106 



THE AGE OF MAMMALS 



taining a mammalian fauna of Torrejon age, including especially the con- 

 dylarth Euprotoyonia and the amblypod Pantolamhda} 



Reptilian fauna. — Abundant remains of three different species of 

 Champsosaurus, the large, aquatic lizard witii a gavial-like snout, have 

 been found in the Puerco. This animal (p. 100) occurs also in tlie Lower 

 Eocene of France (vicinity of Rheims) and of Belgium. From the Puerco 

 has been obtained also the earliest known North American serpent (Hela- 



gris prisciformis) , un- 

 specialized in character 

 and of about the size 

 of the common black 

 snake (Bascanium con- 

 strictor). 



Puerco Life of the 

 New Mexico Region 



Neoplagiaulax or 

 Polymastodon Zone. — 

 This is the earliest 

 known of the Eocene 

 mammal groups, im- 

 mediately succeeding 

 the Cretaceous, and 

 preceding in age the 

 Torrejon and Cernay- 

 sian. In New Mexico 

 and Montana are found 

 these small archaic 

 mammals evolving 

 from ancestors of the 

 Age of Reptiles. Two 

 of the genera date, in 

 family ancestry (Plagi- 

 aulacidae), as far back 



Fig. 28. — Skull of the Basal Eocene plagiaulacid Ptilodus aS the Upper Triassic 

 (X f). In the U.S. National Museum, Washington. After qj. Phaetic namelv of 

 Gidley. . . ' . . 



the diminutive multi- 



tuberculates, (1) Neoplagiaulax, which represents a decided advance upon 



Ptilodus of the Upper Cretaceous (Laramie), and (2) Polymastodon, which 



similarly is much more modern than Meniscoessus of the Laramie. The 



latter animal is as large as a beaver {Castor). In general these mammals 



were the marsupial rodents of the Mesozoic period. 



* Douglass, E., The Discovery of Torrejon Mammals in Montana. Science, n.s.. Vol. XV, 

 1902, pp. 272-273. 



