FOSSIL INSECTIVORA 47 
concealing themselves. The other Insectivora are inhabitants of 
the larger tropical islands—Cuba, Madagascar and some East 
Indian islands—or of South Africa, but have disappeared from 
the great northern continents, Europe, Asia and North America, 
where the struggle for existence has been most severe and where 
all the higher types of mammals have been evolved. 
The Insectivora are a very ancient order of mammals, and in 
past geological periods they were of more importance than now; 
in fact they have been considered by many scientists as represent- 
ing more nearly than any other living order the primitive central 
group from which all other mammals have descended. Through 
the ‘““Age of Mammals’’ they progressed less than most other 
orders and several families of them became extinct during that 
time, while the Moles and Shrews diverged from nearly similar 
habits to their present peculiarities, and the Hedgehogs, prob- 
ably, acquired their coat of spines. 
FIG. 22. ICTOPS ACUTIDENS 
Upper and lower teeth, showing the “ tritubercular’’ molars. Oligocene Epoch, Montana. 
Twice natural size 
LEPTICTID2, OR PRIMITIVE HEDGEHOGS. Extinct. 
Tritubercular molar teeth. Two incisors in upper dentition. Pre- 
molars unreduced, the last one molariform. Tibia and fibula fused, 
ulna and radius separate. Size and proportions like the modern 
