388 W. D. MATTHEW THE CRETACEOUS-TERTIARY PROBLEM 



though some of them may have left descendants in the rare and little 

 known marsupials and small iiisectivores of our Tertiary formations. 

 The numerous phyla of placental mammals which take the place of the 

 dinosaurs and mammals of the Lance are not derivatives of any part of 

 the Lance fauna, but a new appearance. 



Comparison with Wasatch (Lower Eocene) Faunas 



(1) The Multituberculates disappear at the end of the Paleocene, al- 

 though a few rare survivors (three specimens) have been found at the 

 very base of the Wasatch. 



(2) Some of the placental phyla disappear at the end of the Paleocene, 

 but over half of the families survive into the Wasatch, some into the 

 Middle or Upper Eocene (see U. S. Geological Survey Bulletin Number 

 3G1, pages 100-103). 



(3) The larger part of the Eocene fauna from the base of the AYasatch 

 up. is composed of genera of Perissodactyla, Artiodactyla, Bodents, and 

 Primates; orders not found in the Paleocene. They are not descended 

 from known Paleocene ancestors, but represent a newly arriving fauna. 

 In the Clark Fork beds at the top of the Paleocene we find these orders 

 still absent, although the genera of the Paleocene orders are identical 

 with those of the Wasatch and more advanced than those of the Torrejon. 



(4) The Choristodera disappear. The crocodiles and the families 

 Baenidae, Dermatemydida^, and Trionychidae among chelonians continue 

 through with little change. The dominant groups of Tertiary chelonians, 

 Emydidae and Testudinidse, first appear in the Wasatch (but not at first 

 in great numbers) and are not derivable from known Paleocene chelonia. 



Characters of the Paskapoo Fauna 



A small fauna has be«n secured by Mr. Barnum Brown from the Pas- 

 kapoo beds in Alberta. It consists wholly of mammals, no dinosaurs 

 occurring in this formation. The mammals, according to Mr. Brown's 

 identifications, checked by the present writer, are unmistakably those of 

 the Lance fauna in part, but include an element which has not been found 

 in the Lance and appears to belong to the Paleocene groups of mammals, 

 although none of its representatives compare at all closely with any 

 Puerco or Torrejon genera. I suspect that it will be found to compare 

 more nearly with the Fort Union fauna. It is evident at all events that 

 there was a considerable element of ])lac('ntal n.iammals in the fauna. 

 But the Multitulxirculates are those of ihe Lance and some of the tritu- 

 berculates appear to be identical. There is no indication of the presence 

 of any of the Eocene orders of placentals. 



