ENVIRONMENT OF THE TITANOTHEEES 



63 



of the Puerco and Torrejon formations in northwestern 

 New Mexico and southwestern Colorado is accord- 

 ingly related as follows: 



Transition epoch: 



5. Phenacodus-Nothodectes-Conjphodon zone. Represented 



in the "Tiffany beds" of southwestern Colorado and 



in the Wasatch formation (horizon Big Horn A, 



"Clark Fork") of Big Horn Basin, Wyo. 

 Basal Eocene epoch: 



4. Pantolamhda zone. Represented in the upper levels of 



the Torrejon formation of northwestern New Mexico 



and in the upper part of the Fort Union formation of 



Montana. 

 3. Deliatherium zone. Represented in the basal part of 



the Torrejon formation and in part of the Fort 



Union formation of Montana. 

 2. Polymastodon zone. Represented in the upper part of 



the Puerco formation of northwestern New Mexico. 



Not yet recorded in the Fort Union formation. 

 1. Ectoconus zone. Represented in the lower part of the 



Puerco formation. Not yet recorded in the Fort 



Union formation. 



BASAL EOCENE FAUNAL ZONES 



ZONES 1 AND 2: ECTOCONUS AND POLYMASTODON ZONES 



[Puerco fauna; part of Thanetian of Europe] 



No equivalent of the most ancient Puerco fauna has 

 thus far been discovered in the Fort Union beds of 

 the North or in Europe; it is at present unique. 



Puerco mammals and reptiles. — The Puerco mammals 

 are extremely archaic, mostly Meseutheria (Osborn) 

 or paleoplacentals (Matthew), representing groups of 

 placentals that became extinct during the Eocene. 

 The Puerco contains no remains of modern orders or 

 families of mammals except three, one (Miacidae) 

 which is related to the doglike Carnivora, a second 

 which is related to the primitive Insectivora, and a 

 third which is related to the primitive Edentata. No 

 rodents or lemuroid primates have been discovered, 

 and certainly no perissodactyl or artiodactyl ungu- 

 lates were in this region at this time. Matthew 

 (1914.1, p. 383) is of the opinion that most of these 

 archaic placentals have "no known predecessors in the 

 Lance formation. 



About 10 per cent of the fauna consists of rodent- 

 like multituberculates, an extremely ancient order re- 

 lated to the existing monotremes or to the marsupials. 

 These animals are nearly related to ancestral forms in' 

 the Lance. Didelphiid marsupials are also present. 



Similarly the reptiles all belong to families that 

 originated in Belly River or Pierre time (Upper 

 Cretaceous) or earlier. The Choristodera (Champso- 

 saurus) became extinct in basal Eocene time. Note- 

 worthy is the absence of the prevailing Tertiary 

 families of chelonians (Emydidae, Testudinidae), 

 which, with the modernized mammals, first appear in 

 the lower Eocene. 



On comparing the life of the Puerco with that of 

 the Lance we find a mammalian fauna that indicates 

 no very wide gap in time — a fauna that is somewhat 



more ancient than the Torrejon and known Fort 

 Union, also more ancient than the Cernaysian and 

 upper Thanetian of France. It is therefore probable 

 that the Puerco corresponds with the lower Thanetian 

 of France, but its life has no known equivalent either 

 in Europe or in this country. 



The opinion of Cope that the ancestry of the 

 modernized mammals should be sought among these 

 Puerco forms lacks adequate confirmation. The op- 

 posite opinion — that the Puerco mammals are not 

 ancestral to the modern mammals — was developed by 

 Osborn (1893.82, 1894.89) when he applied to them 

 the name Mesoplacentalia (Meseutheria), indicative of 

 their archaic or Mesozoic characteristics. They repre- 

 sent the first known adaptive radiation of the placen- 

 tals into archaic flesh eaters and herbivores. We note 

 the presence of three families of archaic Carnivora 

 (Creodonta) and remote relatives {Psittacotherium) of 

 the Edentata. Among the archaic ungulates we find 

 one varied family (Periptychidae) of the Amblypoda 

 (Taligrada) and two families (Phenacodontidae, Mio- 

 claenidae) of the Condylarthra. 



Puerco sedimentation and physiography . — The Puerco 

 formation is not separated from the overlying Torrejon 

 formation by any lithologic or stratigraphic break. 

 (Sinclair and Granger, 1914.1, p. 308.) The absence 

 of erosional unconformity between the Puerco and 

 Torrejon was also observed by Gardner (1910.1, pp. 

 722-723) and by Bauer (1916.1, p. 277). That the 

 Puerco and Torrejon formations represent a very 

 long period of geologic time is demonstrated by the 

 recorded 6,000 feet of Fort Union sediments, which 

 have yielded the Torrejon fauna alone; and, like the 

 Fort Union, they represent a very long period of uniform 

 conditions of climate and sedimentation. The pres- 

 ence of fish, crocodiles, turtles (Trionyx), and other 

 genera in the same strata with the bones of mammals 

 and at the same level shows conclusively that these 

 deposits were formed by water. That the streams 

 were of low gradient is shown by the complete absence 

 of pebbles in the Puerco and by the wide horizontal 

 extent of some of the clay bands. Bogs, apparently 

 formed in back waters in the channels, were filled with 

 accumulations that preserved impressions of the leaves 

 of figs (Kc-Ms), plane trees (Platanus), poplars {Populus), 

 relatives of the bread fruit (Artocarpus) , and numerous 

 shrubs (Paliurus, Viburnum). The quantity and vari- 

 ety of these plant remains, together with the abundant 

 large drift logs in the clays, indicate a heavy growth 

 of vegetation along the streams. The species of Ficus. 

 Paliurus, Viburnum, and Artocarpus are also found in 

 the Denver and Raton formations of eastern Colorado ; 

 and other species indicate Fort Union age (Knowlton, 

 cited by Sinclair and Granger, 1914.1, p. 306). The 

 mode of occurrence of the fossils in the still-water 

 clays and occasionally in the river-channel sandstones 

 shows that some of the skeletons may have been 



