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Show 110 ZOOLOGY OF TilE VOYAGE OF TilE BEAGLE. d d l the present fossil is equally distinct from Brasiliensis, it may be conclu e t tat both. · · 1 h' d-f t of the Rodent figured at fig. 12, includes The portwn of the ng 1t m 00 d 1 l b 'des external and middle cuneiform bones, an t 1e the calcaneum astraga us, cu OI ' . . 1 1 1 'd . · al phalancres of the toes correspondmg w1th t 1e t Hcc metatarsa s an prox1m b l · fl k bl ~ middle toes of five-toed quadrupeds. The metatars.als are c u.e y rem~~ ~ .. e or I ll d 1 d double trochlear articular surface, and mtermechate ndge. t 1e we - eve ope - .1· d These remam· s, as we 11 as tl e J·aws and teeth of the Ctenomys, were utscovere 1 at Monte Hermoso in Bahia Blanca. . . In the same reddish earthy stratum of that locality, Mr. Darwm d1sc?ver~d the u.1 ecompose d mo 1a r of a Rodent , equalling in size • and closely resemblmg m the disposition of its oblique component lamin~, the hinder mola~ of the Capybara (Hyd 1·ocltcerus). The fossil differs, however, in the greater relattve breadth of the component lamin~. . 1 have, lastly, to notice the head of a femur, and some fragments of pelvtc bones from the same formation which bear the same proportion to the tooth above alluded to as subsists between the teeth and bones of the Capybara, and which are suffici~nt to prove that there once has existed in South America a species of the family Caviidce, as large as the present Capybam, but now apparently extinct. This fact, together with the greater part of those which have been recorded in the foregoing pages of the present work, establishes the correspond~nce, i~ regard. to the characteristic type, which exists between the present anu extmct anunals of the South American Continent: we have abundant evidence likewise of the greater number of generic and specific modifications of these fundamental types which the animals of a former epoch exhibited, and also of the vastly superior size which some of the species attained. At the same time it has been shewn that some of the present laws of the geographical distribution of animals would not have been applicable to South America, at the period when the Megatherioills, Toxoclon, and Macrauchenia existed: since the Horse, and according to M. Lund. the Antelope and the Hy~na, were then associated with those more strictly South American forms. The Horse, which, as regards the American continent, had once become extinct, has again been introduced, and now ranges in countless troops over the pampas and savannahs of the new world. If the small Opossnms of South America had been in like manner imported into Europe, and were now estublisheu like the Squirrels and Dormice in the forests of France, an analogous case would exist to that of the Horse in South America, as the fossil Didelphys of Montmartre proves. FOSSIL llfA:M:M ALIA. 11 1 . With resp~ct to . tl~e geological contemporaneity of the fossils collected by h1m, Mr. Darwm subJoms the following observations:- . "~he remains of the following animals were embedded together at Punta Alta m Bahm Blanca· The 71!Te t 1 • c · .. . .. . . . - . .I.w!Ja Jtenum uvteru, .7J1./Tu egalonyx Jiffersonii, Mylodon Darwzrm, .Scelzdot!tenurn leptocep!talurn, Toxodon Platensis (?) a Horse and a small Dasypocloid quadruped, mentioned p. 107; at St. Fe in Entre Rios a Horse a Ma. todon, T_oxodon Platcnsis, and some large animal with a tessel~ted osse~us derm.a~ covermg; on. the banks of the Tercero the Mastodon, Toxodon, and, accozdmg ~o the Jes.mt Falkner, some animal with the same kind of covering; ncar the .RIO N ~gro m Banua Oriental, the 'Poxodon Platensis, Glossotherium, and some ammal With the same kind of covering. To these two latter animals the Glyptodon clavipes, .described by Mr. Owen in the Geological Transactions, may, .from .the locality where it was discovered, and from the similarity of the deposit wluch . covers the greater part of Banda Oriental, almost certainly be added, as havmg been contemporaneous. From nearly the same reasons, it is p~obable that the Rodents found at Monte Hermoso in Bahia Blanca, co-existed ~VIth the severa~ gigantic mammifers from Punta Alta. I have, also, shown m the Introduct.wn, that the Macrauc!tenia Pataclwnica, must have been coeval, 01: nearly so, .w1th the last mentioned animals. Although we have no evidence of th~ geologtcal age of the deposits in some of the localities just specified, yet. from the pr~sence of the same fossil mammifers in others, of the age of wln.ch we have fmr means of judging, (in relation to the usual standard of comp~ nson, of the amount of change in the specific forms of the invertebrate inhabitants of the sea,) we may safely infer that most' of the animals described in this ~olume, and likewise the Glyptodon, were strictly contemporaneous, and that alt hved at about the same very recent period in the earth's history. Moreover, as ~orne of the fossil animals, discovered in such extraordinary numbers by M. Lund 111 the caves of Brazil, are identical or closely related with some of those which lately lived together in La Plata and Patagonia, a certain degree of light' is thus thrown on the antiquity of the ancient Fauna of Brazil, which otherwise woulll have been left involved in complete darkness." |
