408 0. C. Marsh — Origin of Mammals. 



It may fairly be said that the separate elements of the lower 

 jaw, if present, would naturally be looked for in the Mesozoic 

 mammals, and this point I have long had in mind. I may 

 safely say that I have seen nearly every species of Mesozoic 

 mammals hitherto described, and have searched for evidence 

 on this point without success. I have also sought for the 

 separate elements in the young of recent forms, but without 

 finding any indications of them. 



Beside the crucial points I have mentioned in the skull, 

 there are others of equal importance in the skeleton, which I 

 must not take time to discuss, but will venture to allude to one 

 of them in passing. I refer to the ankle joint, which, when 

 present, is at the end of the tibia in mammals, and in reptiles 

 between the first and second series of tarsals. When we really 

 find an approach between these two classes, the ankle joint 

 will probably show evidence of it. 



Having thus shown, as I believe, that we cannot with our 

 present knowledge expect to find the origin of mammals among 

 the known extinct reptiles, and that in attempting this we are 

 probably off the true line of descent, it remains to indicate 

 another direction in which the quest seems more promising. 



Since 1876, when Huxley visited me at New Haven, and we 

 discussed the probable origin of both Birds and Mammals, I 

 have been greatly impressed by his suggestion that the mam- 

 mals were derived from ancestors with two occipital condyles, 

 and these were doubtless primitive Amphibians. I have since 

 sought diligently for the ancestors of birds among the early 

 reptiles, with, I trust, some measure of success, but this is a 

 simple problem compared with the origin of mammals which 

 we have before us to-day. 



In various interviews with Francis Balfour, in 1881, at the 

 York Meeting of the British Association, we discussed the 

 same questions, and agreed that the solution could best be 

 reached by the aid of Embryology and Paleontology combined. 

 He offered to take up the young stages of recent forms, and I 

 agreed to study the fossils for other evidence. His untimely 

 death, which occurred soon after, prevented this promised 

 investigation, and natural science still suffers from his loss. 

 Had Balfour lived, he might have given us to-day the solution 

 of the great question before us, and the present discussion 

 been unnecessary. 



The Birds like the mammals have developed certain charac- 

 ters higher than those of reptiles, and thus seem to approach 

 each other. I doubt, however, if the two classes are connected 

 genetically, unless in a very remote way. 



