In our collection, the marsupials are represented, unfortunately, by but a few specimens; though this Deseado fauna included, as is shown by the fragmentary remains, a wide range of forms from Pilchenia, the size of a mouse, up to the bear-sized Proborhyaena. The small forms were probably insectivorous, while the larger forms took the place of the carnivores, the absence of true Carnivora being one of the striking features of the fauna of South America during earlier Tertiary times.
The treatment of these forms has been as varied as their sizes. Ameghino, with his idea that the Casamayor and Deseado beds were Cretaceous in age, groups the larger forms as a suborder, Sparassodonta, and considers them ancestral to the Creodonta; while the small forms make up his Sarcobora which he considered ancestral on one side to the rodents, on the other to the diprotodont marsupials. Sinclair, after showing the marked similarity of the Sparassodonta to the polyprotodont marsupials, especially the genus Thylacynus, abandons that term and puts them in the family Thylacynidae along with the Australian forms; the Microbiotheridae he finds similar to opossums and puts in the family Didelphidae; while the remaining small diprotodont forms he associates with Caenolestes, and using Ameghino’s families as subfamilies makes three divisions of the family, Palaeothentinae, Garzoninae, and Abderitinae. Matthew finds the sparassodonts to be true marsupials, and without phylogenetic relationship with the creodonts. Gregory diagrams the sparassodonts as coming from generalized didelphids and derives them from the same line as the Australian polyprotodonts; while the small caenolestoids represent a line of descent from some still earlier generalized polyprotodonts and a separate stem from the Australian diprotodonts.
Sinclair has had the most complete material on which to work, and with his general grouping I have come to agree. This recognizes three divisions of South American Marsupials, the Didelphidae, representatives of which have not yet been found in the Deseado, though occurring in both the earlier and later formations; the Caenolestidae represented today by Caenolestes, the only survivor of the South American diprotodonts; and the Borhyaenidae (= Thylacynidae of Sinclair this name having been used to indicate a much nearer relationship to the Australian Thylacynus than I feel is warranted), which includes a large range of medium to large sized animals ranging from the Casamayor formation throughout the Santa Cruz beds.
The locality from which these marsupials emigrated to South America and the time of their arrival is not yet agreed upon, and can not be settled until much more complete material is discovered in the Casamayor formation. I feel, however, that the three groups were separate when they entered South America.
Ameghino has grouped in this family a considerable number of genera of powerful, wolf-like carnivorous marsupials, characterized by a dental formula
heavy heads, short limbs with usually five semidigitigrade toes. The genera are mostly distinguished by the 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. The following table indicates the relationships of the best known genera.
| Age | Formula | Protocone | Upper Molar 3 |
Talonid on Lower Molar 3 |
Symphysis | |
|---|---|---|---|---|---|---|
| Cladosictis | Santa | 4 1 4 3 | on pm. 4-m. 3 | Protocone | Small | Symphysis |
| Cruz | 3 1 4 3 | Paracone | basin | |||
| vestigal | with one | |||||
| Metacone | post. cusp | |||||
| Ant. ext. | ||||||
| style | ||||||
| Amphiprovivera | Santa | 4 1 4 3 | on pm. 4-m. 3 | Protocone | Basin with | Ligamentous |
| Cruz | 3 1 4 3 | Paracone | two post. | |||
| Ant. ext. | cusps | |||||
| style | ||||||
| Prothylacynus | Santa | 4 1 4 3 | on pm. 4-m. 1 | Protocone | Small | Fused |
| Cruz | 3 1 4 3 | vestigal | basin | |||
| Metacone | with one | |||||
| post. cusp | ||||||
| Borhyaena | Santa | 3 1 4 3 | vestigal | Paracone | No basin | Fused |
| Cruz | 3 1 4 3 | Ant. ext. | One post. | |||
| style | cusp | |||||
| Pharsophorus | Deseado | 1 4 3 | vestigal | Protocone | Very small | Ligamentous |
| 1 4 3 | vestigal | No basin | ||||
| Paracone | One post. | |||||
| Ant. ext. | cusp | |||||
| style | ||||||
| Proborhyaena | Deseado | Fused | ||||
| 1 4 3 |
From the foregoing, it will appear that Pharsophorus approaches Borhyaena and Prothylacynus in the structure of its upper molars, being, however, nearer to the former, and the same is true of the structure of the talonid; but Pharsophorus differs markedly from both in retaining the metaconid as a small cusp on the side of the protoconid on all of the lower molars; also in the extremely small size of the talonid of the lower molars, which in Pharsophorus have no basin and consist of a single cusp; and, lastly, in the symphysis of the lower jaws being ligamentous, whereas in the two preceding genera, it is fused. Pharsophorus is probably ancestral to Borhyaena. In the case of Proborhyaena, only a mandible, with the canine and premolars 3 and 4 intact, has been found. The fourth premolar is more reduced than in other genera, but, until more teeth are known, its affinities can not be at all closely determined.
Fig. 138. Diagram of a generalized upper molar, U.m., and a lower molar, L.m., of Borhynidae; a.s., ant. style; hld., hypoconulid; mt., metacone; mtd., metaconid; pa., paracone; pad., paraconid; pr., protocone; prd., protoconid; td., talonid.
Pharsophorus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 502.
The genus was founded on a lower jaw with premolar 3 to molar 3 in position. We found beside the above an upper jaw with premolar 3, and molars 2 and 3 complete while premolar 4 and molar 1 are more or less fragmentary; from which the following generic characters may be made out. The incisors are tiny; the canine very large, equal to that of Borhyaena; the upper and lower premolars progressively smaller from front to back. Upper premolar 3 is a simple two-rooted tooth, the crown consisting of a single blunt central cusp. On the upper molars the protocone is not developed as a cusp, though the third inner root is present and carries a rounded shelf. The paracone is the chief cusp, and is developed as a high central pointed denticle. The metacone is not developed as a cusp, but is represented by a long slanting ridge to the rear, the apex of which has been fused to the paracone. The last upper molar is better developed than in most Santa Cruz genera, consisting of a high median cusp, the paracone; a small anterior cusp, the anterior external style; and a shelf-like posterior cusp, the protocone. Lower premolars 1-3 are simple two-rooted teeth, each carrying a single cusp on the crown. The fourth premolar carries a well marked paraconid in front, a large median protoconid on the rear of which is a tiny metaconulid; and a tiny talonid or heel which is without a basin and consists of a single tiny cusp. The molars are all of the same character as the last premolar. The lower jaws are united by a ligamentous symphysis.
Ameghino distinguished four species, P. lacerans, P. tenax, P. mitis, and P. tenuis, in the order of their size. The last two are but little known but are quite certainly another genus.
P. lacerans Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 503.
Fig. 139. Left mandible—½ natural size,
after Ameghino.
The species was founded on a lower jaw with the roots of the incisors, canine, and first two premolars, and with the remaining teeth intact. We did not find the species, so I have reproduced Ameghino’s figure and give his measurements.
| Lower dentition, | length incisor 1 to molar 3 | 114 mm. |
| Lower dentition, | length premolar 1 to molar 3 | 90 mm. |
| Lower dentition, | height of mandible under pm. 4 | 38 mm. |
P. tenax Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 504.
Fig. 140. Left upper jaw—½ natural size;
A, molars 3 and 4 from above;
B, molars from
external side.
The species was based on a fourth premolar which was 10 mm. long as compared with 13 mm. in P. lacerans. We found on the Chico del Chubut, west of Puerto Visser, both an upper and lower jaw belonging to this species, which give us the knowledge of the upper dentition for the genus. The species is distinguished by the smaller size, relatively heavy jaws, and plump teeth, indicating a heavier built animal than P. lacerans. The following measurements distinguish the species.
Fig. 141. Right mandible—½ natural size.
| Specimen 3192 | |||||
|---|---|---|---|---|---|
| Upper dentition, | length premolar 1 to molar 3 | 76 mm. | |||
| Upper dentition, | premolar 3, | length | 10.5 mm., | width | 6 mm. |
| Upper dentition, | molar 1, | length | 11.5 mm., | width | 8.5 mm. |
| Upper dentition, | molar 2, | length | 12 mm., | width | 9 mm. |
| Upper dentition, | molar 3, | length | .55 mm., | width | 12 mm. |
| Specimen 3004 | ||||
|---|---|---|---|---|
| Lower dentition | ||||
| Distance from premolar 1 to molar 3 | 76 mm. | |||
| Molar 1, | length | 11 mm., | width | 6 mm. |
| Molar 2, | length | 13 mm., | width | 6 mm. |
| Molar 3, | length | 13 mm., | width | 7 mm. |
| Distance from premolar 1 to molar 3 | 30 mm. | |||
Fig. 142. Upper
molars 2 to 4—
natural size.
This genus is proposed for the species designated ?Pharsophorus mitis by Ameghino (should probably include ?Pharsophorus tenuis which however never having been figured and not found in our collection I cannot definitely place). While the upper teeth have the same general character as Pharsophorus, they are much more compressed and trenchant. Upper molar 2 is similar to that of Pharasophorus in having the protocone reduced, and the metacone represented by a long sloping ridge. The last molar is also similar in having the antero-external style, the developed paracone, but the protocone is much less developed, appearing only as a ridge. In the lower teeth, however, there is a marked difference, in that the metaconid is lacking on molars, while the talonid is developed into a small basin with a single cusp on the posterior margin. This genus seems to be closest to the Santa Cruz genus Cladosictis.
? Pharsophorus mitis, 1897, Bol. Inst. Geog. Argen., t. 18, p. 504.
Ameghino briefly describes, without a figure, a species in which premolar 4 and molar 3 together measure 14 mm. I have assigned to this two specimens, the one with pm. 2 incomplete, pm. 3 complete, and m. 2 also complete. These teeth measure the same as Ameghino’s and I think are the same. There is also a fragment of the upper jaw with molars 2 and 3, though imperfect. From these it appears that we have to do with an animal not only smaller than the preceding, but on much slenderer lines. The following are the measurements of the two specimens.
| Specimen 3117 | |||||
|---|---|---|---|---|---|
| Upper dentition, | molar 2, | length | 8 mm., | width | 6 mm. |
| Upper dentition, | molar 3, | length | 2 mm., | width | 6 mm. |
| Specimen 3060 | |||||
|---|---|---|---|---|---|
| Lower dentition, | premolar 3, | length | 6 mm., | width | 2.5 mm. |
| Lower dentition, | molar 2, | length | 7 mm., | width | 4 mm. |
Fig. 143. Left mandible—natural size.
? Pharsophorus tenuis Amegh., 1897, Bol. Inst. Geog., Argen., t. 18, p. 504.
This species was founded by Ameghino on a single lower premolar 3 which is 3 mm. in length. No further description is given and no figure.
Proborhyaena Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 501.
The genus is founded on a large lower jaw carrying the canine and premolars 3 and 4 and roots or alveoli for the other teeth. It is the largest carnivore recorded from Patagonia, and as large as a small bear. It is not possible to place its exact relationships, for the most essential teeth are wanting, but it is certainly a distinct genus as indicated by the reduced size of premolar 4 and the plump character of the teeth.
P. gigantea Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 501.
We found no specimens of this great carnivore, so I am reproducing Ameghino’s figure and measurements. The heavy canine is channeled on the sides and much worn on the posterior face. Premolar 3 is a plump tooth, its crown consisting mostly of a single median cusp, but with a small heel behind, and, strikingly enough, premolar 4 is a smaller and simpler tooth with a single cusp.
Fig. 144. Right mandible—½ natural size,
after Ameghino.
| Measurements | ||
|---|---|---|
| Lower dentition, | canine, antero-posterior diameter | 30 mm. |
| Lower dentition, | canine, transverse diameter | 20 mm. |
| Lower dentition, | premolar 1 to molar 3 | 145 mm. |
| Lower dentition, | height of mandible under pm. 4 | 60 mm. |
This species is known only by a single canine 100 mm. long, of which but 15 mm. belongs to the crown. Its antero-posterior diameter is 14 mm., the transverse 12 mm. It seems to me very doubtful whether this is a valid species.
This family, based on the living genus Caenolestes, is represented in Tertiary times in Patagonia by three subdivisions, Palaeothentinae, Garzoninae, and Abderitinae. While diprotodonts, as far as known, the family is in strong contrast to the Australian diprotodonts in that there is no sign of syndactylism in the pes. The American forms are characterized by four subequal upper incisors, a normal canine, the first three premolars vestigal, while the fourth is either normal or enlarged into a sectorial tooth. The three molars are progressively smaller from the front back. The first lower incisor is greatly enlarged and procumbrent, the remaining incisors, the canine, and the anterior premolars being vestigal though usually present. Premolar 4 is enlarged and sectorial in most genera, and the molars as in the upper jaw progressively smaller.
For the practical purposes of this paper the subfamilies are distinguished as follows:
(= Epanorthidae Ameghino)
This group or subfamily was established to hold several genera of tiny marsupials with the dental formula
the lower fourth premolar enlarged into a sectorial tooth; and the molars small and buno-lophodont. From the Deseado beds but one genus of this subdivision has been found, Palaeothentes, designated by Ameghino first Epanorthus then later Palaepanorthus, but as I can see no reason for distinguishing the Deseado species of the genus from those of the Santa Cruz, I have retained the name Palaeothentes.
The genera of this subfamily are distinguished as follows:
Lower Third Premolar
Among the Santa Cruz specimens, this genus is distinguished by having in the lower jaw the large first incisor, then five vestigal teeth, followed by a two-rooted, though somewhat reduced, third premolar, next the enlarged fourth premolar, making the sectorial tooth, and lastly three buno-lophodont molars.
There is considerable confusion as to the use of the generic name. Moreno designated the first specimen, Palaeothentes, without a description; then Ameghino used this term describing the species; later Ameghino thinking that the name Palaeothentes was the same as Palaeothentes proposed the name, Epanorthus, using this for the first description of the Deseado species. Later, however, he changed this for Palaepanorthus. As I can see no generic differences between the Deseado and Santa Cruz species, I shall follow Sinclair in using the generic term Palaeothentes.
Fig. 145. Right mandible—2 times natural size,
after Ameghino.
The species is founded on a tiny mandible with premolar 3-molar 3, on which the third premolar, while reduced, has two roots and reaches the height of the fourth premolar, being in about the same stage of development as the Santa Cruz species. As we found no specimens of this species I reproduce Ameghino’s figure and measurements.
| Lower dentition, | premolar 3 to molar 3 | 19 mm. |
| Lower dentition, | height under premolar 4 | 12 mm. |
This genus was founded on a single lower molar which, in the light of the specimen we found, I take to be the third or last. Our specimen shows pm. 3 and 4 and the three molars. The third premolar is a small two-rooted tooth with a simple crown and no heel. Premolar 4 is an enlarged sectorial tooth, the anterior part consisting of two cusps, closely set near the median line, with an incipient cusp on the inner face of the large anterior cusp. The posterior part of this tooth is arranged as a typical talonid, with one internal and two external cusps on the margin of a shallow inclosed basin. On the rear of the tooth is a small crescent-like cingulum, which occurs in the same place on molars 1 and 2, but is lacking on molar 3. This is a characteristic feature of the genus. On the anterior part of the molars is developed a sort of trigonid of small size, and the cusps are indistinct. The posterior portion of each molar is a large talonid with a shallow basin surrounded by a low wall on which are three tiny cups (the entoconid, hypoconid, and hypoconulid).
Fig. 146. Left mandible with premolar 3 to
molar 4—
4 times natural size.
In the Deseado beds, on the Chico del Chubut River, west of Puerto Visser, we found a single specimen of this species which agrees with the single tooth figured by Ameghino as the type, and which I interpret as molar 3. The description is given under the genus, the measurements are as follows:
| Specimen No. 3110 | |||||
|---|---|---|---|---|---|
| Lower dentition, | distance from premolar 3 to molar 3 | 14 mm. | |||
| Lower dentition, | premolar 3, | length | 2 mm., | width | .75 mm. |
| Lower dentition, | premolar 4, | length | 5 mm., | width | 2.5 mm. |
| Lower dentition, | premolar 4, | length | 5 mm., | width | 2.5 mm. |
| Lower dentition, | molar 1, | length | 3 mm., | width | 2 mm. |
| Lower dentition, | molar 2, | length | 2.5 mm., | width | 2 mm. |
| Lower dentition, | molar 3, | length | 2 mm., | width | 1.75 mm. |
| Lower dentition, | height under pm. 4 | 5 mm. | |||
This genus has not been previously reported from the Deseado beds, but we found a tiny lower jaw with three teeth to represent it. The genus is distinguished by premolar 3 being two-rooted, but so small as not to attain the height of premolar 4.
The type is specimen No. 3020, a fragmentary mandible with premolars 3 and 4 and molar 1 in place. Pm. 3 is two-rooted, but so small as to be entirely overshadowed by the succeeding pm. 4, hardly reaching a half the height of that tooth. On the last premolar and the first molar, the cusps are arranged in a trigonid in front and a talonid behind, the cusps being joined by thick ridges, making two connecting crescents.
Fig. 147. Left mandible with
premolar 3 to molar 2—
4 times natural size.
Fig. 148. Left mandible internal side—
4 times natural size.
| Measurements, Specimen 3020 | |||||
|---|---|---|---|---|---|
| Lower dentition, | premolar 3, | length | 1 mm. | ||
| Lower dentition, | premolar 4, | length | 5 mm., | width | 2 mm. |
| Lower dentition, | molar 1, | length | 4 mm., | width | 2 mm. |
| Lower dentition, | height under pm. 4 | 6.5 mm. | |||
The subfamily is distinguished by the formula
pm. 4 not being enlarged, and the lower molars being turberculo-sectorial. In the Deseado formation this group is only represented by a single species, based on a single tooth found by Ameghino.
P. guaraniticus Amegh., 1903, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 2, p. 83.
Based on a single tooth, similar to those found in the Santa Cruz.
The subfamily is distinguished by the formula
the fourth premolar being enlarged into a sectorial tooth on the sides of which are vertical striae. The molars are buno-lophodont. The Deseado has yielded only a tiny form, designated Parabderites, which differs from the Santa Cruz genus Abderites in pm. 4, the same shape, but with few to no striae on its sides.
P. minusculus Amegh., 1902, Bol. Acad. Nac. Cienc. Cordoba, t. 17, p. 43.
The species as described by Ameghino is based on a lower jaw with pm. 3 to m. 3. The specific character is the lack of striae on pm. 4. No figure is given but the following measurements indicate the size.
| Lower dentition, | premolar 3 to molar 3 | 9 mm. |
| Lower dentition, | height of mandible under pm. 4 | 4 mm. |