CAUSES OF THE EVOLUTION AND EXTINCTION OF THE TITANOTHERES 



867 



pluvial conditions, great inland seas or fresh-water 

 lakes (first surmised by Stuart) favored the develop- 

 ment of large marsupials. Conversely the rise of an 

 eastern coastal range was followed by diminished rain 

 supply and progressive desiccation of the interior 

 region. 



Spencer observes (1896.1, p. 183): 



The larger forms now extinct, such as species of Diprotodon, 

 Nototherium, Phascolonus, Macropus, Protemnodon, etc., reached 

 their greatest development in Pliocene time and were character- 

 istic of the eastern interior, spreading southward round the 

 western end of the Dividing Range into Victoria. They do 

 not seem to have reached the eastern coastal district. * * * 

 In post-Pliocene time, with the increasing desiccation of the 

 whole central area, they became extinct, though this extinction 

 can not be attributed wholly to the drying up of the land, 

 because in certain parts, such as western Victoria, to which they 

 reached, the state of desiccation did not supervene; but at the 

 same time it may perhaps be justly argued that the desiccation 

 of the vast area of the interior was the largest factor in their 

 extinction. 



The discovery (in 1892) of the great Lake Calla- 

 bona bone deposit in the interior of South Australia 

 abundantly confirms the "desiccation" theory. Dr. 

 E. C. Stirling (1899.1, pp. ii-iii) describes this remark- 

 able deposit as follows: 



There is, however, compensation for the unpromising physical 

 features of Lake Callabona in the fact that its bed proves to be a 

 veritable necropolis of gigantic extinct marsupials and birds 

 which have apparently died where they lie, literally in hundreds. 

 The facts that the bones of individuals are often unbroken, 

 close together, and frequently in their proper relative positions 

 (vide pi. A, fig. 3), the attitude of many of the bodies, and the 

 character of the matrix in which they are embedded negative 

 any theory that they have been carried thither by floods. The 

 probability is, rather, that they met their death by being entombed 

 in the effort to reach food or water, just as even now happens 

 in dry seasons to hundreds of cattle which, exhausted by thirst 

 and starvation, are unable to extricate themselves from the 

 boggy places that they have entered in pursuit either of water 

 or of the little green herbage due to its presence. The accu- 

 mulation of so many bodies in one locality points to the fact of 

 their assemblage around one of the last remaining oases in the 

 region of desiccation which succeeded an antecedent condition 

 of plenteous rains and abundant waters. An identical explana- 

 tion has been suggested by Mr. Daintree (1872.1) in his "Notes 

 on the geology of the colony of Queensland." 



Alkali and salt deposits. — One effect of increasing 

 desiccation is the increased number of alkali lakes, 

 licks, and springs, and other localities of salt deposits. 

 Alkali is much sought by certain wild animals as a 

 substitute for salt. Western stockraisers disagree as 

 to the effects of alkali upon sheep and cattle, some 

 believing that it can not take the place of salt. Ches- 

 nut (1901.1, p. 20) notes that alkali may possibly pre- 

 dispose to the "loco habit," the eating of a narcotic 

 weed. When domesticated animals are not salted 

 regularly they soon discover localities where large 

 quantities of alkali are found in the soil and visit 

 such places frequently for the purpose of eating this 

 alkali soil. (Op. cit., p. 87.) 



101959— 29— VOL 2 12 



THE LIVING ENVIRONMENT 



We have thus considered the relations of cold, heat, 

 moisture, and desiccation to the hunger, the thirst, 

 and the feeding and the migrating habits of animals. 

 We may now look at the food supply of the Herbivora, 

 especially in its relation to unusual conditions of life. 



Forestation, deforestation, and reforestation. — Forests 

 furnish a condition necessary to the existence of 

 certain quadrupeds, especially the browsing animals, 

 such as the Cervidae, which have brachyodont (short- 

 crowned) teeth, and the Proboscidea, including 

 especially the brachyodont mastodon. Among Artio- 

 dactyla the deer, among Perissodactyla the tapirs, 

 among Proboscidea the mastodons are typical forest 

 animals. Conditions, therefore, which cause defores- 

 tation would become a means of extinction; such con- 

 ditions are (a) intense cold and heavy snow capping, 

 (b) intense dryness, (c) destruction of young trees by 

 the smaller browsing animals. 



It is probable that the interior of Australia and the 

 Pampean region of South America were in Pliocene 

 and early Pleistocene time partly covered with forests. 

 It is certain that the Holarctic region (the circumpolar 

 belt) was forested in early Pleistocene time. Our 

 western arid region was extensively forested at one 

 period. Several of the smaller islands of the Mediter- 

 ranean have been deforested. Reforestation would 

 confine and limit the desert and plains types. Pro- 

 gressive moisture and reforestation would be very 

 unfavorable to the horse. (Morris, 1895.1, p. 261.) 

 Thus both migration barriers and migration tracts are 

 formed by forests. 



Woldrich (1882.1), in considering the glacial epoch, 

 separates into two subclasses the remains of the 

 Quaternary forest fauna of northern Europe, one 

 living entirely in the forests and the other in the inter- 

 mediate zone between trees and grass. The former 

 comprised Alces pahnatus, Cervus elapJius, C. capreolus, 

 Rangifer tarandus, Bos, Sus, Castor, Sciurus, Myoxus, 

 Arvicola glareolus, Mus sylvaticus, Tetrao urogallus, 

 T. tetrix, etc. The other and intermediate class con- 

 sisted of Rhinoceros antiquitatis, ElepJias primigenius. 

 Hippopotamus (in certain districts), Bison prisons. Bos 

 primigenius, Megaceros, Rangifer tarandus, Equus 

 fossilis, etc. All these animals frequent woods; in 

 fact, their daily need of food compels them to live for 

 the most part of the time in forests. The very abun- 

 dance of their remains proves how luxuriant the 

 contemporary forests must have been, a fact supported 

 by the presence of large quantities of the remains of 

 the capercailzie, essentially a forest-loving grouse, in 

 the caves of Belgium, Yorkshire, etc. 



Torrell (1876.1), a Swedish geologist, has argued that 

 it was largely the destruction of the forests in Denmark 

 and Scania which during Neolithic (late Pleistocene) 



