386 w. d. matthew the cretaceovs-tertiary problem 



Comparison with Lance and Belly Kiver Faunas 



(1) Xhe vertebrates of the Lance and Belly River are: (1) Horned 

 Dinosaurs (C'eratopsia), (2) Duck-billed Dinosaurs (Trachodonts), (3) 

 Large carnivorous Dinosaurs (Megalosaurs), (4) Armored Dinosaurs 

 (Ankylosaurs), (5) Smaller Dinosaurs of the predentate and theropod 

 divisions, not yet cleared up as to relationship, (6) Chelonians of the 

 families Ba^nid^e, Dermatemydidge, and Trion3Thidae, (7) Crocodiles of 

 the family Crocodilidge, (8) Choristodera (fam. Cliampsosauridae), (9) 

 Lizards of the family? Iguanidie (recorded from Lance only), (10) 

 Multituberculate mammals, (11) Trituberculate mammals (positively 

 recorded from Lance only), some demonstrably marsupials, othei*s of 

 uncertain relationship, none demonstrably Placentals. 



Comparing the Belly River with the Lance, we find the same groups 

 represented throughout, exceptions in (9) and (11) being probably a 

 matter of imperfect record, as these groups are extremely rare. Among 

 the Dinosaurs the Belly River types appear to be more varied and less 

 extremely specialized, the phyla which pass through being represented by 

 more primitive stages in the Belly River. Among the mammals the 

 multituberculate mammals are recorded in the Belly River by a single 

 genus, apparently a more primitive stage of one of the Lance phyla. 

 Additional specimens will be diligently searched for. The trituberculate 

 mammals have not yet been found in the Belly River, except for a single 

 tooth of uncertain affinities, and are rare in tlie Lance.^ \Vhatever their 

 affinities, these mammals do not appear to include ancestral stages of the 

 placental phyla of the Paleocene, certainly not of the majority, probably 

 not of any of them. The chelonia, crocodilia, and choristodera belong to 

 the same phyla, in large part to the same genera, in the Belly River sls in 

 the Lance, and afford little evidence of progressive evolution. 



Comparing the Trance with tlio Paleocene. we find that none of tlie 

 numerous Dinosaur phyla pass througli. The entire order becomes ex- 

 tinct and none have been found associated with the placental mammal 

 fauna of the Paleocene (but see Ap])endix A)." The Chelonians, Croco- 

 <liles, and Choristodera pa<?s through, represented by the same phyla and 

 without much progressive evolution as far as known. The Multituber- 

 culata pass through, but with an appreciable amount of progressive evo- 

 lution, amounting in one phylum to generic, in another to marked spe- 

 cific difference. The Trituberculate mammals apparently disappear, al- 



• It Is worthy of note that the greater abiindaiu-e of small uiammals In the Lance as 

 compared with the Belly River is wholly due to the presence of nvimerous ant-hills scat- 

 tered over the exposures. Practically all the Lance mammals have been found in these 

 ant-hillt. 



