ORDINAL TYPES OF MOLARS : MULTITUBERCULATA 



103 



Multitubercular pattern is a primitive one. Forsyth Major's argument on 

 this subject is discussed on pages 205-208, and the conclusion is reached 

 that there is quite as much evidence for considering the rnultituberculate 

 molar as secondary or evolved from a still earlier tri tubercular type. 

 There are several grounds for considering that such an evolution mav 

 have taken place. 



1. The earliest multitubercular molars known, those of J//Vro/,.s/V.s ' 

 (Fig. 48, Xos. 1, 2) are comparatively simple, consisting of a central 

 depression or basin indented on the edges by larger and smaller tubercles. 

 Thus the earliest rnultituberculate molars known have comparatively few 

 cusps, in other words, are paucitubercular, whereas the latest rnultituber- 

 culate molars known have a very large number of tubercles, or are 

 multitubercular. 



Fig. 51. The molar tooth forms of typical Multituberculates. 



.'it, from the Rhsetic (Triassic) of Germany, an upper molar ; la, ditto, in side view, 

 natural size. 2, 'la, Ti'itylmlim, from the Triassic of South Africa, an upper molar, in 2 , wearing 

 surface and outside view, natural size. 3. Pt>liiinst<i<j,i, from the Basal Eocene of North America ; 

 the second upper molar, natural si/.e. 4. Boloil.oii, from the Upper Jurassic of England, the third 

 and fourth upper molars, enlarged about 6 diameters. 5. Shnoymtthus, from the Upper Jurassic 

 of England, a lower molar enlarged about 2J diameters. 6. Chirox, from the Basal Eocene of 

 North America, the upper molars enlarged 1 J diameters. 



2. Basin-shaped crowns more or less similar to those of Microl?*1<-x 

 moorei are known to be secondary or of tritubercular origin in several 

 distinct families of mammals. Thus certain Eodents (p. 205), Fruit-bak 

 (p. 129), the Kinkajou (CVra^/Vx, p. 142), Myrmccobius, (p. 112), exhibit 

 more or less distinctly basin-shaped crowns of which the edges are 

 elevated, and yet retain more or less clearly the primitive tritubercular 

 pattern. 



3. The depression of the centre of the crown to form a basin out of 

 what was primitively a projecting point or cone finds its analogies in the 

 invagination of the incisor teeth of the horse, and in the basin-shaped 



[ J The evidence tending to connect Microlextes with the Multituberculates is briefly that : 

 (1) the M. moorei molar closely resembles that of Pkujinnlax minor (Fig. 48, Nos. 3, 3); (2) 

 Plagiaulax minor presents many resemblances to Ctenacodon and Ptit.odus, typical Multi- 

 tuberculates ; (3) an enlarged grooved premolar, probably representing a less specialized 

 condition than that seen in the later Multituberculates has been recorded by Dawkins from 

 the Rhtetic beds in which the Microlestes moorei molar was found ; (4) Dr. Ameghino 

 brings evidence to connect the Multituberculates (including J/MVO/<:*/VX) with the Diproto- 

 dont Marsupials, especially the South American forms described by him. ED.] 



