Frederic Brewster Loomis

“ The premolars are peculiar in having on the anterior internal corner a highly developed cingulum, which so builds out the tooth that it is usually wide and is rectangular in outline. As this cingulum rises, it incloses a bay on the ant. int. corner of the tooth, which, with wear, becomes first a bay, then a pit, and lastly may disappear entirely in old age. On each premolar the anterior and posterior lobes are developed, inclosing between them an elongated basin, which with wear becomes a long narrow pit. On the molars, the cingulum on the ant. ”

“ The small animals which represent this family are rare in the Deseado beds, much more abundant in the Casamayor. The family seems to have died out in the Deseado as no forms are referred to it in later epochs. We found no specimens belonging to the family; but to make this discussion complete, I will give a digest of Ameghino’s descriptions, with reproductions of such figures as he has given. All of the genera and species are based on very fragmentary material. ”

“ 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. ”

“ This, the type species, is by far the commonest of the rodents, in fact of all the species in the Deseado, and we found forty-seven specimens on the Chico del Chubut River, west of Puerto Visser. In the species there is considerable variation in size for a rodent, but as there are intermediate specimens all the way between the extremes, and as the variation is mostly in the size of the fourth premolar, it does not seem proper to separate the material into more than one species. ”

“ The ancestral type must be sought in some such a form as Henricosbornia, where the upper molars are brachydont, have the four primary cusps distinct, and the connecting crests of small size, and a cingulum moderately developed on the front and rear sides. Progress is in the line of enlarging the crests, so that, in the later forms, the two external cusps are united to make a wall; and the anterior external and the anterior internal cusps are united into the large anterior lobe; while the posterior external and the posterior internal cusps unite to make the posterior lobe. ”

“ 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. ”

“ I find in studying a lower molar of Coresodon that bay 3 becomes a pit after some 6 mm. are worn off, while bays 2 and 4 remain open until some 10 mm. are worn off when they also become pits. Pit 3 will disappear when 12 mm. are worn off, but pits 2 and 4 run to the base of the crown.
The various genera of the Toxodontia in the Deseado I would divide into four families as follows:
Rhynchippidae: molars brachydont, secondary cristae lacking or little developed, none of the incisors caniniform, limbs slender, feet digitigrade, digits 3-3. ”

“ 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. ”

“ The skull has been described under the generic discussion. In young individuals, the furrow in the incisors and canine is marked as a groove, later as a pit, and still later is lacking altogether, as is the case in the specimen figured, for all three of my more complete specimens are old individuals, as is also Ameghino’s type. All the incisors show the cingulum near the base of the enamel. ”

“ 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. ”

“ The genera are mostly distinguished by the [Pg 212] relative development of the protocone on the upper molars and the talonid on the lower ones. Figure 138 gives a typical marsupial upper molar 2 and a lower molar 2 to show the sense in which these terms are used. The Santa Cruz genera are the best known and I therefore use them as a basis for comparison with the less known Deseado forms, of which we found but the one genus Pharsophorus at all abundant. In addition to this, Ameghino has reported a gigantic form designated Proborhyaena. ”

“ 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. ”

“ The skull is relatively light and narrow, especially in the rear, where the swollen hollow capsules of the squamosum bones come within ten millimeters of meeting medianly, whereas, in other species, they are twice as far apart. These hollow capsules are in this species the most marked, and in this genus even more developed than in Pachyrukhos. The lachrymal bone is larger externally than usual, the lachrymal duct opening about four millimeters in front of the margin of the orbit, and continuing to the margin by an open groove. ”

“ We found no specimen of this interesting type, but I give a diagram of Ameghino’s type, which shows the characteristics of the species and genus. The length of the premolar-molar series is 27 mm.
Eutrachytheridae Ameghino
The family consists of larger forms than the other families, and is characterized by the upper molars having the inflexion bifurcated, so that the teeth are at least incipiently three-lobed. I would place in the family the genera, Eutrachytherus, Argyrohyrax, and Isopoedrium.
Eutrachytherus Ameghino Trachytherus Amegh., 1889, Act. Acad. Nac. Cienc. Cordoba, t. VI, p. 918. ”

“ 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 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. ”

“ In the first upper dentition found, incisors 2 and 3 were represented by alveoli only, but our specimen shows these teeth, and we find that they have enamel only on the outer face, making this genus more specialized in this respect than any of the other typotheres. The upper molars have the deep inner inflexion bifurcated, which makes the tooth three-lobed, a character which grows more marked the older the individual is. The premaxillae are high and bring the snout well forward. ”

“ In the upper dentition, the small incisors, pitted on the crown, increase regularly in size toward the rear; and each has an external cingulum around the base. The canine is about twice the size of the adjacent incisor, and also has an external cingulum. The premolars increase regularly in size and also have at least an external cingulum. Figure 101 shows a dentition which Ameghino described as the milk set of A. osborni. At the same time he remarks the unusual character of the deciduous canine in being two-cusped. ”

“ When isolated, however, it is difficult to tell whether one is handling a small upper tush or a larger lower one.
The remaining incisors, the canine, the first and the second premolars are wanting, and their place is taken by a small diastema. The lower premolars and the molars are similar to those of the upper jaw, except the cingulum is on the posterior margin, and the wear is on the posterior face of each transverse crest. ”

“ With the flattening, the deltoid ridge is prolonged enormously making a crest along the outer side of the bone, which at the lower end rises in a prominent process, as in elephants (also in Diprotodon but in this case the rest of the bone is very different) . In addition to this, the supinator ridge is prolonged upward until it almost meets the deltoid, ending in a sharp spur at the top. This spur is more marked in Pyrotherium than in elephants, although they show the same development of the supinator ridge. ”

“ 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 ”

“ 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 [Pg 22] 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. ”

“ 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 [Pg 61] 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. ”

“ 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 addition to the foregoing, Ameghino has made a series of genera and species, [23] Archaeutatus, Amblytatus, Isutaetus, Sadypus, Hemiutaetus, Anutaetus, all based on isolated plates, and distinguished by variations in the central figure and the piliferous pits. I am unable to find a satisfactory basis for distinguishing the genera or species, and feel that, until more complete material is known, it is impossible to say which are valid genera or species. ”

“ The maxillae are also massive, carrying the premolars [Pg 167] and molars, and extending forward to the bases of the tushes. They have developed downward so as to carry the plane of the palate far below the plane of the basicranium, and causing the upward bend in the basicranial axis, which is so characteristic of elephants. This bend leaves the occipital condyles a full foot above the plane of the teeth. The maxilla extends upward so as to bound the major part of anterior margin of the nasal opening, and of the orbit, which latter opening is small and directed forward. ”

“ This species is similar to P. garzoni except for size, the forms running about 12% larger, and being heavier built. In this same line the upper and lower molars are relatively wider and heavier. The top of the skull also is wider. I have drawn carefully the skull and dentition so that the detail can be seen from the figures. Beside triangulidens, Ameghino described P. robustum, which, as far as I can see, differs only in being about 5% larger, which is well within individual variation, so I have considered it as a synonym. ”

“ 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 genus, in general, is similar to Astrapotherium, so that Gaudry considered it the same, but Ameghino has distinguished it by the tushes being relatively of smaller size, the lower incisors larger, and [Pg 144] by the presence of pm. 3 in the lower series. The Deseado forms are also of considerably larger size than the Santa Cruz.
Our material includes a pair of lower jaws, two scapulae, the humerus, and the lower end of the femur.
No skull has been found in the Deseado. Those from the Santa Cruz are enormously swollen over the orbits, the massive bone making a skull wholly unique. ”