224 
The American Geologist. 
October, 1905 
LAW OF LOCAL ADAPTIVE RADJATION 
Contemporary Evolution of Four Phyla of Titanothere s , Lower Oligocene , North America 
Dtreratilt 
Charotftri 
{ 
BRACnrcERRALic 
MES0POOAL 
SHORT HORHS 
INCISOR TEETH 
MEGACEKOPS 
DO LIC HOC £ PHALlI 
DOUCHOPOpAi. 
SHOP T HORHS , 
SO IHCISOR T££ T/l 
TlTANOTHERlUM 
BRACHYCEPHALK 
LOHQ NARAOH HQAHi 
HO IHCISOR TEETH 
SYMB0R000N 
mCsaticephauc 
mesopooal 
lohq 8r0aq horhs 
ihcisor reern 
BROHTOTHIRHJM 
Upper 
JBeds 
Middle* I 
Beds 
Lower' 
■Beds 
M. rob.ustus 
M.dispn 
"-T 
M amplus 
M. dupoi ' 
M rmmfii 
M bmifiuttpholui 
T. ITiqtTIi 
AllopS CIC4JI- 
CO'nii 
-/-- 
A scroti nui 
T. fiiqonocttai / 
T proiifu 
T liiloaros 
Sa«» 
\ 
S torvus 
5 copti 
B plat yet '<ls 
6 ramosum 
B curfum 
B medium 
. I 8. dolichoctrai 
B hatchtJi. 
Btichocerai 
B.h /poc tras/ 
Tctal t/iicR- 
nest, i to ft 
Direct Collateral 
.lint, lines 
Direct 
tint 
Collateral 
lines- 
Collateral 
line: 
Direct 
tin< 
Collateral 
lines 
'Short horheovita/iiothERES 
LONQ HORNEO TITANOTHERES 
PIG. 7. 
The law of local adaptive radiation illustrated in the four phyla of Oligo- 
cene Titanotheres, one or more of which gave off collateral branches. 
Three of these phyla have now been shown to have a separate origin 
in the Middle Eocene. 
being sparsely represented by species of Neohipparion ( Gid- 
ley 2 ) and a doubtful Pliohippus, the Camelidae by Pliau. 
chenia, the Dicotylidae by several pieces of Platygonus, the 
Carnivora by an Amphicyon and other doubtful species of 
Canidas. The collateral lines of Camelidae, so far as we 
know, died out, and the adaptive rediation of the true 
camels begins. 
However, no generalizations can as yet be made from 
this scanty fauna; we are confronted with more gaps in our 
knowledge and more unsolved problems than in any other 
period. Among these, the direct ancestry of the South 
American cameloids ( Auchenia) as well as of the true 
camels (Oamelus) should be found. We also should find 
here the stages directly ancestral to the horse (dYquus), be- 
2 A New Three-toed Horse. Bull. Amer. Mus. Nat. Hist., vol. xix, 
1903, pp. 465-476. 
