Bible Encyclopedias
Zoological Distribution

[TERRESTRIAL

There is also the phenomenon of vertical temperature-control. On this subject Dr A. R. Wallace has written (Ency. Brit., gth 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 mountainranges 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 proposed by Dr P. L. Sclater in 1858, and are chiefly Regions. based on the distribution of birds and mammals, are as follows: I. 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 Yang-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 reccgnized 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, 2 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 anonymously a in 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 4 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 6 (in accordance with a suggestion of 1 Manchester Science Lectures, ser. 5 and 6, p. 202 seq.

Proc. Geol. Soc. (London, 1890), p. 76.

Natural Science, iii. 289.

4 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).

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. 8 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, 9 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. 2. Ethiopian. 3. Malagasy. 4. Oriental.

Nearctic Palaearctic Sonoran Mediterranean II. Neogaea 5. Neotropical.

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, Notonays, &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 ' " 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 and die Geschichte 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).

9 Die Sdugetiere (Jena, 1904), p. 308.

Austro-Malayan III. Notogaea.

6. Australian (?) 7 . Polynesian (?) 8. Hawaiian.

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 barbets (Megalaemidae), the otherwise cosmopolitan woodpeckers (Picidae), the trogons (Trogonidae), and the pheasant and partridge tribe (Phasianidae).

The reptiles, owing probably to their 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 sidenecked group (Pleurodira), now restricted to the southern hemisphere; among these the most noteworthy being the giant horned tortoise (Miolania ) 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 Stringops 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 AustroMalayan 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 EuroAsiatic 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 3 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 4 is also of opinion that the 1 Lydekker, Geographical Distribution of Mammals (1896).

2 Der Indo-Australische Archipel, &c. (Jena, 1902).

American Naturalist, xxv. 260 and 261 (1902).

4 Report of Horn Expedition to Central Australia, pp. 187 and 188 (1896).

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 (1893), 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 (2902). On the other hand, Dr T. Gill (1875) believed in the existence of an " Eogaea " 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 polyprotodonts, 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 landconnexion 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. V¦ het her 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 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 5 Proc. Amer. Phil. Soc., xlix. 73 (2905).

' Report, Australian Assoc., ix. 329 (1903).

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 noteworthy 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 lastnamed 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), sunbitterns (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, elsewhere 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 burrowingsnakes 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 catfishes (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 overwhelmingly 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 (I) 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 of its autochthonous mammalfauna. 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 Arctogaea. fauna. e It y may e be l mentioned, however,s thatmatalthe present day monotremes are wholly wanting, while marsupials are represented only by one or two species of opossums ( Didelphys) in North America and by cuscuses ( Phalanger ) in the AustroMalayan 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 ' Mem. Californian Academy, vol. iv. (1904).

2 Catalogue of the Tertiary Vertebrata of the Fayum (London, 1906).

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 Dr H. S. Packard 3 has suggested that it should be sepa rated from Arctogaea to form a realm by itself, under g 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, 4 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, northward 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 5 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 tahrgoat ( Hemitragus ) in Oman lends some support to this proposal since that genus has no representative in Africa, and occurs elsewhere 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 Arsinditherium, 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 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.

4 Proc. Zool. Soc., London, 1903, pp. 340-368.

5 Natural Science, vol. iv., pp. 353-3 6 4 (1894).

distinct. The Prosimiae, or lemuroids, include the galagos (Galago) and pottos ( Perodictycus ), of which the latter are akin to the Oriental lorises, 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 bearfamily (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 subgenerically 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 (Giraffa) 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 ), foresthogs (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 strandmoles (Bathyergidae), the crested-rats (Lophiomys ), and the canerats (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 Ethiopian. 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 guineafowls (Numidinae) form a subfamily confined to Ethiopia and Madagascar, where true pheasants are unknown. Other peculiar types are plantain-eaters (Musophagidae), colies (Coliidae), woodhoopoes (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 Gerrhosauridae 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 ma

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