Progress in Mammalian Palaeontology. 201 
tion. In connection with distribution our chief advance has 
been to determine the exact geographical location and 
chronological succession of animals, the local conditions of 
geological deposition in relation to habits and habitat or en- 
vironment, as well as its bearing upon the study of past cli- 
mates, or what may be called palseometeorology. 
Adaptive radiation, continental — In connection with 
the comparison of mammals in their intercontinental as well 
as in" their continental relations, the branching system of 
Lamarck and the divergence which impressed Darwin is 
perhaps most clearly expressed by the word "radiation" 3 . 
Elsewhere the conception of adaptive radiation has been 
fully developed in connection with the origin of certain 
orders 4 . f 
It may here be briefly pointed out that Africa 5 , South 
America, North America and Eurasia prove to have been 
the three chief geographical centres of ordinal radiation. 
Adaptive radiation, local* — Quite as important, al- 
though not carried on so grand a scale, is the local adaptive 
radiation which brings about a diversity of type in the same 
geographical regions and is the basis of the polyphyletic law 
of which we shall next speak. It is perhaps best illustrated 
by the Ungulates. In addition to (1) digital reduction 
(Kowalevsky) and (2) carpal and tarsal displacement 
(Cope, Osborn) in relation to the choice of harder and 
softer ground, there is recognized (3) after the primary con- 
version of semi-unguiculate into ungulate types, a reversed 
conversion of ungulate types into clawed types, as seen in 
Dichobune (Artiodactyla), Chalidotherium (Perissodactyla), 
and perhaps in an incipient stage in Agriochoerus (Artiodac- 
tyla 1 ; (4) secondary adoption of aquatic habits, as seen, for 
example, in the Amynodonfidae among the Rhinocerotoidea. 
Divergence by the above factors has long been recognized. 
There are also to be seen phyletic series combining in vari- 
ous ways either of the following eight conditions of foot, 
3 Osborn ii f., Rise of the Mammalia. Proc. Amer. Association, 
Adv. Sri., vol. xiii, 1893, d. 215. 
4 Adaptive Radiation of Orders and Families Ann. X. Y. Ac-ad. Sci. 
vol. xiii. 1900, pp 49-51. 
5 .von. N. V. Acad. Sr-i. xiii. 1! pp. 56-58. 
G osbohn. H F.. The Law of Adaptive Radiation. Amer. Nat. xxxvi, 
1902, pp. 353 
