92 



EVOLUTION OF MAMMALIAN MOLAR TKKTH 



skeleton and characters of the teeth in which they closely resemble 

 primitive mammals. There is moreover the negative evidence that they 

 constitute the only known group from which the mammals could have 

 descended. 



The teeth of Theriodonts exhibit four types as follows : The first 

 or haplodoiit type consists of simple, recurved reptilian -li ke crowns, 

 implanted with single fangs, as in the genus dSlurosaurus. 



Second, of the protortani type, with crowns implanted by partially 

 divided or very slightly grooved fangs, consisting of a single main cone, 

 with lateral denticles somewhat irregular in character. The best example 

 of this type is Cynognatlius (Fig. 44). 



The third, or tt<b<'rt:nlfttc, type is entirely different, and probably 



Pie. 2. 



Fig 11 



FIG. 45. Dental and Cninial structures of the Theriodonts. Dimi, ,,ul<i,i miix/na's, analogous 

 to a low-crowned tritubercuhite, like Arctoci/on. D. tetn/;/on/is, trituberculate structure more 

 obscure ; note the general resemblance to the molar crown of certain squirrels. 2). brnchiitiura, 

 showing the incipient division of the fang. The skull of Triti/loilon is greatly reduced. All 

 upper teeth except Figs. 4, 5. After Seeley. 



belongs to omnivorous or herbivorous animals ;* it is typified by the genus 

 Gromphognathus (Fig. 45); the molar teeth are covered with irregular 

 tubercles (Diademodon mastacus), in which the writer has observed some 

 disposition towards a tritubercular arrangement, or triangle of three larger 



*[0r more probably to carrion feeders (Broom). ED. ] 



