The geographical distribution of animals, with a study of the relations ...
The geographical distribution of animals, with a study of the relations ... The geographical distribution of animals, with a study of the relations ...
288 ZOOLOGICAL GEOGRAPHY. [part m.ancestral type may have been a bird capable of flight, and thatit spread from one of* the three southern continents to the othersat the period of their near approach, and more or less completelylost the power of flight owing to the long continued absenceof enemies.During the period we have been considering, the ancestors ofexisting apes and monkeys flourished (as we have seen inChapter VI.) along the whole southern shores of the old Palaearcticcontinent ; and it seems likely that they first enteredAfrica by means of a land connection indicated by the extensiveand lofty plateaus of the Sahara, situated to the south-east of Tunisand reaching to a little north-west of Lake Tchad ;and at the sametime the elephant and rhinoceros type may have entered. Thiswill account for the curious similarity between the higher faimasof West Africa and the Indo-Malay sub-region, forowing to thepresent distribution of land and sea and the narrowing of thetropical zone since Miocene times, these are now the onlylowland, equatorial, forest-clad countries, which were inconnectionwith the southern shores of the old Palsearcticcontinent atthe time of its greatest luxuriance and development. Thiswestern connection did not probably last long, the junction thatled to the greatest incursion of new forms, and the completechange in the character of the Africanbeen effected by way offauna, having apparentlySyria and the shores of the Red Sea ata somewhat later date. By this route the old South-Palsearcticfauna, indicated by the fossils of Pikermi and the Siwalik Hills,poured into Africa; and finding there a new and favourablecountry, almost wholly unoccupied by large Mammalia, increasedto an enormous extent, developed into new forms, and finallyoverran the whole continent.Before this occurred, however, a great change had taken placein the geography of Africa.It had gradually diminished on thesouth and east ; Madagascar had been left isolated ; while anumber of small islands, banks, and coral reefs in the IndianOcean alone remained to indicate the position of a once extensiveequatorial land. The Mascarene Islands appear to representthe portion which separated earliest, before any carnivora had
chap, xi.] THE ETHIOPIAN REGION. 289reached the country ; and it was in consequence of this totalexemption from danger, that severalgroups of birds altogetherincapable of flight became developed here, culminating in thehuge and unwieldy Dodo, and the more active Aphanapteryx.To the same cause may be attributed the development, in theseislands, of gigantic land-tortoises, far surpassing any others nowliving on the globe. They appear to have formerly inhabitedMauritius, Bourbon, and Bodriguez, and perhaps all theother Mascarene islands, but having been recklessly destroyed,now only survive in the small uninhabited Aldabra islandsnorth of the Seychelle group. The largest living specimen(5^ feet long) is now in our Zoological Gardens. The onlyother place where equally large tortoises (of an allied species)are found, is the Galapagos islands, where they were equally freefrom enemies till civilized man came upon the scene ;who, partlyby using them for food, partly by the introduction of pigs, whichdestroy the eggs, has greatly diminished their numbers andsize, and will probably soon wholly exterminate them. It is acurious fact, ascertained by Dr. Giinther, that the tortoises ofthe Galapagos are morenearly related to the extinct tortoises ofMauritius than is the living tortoise of Aldabra. This wouldimply that several distinct groups or sub-genera ofhad a wide range over the globe, and that some ofTestudo haveeach havesurvived in very distant localities. This is rendered quite conceivableby the known antiquity of the genus Testudo, whichdates back to at least the Eocene formation (in North America)with very little change of form. These sluggish reptiles, solong-lived and so tenacious of life, may have remained unchanged,while every higher animal type around them hasbecome extinct and been replaced by very different forms ; asin the case of the living Emys tectum, which is the sole survivorof the strange Siwalik fauna of the Miocene epoch. The ascertainedhistory of the genus and the group, thus affords a satisfactoryexplanation of the close affinity of the gigantic tortoisesof Mauritius and the Galapagos.The great island of Madagascar seems to have remained longerunited with Africa, till some of the smaller and more active
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288 ZOOLOGICAL GEOGRAPHY. [part m.ancestral type may have been a bird capable <strong>of</strong> flight, and thatit spread from one <strong>of</strong>* <strong>the</strong> three sou<strong>the</strong>rn continents to <strong>the</strong> o<strong>the</strong>rsat <strong>the</strong> period <strong>of</strong> <strong>the</strong>ir near approach, and more or less completelylost <strong>the</strong> power <strong>of</strong> flight owing to <strong>the</strong> long continued absence<strong>of</strong> enemies.During <strong>the</strong> period we have been considering, <strong>the</strong> ancestors <strong>of</strong>existing apes and monkeys flourished (as we have seen inChapter VI.) along <strong>the</strong> whole sou<strong>the</strong>rn shores <strong>of</strong> <strong>the</strong> old Palaearcticcontinent ; and it seems likely that <strong>the</strong>y first enteredAfrica by means <strong>of</strong> a land connection indicated by <strong>the</strong> extensiveand l<strong>of</strong>ty plateaus <strong>of</strong> <strong>the</strong> Sahara, situated to <strong>the</strong> south-east <strong>of</strong> Tunisand reaching to a little north-west <strong>of</strong> Lake Tchad ;and at <strong>the</strong> sametime <strong>the</strong> elephant and rhinoceros type may have entered. Thiswill account for <strong>the</strong> curious similarity between <strong>the</strong> higher faimas<strong>of</strong> West Africa and <strong>the</strong> Indo-Malay sub-region, forowing to <strong>the</strong>present <strong>distribution</strong> <strong>of</strong> land and sea and <strong>the</strong> narrowing <strong>of</strong> <strong>the</strong>tropical zone since Miocene times, <strong>the</strong>se are now <strong>the</strong> onlylowland, equatorial, forest-clad countries, which were inconnection<strong>with</strong> <strong>the</strong> sou<strong>the</strong>rn shores <strong>of</strong> <strong>the</strong> old Palsearcticcontinent at<strong>the</strong> time <strong>of</strong> its greatest luxuriance and development. Thiswestern connection did not probably last long, <strong>the</strong> junction thatled to <strong>the</strong> greatest incursion <strong>of</strong> new forms, and <strong>the</strong> completechange in <strong>the</strong> character <strong>of</strong> <strong>the</strong> Africanbeen effected by way <strong>of</strong>fauna, having apparentlySyria and <strong>the</strong> shores <strong>of</strong> <strong>the</strong> Red Sea ata somewhat later date. By this route <strong>the</strong> old South-Palsearcticfauna, indicated by <strong>the</strong> fossils <strong>of</strong> Pikermi and <strong>the</strong> Siwalik Hills,poured into Africa; and finding <strong>the</strong>re a new and favourablecountry, almost wholly unoccupied by large Mammalia, increasedto an enormous extent, developed into new forms, and finallyoverran <strong>the</strong> whole continent.Before this occurred, however, a great change had taken placein <strong>the</strong> geography <strong>of</strong> Africa.It had gradually diminished on <strong>the</strong>south and east ; Madagascar had been left isolated ; while anumber <strong>of</strong> small islands, banks, and coral reefs in <strong>the</strong> IndianOcean alone remained to indicate <strong>the</strong> position <strong>of</strong> a once extensiveequatorial land. <strong>The</strong> Mascarene Islands appear to represent<strong>the</strong> portion which separated earliest, before any carnivora had