ORIGIN AND DISTRIBUTION OF MAMMALS 291 



however, — the Triconodontidae — indicate by the shape of the angle of the 

 lower jaw that they doubtlessly belong to the Marsupialia. Because of the 

 incompleteness of existing specimens it is well not to go further in dividing 

 the remaining secodont forms into families and orders, but rather to ascribe 

 them to the marsupials in general. 



Mammalian remains from the Cretaceous were first discovered in 1882. 

 The first finds from the Wealden strata in England consisted of small teeth 

 of the genus Plagiaulax, already known from the Jurassic. Soon after Cope 

 discovered a tooth of Meniscmssus in the Laramie strata of Dakota, and a little 

 later Hatcher collected numerous teeth, mostly isolated, in Wyoming and 

 Colorado. Marsh founded many new genera and sjjecies on these specimens. 

 These have, however, been considerably revised by Osborn. Since the 

 majority of the teeth belong to the Allotheria — Ptilodus, Meniscoessus — our 

 knowledge of fossil mammals has not been greatly increased by these dis- 

 coveries, but they are of considerable interest because they bridge the gap 

 between the Jurassic and Tertiary forms of this group. Osborn even believes 

 that a few of the rather infrequent tritubercular and tuberculo-sectorial forms 

 can be determined as Creodonts (Pediomi/s), and that others (Protolambda) 

 can be considered ancestors of Pantolamhda, also of the AmUypoda. If there 

 were more and better preserved specimens far better phylogenetic conclusions 

 could be drawn. 



Eocene. 



The beginning of the Tertiary mai'ks a significant turning-point in the 

 development of mammals. At this time several orders which indisputably 

 belong to the Placentals have their origin, whereas the Allotheria, gradually 

 become extinct. The oldest mammalian remains from the Tertiary of Europe 

 were discovered in the neighbourhood of Eheims. Lemoine distinguishes in 

 this region two chronologically superimposed faunas, that of Cernays and that 

 of Ageia. The former contains representatives of Allotheria — Neoplagiaulax, — 

 of Creodontia — Ardocyon, Dissacus, Hyaenodidis, — of certain questionable 

 insectivores — Plesiadapis, Protoadapis, Adapisorex, — of Condylarthra — Pleura- 

 spidotherium — and of Orthaspidotherium, which seems to be the ancestor of 

 Anoplotheritim. The fauna of Ag6ia will be discussed more fully later. Of 

 course these two faunas demand urgent reconsideration because of the very 

 strange illustrations furnished by Lemoine. The specimens of the approxi- 

 mately contemporary fauna of the Cernaysian of the Puerco beds of New 

 Mexico and of the somewhat more recent Torrejon beds of New Mexico and 

 Montana are more abundant. The former locality still contains several 

 Allotheria, among which are the important genera Neoplagiaulax and Polymastodoti, 

 several Creodontia — Triisodon, Oxydaenidae, — several Condylarthra — Miodaenus, 

 Oxyacodon, Protogonodon, Periptychidae and Taeniodontia (Ganodonta). In the 

 latter locality are the last of the Allotheria, and the Creodontia become more 

 varied. They are represented by the Ardocyomdae, Mesonydiidae, Oxydaenidae, 

 Triisodontidae and the Miacidae, already closely affiliated with the true carni- 

 vores. The Condylarthra are represented by many Miodaenidae, by the earliest 

 Phenacodontidae and Periptychidae, the Taeniodontae (Ganodonta) by Conor ydes 

 and the insectivores by the Mixodedidae. Simultaneous with these appeared 

 the first amblypod, Pantolamhda. 



