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Show 392 DARWINISM: CHAl'. 1 · d of sr)ecial creation or by sudden advances of orgauisu-any nn ' . h l l . h. tion in the offspring of precedmg typ.es, ~uc c ose re n.twns 1 p would not be found ; and facts of tlus kmd become, the~efore, t me extent a test of evolution under nu,tural selectwn or 0 so h l . l. some other law of gradual change. Of c~urse t e re at10ns 11p will not appear when extensive . migratwn has occurred, hy which the inhabitants of one regwn have been a~le to ta~w possession of another region, an~ destroy or dnve out Its original inhabitants, as has sometimes happened. Rnt such cases arc comparatively rare, except where great changes of climate are known to have occurred; and we usually do fiml a remarkable continuity between the existing fauna and ftora of a country and those of the immediately p:·eccding age.. A few of the more remarkable of these cases w1ll now be bneHy noticed. The mammalian fauna of Australia consists, as is well known, wholly of the lowest forms-the. Marsupi~l~ and Monotremata- except only a few species of m1cc. This 1s accon~1te_<l for by the complete isolation of the country from the Asmtw continent during the whole peri?d of the development of the higher animals. At some ear:Jer epoch the ancestral m~u·supials, which abounded both m E~rope and North Amenca in the mi ldlc of the Secondary penod, entered the counb'), and have since remained there, free from the competition of higher forms, and have un~ergone ~.special dev~lopm cnt in accordance with the pecuhar conditiOns of a bm1 tc~l a,rca. 'Vhile in the lar<re continents higher forms of mammaha hn.Ye been developed, ~hich have almost or wholly exterminate<l the less perfect marsupials, in Australia these l~tter have hccomc modified into such varied forms as the lcapmg kangaroos, the burrowing wombats, the arboreal phalang~rs, the inse?tivoroHs ba.ndicoots, and the carnivorous Dasyundre or native ~ats, culminatina in the Thylacinus or "tiger-wolf" of Tasmamaanimals as bunlike each other as our sheep, rabbits, squirrels, and dogs, but all retaining the characteristic features of the marsupial type. . . Now in the caves and late Tertiary or Post-Tertiary depo::nts of Australia the remains of many extinct mammalia have hceu found, but all are marsupials. There are many kan wtroos, some larger than any living species, a,nd others more alh e<l to xrrr THE GEOLOGICAL EVIDENCES OF EVOLUTION 393 the tree-kangaroos of New Guinea; a large wombat as large :ts a .tnpir; the Diprotodon, a thick-limbed kangaroo the size of a rhmoccros ~r small elephant; and a quite different animal, t~e N otothernu~, ~early as large. The carnivorous Thylacmus of Tasmama 1s also found fossil ; and a huge phalanger, Thyla.coleo, the ize of a lion, believed by Professor Owen and by Profe. sor Oscar Schmidt to have been equally carnivoro. u. and clestructive. 1 Besides these, there arc many other species more resembling the living forms both in size and structure, of which they may be, in some ca,ses, the direct ancestors. Two species of extinct Echidna, belonging to the very low Monotremata, have also been found in New South \Vales. Next to Australia, South America possesses the most remarkable assemblage of peculiar mammals, in its numerous Edentata-the sloths, ant-eaters, and armadillos; its rodents ~uch as the cavies and chinchillas; its marsupial opossums, ancl Its ~uaclrumana of the family Cebidro. Remains of extinct specws _of all these have been found in the caves of Brazil of Post-Pliocene ag? i. while in the earlier Pliocene deposits of 'the pampas ma~y d1~tw~t genera of these groups have been found, some _of gigantic size and extraordinary form. There are ar.m ad1.1 lo]s ohf many types, some beino· as larac as ele1)hants · b b ) g1gant10s ot s of the generaMegatherium, MegaJonyx, Myloclon, Les~o.rlon, an.cl many others; rodents belonging to the American farmhes C~vtdre and Chinchillidre; and ungulates allied to the llama; bcstde.s many other extinct forms of intermediate types or of unce.rtam affinities.~ The extinct Moa.s of N cw Zealand - huge wmgless birds allied to the living Apteryx-illustrate the same general law. The examples now quoted, besides illustrrrtina and enforci11 a the general fact of evolution, throw some li o-ht on the usual {)haracter of the modification nncl progrcs. ion ~f animal form s. In the cases where the geological record is tolerably complete we find. a continuous development of some kind-either i1~ <.:omple:x;1ty of omat?entation, as in the fos il Paludinas of the Hungunan lake-basms; in size and in the specialisabon of the : 'ee. 1'he ~l~wnmctlict i~L their Relation to Primeval T imes, p. 102. G r For~ ~.bnef_en~uue~·atiOn and description of these fos ils, .. Pe the author's eograp t1cal Dtstrzb1thon of .-l nimals, Yol. i. p. 146. |