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 ...
—154 DISTRIBUTION OF EXTINCT ANIMALS. [part ii.early times. The true bears (Ursus) are almost the onlyimportant genus that seems to have recently migrated. InEurope it dates back to the Older Pliocene, while in NorthAmerica it is Post-Pliocene only. Bears, therefore, seem tohave passed into America from the Palaearctic region in the latterpart of the Pliocene period. They probably came in on thenorth-west, and passed down the Andes into South America,where one isolated species still exists.Ungulata.—Horses are very interesting. In Europe they dateback under various forms to the Miocene period, and true Equusto the Older Pliocene. In North America they are chieflyPliocene, true Equus being Post- Pliocene, with perhaps one ortwo species Newer Pliocene ;but numerous ancestral forms dateback to the Miocene and Eocene, giving a more perfect " pedigreeof the horse " than the European forms, and going back to amore primitivetypeOrohippus.In South America, Equus isthe only genus, and is Post-Pliocene or at most Newer Pliocene.While, therefore, the ancient progenitors of the Equidae werecommon to North America and Europe, in Miocene and evenEocene times, true horses appear to have arisen in the Palasarcticregion, to have passed into North America in the latter part ofthe Pliocene period, and thence tohave spread over all suitabledistricts in South America. They w T ere not, however, able tomaintain themselves permanently in their new territory, and allbecame extinct ;while in their birth-place, the Old World, theycontinue to exist under several varied forms.True tapirs are an Old World group. They go back to theLower Miocene in Europe, while in both North and SouthAmerica they are exclusively Post-Pliocene. They occur inFrance down to the Newer Pliocene, and must, about thattime, have entered America. The land connection by whichthis and so many other animals passed between the Old andNew Worlds in late Tertiary times, was almost certainly in theNorth Pacific, south of Behring's Straits, where, as will be seenby our geueral map, there is a large expanse of shallow water,which a moderate elevation would convert into dry land, in asufficiently temperate latitude.
Jchap. vii.MAMMALIA OF THE NEW WORLD. 155The peccary (Dicotyles), now a characteristic South Americangenus, is a recent immigrant from North America, where itappears to have.been developed from ancestral forms of swinedating back to the Miocene period.Antelopes are an Old World type, but a few of them appear tohave entered North, and reached South America in late Pliocenetimes.Camels, strange to say, are a special North American type,since they abounded in that continent under various ancientforms in the Miocene period. Towards the end of that periodthey appear to have entered eastern Asia, and developed into theSiberian Merycotheriurn and the North Indian Camelus, whilein the Pliocene age the ancestral llamas entered SouthAmerica.Cervidce are a wide-spread northern type in theirgeneralizedform, but true deer (Cervus) are Palsearctic. They abounded inEurope in Miocene times, but only appear inNorth and SouthAmerica in the later Pliocene and Post-Pliocene periods.True oxen (Bovince) seem to be an Oriental type (Miocene),while they appear in Europe only late in the Pliocene period,and in America are confined to the Post-Pliocene.Elephants (Mephantidce) are an Old World type, aboundingin the Miocene period in Europe and India, and first appearingin America in Post-Pliocene or later Pliocene times.Ancestralforms, doubtfully Proboscidean (Dinocerata), existed in NorthAmerica in the Eocene period, but these became extinct withoutleaving any direct descendants, unless the Brontotheridce andrhinoceroses may be so considered.Marsupials are almost certainly a recent introduction intoSouth and North America from Asia. They existed in Europein Eocene and Miocene times,and presumably over a considerablepart of the Old World ; but no trace of them appears inNorth or South America before the Post-Pliocene period.Edentata.— These offer a most curious and difficult problem.In South America they abound, and were so much more numerousand varied in the Post-Pliocene and Pliocene, that wemay be sure they lived also in the preceding Miocene period. Afew living Edentates are scattered over Africa and Asia, and.
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Jchap. vii.MAMMALIA OF THE NEW WORLD. 155<strong>The</strong> peccary (Dicotyles), now a characteristic South Americangenus, is a recent immigrant from North America, where itappears to have.been developed from ancestral forms <strong>of</strong> swinedating back to <strong>the</strong> Miocene period.Antelopes are an Old World type, but a few <strong>of</strong> <strong>the</strong>m appear tohave entered North, and reached South America in late Pliocenetimes.Camels, strange to say, are a special North American type,since <strong>the</strong>y abounded in that continent under various ancientforms in <strong>the</strong> Miocene period. Towards <strong>the</strong> end <strong>of</strong> that period<strong>the</strong>y appear to have entered eastern Asia, and developed into <strong>the</strong>Siberian Meryco<strong>the</strong>riurn and <strong>the</strong> North Indian Camelus, whilein <strong>the</strong> Pliocene age <strong>the</strong> ancestral llamas entered SouthAmerica.Cervidce are a wide-spread nor<strong>the</strong>rn type in <strong>the</strong>irgeneralizedform, but true deer (Cervus) are Palsearctic. <strong>The</strong>y abounded inEurope in Miocene times, but only appear inNorth and SouthAmerica in <strong>the</strong> later Pliocene and Post-Pliocene periods.True oxen (Bovince) seem to be an Oriental type (Miocene),while <strong>the</strong>y appear in Europe only late in <strong>the</strong> Pliocene period,and in America are confined to <strong>the</strong> Post-Pliocene.Elephants (Mephantidce) are an Old World type, aboundingin <strong>the</strong> Miocene period in Europe and India, and first appearingin America in Post-Pliocene or later Pliocene times.Ancestralforms, doubtfully Proboscidean (Dinocerata), existed in NorthAmerica in <strong>the</strong> Eocene period, but <strong>the</strong>se became extinct <strong>with</strong>outleaving any direct descendants, unless <strong>the</strong> Bronto<strong>the</strong>ridce andrhinoceroses may be so considered.Marsupials are almost certainly a recent introduction intoSouth and North America from Asia. <strong>The</strong>y existed in Europein Eocene and Miocene times,and presumably over a considerablepart <strong>of</strong> <strong>the</strong> Old World ; but no trace <strong>of</strong> <strong>the</strong>m appears inNorth or South America before <strong>the</strong> Post-Pliocene period.Edentata.— <strong>The</strong>se <strong>of</strong>fer a most curious and difficult problem.In South America <strong>the</strong>y abound, and were so much more numerousand varied in <strong>the</strong> Post-Pliocene and Pliocene, that wemay be sure <strong>the</strong>y lived also in <strong>the</strong> preceding Miocene period. Afew living Edentates are scattered over Africa and Asia, and.
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