MORRISON MAMMALS: MULTITUBERCULATA 9 



Microlestidae : 



Thylacothenum {Antp/iUestes), Thylacother'tum {Amfhitherium), Mtcro- 

 lestes. Spalacotlierium, Plagiaulax, Triconodon, Dromatherium, Gale- 

 tliylax, SpalacodoH. 



As with Owen's later tabulation, the genera now referred to the Multituberculata 

 were by Murray separated widely. His Microlestidae contained all the Mesozoic mam- 

 mals then known, except Stereognathus, and also contained two quite unrelated 

 Eocene forms. 



Gill (1872) made Plagiaulax the type of the distinct family Plagiaulacidae and 

 Owen in 1885 recognized, at least by implication, the present accepted limits of the 

 group which he had severed so widely fourteen years earlier, now comparing Plagiau- 

 lax, Xeoplagiaulax. Tritylodon, and Microlestes. The credit for the first clear state- 

 ment uniting the genera of multituberculates into a unit is, however, due to Marsh. In 

 1880 he stated. "Another order of Mesozoic mammals is evidently represented by 

 Plagiaulax, the allied genus Ctetiacodon, and pssibly one or two other genera. These 

 are chiefly specialized aberrant forms, which apparently have left no descendants. This 

 order, which may be termed the Allotheria, can be distinguished from the previous 

 group [ Pantotheria] by the following characters: 



1 . Teeth much below normal number. 



2. Canine teeth wanting. 



3. Premolar and molar teeth specialized. 



4. Angle of lower jaw inflected. 



5. Mylohyoid groove wanting. 



"The characters above do not indeed separate the Plagiaulacidae from some of the 

 marsupials and future discoveries may prove them to belong to that group, where they 

 would then represent a marked suborder." 



In view of later criticisms of this definition, it may be well to point out, first, that 

 Marsh was dealing only with Jurassic mammals and that his definition was, as he 

 clearly states, meant to distinguish the Allotheria from other Jurassic mammals, 

 which it does, and second, that it is an ordinal definition and does separate the multi- 

 tuberculates adequately from the Marsupialia as an order. 



In 1887 Marsh repeated this definition, mentioning "Allodon, Bolodon, Ctetiaco- 

 don, Plagiaulax, and a few other genera." He also mentioned the Microlestidae as 

 members of the group, but he then definitely placed the Allotheria in the Marsupialia. 



Meanwhile, in 1884, Cope had published his paper on Tertiary marsupials, in 

 which he stated, "The extinct marsupials belong to three t)-pes, as distinguished by the 

 form of the superior molar teeth. These are trituberculate, quadrituberculate, or multi- 

 tuberculate. . . . The third division is entirely distinct and is characterized by having 

 at least three longitudinal series of tubercles in its superior molar teeth. To this sub- 

 order I apply the name Multituberculata." Although often accepted in place of Allo- 

 theria on the grounds that the latter was not really defined, the original definition of 

 Multituberculata is seen to be erroneous, for no multituberculate has more than three 

 rows of tubercles on the upper molars and many have only two. 



