406 0. C. Marsh — Origin of Mammals. 



Art. XLI. — The Origin of Mammals ;* by O. C. Marsh. 



The question under discussion is not new, but one of a 

 series of similar nature and difficulty. The origin of Birds, of 

 Reptiles, of Amphibians, and of Fishes really precede it, and 

 offer less difficulties in solution. The answer to each, in my 

 opinion, belongs to the future, and how far it may profitably 

 be sought in the present limited state of our knowledge is a 

 fair question in itself. 



Too often in the past, a discussion on the origin of Mammals 

 has seemed a little like the long philosophico-theologico con- 

 troversies in the middle ages about the exact position of the 

 soul in the human body. No conclusion was reached, because, 

 for one reason, there were no facts in the case that could settle 

 the question, while the methods of investigation were not 

 adapted to insure a satisfactory answer. The present discus- 

 sion is on a much higher plane, and the previous speakers have 

 made an admirable presentation of their side of the case. I 

 cannot, however, quite agree with them as to the value of the 

 facts and theories they have presented, and shall consider the 

 question from another point of view. 



The Mammals, as we know them to-day, are classed by them- 

 selves, yet contain such diverse groups that it may fairly be 

 regarded an open question whether all have a common origin. 

 The attempt to ascertain whence they came is likely to bring 

 out indications that they may have had several sources of 

 origin, and this, if so, may help to explain the great diversity 

 among them. 



It is of course evident that some of the most characteristic 

 features of recent mammals, for example, the hairy covering, 

 the circulatory system, and the milk glands, cannot be used in 

 a comparison with fossil forms. The osseous structure only is 

 now available in the early mammals and other vertebrates, 

 and in this alone points of resemblance must be found if 

 different groups are connected genetically. 



In considering the relations of reptiles to mammals so far as 

 the fossil forms are concerned, which seems to be the main 

 question before us to-day, I have only time to speak of the 

 skull, and shall refer to some of its salient features already 

 mentioned in this discussion ; namely, the teeth, the squamosal 

 bone, the quadrate, the occipital condyles, and with them the 

 lower jaw. These perhaps may serve as crucial points in dis- 

 tinguishing the skull of a reptile from that of a mammal, even 

 if they fail to indicate a near affinity between them. 



* Remarks in the general discussion on the Origin of Mammals, at the 

 International Congress of Zoology, Cambridge, England, August 25, 1898. 



