108 MAMMALIAN DENTITION 



forms. The various families diverged from one another very 

 early and of each there is now living only a scattered rem- 

 nant. It is quite necessary to turn to paleontology to learn 

 exactly what was the general method of evolution. For this 

 purpose the early history of any family will serve provided it 

 is fairly satisfactorily known. One of the modern species 

 which will be figured later is the Specter-lemur Tarsius and 

 the paleontological history of the family to which it belongs 

 will serve as an example. 



In Eocene times, as Dr. Matthew has shown, the various 

 genera of Tarsiidae present a fairly uninterrupted succession. 

 In the earliest species the mandible is slender with gently pro- 

 cumbent incisors and a moderately large canine. There is no 

 crowding of the premolars ; and the molars, in spite of the fact 

 that the talonid is already large, show a well-marked paraconid. 

 The last molar is unreduced. In the upper jaw the premolars 

 are bicuspid and the molars present a typical trigon with no 

 external styles and but an incipient hypocone. The last upper 

 molar is somewhat smaller than the others and shows no hypo- 

 cone. The dental formula is: 



f f 3 3 

 I—, C-,P-,M-. 



2' ° 1' 3' 3 



In later species the mandible becomes short and deeper and 

 the small incisors more vertical though the canine retains its 

 moderate size. The premolars are rather crowded and the 

 molars become shorter with the paraconid showing signs of 

 retrogression although the last lower molar is still unreduced. 

 From these species it is known that the upper incisors num- 

 bered two and that there was an upper canine. In still later 

 species the shortening and deepening of the mandible are more 

 marked, the premolars more crowded, and the molars yet 

 shorter with the paraconid more vestigial. The last lower 

 molar however remains long. In the most recent Eocene 

 group at present known the mandible is very short and very 



