« PreviousContinue »
that the Indian region formed the whole or even a part of such an adaptive centre, yet there is undoubted evidence that in the case of at least two important and mobile groups India must have been extremely near the adaptive centre, if indeed it did not form a part of it. These are (1) the Elephantoid and certain Mastodontoid branches of the Proboscidea; (2) the Bovine or oxen and buffaloes. The first of these groups is discussed on comparative lines in an appendix by my friend Dr. A. T. Hopwood. The second forms. the subject of the succeeding pages.
The proof that the Bovinae were descended directly from some member of the subfamily Boselaphinae is, in my opinion, complete. It is elaborated in a recent work by myself on the Fossil Bovida of India (1939, pp. pp. 140-157). Excluding the Tragocerina which belong to a specialized branch of the Boselaphinæ, somewhat off the line leading to the Bovinæ, there is no other part of the world in which, so far as we are aware, that subfamily is of more than sporadic occurrence. Throughout the Chinji, Nagri and Dhok Pathan stages Boselaphina are not only plentiful, but include several lineages, some of which such as Pachyportax and Perimia resemble very closely the primitive oxen. Other lineages beginning in the Chinji are that of Sivaceros which is the most probable ancestor of Tragocerus; the Helicoportacina, continued as Selenoportax in the Dhok Pathan; and a form Sivaportax, probably Dhok Pathan, which is more closely allied to Boselaphus. The last named genus and the related Tetracerus are Pleistocene and living forms, which so far as we know at present are confined to India, though the allied Duboisia occurs in the Pleistocene of Java. In Europe
Tragocerus latifrons of the Sarmatian, mentioned above (page 461) cannot be separated generically from Strepsiportax. Protragocerus chantrei is a little known form from the Tortonian of Europe apparently with affinities to Tragoportax and Strepsiportax. Tragocerus leskewitschi from the Sarmatian beds of Sebastopol is probably assignable to the Indian genus Tragoportax. Miotragocerus monacensis from the Sarmatian of the Vienna basin is most nearly allied to Sivaceros, but in certain respects approximates to Tragocerus. In the deposits of Sze Chuan in Southern China, probably of Villafranchian age or slightly younger, a genus Proboselaphus
occurs, of which the nearest affinity seems to be found in the Dhok Pathan form Perimia falconeri. The chances are greatly in favour of the Bovine having originated in the region in which the ancestral Boselaphina predominate so overwhelmingly both as to numbers and variety of genera over the rest of the world.
The earliest true Bovinæ known from India occur in the Dhok Pathan stage of the Salt Range and the Irrawaddy series of Burma as two or three species, ancestral to Hemibos and Bubalus, to which I have given the name Proamphibos. A fourth, Proleptobos, from beds in Burma which are probably the equivalent of the Dhok Pathan, is ancestral to Leptobos and possibly to the Taurina. A Bovine is known by some limb bones and teeth from the Pontian of Salonica, which Arambourg and Piveteau refer to the same genus as the remains from the Astian of Montpellier and perhaps from Casino and the Wadi Natrun, described under the names of Parabos cordieri and P. boodon. More plentiful material of Proamphibos has been collected from the Tatrot stage. Parabos is closely allied to Proamphibos and like it is a primitive buffalo. Its dentition is somewhat more primitive and seems to resemble somewhat that of Pachyportax. Leptobos is represented in the Pinjor stage of the Upper Siwaliks by the species L. falconeri and in Europe by various closely related Villafranchian forms known under the names of L. etruscus, L. elatus and L. stenometopon, which are generally more progressive than the Indian species, though they retain a few more primitive features. In the Djetis stage of Java, perhaps Cromerian, Leptobos groeneveldtii represents a decidedly more progressive stage than any of the other species of Leptobos. Leptobos is the only Bovine definitely known from the Villafranchian of Europe. It is replaced in the Cromerian by Bos and Bison of a rather modern type. On the other hand side by side with Leptobos in the Pinjor stage numerous other genera occur: Hemibos, a stage of development intermediate between Proamphibos and Bubalus, species of Bos, Bison and Bubalus which are distinctly more primitive than the earliest representatives of these genera in Europe, as well as other genera such as Bucapra and Platybos, which have not been found elsewhere. Many of these species occur in extraordinary abundance, so as to dominate the fauna, at any rate after the Proboscidea. For the most part they seem to have disappeared from India when the older alluvium of the Narbada was deposited, Bos namadicus and Bubalus palacindicus alone remaining so far as is known. Of these
two species one is closely allied to, if not specifically the same as the living Indian buffalo, and the other is with difficulty distinguished. from the Pleistocene Bos primigenius of Europe.
At Nihowan in China, which is considered to be Villafranchian in age, a bison occurs, B. paloeosinensis, which seems to be as primitive as B. sivalensis of the Pinjor. In Sze Chuan, perhaps rather younger than Nihowan, Bibos geron has been found. This genus has not been recognized fossil in India. Bos acutifrons of the Pinjor is the most primitive species of true Bos which is at present known.
It is inconceivable that Europe should have been very near the area which furnished such a wealth of Bovine types to India. Failing a knowledge of the Middle and Upper Pliocene fauna of countries like Persia, Arabia or Asia Minor one cannot predicate that India was even a part of such an area, but that migration from it to India must have been easier and more plentiful than it was to Europe may, I think, be safely claimed. The occurrence of a progressive species of Leptobos and of progressive species of Bubalus and Bibos in the Djetis stage of Java tells equally in favour of the adaptive centre of the Bovine being remote from Europe.
In spite of these well founded conclusions we are forced to believe, if we accept Matthew's and Colbert's correlation, that the earliest known Bovine appeared in the Pontian of Europe; that it was not until the Astian that the subfamily reached India; nevertheless in these Indian deposits it was represented much more abundantly than in Europe, by at least three different forms, one of which, Proleptobos, is ancestral to Leptobos. Notwithstanding this, Leptobos, although plentiful in Europe in the Villafranchian, did not enter India until the Pinjor stage (ex hypothesi Cromerian or Sicilian). Similarly although the two European species Parabos cordieri and P. boodon are closely related to the Tatrot Proamphibos lachrymans, yet ex hypothesi the former belong to the Astian and the latter to the Villafranchian. In the supposedly Cromerian stage of the Pinjor it dies out and is replaced by numerous Bovine genera which dominate the fauna of that stage. Strange to say, all of these are absent from the Villafranchian of Europe except Leptobos. One cannot conceive of migrational conditions which furnished these forms, all of them primitive ones, to the Cromerian of India but provided Europe as well as Central Asia during the same epoch with but a diminished residue and those much more progressive ypes of Bubalus, Bison and Bos than those of the Cromerian
(ex hypothesi) of India. Were the centre of distribution of the Bovinæ in Europe itself the occurence of the various genera and species as hypothetically described above would pass belief, but if that centre adjoined India, as the facts seem to indicate, then it verges on the impossible.
In the preceding pages I have tried to show that Matthew's and Colbert's hypothesis of successive migrations of mammalian faunas to India between the Vindobonian and the Pleistocene just one stage later than similar migrations to Europe is quite incredible in the face of the knowledge which we possess of the palæontology of these two parts of the world.
Two alternative solutions of the problem, either of which would reconcile the various known facts, have suggested themselves to me. The first of these is that the European correlation of the American Upper Miocene and Pliocene faunas might be predated by at any rate half a stage. I hesitate to stress this strongly in the face of the vast amount of the work that has been done on the American faunas, especially as my own knowledge of the subject is insufficient to warrant it without devoting more time and research to it than I am at present able to spare. I would, however, point out that the accepted correlation was originally based in great part on the first appearance in Europe and America respectively of two members of the Equide, Hipparion and Equus. If this were the only evidence in favour of it, it would be like arguing in a circle if we assert that because Hipparion appears in the Chinji stage of India, therefore the Chinji must be Pontian, seeing that it is an altogether unwarranted assumption on our part that Hipparion arrived in Europe and India simultaneously. Nor indeed is this at all likely to have been the case, when we consider that the Pontian fauna of Europe resulted from a sudden invasion from Asia. I am aware that other factors have been taken into consideration before the correlation was finally decided on, but speaking generally I think that it might be more profitable to try and correlate the Miocene and Pliocene faunas of America with those of India in the first place or better still with those of China, when future discoveries make them known to us. It is obvious that the correlation of the Chinese and Indian faunas with those of Europe is also more practicable. Taking the Pontian specifically, it seems to me that a closer correlation might be found between the Edson, Mount Eden, Hemphill, Rattlesnake and Thousand Creek faunas and
those of the European Pontian, the Hipparion fauna of China, and the Dhok Pathan of India than between the Republican River and Valentine faunas and the old-world ones named. For instance the presence in the American faunas mentioned above of species of Simocyon, Indarctos, Agriotherium, Parataxidea and Plesiogulo closely allied to those found in Europe, China and India seems to be very significant. Possible Pseudalurus intrepidus sinclairi, Heterofelis catocopis and Martes glareae which also exhibit rather close affinities to old world forms may also be of the same age. The absence of European Artiodactyla from America as early as this may be due to climatic hindrances to migration by the Behring Strait route.
No American writer has suggested this idea, and although I think that in time to come this explanation may prove to conform most nearly to the facts, I will now dismiss it, whether possible or not, from further consideration here and proceed to the second suggestion that I have to offer, that of a dual origin for Hipparion.
Matthew and Colbert consider that their migration hypothesis is more credible than that Hipparion should have originated independently in North America and Asia from two different species of Merychippus, with the corollary to suit the facts that the evolution of Hipparion in Asia actually predated its evolution in North America. Is this, however, really so?
During the last half century paleontologists have grown to believe that the development of any particular group of animals has for the most part taken place in one region of the earth and that from this centre the genera one by one, as they arose, have been distributed into other parts of the world. No doubt this is in a general sense true, but the recognition that other branches of the group have sometimes arisen elsewhere so as to originate another allied group, has been forced upon us. The ancestral form of such a group is presumed to be a migrant from the original radiative centre. It has been assumed either that the changed environment which such a migrant might encounter in its new home would inevitably lead to an altogether different type of development from that followed by the main stem, or that through some inherent tendency to variation the same forms could not be produced in two widely distant regions. Where the same genus has been found in different parts of the world the tendency has been to consider that it originated in one of these areas only, and reached the other