94 



H. F. shorn — Origin of Mammals. 



To reconstruct the ancestral Eutherian skeleton, therefore, 

 we should divest the Creodonta and Insectivora, in their 

 anatomy and development, of all their secondary specializa- 

 tions, and combine all their truly primitive characters. This 

 ideal Eutherian is nearer the pro-Marsupial than we supposed; 

 it has the following chief characters : Head large, body rela- 

 tively small. Anterior nares terminal, face elongate. Insectiv- 

 orous or omnivorous habit. Molar teeth pointed, tri tubercular. 

 Typical dental succession. Vertebrae with intercentra. Dorso- 

 lumbars not exceeding 20. Back arched, tail long and powerful. 

 Scapula and ilium narrow, acuminate. Humerus with powerful 



HYPOTHETICAL PHYLOCENYof theMAMMAUA 



AS DERIVED FROM PALJEOAITOLOCYJ898 



Recent insectivora A A . mqnotremata 



Tertiary 



cretac. 



Perm.b 



Carb. 



r 



c 



RODENTIA 

 TILLODONTIA 



~gano~d6nta"~ 



EDENTATA t 



Tprimatesjcqndylarthra" 



\ f /[AWBLYPODA 

 CREODONTA 



THLAE0D0N 



mm™ p R QTJn 



iblCYNODONTIA ZMkODQHTIA 3jriOTHERIA 4 .CQMPHODONT1A 



( progan0sauria= „ (ther0mora = 

 [rhynchocephaua C\ anomodontia 



(MONOCONDYLIA) (M ONO^DICONDYU . 

 &JCQTYLOSAURIA-- t 



STECOCEPHALA- LABYRIHTH, 

 (DICONDYLIA) 



Batrachia 



deltoid crest, condylar crests and entepicondylar foramen. 

 Femur with three trochanters. Feet plantigrade. Centralia 

 and tibiale. Fore-limb more or less prehensile, elbows everted. 



Now the Creodonta are members of that Cretaceous radia- 

 tion, IV, which we find in full bloom in the Basal Eocene, 

 mingled with the dying group of Multituberculates, which 

 belong to the Jurassic radiation, V. 



In the Mid — and Uppermost Jurassic (Stonesfield, Purbeck 

 and Como Beds) however, occur all three types, which theoreti- 

 cally constitute radiation Y: first, the Triconodonts primitively 

 but typically Marsupial in structure; second, the Insectivora 

 primitiva, primitively Placental in type, insectivorous and 

 without a single Marsupial character either in jaw or teeth; 

 third, the Midtituberculata, whose sub-class position is now 

 assumed to be Monolreme. 



