September 2, 1909] 



NA TURE 



293 



must be- admitted that modern systematic researches are 

 continually complicating rather than simplifying the 

 problems we have to solve. Prof. Charles Dep^ret has 

 lately written with scant respect of some of the pioneers 

 who were content with generalities, and based their con- 

 clusions on the geological succession of certain anatomical 

 structures rather than on a successive series of individuals 

 and species obtained from the different layers of one geological 

 section ; but even now I do not think we can do much 

 better than our predecessors in unravelling real genealogies. 

 At least Prof. Dep^ret's genealogical table of the Lower 

 Tertiary pig-like Anthracotheriida;, which he publishes as 

 an illustration of " Evolution r^elle," seems to me to be 

 no more exact than several tables of other groups by 

 previous authors which he criticises. His materials are all 

 fragmentary, chiefly jaws and portions of skulls ; they 

 were obtained from several isolated lake-deposits, of which 

 the relative age cannot be determined by observing the 

 geological superposition ; and they represent a group which 

 is known to have lived over a large part of Europe, Asia, 

 Northern .'\frica, and North America. There is therefore 

 no certainty that the genera and species enumerated bv 

 Prof. Dep^ret actually originated one from the other in 

 the region where he happened to find them ; he has demon- 

 strated the general trend of certain changes in the .Anthra- 

 cotheriidoe during geological time, but really nothing more. 



Even when a group of animals seems to have been 

 confined to one comparatively small region, where the 

 series is not complicated bv migration to and from other 

 parts of the world, modern research still emphasises tile 

 difliculty of "tracing real lines of descent. The primitive 

 horned hooted animals of the family Titanotheriidfe, for 

 example, are only known from part of North America, and 

 they seem to have originated and remained there until the 

 end. As their fossil skeletons are abundant and well pre- 

 served, it ought to be easN' to discover the e.\act connec- 

 tions of the several genera and species. Prof. Osborn has 

 now proved, however, that the Titanotheres must have 

 evolved in at least four distinct lines, adapted " for different 

 local habitat, different modes of feeding, fighting, locomo- 

 tion, &c., which took origin, in part at least, in the Middle 

 or Upper Eocene." They exhibit "four distinct tvpes in 

 the shape and position of the horns, correlated with the 

 structure of the nasals and frontals, and indicative of 

 different modes of combat among the males." The rami- 

 fications of the group are indeed so numerous that the 

 possibility of following chains of ancestors begins to appear 

 nearly hopeless. 



Among early reptiles the same difficulties are continually 

 multiplied by the progress of discovery. About twenty 

 years ago it began to appear likely that we should soon 

 find the terrestrial ancestors of the Ichthyosauria in the 

 Trias ; and somewhat li:ter a specimen from California 

 raised hopes of obtaining ,hem by systematic explorations 

 in that region. During more recent years Prof. J. C. 

 Mcrriam and his colleagues have actually made these 

 explorations, and the result Is that we now know from 

 the Californian Trias a multitude of reptiles, which need 

 more explanation than the Ichthyosauria themselves. Prof. 

 Merriam ha.s found some of the links predicted between 

 Ichthyosaurs and primitive land reptiles, but he has by no 

 means reached the beginning of the marine group ; and 

 while making these discoveries he has added greatly to the 

 complication of the problem which he set out to solve. 



Serious difliculties have also become apparent during 

 recent years in determining exactly the origin of the mam- 

 mals. For a long time after the discovery of the Anomo- 

 dont or Theromorph reptiles in the Permian-Trias of .South 

 Africa, It seemed more and more probable that the 

 mammals arose in that region. Even yet new reptiles 

 from the Karoo formation are continually being described 

 as making an astonishingly near approach to mammals ; 

 and, so far as the skeleton Is concerned, the links between 

 the two grades are now very numerous among South 

 African fossils. Since these reptiles first attracted attention, 

 however, they have gradually been found in the Permian 

 and Trias of a large part of the world. Remains of them 

 were first met with in India, then In North .America, and 

 next in Scotland, while during the last few years Prof. \V. 

 Amalitzky has disinterred so many nearly complete skeletons 

 in the north of Russia that we are likely soon to learn 

 more about them from this European country than from 

 NO. 2079, VOL. 81 J 



the South .\frican area Itself. Quite lately I ha\'e reteivrd 

 numerous bones from a red marl in Rio Grande do Sul, 

 Southern Brazil, which show that not merely Anoniodonts, 

 but also other characteristic Triassic land reptiles were 

 likewise abundant in that region. We are therefore now 

 embarrassed by the richness of the sources whence we may 

 obtain the ancestors of mammals. Whereas some years ago 

 it appeared suflficlent to search South Africa for the solu- 

 tion of the problem, we arc now uncertain in which direc- 

 tion to turn. We are still perhaps inclined to favour the 

 South African source ; but this is only because we know 

 nothing of the Jurassic land animals of that part of the 

 world, and we cherish a lingering hope that they may 

 eventually prove to have included the early mammp.ls for 

 which we have so long sought in vain. 



The mystery of the origin of the marine mammals of 

 the order Sirenia and Cetacea appears to have been 

 diminished by the discoveries of the Geological Survey of 

 Egypt, Dr. Andrews and Dr. Fraas in the Eocene and 

 Oligocene deposits of the Mokattam Hills and the Fayum. 

 It Is now clear that the Sirenlans are closely related to 

 the small primitive ancestors of the eleohants ; while, so 

 far as the skull and dentition are concerned, we know 

 nearly all the links between the early toothed whales (or 

 Zeuglodonts) and the primitive ancestors of the Carnlvora 

 (or Creodonts). The most primitive form of Sirenlan skull 

 hitherto discovered, however, is not from Egypt, but from 

 the other side of the world, Jamaica ; and exactly the same 

 Zeuglodonts, even with an associated sea-snake, occur so 

 far away from Egypt as Alabama, U.S.A. The problem 

 of the precise origin of these marine mammals is therefore 

 not so simple as it would have appeared to be had we 

 known only the Egyptian fossils. The progress of dis- 

 covery, while revealing many most important generalities, 

 has made it impossible to vouch for the accuracy of the 

 details in anv " genealogical tree." 



Another difficulty resulting from the latest systematic 

 researches Is suggested by the extinct hoofed mammals of 

 South America. The llamas, deer, and peccaries existing 

 in South America at the present time are all immigrants 

 from the northern continent ; but during the greater part 

 of the Tertiary period there lived In that country a large 

 number of indigenous hoofed mammals, which originated 

 quite independently of those In other regions. _ They seem 

 to have begun In early Eocene times much in the same 

 manner as those of the northern hemisphere ; but as they 

 became gradually adapted for life on hard ground, they 

 formed groups which are very different from those with 

 which we are familiar in our part of the world. Some of 

 them (Proterotherllda;) were one-toed mimics of the horses, 

 but without the advanced type of brain, the deepened 

 grinding teeth, the mobile neck, or the really effective wrist 

 and ankle. Others (To.xodontlda;) made some approach 

 towards rhinoceroses in shape and habit, even with a trace 

 of a horn on the nose. Until their independent origm was 

 demonstrated, these curious animals could not be under- 

 stood ; and it is probable that there are innumerable smiilar 

 cases 'of parallel development of groups, by which in our 

 Ignorance we are often misled. ■ , t i. 



It would be easy to multiply instances, but I thmk I have 

 now said enough to show that every advance in the study 

 of fossils reveals more problems than it solves. Durmg the 

 last two decades the progress in our knowledge of the 

 extinct backboned animals has been truly astomshmg. 

 thanks especially to the great explorations m fjorth 

 America, Patagonia, Egypt, Madagascar, and South Africa. 

 Whole groups have been traced a long way towards their 

 oriain • but with them have been found a number of pre- 

 viouslv unknown groups which complicate all questions of 

 evolut'ion to an almost bewildering extent. Animals 

 formerly known only by fragments are now represented 

 by nearly complete skeletons, and several which appeared 

 to have a restricted geographical range have now been 

 found over a much wider area; but while this progress 

 has been made, numerous questions have arisen as to the 

 changing connections of certain lands and seas which 

 previouslv seemed to have been almost settled. The outlook 

 both of 'zoology and of geology has, therefore, been 

 immensely widened, but the only real contribution to 

 philosophy has been one of generalities. Some of the broad 

 principles' to which I have reterred are now so clearly 

 established that we can often predict what wiU be the main 



