232 



ANNALS NEW YORK ACADEMY OF SCIENCES 



There are no rodents in the Notostylops Beds of South America (Eo- 

 cene) ; presumably therefore none in preceding epochs. There are none 

 in the Paleocene of Europe and N^orth America; presumably therefore 

 their sudden appearance in the true Eocene of these regions was due to 

 migration from some other region, equidistant from either, as their de- 

 velopment is almost equivalent in the two, — therefore probably Asia. 

 The few Theridomyidse of the Oligocene of Africa are rather primitive 

 forms, certainly not more progressive than their contemporary relatives 



yy/^ Octodontida'e 



\\\^ Dasi^proctLcia'e 

 ^IZZ Chinc/ii/Iidai. 

 Ill Caviida'c 



JVo Tertiary 



Hi/strico- — yf^ 



JT/icridoinyidac 

 ■: In Oh'yoce?-!e. 



Miocent 077 ces tors of 



Octodoiits , Chlnchillids and Cgi/iids 



Fig. 15. — Distribution of the Neotropical families of Ilystricomorphx 

 The Octodontidw are also found in Africa, and tlio Tlieridomyidir of the early Tertiary 



of Europe are apparently ancestral to these families of the Hystricomorpha. 

 pothesis satisfactorily explains the accepted relationship and distribution. 



No hy- 



in Europe, affording thus a slight indication that they were Palffiarctic 

 immigrants. In Australia the evolution of IMarsupial analogues of the 

 more abundant rodent types of Arctoga^a affords strong evidence that the 

 true rodents were absent from Notogfca until the end of the Tertiary; a 

 view confirmed by the limited amount of adaptive radiation which the 

 invading Muridro have undergone in that continent up to the present day. 

 The Australian Murida3 can only be accounted for by over-sea transpor- 

 tation, for the family appeared and evolved during the middle and later 

 Tertiary, and the peculiarities of the Australian fauna are explained by 

 all writers as due to isolation extending throngli tbe Tertiary period. 



