The geographical and geological distribution of animals / by Angelo Heilprin.
- Angelo Heilprin
- Date:
- 1907
Licence: In copyright
Credit: The geographical and geological distribution of animals / by Angelo Heilprin. Source: Wellcome Collection.
28/466 page 10
![marsupials, and tlrey liave likewise been considered to afford proof of a land connection such as has been indicated. A serious diffi- culty, however, tliat lies in the Avay of this explanation is tlie important fact that none of the characteristic African or South American mammals are fountl in Australia, for it might justly be contended that if a migration or transferrence was effected in one direction, it could have been effected in the opposite direction as well. But that such recii)rocal distribution did not obtain is very nearly certain. It may, indeed, be assumed that at the time of a possible Australian migration the extremities of the southern con- tinents were not yet inhabited; but this is very unlikely. Or, it may be further assumed, with Riitimeyer, that the animals under consideration had a polar origin, and that they were distributed northward along continental lines that possibly now lie buried beneath the sea ; but positive evidence in this direction is still wholly wanting. An element in the problem which very materi- ally narro-\vs the issue is the circumstance that marsupial remains have been found in the temperate regions of the Northern Hemi- sphere, and in both Europe and North America in deposits as an- cient as tlie Tria.ssic })eriod. In this upper tract, therefore, we iind a possible and more probable clue towards the ex])lanation of tlie existing distribution of the animals in ipiestion ; and if it be objected that some such living forms ought still to be found in the connecting region, the fact, nevertheless, remains that they did tlicrc once exist, but have since become largely extinct. It will be evident that the key to the solution of the more marked peculiarities of modern distribution must be sought in the records of the past, for in the comparison between existing and preexisting faunas alone can we expect to determine the condi- tions upon which present faunas were established, and to ascertain the dates of their respective appearances or antiquity^ In most regions of the earth’s surface a most intimate relationship links together the existing fauna and the fauna of the geological ])eriod or periods immediately preceding. The Pliocene and Post-Pliocene maiine shell-fish faunas of the Western United States are ])ractically identical with the equivalent fauna of the (modern) adjoining seas; the Post-Pliocene mammals of Britain are such as still roam about the land, although they include numerous forms which no longer exist there; lu India a large proportion of the mammalian types](https://iiif.wellcomecollection.org/image/b29011115_0028.jp2/full/800%2C/0/default.jpg)
