2^6 



NA TURE 



[January 4, 1894 



Twenty years ago an era opened in the mammalian palae- 

 ontology of Europe and America. Partly inspired by the 

 Odontogi-aphie of Kutimeyer, Kowalevsky completed and pub- 

 lished in 1873 his four remarkable memoirs upon the hoofed 

 mammals. He wrote these four hundred and fifty quarto pages 

 in three languages not his own, in French upon Anchithcrium 

 and the ancestry of the horses, in English upon the Hyopo- 

 tamid<r, in German upon Gelocus, Antliracotherium and Ente- 

 lodon, including the first attempt at an arrangement of a great 

 group of mammals upon the basis of the descent theory. These 

 iTiemoirs swept aside all the dry traditional fossil lore of Europe ; 

 they breathed the new spirit of Darwin, to whom the chief one 

 was dedicated, making principles of descent of more importance 

 than new genera and species. Kowalevsky thus summed up the 

 conteniporary paljeontology : 



" After the splendid osteological investigations of Cuvier had 

 revealed to science a glimpse of a new maumialian world of 

 wonderful richness, his successors have been bent rather upon 

 multiplying the diversity of this extinct creation, than on dili- 

 gently studying the organisation of the fossil forms that succes- 

 sively turned up through the zeal of amateurs and collectors. . .. 

 With the exception of England (referring to Owen, Huxley, 

 Falconer, and others), where the study of fossil mammalia was 

 founded on a sound basis, and some glorious exceptions on the 

 Continent (referring to Riitimeyer, Gaudry, Fraas, Milne- 

 Edwards), we have very few good palseontological memoirs in 

 which the osteology of extinct mammals has been treated with 

 sufficient detail and discrimination ; and things have come to 

 such a pass, that we know far better the osteology of South 

 American, Australian, and Asiatic genera of fossil mammals 

 than of those found in Europe." 



At the same time, between 1871 and 1873, the pioneers of 

 American paleontology, Leidy, Marsh, and Cope, began the 

 exploration of our ancient lake basins rich in life. The first ten 

 years of their work not only revolutionised our ideas of mam- 

 malian descent, but brought together the data for the generalis- 

 ations of the second decade ; (or Marsh's demonstration of the 

 laws of brain evolution in relation to survival ; for Copes proof 

 of ungulate derivation from types with the simple foot resting 

 upon the sole, and with the ancestral conic or Imnodont molar 

 tooth ; and finally for Cope's demonstration of the tritubercular 

 molar as the central type in all the mammalia. These four 

 generalisations furnished a new working basis for morphology 

 and phylogeny. 



In these twenty years, thanks to energetic field work, we 

 have accumulated vast materials for the history of the rise of 

 the mammalia, enough for ten students where there is one, 

 and the questions arise : How shall we take best advantage 

 of it? What methods shall we adopt ? In this address, besides 

 bringing before you the more recent achievements of explora- 

 tion and research, I will try to illustrate the advances already 

 made in lines of thought, observation and system in palason- 

 tology, and indicate other advances which seem to me still de- 

 sirable. In the problem of how to think and work most effec- 

 tively, and with most permanent results, all the sciences meet 

 on common ground. 



It is to the renown of the veteran Riitimeyer and of Kowa- 

 levsky, whose death we have to deplore, that, while their main 

 inductions suffer by American discoveries, their methods of 

 thought have not been displaced. It matters little that their 

 theory that ungulate molars sprang from lophodont or crested 

 forms, has been disproved ; that Kowalevsky's tables of descent 

 are full of errors: that his main generalisation as to the per- 

 sistence of adaptive and extinction of inadaptive foot types 

 does not hold good ; that the horses and Anchitherium spring 

 not from Palteotherium as he supposed, but from Pachyitoloplms 

 and Hynicotherium, types which he carefully studied and yet 

 omitted from the horse line ! It is the right system of thought 

 which is most essential to progress ; better in the end wrong 

 results such as the above, reached by the right method, than 

 right results reached haphazard by a vicious method. If a 

 student asked me how to study paiajontology, I could do no 

 better than direct him to the Versiich cincr natiirlichen Classi- 

 fication dcr fossilen Hufthiere, out of date in its facts, thor- 

 oughly modern in its approach to ancient nature. This work 

 is a model union of the detailed study of form and function 

 with theory and the working hypothesis. It regards the fossil 

 not as a petrified skeleton, but as moving and feeding; every 

 joint and facet has a meaning, each cusp a certain significance. 

 Rising to the philosophy of the matter, it brings the mechanical 



NO. 1262, VOL. 49] 



perfection and adaptiveness of different types into relation with 

 environment, the change of herbage, the introduction of grasses. 

 In this connection it speculates upon the causes of the rise, 

 spread and extinction of each animal group. In other words the 

 fossil quadrupeds are treated biologically — so far as is possible 

 in the obscurity of the past. From such models and from our 

 own experience we learn to abandon such traditions in 

 the use of the tools of science as mere methods of description 

 and classification, and to regard priority only in the matter of 

 nomenclature. 



To illustrate some of these modern methods, let us first 

 look at the evolution of the teeth in the rise of the 

 mammalia. The teeth and the feet are the foci of mammalian 

 evolution, the only direct points of contact with food and the 

 earth. Their combined iise in phylogeny has increased in in- 

 terest, because their evolution has proved to be wholly indepen- 

 dent. We recall Cuvier's famous claim, of which Balzac said at 

 the time : " Rebuilt like Cadmus, cities from a tooth." 



No generalisation has been more thoroughly routed than that 

 of a necessary law of correlation between tooth and foot structure. 

 Besides the orthodox clawed carnivores and hoofed pachyderms 

 of the great French anatomist, we have discovered hoofed carni- 

 vores such as Mesonyx, and clawed pachyderms such as Chali- 

 cotherium. P2ven the apparently lasting barriers of correlation, 

 which Owen raised between the even and odd-toed ungulates, 

 have broken down by Ameghino's discovery of a Litoptern odd- 

 toed horse with an even-toed type of astragalus. Not only is 

 there no correlation of type, but none in the rate of evolution. 

 Ilipparion, the most progressive horse in tooth-structure, ))ro- 

 bably owed its extinction to its conservative preservation of its 

 ancestral three toes. For these reasons the teeth and feet, 

 owing to the frequent parallels of adaptation, may wholly mis- 

 lead us if taken alone ; while, if considered together, they give 

 us a sure key ; for no case of exact parallelism in both teeth 

 and feet between two unrelated types has yet been found, or is 

 likely to be. This, I believe, is the one lesson of later work 

 which reverts to older methods ; we should not base either classi- 

 fication or descent upon the teeth or feet alone. Every additional 

 character diminishes the chances of error. 



Lower Alesozoic Pro-manwialia. 



With the exception of the triassic Thcriodesmus of Seeley, 

 no mammal is known by its limbs or skeleton until we reach 

 the basal Eocene ; in studying the first steps in the rise of the 

 mammalia, we are thus practically driven to the teeth and jaws 

 alone. In these straits of the fossil-hunter, embryology has 

 lately come to our aid. 



Assuming their remote reptilian origin, agreeing with Baur 

 and Kiikenthal that the theriomorph reptiles were parallel with 

 rather than ancestral to the mammals, and therefore placing 

 before both groups the hypothetical Saiiro-mammals in or 

 below the Permian, we come to the old question which Huxley 

 discussed in his famous anniversary address : "Was there a 

 succession between Monotremes, Marsupials, and Placentals, or 

 a parallel development from a common pro mammalian type?" 

 Then we look to the newer questions : " When were the Eden- 

 tates and Cetaceans given off?" 



Modern tooth science springs first from the recent demon- 

 stration of Riitimeyer's hypothesis of 1869, that the teeth of 

 all the mammals centre around a single reptile-derived type. 

 With a single exception, which I believe can be disposed of, 

 various stages of trituberculism or a three-cusped condition 

 have become the standard for the teeth, as pentadactyly has 

 long been for the feet, except that this is developed within 

 the mammalian stem, while our five fingers are a reptilian 

 legacy. Second, it springs from the recent thorough explora- 

 tion of the youngest jaws for evidences as to the primitive 

 form and succession of the teeth. This also supports the 

 reptile theory of tooth descent by proving, what has been in 

 considerable doubt, that the Pro-mammalia had a multiple suc- 

 cession of teeth like the reptiles, and that even some of the 

 modern mammals retain dim traces of four series of teeth. 



The brilliant discoveries of Kiikenthal, Leche, and Rose 

 begin to show how in various ways the mammals early modified 

 the regular succession of all the teeth by suppression of parts 

 of the multiple series. This is the first thing to consider. The 

 next is how heterodontism arose, how the rows of conic teeth 

 were specialised in different parts of the jaw for three or four 

 functions. As a certain number of teeth took up each function, 

 the question arises whether their number or dental formula was 



