gondwanaland revisited: new evidence for continental drift || fossils and gondwanaland

Fossils and GondwanalandAuthor(s): Alfred Sherwood RomerSource: Proceedings of the American Philosophical Society, Vol. 112, No. 5, GondwanalandRevisited: New Evidence for Continental Drift (Oct. 17, 1968), pp. 335-343Published by: American Philosophical SocietyStable URL: http://www.jstor.org/stable/986054 .

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FOSSILS AND GONDWANALAND

ALFRED SHERWOOD ROMER

Alexander Agassiz Professor Emeritus of Zoology, Harvard University

(Read April 19, 1968, in the Symposium on "Gondwanaland Revisited: New Evidence for Continental Drift")

I SHALL concern myself here mainly with the Gondwanaland problem, in which I have become interested only in recent years, although my doubts about continental stability began much earlier, with qualms about the early existence of the North At- lantic Ocean. I was educated, as regards paleo- geography, in an "orthodox" school of thought which decreed that the continents always have been and always shall be in essentially the position in which we find them today. As a paleontologist, I tended to have such beliefs strengthened by W. D. Matthew's 1915 paper on "Climate and Evolu- tion." In this classic essay, he reasonably reached the conclusion (since reinforced by the work of Simpson and others) that most of the varied land bridges and unusual continental juxtapositions believed by many authors to have existed during the Tertiary rested upon insecure foundations, and that the present distribution of vertebrate life can be best accounted for on the assumption that during the Age of Mammals, intercontinental connections were essentially as they now exist or (as in the case of Bering Strait) as they existed in the not distant past.

Once granting that Matthew's case is well sub- stantiated for the Tertiary, it is easy to extrapolate backward and assume that the same stability existed in earlier, pre-Tertiary times. Many of my colleagues in mammalian paleontology do so extrapolate; but as a student of lower vertebrates, I have found my belief in the fixity of continental positions and connections in earlier epochs of earth history gradually weakening; particularly I have begun to doubt whether there was such a thing as the North Atlantic Ocean in Paleo- zoic times.

I will briefly summarize the evidence. In the Devonian period, the "Age of Fishes," a considerable fauna of freshwater fishes is known from both Europe and North America. An abundance of fishes exists today in these areas, but the forms present in the two continents are very different; for example, of an incomplete (but probably repre- sentative) list of 42 genera of fishes found today

in North American streams and lakes, only 9, or 21 per cent, are present in Europe as well. One would assume that similar differences were present in the Devonian, and this was once believed to be the case. But currently, owing to more intensive study, we find that of some 58 Devonian genera known from North America, 33, or 57 per cent, are likewise present in Europe. This defi- nitely indicates better connections between the two continents than that which exists now or existed in the recent geological past. It is possible that this contrast is due in some degree to a greater facility of interchange via Asia in ancient times.1 But it strongly suggests-although it does not prove-that the continental "redbeds" of the De- vonian of Europe and eastern North America w<ere adjacent to one another.

As regards the Carboniferous period, the Coal Measures, following the Devonian, Westoll ( 1944) analyzed the freshwater fish faunas of North America and Europe, and reached a conclusion comparable to that cited above for the Devonian- namely that at that time the North Atlantic Ocean did not exist. In the Carboniferous we have, in addition to fishes, a considerable fauna of amphibians in fresh water. Results of their study parallel that of the fishes. Two decades or so ago, it was thought (as in the case of the Devonian fishes) that the North American and European amphibian faunas were very different; for example, in the 1945 edition of my Vertebrate Paleontology, only three of the North American genera listed were thought to be present in Europe as well. But more recent careful studies, notably by Drs. Donald Baird and Robert L. Carroll, show the picture to be very different; of 33 currently recognized North American genera, 15-about 45 per cent-are also present in Europe.

The early Permian of North America has a verv

'Cold climates in the Pleistocene and late Tertiary would, of course, have hindered relatively recent migration; but many of the modern fish genera were surely in existence in earlier Tertiary times, when no major tem- perature barrier appears to have existed.

PROCEEDINGS OF THE AMERICAN PHILOSOPHICAL SOCIETY, VOL. 112, NO. 5, OCTOBER, 1968

335



336 ALFRED SHERWOOD ROMER [PROC. AMER. PHIL. SOC.

rich fauna of amphibians and reptiles. The comparable European beds have yielded relatively little material, but there are a number of forms generically identical with North American types, and the two faunas are obviously very similar. For example, I studied some years ago the faunas of Kounova, Bohemia, lying on the Carboniferous- Permian boundary, as described by Fritsch (1879). His material was fragmentary; but of 16 forms described by him, 13, if they had been found in Texas, would have been confidently as- signed to known American types (Romer, 1945). Obviously, in the Permian, as in the Devonian and Carboniferous, intercontinental connections were much closer than at present, again strongly suggesting direct apposition of Europe and eastern North America, without the interposition of an ocean.

Having thus found reasons in the north for a weakening of my faith in the gospel of rigid continental fixity, I was able to consider, without horror or biased incredulity, the possibility of the former existence of a great southern continent, Gondwanaland, when my attention was brought to this problem through Harvard collecting expedi- tions to the Triassic of Argentina in 1958 and 1964-1965.2

The Gondwana concept had its origins nearly a century ago as the result of geological work in peninsular India. Here, in the late Paleozoic and early Mesozoic, there were discovered continental beds with coal, a distinctive flora, and evidences of glaciation. These beds lay in an area called Gondwana, the land of an aboriginal tribe, the Gonds, and the beds were presently termed the Gondwana beds. Similar beds were discovered in South Africa and later in other regions-Australia, Madagascar, southern South America, and even Antarctica. The term "Gondwana beds" presently came into common usage amongst geologists and paleontologists studying beds of this sort in the various southern continental regions, and Suess, in 1885, first made the suggestion, later elaborated by him and many other workers, that the southern continents at one time were parts of a great common land mass, Gondwanaland, the components of which later separated and drifted apart-South America to the west, Africa to the North, the fu- ture Indian peninsula drifting far north to ground

2 Excellent brief discussions of the Gondwana problem are contained in works on historical geology such as those of Kummel (1961: pp. 329-349) and Woodford (1965: pp, 339-366).

on the southern margins of Asia, and Australia, like a great Noah's Ark, floating northeast across the Indian Ocean to its present position near the East Indies.

Until recent years, when geophysical and ocean- ographic work contributed suggestive new data, the main arguments tending to support the hypothesis of Gondwanaland were derived from two types of evidence present in deposits of Gondwana type-glaciation and a distinctive flora. Glacia- tion is beyond the scope of the title of the present article, but since it has not been discussed by other speakers, it may be mentioned here.

In India, the oldest of the Gondwana beds, the Talchir formation, is notable for the presence of prominent elements of a sort associated with glaciation-boulder beds and tillites, the latter con- sisting of clays, sands, and "cobbles," laid down in a fashion similar to that seen in Pleistocene and Recent glacial deposits. In New South Wales, Australia, the "Lower Marine Series," lowest of Gondwana-like deposits, also shows a marked series of glacial beds. In South America, the Itarare formation of southern Brazil shows a strong development of glacial tillites, and such tillites are also present in western Argentina, notably in the Sierra de la Ventana and San Juan Province. To the east, the Falkland Islands have Gondwana beds with notable tillites. In South Africa, glacial traces are widespread in the lower part of the Dwyka formation, oldest of South African Gondwana deposits, including not only tillites and boulder beds, but exposures showing striations of underlying rocks due to the passage over them of heavy glaciers carrying rock fragments with scouring potentialities. In Africa, evidences of this ancient glaciation extend far north, even into the tropical areas of the eastern Congo- although here it is possible that we are dealing with local mountain glaciation rather than a con- tinuous ice cap.

Although exact dating is difficult, there seems to be some variation in the age of these various deposits, some being well down in the Carbonif- erous, others close to the Carboniferous-Permian boundary, or even earliest Permian in age. Very probably there was in this ancient glaciation a situation comparable to that of the Pleistocene glaciation of the north-a series of glacial "peaks" separated by relatively warm interglacial periods, the whole occupying an extensive period of time.

Can we account for this widespread glaciation on the assumption of continental fixity? Western



VOL. 112, NO. 5, 1968] FOSSILS AND GONDWANALAND 337

Argentina, Cape Colony in South Africa, and New South Wales are as far from the South Pole as are, for example, Alabama and Mississippi from the North Pole, and the Brazilian deposits are as far from the South Pole as Miami from the North. It is difficult to conceive of a glaciation that would have spread nearly three-quarters the way from the pole to the equator, leaving free of ice in the Southern Hemisphere only a small tropical belt.

And there is still to explain the Indian glaciation. This was a heavy and extensive glaciation, not a restricted affair of some high mountain. Quite surely this was part of the southern glaciation; there is no indication of any intensive Permo- Carboniferous cold period in the north. And yet we are here across the equator, well into the Northern Hemisphere! The only rational ex- planation is the Gondwanaland hypothesis-that South America, Africa, and Australia in Permo- Carboniferous times lay farther south than they do at present and, further, that the present peninsula of India at that time was part of this same complex, only later drifting northward and joining itself to Asia.

And now, at long last, to come to my proper subject-fossils. All paleontology is (like Gaul) divided into three parts-vertebrate paleontology, invertebrate paleontology, and paleobotany. The vertebrates, discussed later, give us interesting although not conclusive evidence. We need not concern ourselves with invertebrate faunas-mainly marine; they can furnish paleogeographic evidence as to whether or not two bodies of water were connected; but we are here concerned with connections between land areas, not seas. (It is, however, interesting that there are few traces, in late Paleo- zoic and early Mesozoic days, of marine deposits along the facing margins of modern fragments of Gondwanaland.) Plant fossils, in contrast, form a major body of evidence supporting the Gond- wanaland hypothesis.Y

The plant life of the Carboniferous is particularly well known from coal swamp deposits, which contain remains of a large series of trees and smaller plants, mostly of types long since extinct. Nearly as well known are the floras which succeeded them in the Permian. In the northern continents, these appear to have evolved rather gradually out of those of the coal swamps. Two

3Except that it does not contain the more recently published data, an excellent resume of the floras concerned can be found in Seward's Plant Life Through the Ages (1931).

FIG. 1. Leaves of Glossopteris (left) and Gangamopteris (right), characteristic genera of the Permian Gond- wanaland flora.

major northern floras were present. Once, char- acterized by the presence of a distinctive genus, Gigantopteris, occurred in eastern Asia and the western United States. A second flora was present in much of the United States, Europe, and southwestern Asia; the general Siberian region possessed a flora rather transitional between the two.

Very different is the situation in the Gondwana regions. In the early Permian, following on the glacial beds (and even, in places, intercalated between glacial layers), there developed a new flora of a distinctive type, which was destined to sur- vive throughout the Permian. Of the new forms present here, two of the most readily identifiable are remains (mainly leaves) termed Glossopteris and Gangamopteris (fig. 1); the whole assemblage, including two score or more genera, is called the Glossopteris flora. This flora is widespread. It is present in the Permian of India, Australia,



338 ALFRED SHERWOOD ROS'IER [PROC. AMER. PHIL. SOC.

0:

FIG. 2. Mesosauus, a small early Permian reptile from South Africa and southern Brazil. (After Osborn.)

South Africa, South America, and even Antarc- tica. Its components differ little from region to region. And this flora is absolutely distinct re- gionally from the northern floras.4 Can the distribution of this distinctive Glossopteris flora be accounted for on the basis of present continental positions? It seems quite certain that it represents a new southern temperate-to-subarctic assemblage. Leaving peninsular India out of the picture, its lack of common elements with the northern floras of the time could be due to the fact that these temperate plants could not cross the tropics; a cli- matic barrier may have prevented admixture. And while it is hard to see how such a great similarity could have been present between areas now so widely separated in space as South America, Africa, and Australia, aerial or over-water transportation of plant materials is possible (although such widespread transportation over long distances stretches the credulity).

But when India is added to the picture, reten- tion of a botanical interpretation on the basis of present land distribution seems hopeless. If long- distance transportation is assumed to be respon- sible for the close similarity of the Indian flora to that of South Africa, Australia, and South America, why has there been no interchange between India and either of the two northern floras,

4 It was once believed that certain of its members were also present in Eurasia proper, but this has proved to be incorrect.

which are geographically much closer? A tem- perature control will not work here, for India, lying at the northern margin of the tropics, is hardly to be considered as a south temperate zone region. It seems impossible, on the basis of paleobotanical evidence, to escape the conclusion that peninsular India in Permian times lay well down in the southern temperate zone, in association with the other Gondwanaland components carrying the same Glossopteris flora.

In the following period, the Triassic, the argument for southern paleobotanical unity and dis- tinctiveness is less clear. The Glossopteris flora is succeeded by one in which Dicroidium (Thinn- feldic) is a characteristic leaf genus. This flora is widespread in the various Gondwanaland components-in the Panchet and Rajmahal Triassic beds of India, the Ipswich and Wianamatta forma- tions of Australia, the Molteno of South Africa, and in the precordilleran region of western Ar- gentina. There are various time gaps in the se- quence of plant beds in one continental area or another, so that the picture is not too clear. But there are two major statements that can be made concerning the southern Dicroidium floras. On the one hand, they all have many characters in common, suggesting that the Gondwanaland components were still in close contact with one another; on the other, the southern Triassic floras have, particularly toward the end of the period, a considerable number of forms also found in the Northern Hemisphere. This last fact suggests that (as will be seen in considering the vertebrates) the southern regions were not splendidly isolated, but were in free communication in the late Triassic, at least, with the northern world.

And now to come, at last, to my own special field of interest, the vertebrates. Here the evidence is suggestive, but far from as strong as that obtained from plants and glaciation. With one exception, the only items of interest are those derived from a study of Triassic faunas. In South Africa, an abundant fauna of reptiles and amphibians is present from Middle Permian times onward, but while a few late Paleozoic continenatal vertebrates are present in other Gondwanaland regions, they are too few in numbers to afford anly worthy evidence as to continental positions or relationships.

The Permiani exception is Mesosaurus (fig. 2). This is a small reptile, measuring about two feet in length, tail and all. Mesosaurus is peculiar in structure and doubtful as to phylogenetic position.




It has no k-nown close relatives, and very probably evolved independently as a short side-branch from the basic reptilian stock of the Carboniferous. Mesosaurus was an amphibious form. It had well- developed limbs and was perfectly able to walk on land. But it obviously spent most of its time making a living in the water. There was a very long beak, armed with a great battery of slender, needle-like teeth. Mesosaurus is often restored (as in the accompanying figure) pursuing small "minnows." It is, however, highly improbable that its diet was of this nature; its teeth were too dlelicate. Presumably it fed mainly on tiny crus- taceans which were abundant in the waters (seem- ingly of a brackish, deltaic, or estuarine nature) in which the sediments containing Mesosaurus were laid down.

The geographic distribution of Mesosaurus appears highly significant. It is found only in two places in the world: (1) in the early Permian beds of the Dwyka formation of western Cape Colony; and (2) in the closely comparable sediments of the Itarare formation of southern Brazil, almost di- rectly across the South Atlantic. How can this distribution be accounted for under the gospel of continental fixation? It is about 20,000 miles, via "normal" continental shore routes, from one area to the other. If it had traveled thus, one would expect some trace of Mesosaurus in Eura- sia or North America, through which it must have passed, and in both of which there are rather abundant Permian deposits. No such trace has ever been found. If this highly improbable migration route be abandoned, the suggestion may be made that this animal swam the 3,000 mile stretch of the South Atlantic. But Mesosaurus, although a moderately competent swimmer, apparently, does nlot appear to have been well adapted to a truly marine habitat. Possibly this may have happened, but the chances of such a crossing of a broad ocean by this little estuarine form seem close to the limits of probability. Much more reasonable is the assumption that at that time the South Atlantic was non-existent, and that the Itarare and Dwyka for- mations, very similar in nature, were one; no migration was necessary.

A great deal of -valuable data has been gathered in recent years concerning the Triassic vertebrate faunas of the Gondwana lands, notably in South Africa and South America. One would, at first glance, assume that all that is needed here is to compare the faunas of these southern areas, note resemblances between them, and conclude, with

complacency, that these resemblances are due to their being neighboring faunas in a united southern Gondwanaland. Regrettably, the problem cannot be solved that simply. We must consider whether the resemblances which can be found between southern areas are greater than might be expected had migration taken place via "normal" northern land connections. Were such northern connections present at the time ? And what was the nature of the faunas then present in the northern areas through which "normal" migrations might have taken place ?

Whether or not the southern continents were a unit, one should not think of them as completely isolated from the north. In the case of plants, temperatures seem to have acted as a barrier between northern and southern worlds. Such in- fluences were less effective in the case of vertebrates, and there is good evidence that north and south were in contact at various times in the late Paleozoic and Triassic. In the Middle Permian of Russia there is a considerable fauna of reptiles, mainly mammal-like forms rather closely comparable to those of the Middle Permian of South Africa, although slightly more primitive. In the late Permian of northern Russia there is a fauna closely comparable to that of the late Permian of South Africa-so close, in fact, that the genera concerned are identical in several instances. There has recently been discovered in China an early Triassic fauna which is clearly comparable to that of the same age in South Africa; three of the nine known genera are identical with those of South Africa, and the rest are mostly rather similar. Finally, in all three northern continents there are late Triassic faunas notable mainly for the presence of primitive dinosaurs. A corresponding fauna has long been known from South Africa, and a further one of similar nature has recently been found in Argentina.

A corollary to the fact that the southern lands were frequently, if not continuously, in connection with northern continents is the point mentioned above-that comparisons between faunas in southern regions cannot be used as proof of geographic relationship unless the similarity is greater than would be expected had there been migration via "normal" northern migration routes. For example, South Africa and southern South America, we have noted, are 20,000 miles or so apart via Asia and North America; but it is possible to cover this distance in a million years or so (the Triassic period was about 50 million years in




duration) if only a few rods per year are traversed. And it may be noted that the cat genus Felis (in a broad use of that generic term) is common in every continent of the world except Aus- tralia, and that the dog-wolf genus Canis is present similarly in five continents.

But this argument cannot be stretched too far without reaching the breaking point. The two genera mentioned are fast-running forms, and are carnivores capable of existing on almost any type of animal food they might encounter. Few other mammals, even if speedy, have been able to extend their ranges so far, having met with problems in food supply, terrain, or climate. Further, mammals are, on the whole, much more active and competent in migratory activities than the reptiles and amphibians with which we are concerned in Mesozoic times. And again, instead of hopefully citing exceptional cases, let us look at the modern faunal picture as a whole. Below we will be mainly concerned with comparisons between South America and South Africa in the Triassic. How similar are these two continental areas today, even if we restrict ourselves to the relatively versatile and speedy mammals and neglect lower forms? The land route between Africa and South America is wide open except for Bering Strait, and that, we know, afforded dry-shod passage for much of the Cenozoic. The Panamanian connection was non- existent for most of the Tertiary, but during much of the past two million years, migration between South Africa and South America was theoretically a simple matter. Do we find, as a result, that the two areas are faunally similar as regards mammals (to say nothing of lower vertebrates) ? Emphati- cally, we do not. No two regions of the world (if we leave out Australia) differ more radically in their faunas. Except for the cats, there are no genera common to the two; many families of the

FIG. 3. The skull of Cynognathus, best known of early Triassic carnivores in South Africa, and also present in Argentina.

mammals present in one region are absent in the other, and there are differences even in whole or- ders of mammals. Perhaps travel was easier in early days; but one may be skeptical of claims that close similarity in the past between such areas is due merely to long-distance round-about migration.

A consideration of the significance of Triassic faunal resemblances would be relatively simple were we conversant with the nature of the continental faunas in all the continents at every stage of the Triassic. We are not; and our knowledge of these faunas was much more fragmentary before relatively recent discoveries (of special interest to us) in Gondwanaland regions. As its name implies, the Triassic period is customarily divided into three successive stages. Two or three decades ago, a good faunal assemblage was known in the lowest stage of the three only in the Karroo beds of South Africa; of the other southern regions little was known, and in Europe and North America early Triassic continental beds are essentially represented by mud flats; in these are pre- served amphibian remains (which are of little value for present purposes) but almost nothing in the way of potentially significant reptilian fossils. For the Middle Triassic, there was nearly a com- plete world-wide blank; in the Northern Hemis- phere this time period is represented almost en- tirely by marine beds, and even in South Africa the Middle Triassic Molteno beds long appeared to be completely barren. It is only in the late Triassic that we get a view of world-wide conditions. In beds of this age, there had been described numerous land-dwelling reptiles in regions as varied as South Africa, China, Europe, and both eastern and western regions of the United States.

Putting together the fragmentary bits of evidence available not too long ago, then, we knew an early Triassic fauna in South Africa, and a widespread late fauna. The middle was lacking. The early fauna consisted in large measure of therapsids, a great group of reptiles ancestral to mammals, which had evolved in late Paleozoic times and were still dominant at the beginning of the Triassic. Most familiar of South African forms were Cynognathus (fig. 3), a carnivorous member of the therapsid line leading toward the mammals, and Kannemeyeria (fig. 4), a clumsy two-tusked creature with a turtle-like beak, repre- senting an herbivorous side-branch of the therapsid stock. Present in addition were rarer members of other reptile groups, such as the thecodonts, the group from which the dinosaurs were to arise.



VOL. 112, NO. 5, 19681 FOSSILS AND GONDWANALAND 341

The late Triassic fauna differed markedly. The therapsids at that time had dwindled almost to the vanishing point, although some of the smaller members of the group were advancing toward and to the condition of primitive mammals. Dominant were dinosaurs, unknown at the beginning of the period, but now abundant and varied and already attaining large size.

And what was the nature of the fauna of the unknown middle Triassic? Until recently, we could only guess. Judging by what came before and after, one could reasonably assume that the mammal-like forms would have been declining and that, on the other hand, the thecodonts would have been progressing toward the dinosaur stage; there was little reason to expect anything distinctive in the presumably transitional Middle Triassic.

The last two or three decades have seen a re- markable increase in our knowledge of Triassic reptiles. Little new has been found in the northern continents (except that a limited fauna has been recently described from the early Triassic of China). Much of interest, however, has been discovered as the result of exploration in the Gond- wana regions, notably Africa and South America.

In the late '30's Triassic beds were discovered in East Africa and collections made by Parrington of Cambridge, England, and for Huene of Tiubin- gen; quite recently an English expedition made further extensive collections in western Tanzania and further south in eastern Zambesia (Attridge et al., 1964). Only part of the finds have as yet been described, but the collections contain a wealth of specimens of reptiles of Middle Triassic age. In Africa, further, the supposedly barren Molteno beds of similar age have in the last few years begun to yield specimens to Crompton and others.

More extensive, however, have been finds, again principally in the Middle Triassic, in South America. A large collection of reptile remains has been found in the Triassic Santa Maria beds of southern Brazil; the first major collection was made for Huene of Tiibingen and described by him in a volume published in 1944; later collections have been made (in great measure by Price) for Harvard, the American Museum of Natural His- tory, and the Brazilian Geological Survey. Most recently attention has centered on western Ar- gentina. Almost nothing was known of Triassic reptiles in Argentina before the Harvard expedition of 1958 and 1964-1965. By the first of these a very rich deposit of rather late Middle Triassic age was found in the remote desert valley of

FIG. 4. The skeleton of Kannemeyeria, the typical di- cynodont of the South African early Triassic; also found in Argentina. (After Pearson.)

Ischigualasto (Romer, 1962), and exploration of this region has been continued by Argentinian workers, who have published a number of papers on this fauna. The second Harvard trip resulted in the discovery of even richer beds, of somewhat earlier Middle Triassic age, in the region of the equally remote Chafiares and Gualo rivers (Romer, 1966); the fossils found here are currently in process of preparation and description. Stimu- lated in great measure by these finds, Triassic exploration in Argentina has been continued by Bonaparte of Tucuman. He has discovered, but not as yet described, a late Triassic dinosaur fauna in the Los Colorados formation of the general Ischigualasto region. Still more interesting is his finding of a limited series of reptiles in beds of early Triassic age, comparable to those of South Africa (Bonaparte, 1966, 1967).

As regards the dinosaur faunas of the late Triassic, the more recent finds, including the new Argentinian fossils as well as new data on other regions, add little to the picture as known pre- viously. The members present vary somewhat from continent to continent, but the general im- pression is that of a fairly uniform fauna the world around, with as yet, at least, no reason to assume necessarily that, for example, the Argentinian and African faunal regions were in direct land contact.

More interesting is the great amount of data now accumulated regarding the Middle Triassic- all of it from the southern continents. As noted above, it was once assumed that, when found, faunas of this age would prove to be simply transitional in nature between the early Triassic therapsid fauna and the dinosaur-dominated fauna of the latter part of the period. To some extent our finds from Africa and South America fulfill this prophesy, for the therapsids are much reduced in




variety and thecodonts are found to be advancing toward and to the dinosaur stage. But to our surprise, the middle Triassic shows very distinctive characters of its own in an abundance of two types almost completely confined to this period of time-rhynchosaurs and gomphodonts. The rhynchosaurs (fig. 5) are plant-eating reptiles, gen- erally about the size of a sheep, related to a little living reptile of New Zealand, Sphenodon, but with a powerful parrotlike beak and jaws peculi- arly adapted for cracking some sort of hard plant material (probably the sort of objects that I, in my botanical ignorance, would call nuts or fruit pits). A few primitive members of the group were present in the early Triassic beds, and some specimens are known in beds which may be of relatively late Triassic age, but the rhynchosaurs appear to have had an explosive evolution in the middle Triassic; at Ischigualasto, at Santa Maria in southern Brazil, and in East Africa rhynchosaurs make up a large proportion of all specimens found.

The second common middle Triassic group is that of the gomphodonts (fig. 6). These are therapsids, but therapsids of a peculiar sort. They are members of the cynodont group (of which CYnognathus, mentioned above, is a member), but while the typical cynodonts were predaceous, the gomphodonts have developed a powerful dentition of grinding "molar" teeth, obviously indicating a shift in diet from flesh to some sort of vegetable material (what sort, we do not know). The gomphodonts are, like the rhynchosaurs, exceedingly abundant in both African and South American beds; at a venture, I would say that probably two-

FIG. 5. The skull of a rhynchosaurid a family common in Middle Triassic Gondwanaland deposits.

FIG. 6. Side and palatal view of a traversodont gompho- dont, a type characteristic of Gondwanaland Middle Triassic beds.

thirds to three-quarters of all the specimens from the Middle Triassic of both continents belong to one or the other of these two groups. A few gomphodonts are known in the early Triassic of South Africa; however, nearly all the middle Tri- assic specimens of gomphodonts belong to a group termed traversodonts, with a very distinctive tooth pattern.

What do the rhynchosaurs and gomphodonts in- dicate as regards the Gondwanaland hypothesis? The joker in the pack, of course, is that we know nothing whatever about the land life of that time in the northern continents. In this situation, an advocate of continental stability may argue that there was at that time a widespread distribution of rhynchosaurs and gomphodonts, the world over. As regards the rhynchosaurs, this argument can be reasonably adhered to. The rhynchosaurs of Africa and Brazil are generically distinct, and so, probably, are those from Ischigualasto (they are currently under study). Since these areas, even if the South Atlantic were abolished, cosa er a spread of some thousands of miles, it is quite possible to consider them as inhabitants of a common land mass (the modern reptile faunas of California and the eastern United States show many differ-




ences despite topographic continuity). But the opposite conclusion can be reasonably clung to.

A rather stronger case for southern unity can be made as regards the traversodont gomphodonts. This is a tightly knit group. There are obviously some generic differences between forms at different localities (the Ischigualasto traversodonts are obviously a bit later in time and more advanced than those from other localities). But there are very close resemblances, which may include generic identity, in at least one case, between Chainares and East African types. It is possible that the close similarities between South American and African forms may be due to world-wide distribution of traversodont gomphodonts; but that this little group of close relatives had achieved world- wide distribution with maintenance of essential uniformity is not too probable.

Bonaparte's discovery of early Triassic forms in Argentina is highly interesting; very significant, I believe, are his finds from the Puesto Viejo formation in southern Mendoza Province. Only three forms are known. One is a primitive gom- phodont resembling those known from the early Triassic of South Africa. The other two are Cynognathus and Kannemeyeria, the two best- known African genera. Sr. Bonaparte tells me that he attempted to separate his new finds generically from their African relatives, but was un- able to do so, and several competent workers from North America and Europe have studied his specimens and confirmed his conclusions. That these two genera should be present in two areas twenty thousand miles apart (via northern migration routes) and yet preserve their generic identity is possible, but highly improbable. As in the case of the middle part of the period, early Triassic reptiles are sparse in the northern continents, but there is one significant piece of evidence. As noted earlier, there is one known early Triassic northern fauna, that of China (Young, 1957, etc.). We have here an area about a third of the way from South Africa to South America by way of Siberia and North America. If Cynognathus and Kanne- meyeria had traversed the entire route unchanged, we would expect to find these common types in China, en route. We do not. Relatives of both are present there, but even here their generic char- acter has been modified. Generic identity of

Cynognathus and Kannemeyeria in South America and South Africa affords strong evidence for direct Gondwanaland connections between these now widely separated regions.

To sum up, the vertebrate evidence does not furnish conclusive proof of the one-time existence of Gondwanaland, but it is highly suggestive. When this is added to the long-established lines of evidence obtained from fossil plants and glacial deposits and to those derived from more recent studies in oceanography, paleomagnetism, and petrology, Gondwanaland seems to emerge as a concrete reality rather than a nebulous hypothesis.

REFERENCES CITED

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BONAPARTE, J. F. 1966. "Chronological Survey of the Tetrapod-bearing Triassic of Argentina." BresAora, Mus. Comp. Zool., 251: pp. 1-13. 1967. "New Vertebrate Evidence for African-South

American Connexions During the Lower or Middle Triassic." Paleontology 10: pp. 554-563.

FRITSCH, A. 1879. Fauna der Gaskohle w*-d der Kalk- steinze der Permformation Bohmens (Prague, 1879- 1904, 4 v.).

HUENE, F. VON. 1944. Die fossilen Reptilien des siid- amerikanischen Gondwanalandes (Munich).

KUMMEL, B. 1961. History of the Earth. (San Fran- cisco).

MATTHEW, W. D. 1915. Climate and Evolution. Ann. N.Y. Accad. Sci. 24: pp. 171-318.

ROMER, A. S. 1945. "The Late Carboniferous Verte- brate Fauna of Kounova (Bohemia) Compared with That of the Texas Redbeds." Amer. Jour. Sci. 243: pp. 417-442.

- 1962. "The Fossiliferous Triassic Deposits of Ischi- gualasto, Argentina." Breviora, Mus. Comp. Zool., 156: pp. 1-7. 1966. "The Chaniares (Argentina) Triassic Reptile

Fauna. I. Introduction." Breviora, Mus. Comp. Zool., 247: pp. 1-14.

SEWARD, A. C. 1931. Plant Life Through the Ages (Cambridge, England).

SUESS, E. 1885. Das Antlitz der Erde 1: pp. 767-768. WESTOLL, T. S. 1944. "The Haplolepidae, a New

Family of Late Carboniferous Bony Fishes." Buill. Amer. Alus. Nat. Hist. 83: pp. 1-121.

WOODFORD, A. 0. 1965. Historical Geology (San Fran- cisco).

YOUNG, C. C. 1957. "The Significance of the Lower Triassic Reptilian Fauna from Wuhsiang of Shansi." Sci. Rev., n.s. 1: pp. 265-270.



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