8 



AMERICAN MESOZOIC MAMMALIA 



rows in the upper jaw. Nasals large, expanded posteriorly. Zygomata arising opposite 

 middle or anterior cheek teeth, widely expanded. Post-glenoid region very short or 

 practically absent. Mandible powerful, with small, low coronoid and no true angular 

 process, but with a well marked pterygoid crest. 



Distribution. — Triassic, Europe, South Africa. Jurassic, Europe, North Amer- 

 ica. Cretaceous, Mongolia, England, North America. Paleocene, Mongolia, France, 

 North America. Eocene, North America (Wyoming). 



Judged by any criteria other than those of the student of Holocene zoology, this is 

 one of the greatest of all mammalian orders. Although the multituberculates have 

 apparently been totally extinct since early in the true Eocene, the recorded history of 

 the group is longer than that of any other order of mammals. They are known from 

 almost every Mesozoic or Paleocene mammalian horizon and, despite the present im- 

 perfection of our knowledge, it is probable that they were as truly world-wide in 

 distribution as any mammalian order has ever been, with the exception of the primates. 

 With few exceptions, their remains are rare and often leave much to be desired, but even 

 our present relatively scanty record shows that they included a very wide range in 

 morphology and in size. About twenty-five well distinguished genera are now known 

 and even this scattering record shows differences in form and in bulk which compare 

 favorably with many of the vastly better known Tertiary and recent orders. 



The first presumable multituberculate was described by Plieninger in 1847^ — 

 " Microlestes" (now correctly Thomasia) from the Rhaetic of Wurttemberg. In 1857^ 

 Falconer described the first Jurassic form, Plagiaulax. Even in 1871, when Owen's 

 great memoir was published, the existence of the group as such was not clearly under- 

 stood. His arrangement was, briefly, as follows: 



Marsupialia 



More than two 

 lower incisors. 



Not more than 

 two lower incisors. 



More than the type 

 number of molars. 



Type number 

 of molars. 



Less than type 

 number of molars 



Microlestes and 

 many genera of 

 other orders. 



Three tri- 

 conodonts 



Plagiaulax 



I ncertae sedis : Stereo gnathus, Bolodon. 



Owen applied no names of families to the Mesozoic mammals. The earliest names 

 of this sort are to be found in Murray (1866, p. 364) who includes in his systematic 

 table the following undefined and entirely unnatural families : 



Stereognathidae : 



Stereo gnathus, Pliolo-phus. 



^ For these and all other references throughout the memoir consult the bibliography at the end. 



