The geographical distribution of animals, with a study of the relations ...

chap, vii.] MAMMALIA OF THE NEW WORLD. HIto ascertain their relations to each other, and to see how tarthey elucidate the problem of the birth-place and subsequentmigrations of the several families and genera. We have alreadypointed out the remarkable features of the Quaternary (or Post-Pliocene) fauna of North America, and now proceed to discussthat of the various Tertiary periods, which isclosely connectedwith the extinct fauna of Europe.The Tertiary Mammalia of North America at present describedbelong to from eighty to one hundred genera, whilethose of Europe are nearly double that number ;yet onlyeighteen genera are common to the two faunas, and of theseeight are living and belong chiefly to the Pliocene period.Taking first, the genera which in America do not go back beyondthe Pliocene period (ten in number), we find that eight of themin Europe go back to the Upper Miocene. These are Felis,Pseudmlurus, Hipparion, Cervus, Mastodon, Elephas (in India),Castor and Hystrix ; while another, Canis, goes back to theUpper Eocene and the tenth, Equus, confined to the newerPliocene or perhaps to the Post-Pliocene in America, extendsback to the older Pliocene in Europe. Of the seven Europeangenera which are confined to the Miocene period in America,three, Hymnodon, Anchitherium, and Lophiodon go back to theEocene in Europe; three others, Machairodus, Rhinoceros, andAceratherium, are also of Miocene age in Europe; Amphicyon goesback to the Lower Miocene of Europe. Lophiotherium belongsto the Eocene of both countries.If we turn now to families instead of genera, we find that thesame general rule prevails.Mustelidae (weasels), Ursidae (bears),true Equidae (horses), and Bovidae (oxen &c), go no further backin America than the Pliocene, while they all go back to theMiocene in Europe.Suidae (swine) and Anoplotheridae (extinct)are found in the American Miocene and in the European Eocene.Anchitheridae (extinct) reach the Upper Eocene in America,while in Europe they range through Upper, Middle, and LowerEocene. Cervidae (deer) alone are Miocene in both countries.There remain two families in which America has the preeminence.Camelidae (camels) were •wonderfully developed in