222 W. D. Matthew — Fossil Vertebrates and 



real animals.^ ^ If the Puerco is as old as the Lance, or 

 older, the terrestrial placentals were contemporary with 

 the swamp dinosaurs in Western America, but to find 

 them associated in the 'same formation would be a rare 

 and fortunate accident. 



There is no evidence that the dinosaurs survived to 

 the end of the Paleocene. And I do not think the 

 evidence affords anything like conclusive proof that they 

 were contemporary with the Lower Paleocene placentals. 

 Nevertheless the past seven years have much strength- 

 ened the indications to that effect. 



The placentals of the Paleocene are to my mind essen- 

 tially Cretaceous — Mesozoic rather than Cenozoic mam- 

 mals. They belong — except the Carnivora — to extinct 

 orders. They are related only to a minor and disap- 

 pearing element of the typical Tertiary placentals. 

 And — also with the exception of the Carnivora — they 

 show both in Torrejon and Puerco a certain fixity of 

 types in species, and limitations in their specializations, 

 that are characteristic of long established groups moving 

 toward extinction, rather than of newly appeared and 

 flourishing groups. In essentials they have the aspect 

 of the last Cretaceous mammals rather than the first 

 Tertiary mammals — a concept long ago recognized by 

 Osborn in his division of the placental orders into Meso- 

 placentals and Csenoplacentals. The Carnivora^^ are an 

 exception. They appear as forerunners of the Eocene 

 placental invasion — just as in South America they appear 

 in the Pliocene as forerunners of the great northern 

 invasion of the Pleistocene. In a Cretaceous fauna 

 their position would be that of a progressive element 

 which was later to expand and displace the rest. (All 

 the Tertiary ungulates are probably to be derived from 

 unl?:nown primitive stocks of Cretaceous creodonts.) 



The reptiles of the Paleocene are also Cretaceous t^^es, 

 every one of them. As with the mammals, some groups 



^^ Like the dinosaurs the Multi tuber culates are a Mesozoic group in course 

 of progressive extinction, but they last until the end of the Paleocene. They 

 are replaced in the Eocene by placentals of similar adaptations, plesiadapids, 

 rodents, tillodonts and tseniodonts. 



^^ The creodonts are included as a primitive suborder of the Carnivora. To 

 consider them as a separate order, as many authors do, might seem to 

 strengthen the present argument, but I do not think it is warranted by the 

 facts of their anatomy. See Matthew, 1909, Mem. Am. Mus. Nat. Hist., vol. 

 9, pp. 313-335. 



