NO. 2 A STUDY OF MENISCOTHERIUM GAZIN 41 



DENTITION 



Upper dentition. — Although the cheek teeth of Meniscotherium 

 (see pi. 5) are surprisingly precocious in having very early reached 

 a high degree of selenodonty for a condylarth, and the molarization 

 procedure having already extended forward to include the fourth pre- 

 molar by the beginning of the Eocene, the more anterior teeth are 

 decidedly unspecialized and little differentiated. 



The incisors are basically simple, single-cusped teeth, but sub- 

 spatulate in that high medial and lateral crests are developed. They 

 approximate the form of very simple premolars with the shorter 

 anterior (anteromedial) crest deflected medially at its anterior 

 extremity and the longer posterior (posterolateral) crest straight and 

 with a steeper slope, especially I 3 , which may exhibit an incipient 

 lateral cuspule. These teeth may be about the same size or increase 

 slightly to I s . 



The canine is only slightly larger and follows the incisors with 

 essentially no diastema. Its crown is a little higher and the anterior 

 and posterior crests are more subdued and steeper. It evidently 

 functioned more as an extension of the incisor series. 



The only diastemata in the rather closely continuous tooth sequence 

 are the short intervals that separate P 1 from the canine and P 2 . 

 P 1 is a very simple tooth about the size of the third incisor but with 

 the anterior crest more steeply sloping, as in the somewhat larger 

 canine. P 1 , however, has two roots, although these may not be com- 

 pletely divided. 



P 2 is appreciably larger than P 1 and relatively much broader 

 across the posterior root. This tooth is highly variable and in some 

 specimens its crown structure is as simple as that of P 1 but with a 

 stronger posterior crest, whereas in others of the same species there 

 may be developed a posterointernal rugosity to a clearly defined 

 deuterocone with accessory cuspules. 



P 3 is about intermediate in size between P 2 and P 4 and invariably 

 exhibits a well-developed, conical deuterocone (protocone). This 

 tooth seems highly variable with regard to the development of a 

 tritocone (metacone), and when the latter is fairly well defined, 

 although invariably less prominent than the primary cusp, there 

 may be a very weak, posteriorly placed mesostyle. A small cuspule 

 in the position of a tetartocone (hypocone) is invariably present on 

 the cingulum posterolateral to the deuterocone. A similar cuspule 

 symmetrically placed anterolateral to the deuterocone seems invaria- 

 ble and arises from the anterior cingulum when the latter is developed. 



