The skull of Pyrotherium sorondoi Ameghino. ⅛ natural size.
[See page 175.]

The Deseado Formation
of Patagonia

Frederic Brewster Loomis, Ph.D.

Professor of Comparative Anatomy
Amherst College

EIGHTH AMHERST EXPEDITION
1911

PUBLISHED UNDER THE AUSPICES OF
THE TRUSTEES OF AMHERST COLLEGE
1914

Copyright, 1914
By Frederic B. Loomis

THE RUMFORD PRESS
CONCORD · N · H ·

CONTENTS

PREFACE

The results of the Amherst Patagonian Expedition were divided into two parts, the general features, together with the narrative, were reported in a separate volume entitled, “Hunting Extinct Animals in the Patagonian Pampas,” published in 1913. For this volume has been reserved the description of the material found and such conclusions as are directly derived from that material. The material on which this work is based has been prepared out and placed on exhibition at Amherst College.

The material here described forms a unified body of data, which adds materially to our knowledge of the complete animals of the Tertiary period in Patagonia. There are beside this some small collections which offer some isolated new facts, but the working up of these has been reserved for the future for small articles, as the work may come to maturity.

The field has only been touched and a vast amount of further work can be profitably done on the horizons immediately preceding and following the one described in this volume, after which an interesting study can be made on the evolution of a fauna which developed in a considerable degree of isolation.

F. B. Loomis.

March 18, 1914.

THE DESEADO FORMATION
OF PATAGONIA

CHAPTER I
Introduction

The material described and the conclusions drawn in the following pages are the results of the Amherst Expedition to Patagonia in 1911; an expedition organized and sent out by the Class of ’96 as a part of their fifteenth reunion. The party consisted of Frederic B. Loomis ’96, Phillip L. Turner ’11, Waldo Shumway ’12, and William Stein of St. Joe, Wyoming, and left Amherst July 1, 1911, returning the first of February the ensuing year, having spent its time collecting in the early Tertiary beds of Patagonia, as exposed in the Territories of Chubut and Santa Cruz, the aim being to secure from the earlier periods a fuller knowledge of the vertebrate animals, such as the Princeton Expeditions obtained for the Patagonian and Santa Cruz formations. The narrative of the expedition has been told in “Hunting Extinct Animals in the Patagonian Pampas.”

Material was found in various beds, from the Cretaceous up to the Lower Miocene; but the major part of the fossils, and most of the facts new to science came from the work in the Deseado Formation. The collections from the horizon were so complete and interesting that this report of the expedition has assumed the form of a monograph of the Deseado Formation, otherwise known as the Pyrotherium beds.

The first work in this formation was done by Carlos Ameghino who at various times between 1889 and 1894 collected for his brother, Florentino Ameghino, the latter studying and describing the collections of Carlos, whose trips covered the country from Chubut down to the Straits of Magellan, and the various formations from the Lower Cretaceous to the Pampean or Pleistocene. Carlos Ameghino and his brother, Florentino, for years explored in Patagonia, going summer after summer at their own expense, and in the meantime maintaining a small book and stationery store in La Plata, the profits of which gave the two brothers a living and furnished the funds for the continual expeditions. In the back of the store was the workshop from which came the continuous stream of knowledge in regard to these strange faunas. One of the best pieces of work done by the brothers was the collecting and describing of the fauna of the Pyrotherium beds the bulk of which is contained in two papers entitled, Première Contribution à la Connaissance de la Fauna mammalogique des Couches à Pyrotherium, and Mammifères Crétacés de L’Argentine, Deuxième Contribution, etc., both published in the Boletin del Instituto Geográfico Argentino, tomes 15 and 18 respectively. These two papers give names to most of the forms which we found, but the genera and species are based on very fragmentary and incomplete material. It has been a pleasure to find the accuracy with which these descriptions were made; and our part has been chiefly to supplement and increase the knowledge of the various forms, and to determine from the more complete material the relationships of these strange forms. In some cases we have been able to assemble all the parts of the animals, and in the others to add more or less to the completion of the knowledge of the forms. There is one peculiarity of Ameghino’s descriptions, namely the absence of data as to the localities where the forms were found.

About 1900 Tournier, in the interests of the Paris Museum, made a series of expeditions (5) to Patagonia, on some of which he found a Pyrotherium, or as he has termed it Deseado, locality just south of the Deseado River, from which he gathered a considerable collection which has been described by Albert Gaudry in various papers mostly in the Annales de Paléontologie.

These two collections and their collaborations represent all the work thus far done on the Deseado beds and fauna. Our collection is the first one of any considerable size to be brought to North America, and it seems to be by far the most complete, the various animals being represented by more complete skeletons than in any of the previous collections.

The beds were first designated as the Pyrotherium beds, and are always so referred to by F. Ameghino. Tournier and Gaudry, feeling the prejudice which is fairly general among Palaeontologists against names based on any contained animal (which may or may not be present at other localities, which may extend through more than one period, and whose name may be changed as a result of further knowledge) used the term Deseado formation, as his collections came from the neighborhood of this river. This is a geographical name and avoids the chance for confusion; so I have adopted it throughout this paper, it being understood as an equivalent of the term Pyrotherium beds.

Ameghino never gave the exact, or anywhere near the exact, localities from which his Deseado specimens came. It was not until 1906, when his Formations Sedimentaires[1] appeared, that any localities were designated, and there on a sketch map he indicates as Deseado exposures, about a dozen points, scattered between the upper part of the Chubut River to some 25 miles south of the Deseado River. These are included in an oval area some 500 miles long by 150 miles wide. Ameghino also suggests on this occasion that the Deseado formation originally extended over at least the whole of this area. As will be seen in the next chapter, I believe that the deposits of this age and character have always been local and isolated. We sought for several of these localities and failed to locate them, especially those near Mazaredo, and the northern one on the Gulf of St. George. The point where we did find our material I believe was one of Ameghino’s localities, though the settlers of that region had never heard of anyone hunting for fossils there; but the settlement had been practically all within the previous six years, which was much later than the time when Carlos Ameghino worked in the region.

Beside the foregoing, an exposure of this age is reported by A. A. Romero, just above the fork of the two branches of the Rio Negro, which is some 500 miles north of the first group of localities mentioned. Ameghino also refers to another locality in the Province of Misiones which would be 1,500 miles north of the typical localities.

The collections made by Tournier for Gaudry came chiefly from an exposure south of the Deseado River, some 15 miles above the mouth of the river.[2]

Our collection came from the Chico Branch of the Chubut River, about three miles east of the river, and almost due west of Puerto Visser. As mentioned above on account of the close coincidence of the various species and because Ameghino indicates a locality in the neighborhood, I think that our locality is the same as one of his, I should judge it the one from which he obtained a considerable part of his types. This is of importance; for, if in Ameghino’s type locality, the determination of the species, as the same as those of Ameghino’s, is much more certain.

In the accompanying map I have indicated the localities given by Ameghino, those of Tournier, and our own.

Fig. 1. Map of Patagonia showing localities of Deseado beds.

CHAPTER II
Age of the Deseado Formation

The locality worked by the Amherst party is situated about three miles east of the Chico River, just across the line of the homestead of D. J. Venter as plotted on the Plano de la Gobernation del Chubut, 1910, by A. Lefrançois. This would be 45° 10ʹ S., and 67° 32ʹ W. (or as on the map 9° 15ʹ W. of the meridian of Buenos Aires). The exposure is on all sides of an elongated hill about a sixth of a mile long, averaging 200 feet wide, and constricted in the middle to a narrow neck. [Figure 2] shows a section of the hill, made along the north side, and indicates the varied character of the stratified deposits.

The material varies from brown sandy clay shales, to yellow sandy clay with concretions, and is capped with a varying layer of greenish sand, which, in some places, is coarse and irregular, in others fine and uniform, and in still other places is mixed with considerable quantities of volcanic ash. In it are many mud balls and also bits of bone which have been worn round, others but slightly worn, and finally bones and skeletons which apparently have been buried where they fell. This green sand is mostly covered with a layer of two feet of hard sandstone of the same composition as the rest of the bed, but cemented into a dense layer. Above the green sand is a layer of fine grey sand, prettily crossbedded, and of varying thickness, but without fossils. Remains of vertebrate animals occurred in the brown clay, the yellow clay and the green sand, and in all the cases fossils were of unusual abundance so that in this limited locality we collected over 300 specimens.

Fig. 2. Section of Deseado exposure showing character
of the various materials.

Above the Deseado (layers 2 to 5) lies the Patagonian in its typical development, filled with Ostrea ingens, Turritellas, Brachiopoda, sharks’ teeth, etc. It is separated from the Deseado by a marked unconformity, one of the finest examples of unconformity I have ever seen. Evidently the upper surface of the Deseado was fairly new at the time of the transgression, or it is much disturbed by the transgression, the upper layers in places being broken up into sort of blocks and the crevices filled with Patagonian sands with the contained shells; just as I saw the beds on the seashore being disturbed by the waves of today. Then too in the basal foot of the Patagonian I found material which without question came from the underlying Deseado beds, various fragments of mammal bones bored by seashells, and with the Patagonian barnacles on them, but these were never more than a few inches up in the Patagonian. The contact was not horizontal, but in the middle of the hill dipped down so that it came there onto the yellow beds of clays, and it was at this point only where we found bones had been washed out by the Patagonian sea.

In the section the Deseado consists of layers 2 to 5, the white sandy clay below belonging to the St. George series and being Cretaceous. The contact below was also an unconformity, clearly marked for the white sandy clays were all horizontally bedded, while the Deseado is crossbedded in every direction, and has a distinct color. These white sandy clays of the St. George series are similar to the same beds as shown in sections A and B (figures [3] and [4]), and extend in all directions for miles. Going down toward the Chico River one passes into the green shales that make up the upper part of the Salamanca and had similar invertebrate fossils. About ten miles to the north was another bed of fossil trees similar to the one to be described on the Puerto Visser side of the pampa.

The character of the material making up the Deseado deposit, its variations in size and material, the presence of worn pebbles and bits of bone, show these layers to be a water deposit. The absence of any marine fossil in a bed otherwise rich in fossils indicated that it was a fresh water formation. The crossbedding, the irregularity of the deposits and the mud balls, prove that it was the work of a river. As there are no aquatic forms in the fauna I further conclude that it was the deposit of a temporary or intermittent stream, such as occur in arid and semiarid countries. The layer could hardly be interpreted as a part of a flood plain; for it is very limited in extent, there being bluffs on three sides of our exposure, but in them no trace of the Deseado was found, nor was I able to pick up the formation again across the Chico River. Then the bedding is very irregular, much more so than is typical of flood plain deposits. The conclusion I reach then is that this Deseado pocket represents the bottom of an ancient stream, which flowed over a land surface made up of the white sandy clays of the St. George age.

The age then of the Deseado beds must be older than the Patagonian, and younger than the white sandy clays of the St. George.

As to the age of the Patagonian two very divergent positions have been taken, which may be best indicated by the following table.

Without going into the history of the various positions which different authors have taken, and which will be found given in detail in Wilckens’ paper, or in less detail in Ortmann’s, we will consider the positions of the most recent students of the question. Ameghino postulates a marine and a continental series of deposits being laid down more or less simultaneously. In the marine series below the Deseado, which is grouped as Guarantic, he places the Luisa, the Roca and the Salamanca, followed by a hiatus, then the Sehuen, which in turn is followed by another hiatus and the end of the Cretaceous is reached. The Patagonian is his Eocene. Parallel to the marine series is the terrestrial, where the Casamayor (= Notostylops) is contemporaneous with the Salamanca, the Deseado with the Sehuen, and the Colpodon, the Notohippus and Astrapothericulus with the Patagonian, thus making the Deseado of Cretaceous age. After a very detailed study of a large series of Patagonian fossils, Ortmann concludes that the Patagonian is of Lower Miocene age. This is the most detailed study which has been made. Wilckens coincides with this view, though feeling that the Patagonian may have extended down a trifle into the last of the Oligocene. This latter author finds a long gap between the Upper Cretaceous and the Patagonian, a period when Patagonia was above water. It was during this interval that the Casamayor, the Deseado and possibly other beds were deposited on the continent. I have gone over Ortmann’s argument, and studied a large collection of Patagonian fossils, both vertebrate and invertebrate, of my own; and while there are some places where we would like further data, I can come to no other conclusion but that these Patagonian beds are Lower Miocene, the exact relationship with beds in North America and Europe, being as yet not definitely settled, nor will this be possible until a study of the migrations of the elements of the Patagonian fauna has been made.

As to the beds underlying the Patagonian, I am sure that a considerable study of the marine series is still requisite to determine the relationships of the beds in different parts of Argentine, and their relative positions as compared with beds in other countries. Ameghino appended to his paper on the Formations Sedimentaires a section of the strata exposed on the coast of Patagonia from Rio Negro to Cape Virgenes, on which from above Punta Atlas south to below Pico Salamanca, the Casamayor (= Notostylops) beds fill the interval from the Salamanca formation up to the Patagonian. On the strength of this map I followed these beds the whole distance looking for vertebrate fossils of Casamayor age. Nowhere did we find a Casamayor fossil. Instead at several points we did find marine fossils. I can not but feel that these beds are plotted as Casamayor, because of their resemblance in color and general texture to the beds carrying the Notostylops fauna at Casamayor.

Of several sections of these beds I pick out two as typical, and also because they are near the locality which we worked for the Deseado fauna. On the map they are indicated as A and B. The former passes through a bed of green sands which is, I think, the locality indicated as his northern locality for the Pyrotherium fauna.

Fig. 3. Section at A on [map page 5], showing
strata from sea level up to the Patagonian.

Fig. 4. Section B on [map, page 5], showing
strata from sea level up to the Patagonian.

From Punta Atlas to Pico Salamanca, Ameghino plots at or just below sea level a bed known as the Salamanca, being typically developed opposite Pico Salamanca. In this in the neighborhood of Pico Salamanca we found the fauna typical of this horizon.

• Ostrea rostigera v. Ih.
• Ostrea riongrensis v. Ih.
• Ostrea ameghinoi v. Ih.
• Chlamys salamanca v. Ih.
• Rostellaria striatissima v. Ih.
• Rostellaria sp.
• Cytherea calcedonica H.
• Discinia sp.
• Diplodon sp.

This Salamanca formation is considered by Wilckens as the equivalent of the Roca as exposed on the Rio Negro, and to the Luisa as exposed on the Rio Coyle. All agree that the Salamanca is Upper Cretaceous and a period when Patagonia was covered by the ocean.

In section B we found the above fauna in layer 1 which is just above sea level here. In layer 2 we found casts of delicate marine shells (30 to 40 in number), representing four or five species and as yet undescribed. They seem to represent a deeper water facies of the Salamanca. In fact all the shales represented by layers 1 to 5 evidently belong to the Salamanca. Layer 5 was distinguished by having in it at a point some 200 yards north of the section line a quantity of turtle shell fragments.

Layer 7, consisting of coarser sandstones, was at the point of the section, simply filled with a vast quantity of fossil wood, most of it agatized, though some was carbonized, and representing some eight species, mostly pines and palms, the latter much scarcer. The tree trunks, hundreds in number, lay scattered in all directions; but all were lying horizontal, and there was no indication of stumps in place; so I consider that the wood was driftwood. It is common in the series of beds of this general horizon along the Gulf of St. George. In the other layers up to the Patagonian we found no fossils. The contact with the Patagonian was unconformable, in some places being 50 feet higher than in others near by.

In section A the typical Salamanca is below sea level, and the lower parts of the section are made up of the white sandy clay shales, so typical all along the Gulf of St. George. In the midst of these clays at the level indicated as 2 occurred a layer of concretions. On breaking these we found two specimens of Nautilus valencienni H., clear evidence that they were of marine origin. Layer 5 was filled with hundreds of the very characteristic oyster, described as Ostrea (Gryphaea) pyrotheriorum. Though in earlier papers suggesting that O. pyrotheriorum represented a horizon of marine sediments corresponding in age to the Deseado (= Pyrotherium) formation, in his Formations Sedimentaires, Ameghino places this fossil in the Salamanca fauna, though it here occurs at least 275 feet above the typical Salamanca fauna. I believe the layer should be distinguished. It is later than the typical Salamanca, though belonging to the same transgression of the sea over Patagonia. In layer 7 we found still another marine fauna consisting of

• Ostrea guarantica H.
• Venericardia sp.
• Corbula sp.
• Aporrhais.
• Patomides.
• Oxyrhinca.
• Milobates.
• Fragments of the limbs of a crab in abundance.

This seems to be the same fauna as that described by Ameghino as the Sehuen developed on the Rio Sehuen.

In layer 8 we found large quantities of gypsum, occurring mostly in balls of radiate structure. Layer 11 was a coarse green sand, and in it we found some fragments of some sort of a bone. I think this layer is what Ameghino designated as a Deseado exposure; and it has the same general appearance and color which is found in the green sands of the Deseado pocket on the Rio Chico. However it is conformable interbedded with the underlying and overlying marine beds and I consider it a part of the marine series. Above it come more white sandy clays that are characteristic of the most of the section.

Wilckens takes all of this series, from the base of the Salamanca, up to the unconformity below the Patagonian, and makes of it his St. George Period, a transgression epoch, lasting to the end of the Upper Cretaceous. I believe it is all marine, and is all a part of the Upper Cretaceous transgression of the sea over Patagonia. However the Salamanca is a clear cut deposit and I feel it should be retained as a distinct horizon. The overlying light colored (white, grey, brown, yellow, or green) sandy clay shales represent a deeper water and later facies, which is characteristically developed on the Gulf of St. George, and may well be distinguished as the St. George epoch or series, but I should use the term only in this more limited way. It is the same series which Ameghino has plotted as the Notostylops beds on his section of the coast of Patagonia. This last it certainly is not.

The unconformity between these white (or light) sandy clays and the Patagonian represents a regression period, during which Patagonia was not only above water, but extended an unknown distance further to the East.

It was during this interval of time between the Upper Cretaceous and the Lower Miocene (Patagonian) that the limited and local land deposits known as Casamayor (= Notostylops), the Astraponotus, and the Deseado (= Pyrotherium) and probably other beds were laid down. In each case the age must be determined for the individual bed by its contents mostly; for as far as I know none of them overlap anywhere.

In regard to the discussion as to whether Dinosaurs were contemporaneous in South America with the fauna of the Deseado, I can only say, we found no trace of a dinosaur or any other Cretaceous animal in the Deseado beds which we worked. As the Cretaceous beds lie as high as the Deseado and are also practically horizontally striated, dinosaur remains might be found on the same level. I think the assigning of any such material to these beds was due to failing to recognize the unconformity under the Deseado beds. As to the Notostylops fauna and dinosaurs being contemporaneous, I only worked the Notostylops beds at Mazaredo, but there I found nothing to indicate the contemporaneousness of these two groups. As I have shown above, Ameghino’s idea of the extent of the Notostylops or Casamayor beds was mostly at fault, and very much of that which he has designated as of Notostylops age is Upper Cretaceous. It is in these Upper Cretaceous beds that dinosaurs do occur and this seems to me to be the basis of the confusion.

This Upper Cretaceous series is a field where considerable work may profitably be done, in straightening out the relationships of the various layers to each other, their extent, and their relationship to the Salamanca and other Upper Cretaceous formations in other parts of Argentine.

As to the age of the Deseado deposit which we worked. It is under the Patagonian, and therefore must be as old as the Oligocene. On the other hand it must be as young as the Eocene, lying as it does above the Upper Cretaceous. Of the three general faunas described it is clearly more advanced than either the Casamayor, or the Astraponotus; so should be put as the youngest of these three. The Colpodon, the Astrapothericulus and the Notohippus, faunas are said to be interstratified with the Patagonian and therefore of the same age. The amount of advancement from the Casamayor to the Deseado is considerable and the relationships of the Deseado are fairly close with the various genera of the Santa Cruz; so that I should put the Deseado as far up as possible toward the Santa Cruz. The Santa Cruz is above the Patagonian, and I think that the Deseado should be put just before the Patagonian; that is in the Oligocene, but just what part of the Oligocene can only be determined when the other faunas have been further studied.

CHAPTER III
The Deseado Fauna

The exposure of the Deseado, which the Amherst party worked, yielded 293 specimens, each presumably representing an individual. (There were besides these a few that were indeterminate and are not therefore included.) The consideration of the fauna as a whole suggests certain ideas as to the country in which the animals lived, and also certain comparisons with the fauna of the preceding and later faunas.

The first striking feature is the presence of so many excessively large animals, as Asmodeus, Parastrapotherium, and Pyrotherium, in each case forms larger than a rhinoceros. Further than that they are in each case the largest members of their family, even larger than the representatives in the later Santa Cruz. This would indicate a period in which living conditions were at a high grade, suggesting both abundance of food and a moderate climate.

The following table will give a good idea as to the range of species, and their relative abundance in the fauna, also a suggestion as to the class of food they used; and from that an idea as to what sort of country they occupied:

In our collection, all from one point, there are thirty-nine different species. Beside these Ameghino has described a considerable number of species, some of which in time will probably turn up at our locality; but others and I think the majority will be found to be representative of other localities which he worked. It is to be expected that a difference of locality will make a little difference in the fauna. Further I expect that no two localities represent exactly the same period of time, though they may do so approximately; but some of these local deposits must have been begun earlier, and others probably lasted to a later period. Thirty-nine species of mammals and land birds is a fairly varied fauna for one spot; and the time element involved in laying down the 50 feet which separated the bottom from the top of the Deseado deposit is not probably very long; for the material of which the deposit is composed is of a character which would have been laid down fairly rapidly.

Of this fauna only 8 per cent belongs to the edentates; and if any element were disproportionately represented it would be this one, for the armadilloes have in addition to the skeleton the hundreds of tiny plates of the carapace, and several of the forms are represented by one or two plates only. When compared with the condition in the Santa Cruz this 8 per cent is strikingly small, for in that later bed, fully 50 per cent of the finds represent edentates. Are the Edentata just originating? Or, was the country less favorable to their habitation? The edentates which we did find are only slightly less advanced in their development than those of the Santa Cruz. Also, though infrequent, all of the families of the Santa Cruz are represented. It would seem therefore that the origin of the edentates was much earlier than the Deseado; and this relative paucity of edentates is also characteristic of the Casamayor and Astraponotus beds; but they are there, and in considerable variety, though small numbers. It would seem then that the country for some reason was less adapted to edentates, and that in some other part of South America they were flourishing and evolving.

In the Deseado the rodents appear for the first time in South America. They are all Hystricomorpha and in a relatively primitive stage of development, but they are typically developed already. Did they migrate in from some other locality, or were they evolved on the spot? Ameghino believed that they were developed from some such form as Promysops or Propolymastodon of the Casamayor, and that these forms were ancestral to rodents all over the world. If my interpretation of the age of these beds is anywhere near correct, this last at least is impossible, for in North America and Europe typical rodents are present in the Eocene. Then as to even the hystricomorphs being developed in Patagonia, I am very skeptical, for the material offered in evidence of this is very insufficient, especially in the region of the incisors; and may be interpreted in other more probable ways. I am confident that either just before the beginning of the Deseado, or at the beginning, the rodents of these beds migrated, either from some other continent, or at least from some other section of South America into this Patagonian region.

Some idea of the type of country and the climate of the Deseado period in Patagonia may be obtained by analyzing the fauna as to the character of its teeth as indicative of the food; and by studying the feet as indicative of the ground on which they were used.

The Typotheria with their chisel-like front teeth, lack of canines, and their permanently growing grinders evidently ate a hard type of vegetation. Deep and permanently growing molars are characteristic of the eaters of grass, a form of vegetation which is especially hard on the grinding teeth, on account of the silica in the stems and leaves. This however would scarcely necessitate the development of permanently growing incisors. They are typical of gnawing animals, eaters of bark, twigs, and possibly also leaves, the wood and bark being also a hard type of vegetation to grind. In the case of these forms I believe they were feeders on grass and bark. Their feet are developed either for running or hopping and would suggest hard ground for their habitat.

The Litopterna are typically plains animals, paralleling in their development the horses. The cropping teeth and the grinding molars become progressively longer. The limbs are progressively elongated, the animals walking more and more on the tips of the toes. With this, the metapodials especially and the other limb bones to a less degree, are progressively lengthened. At the same time the side toes are progressively reduced. The teeth indicate grass eating; the limbs life on the plains.

The Rhynchippidae, while not as advanced as the Litopterna, show cropping front teeth, and the molars developing in depth. The locomotion is semidigitigrade, the feet small, and the number of toes reduced to three. They too must be interpreted as grazing or grazing and browsing animals, living on hard ground.

The Leontinidae are heavier forms, but with much the same features as Rynchippidae, though less specialized. On account of the broad upper molars and the less specialization of the dentition, I should feel that these forms were browsers and lived among bushes, but the feet were three-toed and semidigitigrade and they seem to have walked on hard ground.

The Nesodontidae belong to the same type of adaptation as the foregoing family, but have the grinding teeth more complicated, indicative of a more advanced adaptation to hard vegetation. The feet were also adapted to hard ground.

The Homalodontotheria, the Astrapotheria, and the Pyrotheria were all very large animals, known mostly by their dentition, which is adapted to browse. Whether they lived on soft or hard ground is not known, as the feet are not known in any case but the Homalodontotheridae, where they are five-toed and adapted to soft ground. Such large animals were probably inhabitants of some river bank.

The rodents do not contribute much in the determination as to the type of the country, for they could have lived in the open or in the wooded country, but their relative abundance is rather typical of open country.

The birds are all running birds, and indicative of the country having been an open one.

Of our fauna 11 per cent were flesh or insect eating, and for the purpose of determining the type of country may best be omitted. The rodents could have been either forest or open country forms. Of the remaining 54 per cent, the typotheres, the litopternas, the Rhynchippidae, the Leontinidae, the nesodonts and the birds (46 per cent) were distinctly adapted to live on hard ground; the other 8 per cent being evidently suited to living near a river. All 54 per cent ate either grass or browse. The litopternas are grass eaters; the typotheres were specialized to eat grass or bark; nesodonts, Leontinidae, and Rhynchippidae are grass and browse eaters. Even the Pyrotherium has a pair of gnawing tushes. The picture arising from these considerations is a bush covered prairie, a country not unlike the upland bush pampas of Patagonia today.

There is not an aquatic form (fish or turtle) in the whole list, so it is evident that the stream which deposited these Deseado beds was not abundantly inhabited. To me it looks like so many of the streams in an arid country, dry through a considerable part of the year, and so uninhabited. In the whole list I see nothing to indicate forests or swamps. The arid bush covered plain alone seems to suit the requirements.

As I see this fauna it is composed of several distinct elements, representing different invasions and an element which arose in situ. The reasons for the affinities expressed in the different groups will be found in the introductory paragraphs of the systematic discussion of each group.

The Notungulata, including the Typotheria, the Toxodontia, the Litopterna, the Homalodontotheria, and the Astrapotheria are a group with apparently a common ancestry. In Patagonia they have specialized into the various subdivisions as we find them in the Deseado. This group was in Patagonia as early or earlier than the Casamayor. Their relationships appear to me to be with the Hyracoidea which are generally credited with originating in Africa.

The Pyrotheria are related to the early elephants which also arose in Africa, but it seems to me that this form came to Patagonia at least at a later period, making its first appearance in the upper part of the Astraponotus period. Ultimately the elephants and Hyracoidea had a common origin in Africa.

The Rodentia are all hystricomorphs and appear in South America for the first time in the Deseado. They also occur in the Oligocene of Europe and the Fayum of north Africa. They never reached North America so must have come to South America by some southern route.

The Edentata are an element of the Casamayor fauna and as there is no evidence of their originating anywhere else it would seem that they were indigenous to South America, where they later flourished and developed the greatest variety and profusion of numbers.

The group of marsupials is an element the origin of which presents a most difficult problem. Some belong to the opossum series which could well have been developed from some remnant of the Mesozoic marsupial fauna that had a world wide distribution; but the presence of diprotodonts, which are characteristic of Australia, and of the Borhyaenidae which are closely related to the Thylacinidae of Australia, suggests a migration from that continent as late as Tertiary times; but to my mind this involves a connection which is most too difficult to postulate. There is no evidence that they came to South America in company with other faunas, for they have not been found associated with any other fauna outside of Southern Patagonia. The explanation of the affinities of the Patagonian marsupials with the Australian marsupials is a problem which is not yet in position to be settled.

The birds probably came from Africa with the invasion of the ancestors of the Notungulates.

The idea of an invasion from Africa in Upper Cretaceous times, and possibly another at a later time is correlated with the other evidence of a land bridge between these two continents, as deduced by students of other groups.

• Eigenmann, working on the freshwater fishes,[6]
• Lydekker, studying the hystricomorphs,[7]
• Von Ihering, studying the freshwater mussels,[8]
• Ortmann, studying the freshwater crabs,[9]

not to mention several others studying mullocks, insects, plants, etc., have all postulated a land connection from Brazil to northern Africa during Cretaceous time to explain the distribution of their various groups. The divergence is in the time when this land bridge sank, some believing it to have lasted into Tertiary times, most feeling that it sank in Upper Cretaceous times. Another body of evidence is presented to show that a land bridge connected the West Indies with the Mediterranean regions.[10] There was presumably but one such transatlantic connection. Its position further to the south would seem to me to explain the distributional facts found in the West Indies, but the striking resemblances between the faunas of Africa and South America require a connection from the South Upper American Continent and Africa.

It was along this land bridge which the ancestors of the Notungulata traveled, and when in South America, due to their isolation, developed all the peculiarities of the group. This must have been not later than the latter part of the Cretaceous.

Either this bridge remained until into the early Tertiary; so the Pyrotheria and Hystricomorpha made their migration later, or these two groups did not reach the isolated Patagonian section until later than the first invasion. I am inclined to believe in the migration being at a later period. This bridge does not explain the presence of the edentates, for which there is every reason to believe that they developed in situ. The Marsupial invasion must have been from some other direction, or their presence in Africa has not yet been discovered.

CHAPTER IV
Ungulata

The systematic arrangement of the South American ungulates is of such a nature that scarcely two students of these forms have agreed. I feel that the Pyrotheridae are proboscideans as did Ameghino, but there my agreement ends. The other varied groups I believe have a common ancestry, their great divergencies being due to adaptations to the greatly varied characters of the country they occupied. In spite of the great variation they have certain features in common so that I agree with those who have developed the term Notungulata to include them all.

From what source they originally came is not clear, but it seems to me that these notungulates have more in common with what we know of the African fauna of the Fayum than with any other fauna; so that my feeling would be that these two faunas had a common ancestry at least, and possibly the South American ungulates are derived from the African. The lophiodont upper dentition, the bicrescentric lower molars with a “pillar” in the posterior crescent, the development of the tympanic bulla with the extension of the inflated cavity up into the squamosal bone, the development of the post-tympanic portion of the squamosum, and the general arrangement of the basicranial foramena indicate in my mind that these notungulates have all risen from the same stock, and that that stock had much in common with the hyracoids.

I should therefore arrange the various groups as follows.[11]

NOTUNGULATA

Order I. Upper molars composed of an external longitudinal crest and two transverse crests, the posterior the less developed; lower molars composed of two joining crescents with a “pillar” in the posterior crescent; structure of the feet and limbs varying.

Suborder 1. Litopterna: teeth brachydont to hypsodont; lower molars with the anterior and posterior crescents subequal; squamoso-periotic region not inflated; limbs elongated; pes unguligrade; digits 3-3 or 1-1.

Suborder 2. Typotheria: teeth hypsodont lower molars with the anterior crescent shorter than the posterior; squamoso-periotic region inflated; limbs elongated in varying degrees; pes plantigrade to semi-plantigrade; digits 5-4 or 4-4.

Suborder 3. Toxodontia: teeth brachydont to hypsodont; lower molars with the anterior crescent shorter than the posterior; squamoso-periotic region inflated; limbs short; pes semidigitigrade to digitigrade; digits 3-3.

Suborder 4. Homalodontotheria: teeth brachydont; lower molars similar to those of Toxodontia; limbs moderately elongate; pes semidigitigrade; digits with large curved claws, 5-5.

Suborder 5. Astrapotheria: teeth brachydont to moderately hypsodont; canines enlarged into tushes; molars similar to those of Toxodontia; limbs greatly elongated; feet unknown.

PROBOSCIDEA

Order II. ([see page 68])

Suborder 1. Pyrotheria: incisors developed into tushes; molars bilophodont; limbs short, especially the lower element; feet digitigrade.

LITOPTERNA

This order of South American ungulates is less abundantly represented in the Deseado formation than in the Santa Cruz, but most of the genera of this latter formation have representatives in the Deseado so that they seem to have diverged still earlier.

By Scott the order is divided into two families, the Proterotheriidae and the Macrauchenidae, the less known Adiantidae being placed under the latter family until better known. I feel that I should prefer to retain the Adiantidae for the present, until they can be shown to be subordinate to another family, so that in this paper the three families are retained. The striking features of the two larger families may be best brought out by a comparison of their chief features as follows.

Proterotheriidae Ameghino

In the Deseado, this family is scantily represented as compared with the rich fauna, both as to species and numbers of individuals in the Santa Cruz, but of the four chief genera of the Santa Cruz, three have been found, though the remains are very fragmentary. They are the genera Eoprototherium, belonging to the Prototherium series, Deuterotherium belonging to the Thaotheriumseries, and Notodiaphorus representing the Diadiaphorus series.

The following table will give what is known in comparing the two series.

Eoproterotherium Ameghino

Eoproterotherium Amegh., 1904, Anal. Mus. Nac. B. A., ser. 3, t. 3, p. 441.

The genus is founded on single teeth of the upper molar series, which, except for size, are very like those of Proterotherium. Limbs, etc., are unknown, so that this genus is simply a carrying back of the Proterotherium line into the Deseado. We found no teeth of this form, but one species has been described, E. inaequifacies, of which I reproduce [Ameghino’s figure] compared with Proterotherium, which shows this species to have the metaconule better developed.

Fig. 5. A, Eoproterotherium inaequifacies, third upper molar—natural size; C, Protherotherium karaikense, third upper molar—natural size, after Ameghino.

Notodiaphorus gen. nov.

The basis of this genus is particularly a hind limb found associated which is much less developed than the Santa Cruz genus Diadiaphorus to which it is most nearly related. These two genera are unique in having the ectal facet on the astragulus developed in two planes so that it appears as a deep notch. In the case of the new genus the toes are almost equal in size, giving us a stage in the development of this three-toed form which is much more primitive than the well-known Santa Cruz genus.

Notodiaphorus crassus sp. nov.

Fig. 6. Distal end of right
humerus—½ natural size.

The specimen selected as type is number 3287 of the Amherst Collection, consisting of a complete pes, tarsus, lower end of the tibia, and the femur, from the Deseado on the Chico del Chubut River, west of Puerto Visser. Beside this, there are seven other specimens, mostly parts of hind limbs, but others having also the lower end of the humerus, the radius and ulna, metacarpals, and some phalanges. The species is distinguished by its large size, being larger than the species of the Santa Cruz, and, at the same time, the three toes of both the pes and the manus are subequal in size.

The distal end of the humerus associated indirectly with this species is moderately heavy, with fair-sized epicondyles, and no entepicondylar foramen. The supratrochlear fossa is moderately deep, the anconeal very deep, the two being connected by a small foramen, as is typical for this family. The trochlearis, slightly oblique to the long axis of the shaft, has a simple pulley-like articular end without ridges of division, the internal border being narrower and higher than the external.

Fig. 7. Right radius and ulna, distal end of ulna
from specimen No. 3275—½ natural size.

Fig. 8. Left femur posterior side—½ natural size.

The radius and ulna were from another specimen which, however, was associated with a typical astragulus. The two bones are long, slender, strongly curved, and in contact with each other throughout their entire length, so that there could have been no rotary movement of the forearm. The radius is a slender bone with the proximal articular facet relatively small, the facet being slightly concave, of ovoid outline and with the transverse diameter the greater. There is but a tiny band-like facet for the ulna situated on the posterior side near the inner margin. Distally, the radius widens into a heavy end with a rugose area on the outer side for contact with the ulna, and with two distal facets, a larger for the scaphoid, and a smaller for the lunar, the two being separated by a low ridge.

The ulna is heavier above, with a strong backwardly directed olecranon process. The sigmoid notch makes almost a semicircle, the articular surface being broad and extending well onto either side of the bone. The facets for the radius are tiny. The distal end of this bone is wanting.

Fig. 9. Distal end of
left tibia—½
natural size.

The femur belongs to the type specimen which is about 5% larger than the other specimens. This bone is long and rather slender, with the greater trochanter rising well above the head, which is rounded, on a short neck, and has the ligamentary pit on the posterior margin. The thick, rugose, greater trochanter bends in over the head at its upper end. The lesser trochanter is relatively small, and prolonged into a ridge. Unfortunately the third trochanter is broken off in my specimen. The digital fossa is extremely large and deep. Proximally the shaft is flattened, but becomes rounded distally. Just above the condyles there is a deep rugose pit for the plantaris muscle, and on the anterior side the suprapatellar fossa is well marked. The condyles are placed a trifle obliquely; the internal one being shorter and with a rounded articular face, the external condyle being longer, and with a flattened articular face which slopes obliquely inward.

Of the tibia, only the distal end is preserved. This indicates a rather slender bone, with a shallow, fairly wide concavity for the external astragular trochlea, and a narrower and deeper concavity for the internal astragular trochlea. On the internal side of the tibia there is a rugose surface for the fibula.

An isolated lower end of a fibula indicates a slender bone, enlarged distally where it comes in contact with the tibia. The fibula carries on its inner face a moderately large facet for the external side of the astragulus, and on the distal end a wider one for contact with the calcaneum.

The tarsus is compactly built, wider than that of Diadiaphorus, because the external digits are not as much reduced. This especially shows in the greater development of the cuboid and the mesocuneiform, but in other features it is similar to that of its descendant.

Fig. 10. Left pes, dorsal side, ungual phalanx
from specimen No. 3275—½ natural size.

The astragulus is a very characteristic bone. The trochlea is asymetrical, the external condyle rising higher than the internal, and the median groove being wide and shallow. On the nearly vertical outer face of the astragulus, there is a semicircular band-like facet for the fibula. The trochlea extends well around the top of the bone, allowing a wide movement of the foot. The neck of the astragulus is long and wide, carrying a broad flattened head, with its convex facet for the navicular, covering the entire end. On the plantar side are the most marked features. The ectal facet is in two planes, the anterior portion being bent down to nearly right angles with the posterior, which seems to be characteristic of this Diadiaphorus series. The sustentacular facet also is characteristic, being gently rounded and extending clear to the navicular facet on the head, in Diadiaphorus becoming actually confluent with the navicular facet. Just at the edge of this sustentacular facet is a tiny surface where the astragulus rubs on the cuboid, the only case, as far as I am aware, where this occurs in any Litopterna.

Fig. 11. Left astragulus
plantar side:
a, ectal facet—½ natural size;
b, sustentacular facet;
c, facet for cuboid.

The calcaneum is long and slender, the tuber being but slightly enlarged, its sustentacular facet being a broad oval surface, while the ectal facet is in two planes to correspond to that on the astragulus. The facet for the cuboid is at the distal end, but is unusually oblique, its inner margin sloping up almost to the sustentacular facet. It is this slope which brings the cuboid in contact with the astragulus.

The navicular is broad and low, with a prominent hook behind. On its upper face there is only the broad facet for the astragulus head; on the lower face are three facets, externally, a large, more or less triangular area, for the ectocuneiform; medianly a smaller similar facet for the mesocuneiform; and on the internal side, sloping up onto the internal face, a small facet for the reduced endocuneiform. On the external face of this bone there is a tiny beveled facet for the cuboid.

The endocuneiform is a large scale-like ossicle articulating on the lateral internal face of the navicular, and overlapping markedly the inner surface of Metatarsus II.

The mesocuneiform is considerably reduced in size, carrying a broad flat facet on the upper surface for the navicular, and a shallow saddle-like one below for Mt. II, which is entirely carried by this bone.

The ectocuneiform is considerably larger than the mesocuneiform, resting above on the navicular, and carrying below the whole of Mt. III. On its inner side are two facets which rub against the upper end of Mt. II.

The cuboid is a nodular bone, its upper surface occupied by the facet for the calcaneum, the lower face occupied by the facet for Mt. IV, while on the external side there is a tiny beveled facet for the vestige of Mt. V, and with a small boss on the inner surface which carries two tiny facets, the upper one for the ectocuneiform and the lower for the navicular. On this same inner side, near the top there is a second small boss, which carries a tiny facet to rub on the astragulus, and below that a second tiny facet for the navicular.

Fig. 12. Cuboid internal side
to show:
a, facet for astragulus;
b, upper facet for navicular;
c, facet for calcaveum;
d, lower facet for navicular;
e, facet for mesocunieforms
—½ natural size.

The pes consists of three digits, with a vestige of Mt. V. Of the developed digits, the median one is the largest, but the two lateral digits are only a little smaller and were functional, so that this form was truly three-toed, comparable in the digital reduction to Mesohippus.

Mt. II is flattened above but soon broadens into a rounded shaft of considerable length, on the end of which is the articular trochlea, with the carina extending onto both the upper and lower surface, being, however, higher on the lower surface. Proximally this bone is overlapped by the endocuneiform, is carried by the small mesocuneiform, and also articulates on the inner side of the ectocuneiform. Mt. III is also compressed at the upper end, broadens below, and carries an articular trochlea similar to that of Mt. II, except that the carina does not extend so far onto the upper surface. Like Mt. II, Mt. IV is carried high on the tarsus, and therefore, though nearly as long as Mt. III, it does not have the same effective length. Proximally it articulates entirely on the cuboid; distally it has a trochlea similar to that of Mt. II, the carina extending onto the dorsal surface. While Mt. V is lacking, it is clearly indicated that a vestige of it should have been present, as there is a tiny articular surface for it on the cuboid, and a rugose surface on the outside of Mt. IV.

The phalanges are long and have the articular ends swollen somewhat as in camels. The phalanges of the first row are nearly equal in size, each with the proximal trochlea deeply notched for the carina of the metatarsus; and with the distal trochlea simple, though slightly concave from side to side, and reflexed well onto the dorsal surface. The phalanges of the second row are shorter and simpler, and somewhat depressed distally. The ungual phalanges are flattened from top to bottom, of moderate size, somewhat longer than wide, and without any indications of a cleft.

Deuterotherium Ameghino

Deuterotherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 633.

Deuterotherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 452.

This genus was first founded on a clacaneum and a bit of the mandibular symphysis, to which were added, later, both the upper and lower premolar and molar teeth. As far as it is known, it is distinguished by the upper molars lacking the metaconule entirely, and being approximately like those of Thaotherium. The dental formula is given by Ameghino as

• 1 0 4 3
• ———,
• 2 0 4 3

the same as Thaotherium. But one species has been described.

Deuterotherium distichum Ameghino

We did not find this species, but the teeth assigned to it are very characteristic, and so I reproduce Ameghino’s figure of them. The species is distinguished by its size primarily. The following are the chief measurements given.

Fig. 13. Upper pm. 3-m. 3 of the left side—natural size, after Ameghino.

Upper dentition, pm. 3 to m. 3, length 50 mm.
Lower dentition, inc. 1 to m. 3, length 80 mm.

Macrauchenidae
(= Mesorhinidae Amegh.)

This family is distinguished, first, by the complete dental series in which none of the anterior teeth are developed into tushes; by the nasals being shortened, apparently in connection with the development of a proboscis; by its long neck; and by its feet being permanently tridactyl, all the three toes being equally developed. In the Deseado it is infrequent, but to it Ameghino has assigned two genera; Protheosodon, which he describes as similar to Theosodon, but which I find much nearer to the Casamayor representatives of this family, such as Lambdaconus, though it doubtless belongs to the series which is represented in the Santa Cruz by Theosodon. He has also made a second genus, Conioptotherium, which represents a large Macrauchenid, equal in size to Theosodon. This genus is based on the calcaleum and astragulus and seems to be rare.

Protheosodon Ameghino

Protheosodon, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 453.
Protheosodon, Amegh., 1904, Anal. Mus. Nac. B.A., ser. 3, t. 3, p. 421.

This genus was founded on an upper second molar and the fourth premolar. I figure m. 2, and it will be seen that they represent a form little specialized, resembling in the low crowns, plump cusps, and presence of both protoconule and metaconule, the Casamayor types, such as Lambdaconus or Didolodus, rather than the advanced type like the Santa Cruz genus, Theosodon. We found a specimen with the lower jaws complete and with the hind limb complete, which, I am confident, is the same form, though I can not duplicate any tooth, for we found no upper teeth; but in size they agree with Protheosodon, also in the primitive character; and, were one from the lower teeth to postulate the upper, they would be just such as Ameghino has described under the name Protheosodon. Therefore I have assigned my material to this genus and species. It adds to the genus characters the fact that this form had a shorter back, relatively as well as actually, than Theosodon; that the hind limb, at least, was much heavier and also shorter than that of Theosodon, especially in the metatarsal region where relatively the elements are only about half as long. The pes is of the same character as in Theosodon, but again relatively much shorter. I believe in Protheosodon we have to do with a form intermediate between Lambdaconus and Theosodon, and nearer to the former.

Protheosodon coniferus Ameghino

P. coniferus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 453.

Ameghino has described two upper teeth. Specimen No. 3001 of the Amherst Collection from the Chico del Chubut River, west of Puerto Visser, adds to this the knowledge of twelve vertebrae (seven dorsal and five lumbar), the lower dentition complete, the left hind limb complete, and the right hind limb complete except for the femur. In general, the animal is about ⅗ the size of Theosodon garrettorum, but in parts varies from this as follows. The lower jaw is ⅗, the vertebrae are ⅖ in length, the hind leg is ⅗ in length but ¾ in diameter of bones, while the metatarsus is only ⅓ in length. This makes an almost plantigrade form of heavy, clumsy proportions.

Fig. 14. Upper molar. 2 of
the right side—natural
size, after Ameghino.

Of the upper dentition we know only what Ameghino has given us. The molar is distinguished by the presence of both the protoconule and metaconule, by the development of the posterior cingulum and by the presence of three external styles.

Measurements

Upper premolar 4, length 12 mm., width 15 mm.
Upper molar 2, length 14 mm., width 17 mm.

Fig. 15. Right lower dentition—natural size.

In the lower dentition, none of the teeth are reduced, and all are in a continuous series, except that there is a small diastema either side of pm. 1. The incisors are simple, compressed teeth, with but a trace of a cingulum. The canine is incisiform and a trifle larger than the incisors. Premolar 1 is also incisiform, and is isolated by a small diastema on either side. The second premolar is longer and wider than the first, and begins to show molariform characters, the anterior portion being composed of a high compressed cusp, the posterior portion by a low crescent on which but one cusp is fully developed. The third premolar is composed of two complete crescents, and has the “pillar” already developed opposite the posterior end of the back crescent. In fact, the tooth is molariform, except as to the tiny extra cusp found on the molars. Premolar 4 is more completely molariform consisting of the same parts as the preceding tooth.

The molars may be distinguished by the presence of a tiny median cusp on the rear of the tooth, behind the crescent, which, when the tooth is worn, makes a median spur to the rear. In both the premolars and molars, the teeth are characterized by their plumpness, and the isolation and lowness of the cusps.

Fig. 16. Right mandible—½ natural size.

The two halves of the lower jaw are completely fused at the symphysis. The horizontal ramus is thick, but low dorso-ventrally, giving the appearance of a slender jaw. The posterior angle is prolonged backward and bent inward. The fossa for the masseter muscle, while large, is but faintly outlined. The ascending ramus hardly rises above the level of the teeth, except as the slender coronoid projects to a good height above the articular condyle and curves backward over it.

The dorsal vertebrae have short, wide, and somewhat depressed centra (in this individual the epiphyses are free, though this is the only indication of youth). The lower rib facets are small, that on the posterior margin of the centrum being a mere streak, while the one on the anterior margin is narrow. The upper rib facet is a rounded convex surface on the end of a short stout transverse process. The prezygapophyses are convex surfaces, wide transversely, but narrow in the antero-posterior direction, while the postzygapophyses are correspondingly narrow concave facets under the rear of the spines. The spines are thin and high, and the neural canal is nearly circular in section.

The lumbar vertebrae have laterally compressed, deep centra, with very long transverse processes, shorting spines, and zygapophyses of the subcylindrical interlocking type. In all their features the vertebrae resemble those of Theosodon, being nearly as highly specialized and in the same manner.

The femur is short and very stocky. The rounded head is carried on a short neck, and does not rise nearly as high as the greater trochanter, the sulcus for the round ligament being a broad, deep notch on the posterior margin. The greater trochanter is rugose, heavy, and high, but not incurved at the top. The lesser trochanter is a small, thin ridge well below the head. The third trochanter is a large, thin process, projecting almost directly backward, though curved inward at the end, and is situated well below the middle of the bone. The shaft of the femur is flattened above, but thick, and changes in the lower part to subcylindrical. The condyles are small, subequal in size, and widely separated, while the rotular trochlea is relatively wide and shallow.

Fig. 17. Left femur anterior side—½ natural size.

Fig. 18. Tibia and fibula (right)—½ natural size.

The tibia is about three-fourths the length of the femur, very stocky and heavily built. On the proximal end, the convex external condyle is much narrower antero-posteriorly than the larger and slightly concave internal condyle. The low spine is bifid. A cnemidial crest extends to the middle of the bone. On the distal end, the broad and shallow external articular facet is separated from the narrow and deeper internal facet by a low intercondylar ridge. The fibula is fused to the tibia at the upper end, but is free below, being approximated to the tibia along a rugose surface nearly an inch long. This bone is rather slender and strongly bowed outward. Distally, there is a large facet for the outside of the astragulus, the back part of which rests on the calcaneum. This is peculiarly developed so that the articulation represents what is two separate facets, the one for the outside of the astragulus the other for the calcaneum. Here, however, they are blended.

Fig. 19. Right foot, the phalanges in outline
from the left foot—½ natural size.

Fig. 20. Astragulus
plantar side—
a, external facet;
b, sustentacular facet—
½ natural size.

While in general the tarsus is similar to that of Theosodon, there are some marked contrasts. The astragulus has an asymetrical trochlea with a shallow groove, the external condyle being higher and narrower than the internal. The head is depressed in the dorso-plantar plane, is carried on a moderately long neck, and has a broad convex facet for the navicular on which alone it articulates. On the plantar side, the ectal facet is broadly oval and slightly concave, differing from that of Theosodon in having no sulcus dividing it into lobes. The broad sustentacular facet is slightly convex, and widely separated from the ectal. On the external side the astragulus carries an expanded articular facet for the inner side of the fibula, which, instead of being vertical, is expanded below, making an oblique face which is continuous with the fibular facet on the calcaneum. In this feature Protheosodon is, as far as the feet are known, unique.

The calcaneum is a long bone with a club-shaped expansion of the upper end. The fibular facet is small, being continuous, as above described, with that on the outer side of the astragulus. On the face toward the astragulus, the ectal facet is broadly convex (not divided as in Theosodon), while the sustentacular facet is slightly concave. The distal end is occupied by the large concave facet for the cuboid.

The navicular is of moderate height, with a prominent hook behind. On the upper surface is only the broad, deep facet for the astragulus; while the lower surface is divided into facets for the three cuneiforms, and the external distal margin is beveled to make a narrow facet for the cuboid. This navicular differs from that of Theosodon in that the facet for the ectocuneiform is not cut step-like into its external face.

The endocuneiform is a small scale-like bone with a narrow facet on the navicular, and overlapping the inner side of Mt. II. The mesocuneiform is small, with a flat facet above for the navicular, and a convex one below for Mt. II, which is carried wholly on this bone. The ectocuneiform is far the largest of these three bones, and carries a broad facet above for the navicular, a similar one below for Mt. III, a small facet on the internal side for the mesocuneiform and a second one below that for the side of Mt. II, while externally there are facets for the cuboid and for the side of Mt. IV.

The cuboid is large, the external side being longer than the internal. The upper surface is entirely occupied by the facet for the calcaneum, while the lower face is mostly devoted to the facet for Mt. IV, with a narrow streak on the external margin for the vestige of Mt. V. The internal face carries a boss beveled above by the facet for the navicular, and below by the facet for the ectocuneiform.

All the metatarsals are short and heavy as compared with those of Theosodon. Mt. II is compressed above, but enlarges below into a subcylindrical bone, ending in an extensive articular trochlea for the phalanx, the trochlea carrying a carina which extends into the upper surface of the articular area. Proximally, it is so closely approximated to the adjacent metatarsus that these could have had very little independent movement. On the upper internal surface, there is a roughened area, where the endocuneiform overlaps this bone. Mt. III is slightly heavier than the others. On the distal end, its articular trochlea extends well onto the dorsal surface, as does also the carina. Mt. IV is a trifle shorter than the others and stouter. Mt. V is absent but its former presence is indicated by the beveled facet on the cuboid, and by the small roughened surface on Mt. IV.

The phalanges of the third digit are a trifle heavier than those of the other two digits, but of approximately the same lengths. The ungual phalanges were broad compressed hoofs, without traces of clefts.

Fig. 21. (Half tone.) Restoration of Protheosodon coniferus
to show the relatively short limbs, and heavy build as
compared with Theosodon—⅕ natural size.

Restoration

In order to get a comparison of what is known of this form with Theosodon I have outlined a restoration of the animal as a whole, realizing that some essential parts are lacking, but the general proportions can hardly vary greatly from those given. It appears, first, that this form has an unusually short back. Though the limbs and lower jaw are ⅗ the length of those of Theosodon garrettorum, the vertebrae are ½ as long. I have assumed that the number of vertebrae would prove to be the same as in Theosodon. While the limb bones are ⅗ as long as in the Theosodon, they are relatively half again as heavy and with the processes much more developed. The greatest difference is found in the tarsus which is only ⅓ as long as that of Theosodon, though relatively as heavy, and the foot was carried in a nearly plantigrade position the heel raised but a little from the ground, though the anticular ends of the metatarsals and the phalanges indicate that there was a considerable freedom of movement of the various elements. The form seems to be fairly close to the ancestral types such as Lambdaconus of the Casamayor, the limbs of which, however, are entirely unknown, but I should expect that when found these earlier forms would prove to be approximately plantigrade.

Coniopternium Ameghino

Coniopternium Amegh., 1895 Bol. Inst. Geog. Argen., t. 15, p. 632.
Coniopternium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 453.

The genus is based on a calcaneum and astragulus of the macrauchenid type, but of unusually large size. The real generic characters are not evident in the description, but the presence of these bones, and of three cervical vertebrae, which we also found, indicating a macrauchenid of about the same size, are evidence that a form larger than the Santa Cruz representatives will turn up in the Deseado beds, for which this name may be reserved. The material is described under the specific name C. andinum.

Adianthidae Ameghino

This family is based primarily on the genus Adianthus of the Santa Cruz to contain some macrauchenid-like forms which, however, are of much smaller size, and differentiated by the narrow character of the teeth and their early tendency to hypsodonty. It seems to be a valid series of dwarf types, which are all scarce and known only by the most fragmentary remains. Two genera are described from the Deseado, Tricoelodus, peculiar in having the posterior lobe of the lower molars somewhat subdivided so that the tooth appears three-lobed; and Proadianthus, known only by premolars which however show an unusual development of the styles on the inner side of the teeth.

Tricoelodus Ameghino

Tricoelodus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 454.

The genus is based primarily on the three-lobed character of the molars, which is a secondary effect of an infolding on the inner side of the posterior lobe. They are rooted, but strongly hypsodont. The margins of the crescents are well developed and the “pillar” is a prominent feature in the posterior crescent.

Tricoelodus bicuspidatus Ameghino

T. tricuspidatus Amegh., loc. cit. above.

Fig. 22. Lower right pm. 3-m.
1—natural size,
after Ameghino.

The species is the only one known of the genus, and its features are those of the genus. The following measurements indicate the size, lower pm. 3 to m. 1, 25 mm.; height of the mandible under molar 1 is 12 mm.

Proadianthus Ameghino

Proadianthus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 455.

This genus is known only by the last two premolars of the lower jaw, which are compressed and moderately high. The two crescents are markedly separated by a cleft from the external side of the tooth, opposite to which is a high denticle, made by the fusion of the two ends of the crescents where they come together.

Proadianthus excavatus Ameghino

Fig. 23. Lower right
pm. 3 and 4—
natural size,
after Ameghino.

P. excavatus Amegh., loc. cit. above.

The species is based on the two lower premolars described above. I reproduce the figure given by Ameghino. The measurements are: length of pm. 3 and 4, 10 mm.; height of mandible under pm. 4, 8 mm.

CHAPTER V
Typotheria

In the Deseado beds this group of running and hopping animals is well represented, making about 14% of the Amherst collection, and varying in size from a little larger than a rat to larger than a sheep.

The group all have the front teeth modified into cropping or gnawing types, which grow permanently from persistent pulps; and the back teeth also growing through the whole or a large part of life, and also rootless, the crowns being variously infolded to make grinding surfaces. The skull is flattened above, and abruptly truncated behind; the cranium being large and swollen, the facial portion broad above and excavated on the sides. The orbits are centrally located, of considerable size, and unbounded behind. The tympanic bulla is swollen and may be hollow or filled with cancellous tissue. This cavity of the tympanic is continued above and expands in the upper part of the squamosum, making a swollen capsule on either side of the back of the cranium. The openings of the auditory meatus are well back and in a tubular growth of the periotic which is directed back, and upward in an entirely characteristic manner. The strong paroccipital processes project far below the base of the carnium. The concave palate is wide and carried well back behind the teeth ending in two strong pterygoid processes. The mandible is deep, especially the back portion; has a slender coronoid process, and a small rounded articular condyle which would seem to indicate a forward and backward motion of the jaws. On account of the agreement with these general features, I have placed among the Typotheria the forms which Ameghino classified as Hyracoidea.

While agreeing in the above general features, there is great variation among the various forms. The first upper and lower incisor may be greatly enlarged or of normal size. There is a tendency for the third upper and lower incisor, the canines, and the first premolars to be reduced and disappear, and all intermediate grades are found. In the molars there is a regular tendency toward simplification; so that in the upper molars of the earlier forms there is a deep inner fold and a more moderate outer fold, either or both of which may disappear completely, though in one series the fold seems to have been accentuated instead of lost. The feet may be adapted to running or hopping.

In the Deseado and Santa Cruz material, four series of modifications may be distinguished which I have designated as families; (1) the Archaeohyracidae, primitive forms in which the incisors are little enlarged, with inner and outer folds on the molars, those on the inner side of the upper molars being very deep, bulla small, feet unknown; (2) Interatheriidae, first upper and lower incisors rooted and of moderate size, inflexions on both the inner and outer sides of the molars, bulla large, feet adapted to running; (3) Hegetotheriidae, incisor 1 of upper and lower dentition greatly enlarged and rootless, molars simplified, bulla large, feet adapted to running or to hopping; (4) Eutrachytheridae, large forms with the first upper and lower incisor enlarged and rootless, the upper molars with the inner fold developed and bifurcated, bulla large, feet unknown.

For comparison of the various genera, they are charted [on page 55], the dental character being used, as but few have the skeleton known, which is especially so of the earlier genera.

CHART OF TYPOTHERIA

From the foregoing chart and the comparative figures of the upper and lower dentitions, the variety and at the same time the homogeneity of the Typotheria is evident. The gnawing front teeth resemble those of rodents, especially in the genera where the enamel is lacking on all but the front face, but this is entirely a parallelism and there is no evident phylogenetic relationship. As to affinities with the Hyracoidea, Sinclair[12] has carefully balanced them and finds so little in common between the two groups that he makes them a separate suborder. I find certain features in common, like the lophiodont dentition with the tendency toward hypsodont incisors, the inflation of the tympanic and the extension of this up into the periotic region, and the general arrangement of the basicranial foramena. On the other hand, there are also numerous features in common with the Toxodonts, and several peculiar to the group, so that I would feel that all the Notungulates are descended from the Hyracoidea, and this group has developed its peculiarities in South America, retaining however a little more of the hyracoid aspect.

Fig. 24. Comparative series of upper dentitions
of Deseado and Santa Cruz Typotheria;

Fig. 25. Comparative series of lower dentitions
of Deseado and Santa Cruz Typotheria;

The Archaeohyracidae are the most primitive of the Deseado forms, but as all the families are already separated before this time the Deseado genera can not be considered as the ancestral ones, though they seem to have retained more of the primitive features.

The Interatheriidae represent an offshoot line of development in which the incisors are not much enlarged and the infoldings of the teeth remain. The genus Archaeophylus seems to be directly ancestral to the Santa Cruz genera Interatherium and Protypotherium. In the family Hegetotheriidae there is a strong tendency for the incisors to develop into very large gnawing teeth, while the lateral incisors, the canine and the first premolar, tend to drop out, and the molars become more simplified. Propachyrucos seems to represent a hold over of the most primitive type of these. The Prohegetotherium and Hegetotherium have retained the less specialized feet and less advanced type of teeth, while Prosotherium has tended to the development of the hopping mode of locomotion, which is attained in Pachyrukhos later. There thus seem to be two series inside of this family. When the material is better known, it may be best to separate the two series. The Eutrachytheridae have retained the complexity of molars united with a permanently growing incisor. They seem also to have developed into a series of comparatively large forms, which, as they have advanced, have developed a bifurcated fold on the inner side of the upper molars, which in its complete development makes the upper molars three-lobed, as is seen in the typical Typotherium, representing the end of the series up in the Pampean formation. These relationships may be expressed graphically as in [fig. 26].

Fig. 26. Phylogeny of the Deseado and
Santa Cruz Genera of Typotheria.

Adaptations

Most striking of all the typothere peculiarities, is the development of the first upper and lower incisor into permanently growing teeth, having the enamel reduced to the anterior side only, making thus a self-sharpening tooth similar to that of rodents. Such teeth are characteristic of gnawing forms and would indicate that the form lived, in at least a considerable part, on bark and twigs. In the eating of such food and breaking up the wood cells for the contained protoplasm and starch, an immense amount of chewing is involved, followed by a rapid wear of the molars. This is met, as is characteristic in rodents and grass eaters, by the development of first high-crowned, then permanently growing molars. In acquiring the permanently growing tooth, some of the irregularities of the crown are lost, others which are deep-seated enough to affect the tooth even to the root are maintained, so that especially the external and internal infoldings become a persistent part of the tooth, having been impressed into the dental papilla. A further supplement to the resistant character of the teeth is seen in the development, in the most advanced types, of a cement layer on the outside of the molars, a feature apparently also a part of permanently growing roots.

The feet are generally those of a running type, but a single phylum has acquired the hopping habit.

The above features seem to indicate a more special adaptation than grass feeding. From the aspect of the whole Deseado fauna, we would seem to be dealing with the inhabitants of an arid area, where bushes have, in part at least, replaced the grass. The typotheres seem to me to represent a part of the fauna which lived by gnawing the bark and eating the twigs and leaves of bushes. This does not preclude the eating of grass also, but I do not see how they would have developed all their peculiarities by eating grass alone. The rodents are of such insignificant size that they could hardly have monopolized this food supply, and the typotheres seem to have adjusted themselves to, and occupied the place of rabbits on our western plains; but went even farther in developing in great numbers and varieties.

Systematic Descriptions

Archaeohyracidae Ameghino

This family is differentiated by the presence of enamel on all sides of the first incisor, by the unreduced condition of the lateral incisors, and by the small bulla of the mastoid. These are primitive features. Ameghino considered this family to belong to the hyracoids; but, as explained earlier, I believe them to be true Typotheria, though less specialized than the other families.

Archaeohyrax Ameghino

Archaeohyrax Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 431.

This interesting genus is known by a complete skull found by Ameghino and of which we found no duplicates. I insert a reproduction of the side view of the skull, and the dentition is shown in [fig. 24 a], and [fig. 25 a]. The dental formula is

• 3 1 4 3
• ———.
• 3 1 4 3

Incisor 1 is a little larger than the other incisors. Each upper molar has a vertical groove near the anterior external margin. In each upper premolar (after the first) and molar, there is a central pit surrounded by enamel, which is opposite the internal inflexion, and in a young individual, is presumably connected with the fold. In the same way, the last three lower premolars and the lower molars each have an internal pit, adjacent to the external inflexion. With advanced age all the teeth show closed roots, another primitive feature. In spite of the closed roots, the full dentition, and the enamel on the incisor; and on account of the deep inflexions and the isolated pits, I consider this genus a specialized side line, retaining many primitive features, and expect to find the ancestor of the typotheres in some one of the related Casamayor genera.

Fig. 27. Archaeohyrax patagonicus, after Ameghino—natural size.

Ameghino described three species, A. patagonicus, which we have figured, and which has a length of 84 mm. from inc. 1 to m. 3 in both the upper and lower dentitions; A. propheticus, of the same size, but with the dental series closed; and A. concentricus of larger size, the three lower molars having a length of 38 mm.

Plagiarthrus Ameghino

Plagiarthrus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 436.

This genus is known only by the lower premolars and molars, which are permanently growing teeth, composed of two subcylindrical cylinders almost entirely separated by the external and internal folds which almost meet in the median line. On the outside, each tooth is coated with a layer of cement. When better known it may prove that this genus, so specialized in the character of the teeth, does not belong in this family.

Plagiarthrus clivus Ameghino

Fig 28. Left lower
premolars 3 and 4
and molars 1-3—
natural size.

P. clivus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 436.

This species is represented by a single specimen from the Chico del Chubut, west of Puerto Visser, which preserves pm. 3 and 4 and the molars. The characters of this, the type species, are those of the genus. The total length of the five teeth is 36 mm., and [fig. 28] shows in natural size the various individual teeth.

Hegetotheriidae Ameghino

This family includes a large variety of forms from the formations from the Deseado up to the Mt. Hermosa, but all agree in having the first upper and the first two lower incisors enlarged into strong gnawing teeth; in the reduction or absence of in. 3, the canine, and premolar 1 of the upper and lower dentitions; in having the external face of the upper molars not inflexed; in lower molar 3 being three-lobed; and in the bulla being inflated and hollow. There are in the family two series of forms, at least, the one leading to the running Hegetotherium, the other to the hopping Pachyrukhos, and the very little known form Phanophilus which may fit into one of the other series when better known.

In the Deseado the following genera are assigned to the family.

Prohegetotherium, like Hegetotherium, except that the last premolar and the molars have a vertical furrow near the external anterior margin.