34 



CENOZOIC MAMMAL HORIZONS 



{Clsenodon protogonoides) . Edentata-Taeniodonta, with enameled 

 teeth, 2 famihes: (1) Styhnodontidse, (2) Conoryctidae. 



Summary of genera and species. 



Genera. Species. 



Archaic Triassic mammals 3 5 



Archaic Cretaceous mammals 15 24 



Total archaic mammals 18 29 



Modernized or distinctively Tertiary mammals 0 0 



The Puerco is a fauna wholly of Mesozoic origin, and mostly 

 destined to disappear; not a single representative or ancestor of any 

 existing order of Tertiary mammals is certainly known. Cope's 

 opinion^ that many of these mammals were ancestral to the modern- 

 ized mammals lacks direct confirmation at present. Other paleontol- 

 ogists, however, are inclined to connect certain of the creodont 

 families with the modern Carnivora. These and other ancestral con- 

 nections may be demonstrated in future. 



Negatively, therefore, the Puerco is distinguished by the absence 

 of primates, rodents, true carnivores, specialized insectivores, arti- 

 odactyls, perissodactyls, etc.^ This generalization has hardly less 

 important bearings on paleogeography than on })aleozoology. 



2. TORREJON FORMATION; PANTOLAMBDA ZONE. 



(Fig. 1; PI. I.) 

 HOMOTAXIS. 



North America. — 1, Torrejon formation (300 feet), continuous with 

 Puerco formation, San Juan basin, northwestern New Mexico. 2, A 

 portion of the Fort Union formation, Montana (Douglass,*^ Farr). 



Europe. — Thanetien or Cernaysien. Homotaxis with Europe is 

 indicated by the common presence in France and North America of 

 similar stages of evolution in representatives of 3 families, namely, 

 (1) Plagiaulacidse, (2) Arctocyonidse, and (3) Mesonychidse-Triiso- 

 dontinae. Other identifications are very uncertain.^ 



FAUNA.^ 



Like the Puerco, this is almost exclusively a Mesozoic fauna, 

 destined to become extinct during the Eocene. The known excep- 



a The opposite theory of the nonancestry of the Puerco-Torrejon to the modem fauna was developed 

 by the writer, in Rise of the Mammalia in North America: Proc. Am. Assoc. Adv. Sci., vol. 42, 1893 (1894), 

 p. 214. See also Ten years' progress in mammalian paleontology: Compt. Rend. 6° Cong, intern, 

 zoologie, Berne, 1904, pp. 86-113. 



b Certain incompletely known mammals (e. g., species of Mioclaenus and Pentacodon, of the Oxy- 

 claenidse and Mixodectidae) may prove to be Insectivora. — W. D. M. 



c Douglass, Earl, A Cretaceous and lower Tertiary section in south-central Montana: Proc. Am. 

 Philos. Soc, vol. 41, pp. 207-224. Also, New vertebrates from the Montana Tertiary: Ann. Carnegie 

 Museum, vol. 2, 1903, pp. 145-200. 



dOsboni; H. F., A review of the Cernaysian Mammalia: Proc. Acad. Nat. Sci. Philadelphia, May 6, 

 1890, pp. 51-62. 



e Matthew, W. D., A revision of the Puerco fauna: Bull. Am. Mus. Nat. Hist., vol. 9, 1897, pp. 259^-323^ 

 (See Appendix to this volume, p. 91.) 



