January i i, 1894] 



NATURE 



257 



At a meeting of the Royal Scottish Geogrnphical Society, 

 held last week at Edinburgh, with Prof. J. Geikie in the chair, 

 to consider the question of Antarctic research, the following 

 resolution by the council of the Society was read : — " That at 

 this meeting, held for the discussion of Antarctic research, the 

 Royal Scottisii Geographical Society resolves to give its hearty 

 support to the promotion of further exploration in the Antarctic. 

 The Society's council is of opinion that at the present time a 

 properly equipped Government expedition would, with the in- 

 creased advantages of steam and modern appliances, have every 

 prospect of successful explorations in the South Polar regions. 

 The council is also convinced that the additions which might 

 be made to our knowledge of climatology, terrestrial magnetism, 

 geology, and natural history, would be of such practical scientific 

 value as to fully justify the equipment of such an expedition at 

 national expense. Towards the promotion of this object the 

 council considers it desirable to submit a memorial on this sub- 

 ject to her Majesty's Government, and in this action they invite 

 the cooperation of all the leading scientific societies of Scotland. 

 To this end the Society appoints an Antarctic committee, con- 

 sisting of Dr. John Murray, Prof. James Geikie, Dr. Buchan, 

 and Mr. J. G. Bartholomew, together with the delegates of the 

 other scientific societies, with instructions to draft such a 

 memorial and take such steps towards the promotion of Antarctic 

 exploration as is deemed desirable." A committee of the Royal 

 Geographical Society was formed on the occasion of Dr. Murray's 

 paper (Nature, vol. xlix. p. 112), and has already been at 

 work for some time with a view to bring the whole question of 

 Antarctic exploration before Government. The course of action 

 of this committee we understand to be the memorialisation of 

 the Royal Society, requesting that body to take the lead in 

 approaching the Government after ascertaining the feeling of all 

 the leading scientific societies of the United Kingdom. 



THE RISE OF THE MAMMALIA IN 

 NORTH AMERICA} 



II. 



Primitive Trituberailism . 



There is a very general tendency among the vertebrates as a 

 whole, fishes and reptiles as well as mammals, to form what are 

 called " triconodont " crowns by the addition of lateral cusps to 

 simple cones. In the mammals alone, these three cusps pass 

 into higher stages of evolution, through what is called " tri- 

 tuberculy," in which these cusps form a triangle. The discovery 

 of primitive widespread trituberculy by Cope was a great step 

 forward. In looking over the odontographies of Cuvier, Ot\en, 

 Tomes, and Baume, we find there is no suspicion of this com- 

 mon type around which the highly diverse mammalian molars 

 centre. The molars of the clawed and hoofed mammals can 

 now be compared, as we compare the hand or foot of the horse 

 with that of the cat, because they spring from a common type. 

 All the specialised mammalian series — ungulates, primates, car- 

 nivores, insectivores, rodents, marsupials — are found playing 

 similar yet independent adaptive variations upon one type. We 

 thus have a clue to the comparison of all molars with each other 

 and with the reptile cones ; take the human grinders, for 

 example. The anterior outer cusps in the upper jaw, and the 

 anterior inner cusps in the lower jaw, are homologous with each 

 other and with the reptilian cone. Leaving aside for the moment 

 Multituberculates and Monotremes, every known triassic, 

 Jurassic, cretaceous and basal eocene mammal (excepting Dicro- 

 cynodon) is in some stage of trituberculy ; all the known cre- 

 taceous molars are simple triangles above ; all later fossil 

 mammals also converge to trituberculy, until in the lowest 

 eocene every molar is tritubercular, and the early stages of 

 divergence are so similar that it requires a practised eye to dis- 

 tinguish the molar of a monkey from that of a horse. Embry- 

 ology supports the evidence of these fossil series. Thanks to the 

 recent admirable researches of Rose and Tsecker, we find in the 

 primates, ungulates and marsupials, that in the calcification of 

 its dental caps every molar is heralded by three cones placea 

 in a triangle, and in the lower jaw these three cones 

 invariably appear in the same order (protocone, paracone, and 



Continued from p. 238. 



NO. 1263, VOL. 49] 



metacone) in which they arose duiing the remote geological 

 periods. 



It is necessary to mention this overwhelming pala:onlolo- 

 gical evidence, because "trituberculy " is still not universally 

 recognised ; Fleischmann and others have questioned the homo- 

 logies of the upper and lower triangles, and two able writers. 

 Rose and Forsyth Major, have independently ptojiosed an 

 opposition theory that " multituberculy " or " polybuny "is the 

 mammalian archetyjie, the latter author believing trituberculy 

 has become a " dogma." So far, however, from there being any 

 decline of evidence, I am now able to add the Cretaceous mam- 

 malia to the tritubercular lists and bring forward evidence that 

 the multitubercular molar instead of being primitive was derived 

 from the tritubercular; moreover, all the researches I have 

 been quoting tend to draw the mammals without exception into 

 one of three great primary forms. The haplodont form, from 

 which Dromotherium is just emerging in the Trias, is the 

 oldest and nearest the reptiles ; the triconodont, or three cones 

 in line, was a predominating lower Jurassic type ; the trituber- 

 cular, or three cones in a triangle (trigonodont, Rlitimeyer), was 

 the prevailing upper Jurass-ic and later form. The final pre- 

 dominance of the tritubercular over the others was due to its 

 possibilities of mechanical adaptation to work of every kind — 

 its potential in evolution. Upon the polyphyletic theory of the 

 origin of the mammals here advocated, we must admit, first, 

 the independent evolution of trituberculy in different phyla ; 

 and second, the branching off of several great groups in the pre- 

 tritubercular stages. 



The tendency of late research is to show that all stem mam- 

 mals were related in their diphyodontism, in their dental 

 formula, and in their primitive molar form. These features 

 point, not to a succession, but to a unity of ancestry of the 

 Monotremes, Marsupials, and Placentals. 



Divergence of the Three Groups. 



The discovery of the complete double series seems to have 

 removed the last prop from the theory of the Marsupial 

 ancestry of the placentals, for the peculiar mode of suppres- 

 sion of the second series in the Marsupials has been constant 

 since the Purbeck ; this difficulty is added to the structure of 

 the jaw, the epipubic bones, the profoundly dift'erent mode of 

 foetal nutrition. None the less, any conclusion we can draw 

 now as to the primary relations of the three great groups is 

 more or less of a " Schwindelbau," and I put together the 

 results of these later discoveries with a full realisation of the 

 temporary character of present conclusions. 



The Permian Sauro-]\Iammalia (Baur) with a multiple suc- 

 cession of simple conical teeth divided into : A, Theromorpha, 

 which lost the succession and in some lines acquired a hetero- 

 dont dentition and triconid single-fanged molars ; B, Pro- 

 mammalia. 



The hypothetical lower Triassic Pro-mammalia retained a 

 double succession of the teeth ; they became heterodont, with 

 incipient triconid double-fanged molars; dental formula approx- 

 imating 4, 1. 4-5. 8. They gave rise to three groups : I. 

 The Prototheria which passed rapidly through the tritubercular 

 into the multitubercular molars in the line of Multituberculates, 

 and more slowly into trituberculy and its later stages in the 

 ine of Monotremes. II. The Metatheria or Marsupials tended 

 to suppress the second series of teeth, except those intercalated 

 with the first; by this and by reduction the formula became 

 5. 1.3. 4-6 ; the molars passed slowly through the triconodont 

 into the typical triiubercular type. III. The Eutheria or Pla- 

 centals divided early into a number of branches, in which 

 there was heterodontism, but no uniform modification of suc- 

 cession. 



We may distinguish four chief branches among these, as 

 follows : (A^ forms suppressing the .'^econd series in the molar 

 region only, and acquiring a typical Eutherian dentition, 

 3. 1.4. 3-4. I. The Insectivores tended to partly suppress the 

 anterior teeth of the second series or intercalate them with teeth 

 of the first series ; the molars became tritubercular. 2. The 

 higher Placentals retained the succession of the first and second 

 series as far back as the first molar ; the molars entered rapidly 

 into trituberculy and its higher stages. (B) forms retaining the 

 double succession in part of the molar region, and retaining 

 more of the primitive dentition, 4. i. 4. 8. 3. The Edentates 

 branched off from an early triconodont or tritubercular 



