108 



THE AGE OF MAMMALS 



Puerco phase, and thus represent a very long interval of geologic *time. 

 They are of somewhat larger size, considerably more varietl, and in the 

 presence of one new family (Miacidae, genus Didymictis) more modern. 

 The diprotodont multitulierculates, including the diminutive Neoplagiaulax 

 and Ptilodu.s, and the much largx^r Polymastodon, still occur in this zone. 

 Gidley ^ has recently made the most important discovery that the animal 

 called Chirox by Cope - is actually the same as Ptilodus or Neoplagiaulax; 

 that is, it represents the superior dentition; a beautifully preserved skull 



Fig. 29. — Archaic hoofed mammals of the Pantolambda Zone. Outline restorations to 

 same scale (X j^). A. Meniscotherium, a condylarth. (See also Fig. .39.) B. Pantolambda, 

 an amblypod, short-footed, semi-plantigrade. C. EuprotoQonia, a condylarth, long- and 

 slender-limbed. 



and part of the skeleton of Ptilodus found in the Fort Union of Montana 

 demonstrates beyond question that this animal, and consequently all the 

 multituberculates, are true marsupials, aberrant diprotodonts, as was 

 originally surmised by Owen ^ in describing Plagiaulax from the Upper 

 Jurassic. The chief peculiarity is that (Fig. 28) the upper and lower 

 teeth are fundamentally different in numbers and in arrangement and do 

 not oppose each other. Gidley is inclined to consider these animals as 

 frugivorous, the incisors being well fitted for picking small fruits or berries. 

 The previous view has been that they were gnawing types analogous to the 

 rodents. It is important to note that these are the very last survivors of 

 this very ancient family of plagiaulacids (Plagiaulacidse). 



As compared with the Puerco, the faunal smiimary is as follows: 



Archaic multituberculates, Marsupialia Diprotodontia 

 Archaic or primitive mammals of Cretaceous ancestry 

 Modern, or possibly related to the modern Carnivora 



' Gidley, J. W. Notes on the Fossil Mammalian Genus Ptilodus, with Descriptions of 

 New Species. Proc. U.S. Nat. Mus., Vol. XXXVI, June 19, 1909, pp. 611-626, PI. 70. 



~ Cope, E. D., Proc. Amer. Philos. Soc, Vol. XXI, 1883, p. 321. 



^ Owen, R., Monograph of the Fossil Mammalia of the Mesozoic Formations. Mon. Pal. 

 Soc, 1871. 



