptiles.
"The fauna of the coast," observes Prof. H. N. Moseley, "has not only given origin to the terrestrial and fresh-water faunas, it has through all time, since life originated, given additions to the pelagic fauna in return for having received from it its starting-point. It has also received some of these pelagic forms back again to assume a fresh littoral existence. The terrestrial fauna has returned some forms to the shores, such as certain shore-birds, seals and the polar bear; and some of these, such as the whales and a small oceanic insect (Halobates), have returned thence to pelagic life.
"The deep-sea fauna has probably been formed almost entirely from the littoral, not in most remote antiquity, but only after food, derived from the debris of the littoral and terrestrial faunas and floras, became abundant in deep water. It was in the littoral region that all the primary branches of the zoological family-tree were formed; all terrestrial and deep-sea forms have passed through a littoral phase, and amongst the representatives of the littoral fauna the recapitulative history, in the form of series of larval conditions, is most completely retained."
From the distribution of certain groups of animals, it has been Marine zoological regions.attempted (as stated) to divide the ocean into a number of zoological provinces, or regions. Among the more important of such schemes, the following may be mentioned.
The reef-building corals, whose limitations are defined by conditions of temperature and depth, are necessarily restricted to certain seas and coasts within or near the tropics. "They abound," wrote Dr A. R. Wallace in the ninth edition of the present work, "in and near the West Indies, on the east coast of Africa, in the Coral regions.Indian Ocean, in the Malay and Pacific archipelagoes, and on the coast of Australia; while they are absent from the whole of the west coasts of South America and of Africa, from the Indian peninsula, and from much of the east coast of South America. The coral-reefs of the Bermudas, in 33° N. lat., are the farthest from the equator; in the Red Sea they reach 30° N., in the Pacific 27° N., while they nowhere extend to more than 29° S. of the equator. . . . The coral regions are therefore somewhat peculiar, and differ considerably from those which best exhibit the distribution of other marine animals. The regions adopted by Prof. J. D. Dana are three—the first comprising the Red Sea and Indian Ocean; the second, the whole of the Pacific islands and the adjacent coasts of Australia; and the third the West Indies. This last region is the most isolated in position; and it is not surprising that it should contain the largest proportion of peculiar forms. The corals of the Central Pacific are also very peculiar, as are those of the Red Sea and Indian Ocean."
Prof. J. D. Dana proposed to divide the oceans into three main areas according to the distribution of Crustacea. These areas are respectively termed the Occidental, the Africo-European and the Oriental.Crustacean regions. The first comprises both coasts of America; the second, the western shores of the Atlantic, both African and European; while the third comprehends the vast area from the east coast of Africa to the Central Pacific. Each of these regions is subdivided into climatal and local provinces but the primary divisions can alone be mentioned here. The facts adduced in support of this scheme of distribution are interesting. At the date of Prof. Dana's memoir 47 genera were known to be exclusively American, 15 being common to both the east and west coasts; but as 26 genera were said to be confined to the west and 6 to the east coast, these two provinces are really distinct, even if they do not form primary regions. The Africo-European region had 19 peculiar genera, and only 8 in common with the ​American region; so that the eastern and western shores of the Atlantic appear decidedly more distinct than the eastern and western coasts of America. The extensive Oriental region is by far the richest.
From the distribution of the species (not genera) of barnacles, or cirrhipeds, which are an aberrant group of Crustacea, Darwin considered that the ocean might be divided into the following regions, viz.:—(1) The North Atlantic, comprising North America and Europe down to N. lat. 30°; (2) The West American, from Bering Strait to Tierra del Fuego; (3) The Malayan, from India to New Guinea, and (4) The Australian, comprising Australia and New Zealand: the Malayan and Australian regions being the richest in cirrhipeds.
One of the earliest students of the geographical distribution of marine animals was Dr S. P. Woodward, who, in his Manual of Mollusca, proposed a scheme of zöo-geographical regions. He adopted three main divisions for the warmer parts of the ocean, namely, the Atlantic, the Indo-Pacific and the West American; and these Wallace was inclined to regard as the only valid marine molluscan regions.Molluscan regions. The Indo-Pacific region extends from the Red Sea and the east coast of Africa to the eastern Pacific islands, and corresponds to Prof. Dana’s Oriental region for Crustacea, many species ranging over nearly the whole area. The Atlantic region unites the fauna of the east coast of America with that of West Africa and South Europe, but has considerable affinity with that of West America, many genera being common to both areas. Several genera appear restricted to the north temperate zone, which in Wallace’s opinion should perhaps form a distinct region. Numerous genera are confined to the Indo-Pacific region. The Atlantic coasts have few peculiar genera of importance, while the west coast of America has hardly any, the difference of its fauna from that of the Atlantic on the one side and the Pacific on the other being chiefly specific. It is stated that while there is not a single species common to the east and west coasts of tropical South America, the corresponding coasts of North America have a large number in common, while others are so closely representative as to be almost identical. Inclusive of an Arctic province of somewhat doubtful value, Dr Woodward’s three main regions were divided into 18 subregions; but, according to a somewhat modified later scheme, these may be arranged in four main groups, as follows:—
| Regions. | Subregions. |
| A. Atlantic and Circumpolar | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 1. Arctic. 2. Boreal. 3. Celtic. 4. Lusitanian. 5. W. African. 6. S. African. |
| B. Indo-Pacific | $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ 1. Indo-Pacific. 2. Japanese. |
| C. Australian | $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ 1. Australian. 2. Neozealanian. |
| D. American | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 1. Aleutian. 2. Californian. 3. Panamic. 4. Peruvian. 5. Magellanic. 6. Argentinian. 7. Caribbean. 8. Transatlantic. |
Fish Regions.— From the distribution of shore-haunting fishes, Dr A. C. L. G. Günther suggested the following marine zoological regions, the characteristic family and generic types of which we are prevented by limitations of space from discussing:—
I. Arctic Ocean.
II. Northern Temperate Zone.
    A. Temperate N. Atlantic.
    1. British district.
    2. Mediterranean district.
    3. N. American district.
    B. Temperate N. Pacific.
    1. Kamchatkan district.
    2. Japanese district.
    3. Californian district.
III. Equatorial Zone.
    A. Tropical Atlantic.
    B. Tropical Indo-Pacific.
    C. Pacific Coast of Tropical America.
    1. Central American district.
    2. Galapagos district.
    3. Peruvian district.
IV. Southern Temperate Zone.
    1. Cape of Good Hope district.
    2. South Australian district.
    3. Chilean district.
    4. Patagonian district.
V. Antarctic Ocean.
Mammalian Regions.— The last scheme of marine zoological regions necessary to mention is one proposed by P. L. and W. L. Sclater on the distributional evidence afforded by seals, sea-cows and cetaceans. According to this, we have the following six regions, viz.:—
(i) Arctatlantica (North Atlantic), characterized by the presence of seals of the subfamily Phocinae, with the genera Halichoerus peculiar to it, and Phoca common to it and No. iv.; the absence of sea-cows; and (it is stated) by the bottle-nosed whales (Hyperoodon) being peculiar to this area.
(ii) Mesatlantica (Mid Atlantic), the sole habitat of the monk-seal (Monachus) and the manatis (Manatus).
(iii) Philopelagica (Indian Ocean, &c.), characterized by the presence of dugongs and the absence of seals,
(iv) Arctirenia (North Pacific), agreeing with No. i. in the possession of Phoca but distinguished by also having sea-bears and sea-lions (Otariidae); formerly the habitat of the northern sea-cow (Rhytina), and now of the grey whale (Rhachianectes).
(v) Mesirenia (Mid Pacific), without Phocinae or sea-cows, but with the elephant-seal (Macrorhinus), from the south, and also Otariidae.
(vi) Notopelagica (Southern Ocean), with four peculiar genera of seals (Phocidae), numerous sea-bears and sea-lions, and two peculiar genera of cetaceans, the pigmy-whale (Neobalaena) and Arnoux’s beaked-whale (Berardius).
To explain the absence of sea-bears and sea-lions from the North Atlantic, and likewise the existence of manatis on both Atlantic coasts, the authors of this scheme call in the aid of a land-connexion between Africa and South America, which presented a barrier to the northward progress of the former, while its coasts afforded a means of dispersal to the latter. As the Otariidae are at present unknown previous to the Miocene, such an explanation, if valid, requires the persistence of the ancient land-bridge across the Atlantic to a much later date than is commonly supposed.
III. Distribution in Time
The subject of the distribution of animals in time, i.e. the relative dates of their first appearance on the earth, and in the case of extinct forms the length of their sojourn there, can be treated but briefly; reference being restricted to the larger groups, and not even all of these being mentioned. The dates of appearance and disappearance of the various groups are only relative, for although many more or less vague attempts have been made to determine the age of the earth, there is no possibility of indicating in years the length of time occupied by the deposition of any one stratum or series of strata. All that can be attempted is to say that one stratum (and consequently the remains of animals that may be entombed in it) is older or younger, as the case may be, than another. For the sequence and names of the various strata, or time-periods of the geological record, see Geology. An important factor in regard to the past history of animals is the imperfection of the geological record. Recent discoveries have rendered this imperfection much less marked than was formerly the case. There are, however, still many very serious gaps; and we have, for instance, no definite information as to where and when the transformation from reptiles into mammals took place.
It may nevertheless be emphatically affirmed that the geological, or rather the palaeontological, record indicates a gradual progression in the status of animals from the lowest to the highest fossiliferous strata. That is to say, the earlier animals were creatures of comparatively low grade (although certain representatives of such groups may have attained a relatively high degree of specialization), and that as we ascend the geological ladder higher and higher types of animals make their appearance, till the series culminates in man himself—the crowning effort of creation, in the modern evolutionary signification of that term. It is not, indeed, to be supposed that the higher groups made their appearance exactly according to their relative grades (or what we regard as such); all that can be affirmed is that in the main the higher forms have made their appearance later than the lower. The record is thus almost exactly what it might be expected to be on the theory of evolution; while it also accords fairly well—if regarded with sufficient breadth of view—with the Biblical narrative of creation.
A brief survey of the time-distribution of the leading groups of animals may now be undertaken, commencing with the highest and concluding with the lowest groups.
As the highest of all vertebrates, it is natural to expect that mammals should be one of the latest groups of that assemblage to make their appearance; and this as a matter of fact they are, although it is by no means improbable that birds are the latest of all.Mammals. Mammals are commonly stated to commence in the Trias, where they are presumed to be represented by Microlestes in Europe and by Dromatherium in North America. From the fact, however, that the approximately contemporary Tritylodon, which has cheek-teeth very like those of the former, appears to be in great degree intermediate between reptiles and mammals, it is by no means improbable that none of these Triassic creatures were true mammals. Undoubted mammals occur in the lower Jurassic Stonesfield Slate, in the upper Jurassic Permian beds, and, very sparingly, in the Wealden of England; while a large fauna has been discovered in the upper Cretaceous of North America. The mammals included among these Mesozoic forms appear, for the most part at any rate, to be referable to the Marsupialia, Insectivora, and, not improbably, the Monotremata (see Marsupialia). After the lowest Eocene (when the Puerco fauna represented an inferior and apparently non-progressive type) mammals became abundant; and during that epoch most if not all of the existing orders made their appearance. The lower Eocene representatives of several of the orders, such as the Condylarthra among the Ungulata and the Creodonta among Carnivora, belonged, however, to low suborders which disappeared more or less completely by the Oligocene. Several subordinal groups of Ungulata developed and became extinct at later periods than the Eocene; but with the exception of the Ancylopoda and Tillodontia (whose right to ordinal distinction is by no means universally admitted), none of the Tertiary orders of mammals are extinct. At the present day—as during the greater part of the Tertiary epoch—mammals are the dominant terrestrial representatives of the Vertebrata. We have at present no evidence of the existence of Cretacea before the lower Eocene.
Although some of the three-toed bipedal tracks in the Trias of the Connecticut valley were formerly supposed to have been made Birds.by birds, there is little doubt that they are really due to dinosaurian reptiles. The class Aves, so far as we know, is therefore first represented by the long-tailed Archaeopteryx of the upper Jurassic, which represents a subclass (or order) by itself. Toothed birds also existed in the upper Cretaceous of both Europe and North America, but all these appear referable to existing ordinal (or subordinal) groups. By the lower Eocene, when teeth appear to have been entirely lost, most or all of the existing ordinal groups were developed, since which date the majority at all events have steadily increased.
In contradistinction to both the preceding classes, reptiles, which date from the Permian, are a waning group, at all events so far as both terrestrial and marine forms of large bodily size are concerned.Reptiles. The Permian reptiles were small or medium-sized creatures, few in number, and of generalized character. The one existing order dating from that epoch (when it was represented by Protorosaurus) is the Rhynchocephalia, of which the sole survivor is the New Zealand tuatara (Sphenodon). The Mesozoic period, from the Trias to the Chalk, is the true "age of reptiles," a number of orders being confined to that period. It is noteworthy, however, that the Triassic forms were in the case of the marine groups very generally of small size, and apparently amphibious, or perhaps freshwater. Of the various extinct Mesozoic orders, the Dinosauria, as demonstrated by their footprints in the sandstone of the Connecticut valley, were represented by species of huge size even in the Trias. The other extinct orders whose distribution was approximately coequal with the Mesozoic period were the ichthyosaurs (Ichthyopterygia), the plesiosaurs (Sauropterygia), and the pterodactyles (Ornithosauria). The Chelonia and Crocodilia (if we include the Phytosauria) date from the Trias, but are also dominant forms at the present day. But the mammal-like Anomodontia (Theromorpha), which ranged from South Africa to India and Russia, were solely Triassic. The Squamata, including lizards and snakes, together with the extinct Cretaceous Pythonomorpha (Mosasaurus, &c.), did not come into being till the upper Jurassic, or lower Cretaceous, and constitute the great bulk of the existing members of the class.
Batrachia, as represented by the labyrinthodonts, or Stegocephalia, carry the origin of vertebrates one tage further back, namely, to the upper Carboniferous.Amphibians. The stegocephalians, which appear to have included the ancestors of the anomodont reptiles, died out at the close of the Triassic epoch. The existing representatives of the class date, so far as is known, only from the Tertiary, but it is not improbable that the limbless caecilians (Apoda) may really be much older, since they appear to be related to the Stegocephalia.
The class Pisces is the lowest and at the same time the oldest representative of the Vertebrata, dating from the lower Ludlow Fishes.beds of the upper Silurian. The oldest group is that of the sharks and rays (Elasmobranchii), in which the orders Pleuropterygii, Ichthyotomi and Acanthodii are confined to the Palaeozoic. The lung-fishes (Dipnoi) are also an ancient group, although surviving in the form of three genera widely sundered in space; the order Arthrodira (as represented by Coccosteus of the Devonian) was solely Palaeozoic. Of the subclass Teleostomi, the fringe-finned group (Crossopterygii) attained its maximum in the Palaeozoic, although it survives in the shape of two African genera. In the case of the subclass Teleostomi the enamel-scaled, or ganoid, division was abundant during the Palaeozoic and early Mesozoic periods (and still survives in North America), but the modern soft-scaled bony fishes did not make their appearance till the Cretaceous, or thereabouts.
Of the class Agnatha, as typified by the modern lampreys, the palaeontological record is very imperfect. There is, however, an armoured subclass, the Ostracodermi, represented by Lampreys. Pterichthys, Cephalaspis, &c., which was confined to the upper Silurian and Devonian; and Palaeospondylus of the Devonian has been regarded as an early lamprey (Cyclostomi). Whether the so-called conodonts, ranging from the upper Cambrian to the Carboniferous, are really teeth of lampreys, has not been definitely ascertained.
The lamp-shells, or Brachiopoda, form an exceedingly ancient group, dating from the lower Cambrian, and surviving at the present day, although in greatly diminished numbers compared to the Palaeozoic epoch, when they far surpassed the now dominant bivalve molluscs.Brachiopods. The group attained its maximum in the Silurian, when, as in the Palaeozoic genera, nearly all the forms belonged to the hingeless section. With the beginning of the Mesozoic period the waning of the brachiopods, which had set in with the Devonian, became more pronounced, and was continued throughout the Mesozoic formations. A remarkable feature is the survival to the present day of the Cambrian genera Lingula, Discma and Crania (or closely allied types).
The Polyzoa, of which the sea-mats (Flustra) are well-known representatives, date from the Ordovician;Polyzoans. the Palaeozoic forms belonging almost exclusively to the section Cyclostomata, which attained its maximum in the Jurassic; while the dominant modern Chilostomata came in with the Tertiary.
The Mollusca, of which the great bulk are marine and the majority of the remainder freshwater, are perhaps the most important of all fossils from the chronological point of view.Molluscs. Since the three principal classes (Pelecypoda, Gastropoda and Cephalopoda) are represented in the upper Cambrian, it is evident that the origin of the group was much earlier. In the Palaeozoic the chambered cephalopods of the section Tetrabranchiata (now represented by the nautilus) were the dominant forms; the bivalves (Pelecypoda) and gastropods showing a relatively poor development. The tetrabranchiate cephalopods continued throughout the Mesozoic, when they were specially represented by the ammonites; but by the Tertiary they had become almost extinct. The section Dibranchiata (cuttle-fishes) commenced with the Mesozoic. The bivalves and gastropods have shown a steady increase to the present day, and are now the dominant forms.
Insects date from the Ordovician graptolite-slates of Sweden, where they are represented by Protocimex; the next oldest being Palaeoblattina of the French upper Silurian. From theInsects. Devonian about a dozen forms are known, belonging to several groups; and from the Coal-measures extensive insect-faunas have been described. All the Palaeozoic forms lack most of the distinctive features by which the modern groups are characterized, the majority of them showing kinship to the cockroach group.
The Myriapoda (centipedes and millipedes) are of comparatively little importance as fossils. The class dates from the Devonian, and is abundant in the Coal-measures; the Palaeozoic formsMyriapods. for the most representing two orders—Archipolypoda and Protosyngnatha—peculiar to that period, of which the second has only a single known species. The modern centipedes (Chilopoda) date mainly from the Tertiary, although several Carboniferous genera have been assigned to the group. Millipedes (Diplopoda), although known from the Cretaceous of Greenland, elsewhere date from the Tertiary.
The class Arachnida, now taken to include trilobites and king-crabs, as well as scorpions and spiders, is ancient. Scorpions—not far removed from existing types—are known in the Arachnids. Silurian, while true spiders occur in the Coal-measures. The great majority of the more typical Palaeozoic arachnids are, however, referred to an order by themselves—the Anthracomarti. King-crabs (Xiphosura) date from the Silurian, the existing genus Limulus occurring in the Trias; but the gigantic eurypterids (Eurypterida) and the trilobites (Trilobita) are exclusively Palaeozoic, the former dating from the Ordovician, and the latter from the upper Cambrian.
Most of the existing ordinal groups of the class Crustacea appear to date from the Palaeozoic; the decapods (lobsters and crabs) which represent the highest development of the class, did not, Crustaceans.however, attain a dominant position till well on in the Mesozoic, and are at their maximum in the present day; genuine crabs (Brachyura) apparently not having come into existence till the Cretaceous.
Among the Echinodermata, the classes Blastoidea and Cystoidea are exclusively Palaeozoic, while the stone-lilies (Crinoidea) form a ​group, dating from the same epoch, now on the verge of extinction. Echinoderms.The sea-urchins (Echinoidea), which date from the Ordovician but attain no great development till the Mesozoic, the starfishes (Asteroidea) and brittle-stars (Ophiuroidea), which also date from the Ordovician, and the sea-cucumbers (Holothuroidea), which appear to be represented in the Carboniferous, do not seem, however, to have attained their full development till the modern period.
That the Annelida are a very ancient group is indicated by the occurrence of remains of marine worms in the Ordovician; while “tracks” or “burrows” apparently point to the existence of the class in the lower Cambrian, if not indeed in the Laurentian.Annelids.
The earliest-known representatives of the Coelenterata occur in the upper Cambrian, where we find primitive types of hydroid polyps, especially the graptolites, which lived only till the Silurian, and have no near relatives. The equally isolated stromatoporids, on the other hand, commenced in the Ordovician and survived till the Devonian. Coelenterates.The corals (Actinozoa) were completely differentiated from the Hydrozoa in the Ordovician. Most of the Palaeozoic actinozoans belong to the Rugosa (inclusive of the four-rayed corals) which did not survive the Permian, but the Aporosa are also well represented. In the Mesozoic and Tertiary as well as at the present day the Aporosa and Porosa became, however, the dominant forms.
As might have been expected from their low grade of organization, the sponges (Porifera) were strongly represented in the early formations; the oldest known form occurring in the Welsh Cambrian. In the Silurian and Carboniferous silicious sponges were extraordinarily abundant, and Sponges.are represented by several extinct groups.
Foraminifera, extremely abundant in the Carboniferous, date at any rate from the Ordovician, where the existing genus Saccammina has been identified. The Chalk consists almost entirely of foraminifers. The Radiolaria, as represented by the Polycystina, are believed to date from the Silurian, or even Protozoa.the Cambrian, but did not attain their maximum till the Mesozoic or Tertiary. The so-called Eozoon of the Laurentian is not admitted to be of organic origin.
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* ↑ For the distribution of plants, see Plants: Distribution.
* ↑ Proc. Academy of Philadelphia, 1906, p. 123.
* ↑ Manchester Science Lectures, ser. 5 and 6, p. 202 seq.
* ↑ Proc. Geol. Soc. (London, 1890), p. 76.
* ↑ Natural Science, iii. 289.
* ↑ Geographical Distribution of Mammals (London, 1896), p. 27.
* ↑ "Correlation between Tertiary Mammal Horizons of Europe and America," Annals New York Academy, xiii. 48 (1900).
* ↑ The Geographical and Geological Distribution of Animals (London, 1878).
* ↑ "The Geographical Distribution of Life in North America with special reference to the Mammalia," Proc. Biol. Soc, Washington, vol. vii. pp. 1-64 (1892).
* ↑ See W. L. Sclater, "The Geography of Mammals," part v., Geographical Journal, 1896; M. Weber, "On the Origin of the Fauna of Celebes," Ann. Mag. Nat. Hist., ser. 7, vol. iii. pp. 121-136 (1899), and Der Indo-australische Archipel und die Ceschichte seiner Tierwelt (Jena, 1902); Lydekker, "Celebes; a Problem in Distribution," Knowledge, vol. xxi. pp . 175-177 (1898); see also Deer of All Lands, p. 168 (1898).
* ↑ Die Saugetiere (Jena, 1904), p. 308.
* ↑ Lydekker, Geographical Distribution of Mammals (1896).
* ↑ Der Indo-Australische Archipel, &c. (Jena, 1902)
* ↑ American Naturalist, xxv. 260 and 261 (1902).
* ↑ Report of Horn Expedition to Central Australia, pp. 187 and 188 (1896).
* ↑ Proc. Amer. Phil. Soc., xlix. 73 (1905).
* ↑ Report, Australian Assoc., ix. 319 (1903)
* ↑ Mem. Californian Academy, vol. iv . (1904).
* ↑ Catalogue of the Tertiary Vertebrata of the Fayum (London, 1906).
* ↑ Science, ser. 2, vol. xix. p. 221 (1904). Dr Packard groups Notogaea and Neogaea in a single realm under the name Antarctogaea. Some other writers, such as Dr H. Gadow, take Notogaea to include all the three southern continents, and employ the term Arctogaea for the rest of the world.
* ↑ Proc. Zool. Soc, London, 1903, pp. 340-368.
* ↑ Natural Science, vol. iv., pp. 353-364 (1894).
* ↑ The fossils of the Uitenhage beds, now generally classed as Jurassic, consist chiefly of invertebrates and plants.
* ↑ Index Faunae Novae-Zealandiae (London, 1904).
* ↑ One member of this group has recently been described from the Shan States.
* ↑ The American form is often separated as Neurotrichus, but this does not affect the relationship of the two areas.
* ↑ "The Origin and Relationship of the Large Mammals of North America," Rep. New York Zool. Soc. (1904), p. 7.
* ↑ Proc. Zool. Soc, London, 1903, vol. i. p . 340.
* ↑ Proc. Amer. Phil. Soc, xli. p. 267 (1902).
* ↑ Rep. Eighth International Geographic Congress, p. 619.
* ↑ See Amer. Journ. Science, ser. 2, vol. xvi. p. 155 (1853).
* ↑ See Study of Fishes (London, 1880).
* ↑ The Geography of Mammals (London, 1899).