CHAPTER XV_The Deseado Formation of Patagonia

MARSUPIALIA

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.

=Borhyaenidae=

Ameghino has grouped in this family a considerable number of genera of

powerful, wolf-like carnivorous marsupials, characterized by a dental

formula

4-3 1 4 3

----------,[24]

3 1 4 3

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.

[Footnote 24: There is a discussion as to the homologies of the

premolars of marsupials and placental mammals, the one proposition

being that marsupials have three premolars and four molars, the other

that they have four premolars and three molars as in placentals. The

evidence is not conclusive as to either proposition, but in this paper

I have designated these teeth along the latter line of thought.]

==========================================================================

| | | | 3 | 3 |

--------------+-------+-------+---------+---------+----------+------------

| Cruz |-------| 4-m. 3 |Paracone |basin |

--------------+-------+-------+---------+---------+----------+------------

| Cruz |-------| 4-m. 3 |Paracone |two post. |

--------------+-------+-------+---------+---------+----------+------------

| Cruz |-------| 4-m. 1 |vestigal |basin |

--------------+-------+-------+---------+---------+----------+------------

| Cruz |-------| |Ant. ext.|One post. |

--------------+-------+-------+---------+---------+----------+------------

| |-------| |vestigal |No basin |

--------------+-------+-------+---------+---------+----------+------------

| |-------| | | |

| | 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.

[Illustration: 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= Ameghino

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.

=Pharsophorus lacerans= Ameghino

P. lacerans Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 503.

[Illustration: 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.

=Pharsophorus tenax= Ameghino

P. tenax Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 504.

[Illustration: 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.

[Illustration: 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.

Height of mandible under premolar 4 30 mm.

=Notogale= gen. nov.

[Illustration: 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_.

=Notogale mitis= Ameghino

? 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.

[Illustration: Fig. 143. Left mandible—natural size.]

=Notogale tenuis= Ameghino

? 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= Ameghino

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.

=Proborhyaena gigantea= Ameghino

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.

[Illustration: 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.

=Proborhyaena antiqua= Ameghino

? Borhyaena antiqua Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p.

655.

Proborhyaena antiqua Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p.

502.

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.

Caenolestidae

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:

Caenolestinae, lower pm. 4 not developed into a sectorial tooth.

Palaeothentinae, lower pm. 4 is developed into a sectorial tooth.

Abderitinae, lower pm. 4 is developed into a sectorial tooth and

striated.

=Palaeothentinae= Sinclair.

(= Epanorthidae Ameghino)

This group or subfamily was established to hold several genera of tiny

marsupials with the dental formula

? 1 4 3

-------;

4 1 2 3

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

Palaeothentes 2-rooted, fairly large, equals pm. 4 in height.

Pilchenia 2-rooted, moderate size nearly equals pm. 4 in height.

Callomenus 2-rooted, small size much lower than pm. 4.

Decastris, 1-rooted, vestigal.

=Palaeothentes= (Moreno) Ameghino

Palaeothentes Moreno, 1882, Patagonia, Resto de un Continente hoy

submergido, p. 22, (nomen nudum).

Palaeothentes (Moreno) Ameghino, 1887, Enum. Sist. Espesies Mamif. Fos,

Patagonia, p. 5.

Epanorthus Ameghino, 1889, Act. Acad. Nac. Cienc. Cordoba, t. 6, p. 271.

Epanorthus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 500,

(nudum).

Palaepanorthus Amegh., 1901, Anal. Soc. Cienc. Argen., t. 51, p. 77,

(nomen).

Palaepanorthus Amegh., 1902, Bol. Acad. Nac. Cienc. Cordoba, t. 18, p.

123.

Palaepanorthus Amegh., 1903, Anal. Mus. Nac. Buenos Aires, t. 9, (ser.

3, t. 2) p. 239.

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_.

=Palaeothentes chubutensis= Ameghino

Epanorthus chubutensis Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p.

500.

Palaepanorthus chubutensis Amegh., 1901, Anal. Soc. Cienc. Argen., t.

51, p. 77.

Palaepanorthus chubutensis Amegh., 1902, Bol. Acad. Nac. Cienc.

Cordoba, t. 18, p. 123.

Palaepanorthus chubutensis Amegh., 1903, Anal. Mus. Nac. B. A., t. 9

(ser. 3, t. 2) p. 239.

[Illustration: 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.

=Pilchenia= Ameghino

Pilchenia Ameghino, 1903, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 2,

p. 128.

Pilchenia Ameghino, 1904, Anal. Soc. Cienc. Rep. Argen., t. 58, p. 259.

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).

=Pilchenia lucina= Ameghino

P. lucina Amegh., 1903, Anal. Mus. Nac. B. A., ser. 3, t. 2, p. 128.

P. lucina Amegh., 1904, Anal. Soc. Cienc. Rep. Argen., t. 58, p. 259.

[Illustration: 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, 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.

=Callomenus= Ameghino

Callomenus Amegh., 1891, Neuvos Restos Mamif. Fos. Patagonia Austral,

p. 20.

Callomenus Sinclair, 1901-6 Princeton Patag. Expeditions, vol. 4, p.

434.

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.

=Callomenus praecursor= sp. nov.

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.

[Illustration: Fig. 147. Left mandible with premolar 3 to molar 2—4

times natural size.]

[Illustration: 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.

Caenolestinae

The subfamily is distinguished by the formula

4 1 4 3

-------,

4 1 3 3

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.

=Pseudhalmarhiphus guaraniticus= 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.

Abderitinae

The subfamily is distinguished by the formula

? ? ? ?

-------,

4 1 2 3

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.

=Parabderites minusculus= Ameghino

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.