G. 1. Adams — Extinct Felidm of North America. 435 



The cause of the reduction of the molar series seems to lie 

 in the following facts. If the jaws of one of the primitive 

 Felidse are examined it will be found that when they are 

 closed the teeth which first come in contact are the sectorials, 

 because of their elevated crowns. The premolars being 

 further from the condyles are the last to come in contact. 

 The function of seizing and holding is performed by the 

 greatly developed canines and the function of cutting by the 

 sectorials, hence no important function devolves upon the 

 anterior pre-molars and posterior molars. Inasmuch as the 

 lower series bite in front of the upper, it will be seen that the 

 last inferior molar and the first superior premolar are only 

 partially opposed by the teeth of the opposite series, conse- 

 quently they are less functional and are the first to disappear. 



The most primitive form of superior sectorial among the 

 Felidse consists of a principal, posterior, and antero-internal 

 cusps, as is seen in Dinictis. To this form there is added in 

 Hoplophoneas an incipient anterior basal cusp which in 

 Machcerodus is well developed. In Smilodon there is a second 

 anterior basal cusp. The internal cusp present in Dinictis 

 disappears in later genera, where it is represented only by a con- 

 vex buttress, which descends from the principal cusp, and, as 

 a more perfect shearing action is developed, this becomes less 

 prominent until in Dinobastis it is absent and the internal 

 root which supported it is lost. 



The inferior sectorial in the most primitive genera consists 

 of a principal, anterior, posterior and postero-internal cusps. 

 The fate of the internal cusp is similar to that of the internal of 

 the superior sectorial. Since it meets with no opposing cusp it is 

 soon lost. The posterior cusp or heel is reduced in genera in which 

 the superior molar is rudimsntal and does not oppose it. In 

 Eusmilus dakotensis, it becomes a mere sharp line on the 

 posterior border of the principal cusp. The function of the 

 inferior sectorial devolves chiefly upon the principal and 

 anterior cusps, which are well developed. 



As the number of teeth was reduced the individual teeth 

 become larger and the premolars developed posterior basal 

 cusps by the elevation of the cingulum, as is seen in Felis. 

 The incisors also became more robust in the Machserodont 

 genera. In Dinictis they are small and form an even series. 

 In Hojploj>honeus they are more robust, and in D inobastis we see 

 their most specialized form. In this genus they have minute 

 basal cusps and their margins are crenulated. 



The development of saber-like canines characteristic of the 

 Macheerodont type is easily traced in A?'cAcelurus, in which the 

 inferior and superior canines are sub-equal ; in JElurogale, 

 where the posterior border is denticulate, and then in Dinictis, 

 where both the anterior and posterior borders are denticulate. 



