CHAPTER V_The Deseado Formation of Patagonia

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

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

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

| Cruz |-------| |fold | | |

| |3 1 4 3| | | | |

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

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

| Cruz |-------| |fold | |cleft |

| |2 0 3 3| | | | |

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

| |-------|reduced | | | |

| |3 1 4 3| | | | |

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

| |-------| |inner | |cleft |simple

| |2 0 4 3| |fold | | |

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

| |-------|large |slight fold,| | |

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

| Cruz |-------| |and outer | |cleft |

| |3 1 4 3| |folds | | |

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

| Cruz |-------| |and outer | |cleft |series

| |3 1 4 3| |folds | | |

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

| |-------| |inner fold | | |

| | | | | | |

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

| |-------| |inner fold | | |

| |2 1 4 3| | | | |

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

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

| |? ? 4 3| | | | |

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

| |-------| |fold, slight| | |

| |3 1 4 3| |outer fold | | |

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

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

| |? ? 4 3| | | | |

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

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.

[Footnote 12: Princeton Expeditions Reports, Vol. VI, p. 7, 1909.]

[Illustration: Fig. 24. Comparative series of upper dentitions of

Deseado and Santa Cruz Typotheria; _a_, Archaeohyrax patagonicus; _b_,

Hegetotherium mirabile; _c_, Prosotherium garzoni; _d_, Pachrukhos

moyani; _e_, Archaeophylus patrius; _f_, Interatherium extensum; _g_,

Protypotherium australe; _h_, Argyrohyrax proavus; _i_, Eutrachytherus

spegazzinianus—all natural size.]

[Illustration: Fig. 25. Comparative series of lower dentitions of

Deseado and Santa Cruz Typotheria; _a_, Archaeohyrax patagonicus; _b_,

egetotherium mirabile; _c_, Prosotherium garzoni; _d_, Pachyrukhos

moyani; _e_, Interatherium sp.; _f_, Protypotherium australe; _g_,

Plagiarthrus clivus; _h_, Eutrachytherus spegazzinianus; _i_,

Isoproedrium solitatium—all natural size.]

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.

[Illustration:

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

| | | | |

| | | | |

| | | | |

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.

[Illustration: 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

[Illustration: 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.

_Prosotherium_,

1 0 4 3

-------,

2 0 4 3

upper inc. 2 and 3 and lower inc. 3 vestigal, upper pms. not

molariform, molars with a deep internal fold.

_Propachyrucos_,

-------,

3 1 4 3

lower jaw only, similar to _Pachyrukhos_ but have inc. 3, the canine,

and pm. 1 present and only a little reduced.

_Phanophilus_, upper molars only, but peculiar in having a strong

external medial column.

=Prohegetotherium= Ameghino

Prohegetotherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 424.

This little known genus is characterized by the upper molars having

an external furrow near the anterior margin of the tooth. Otherwise

it is similar to _Hegetotherium_. Ameghino described a species where

the external surface of the bones was sculptured “like reptiles.” I

do not see how, with the arrangement of the muscles usual to mammals,

the sculpture could be similar to that of reptiles, and feel that this

is due to conditions of weathering. We did not find this species, but

did find a form which resembled it in general, but differed in being

smaller and with the external furrow less developed.

=Prohegetotherium sculptum= Ameghino

P. sculptum Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 424.

This species is characterized by the deep external furrow on the upper

molars. The measure given is 34 mm. for the length of the three upper

molars.

=Prohegetotherium shumwayi= sp. nov.

Founded on a portion of the right maxilla, carrying pm. 2 to 4 and

m. 1, found on the Chico del Chubut, west of Puerto Visser, by Waldo

Shumway.

[Illustration: Fig. 29. H. Shumwayi—natural size.]

The teeth are simple, with but a shallow external furrow near the

anterior margin of the premolars and molar. A film of cement covers

each tooth and extends to the top of the crown. The form is smaller

than P. sculptum.

MEASUREMENTS

Upper premolar 3, length 6 mm., width 3¼ mm.

Upper premolar 4, length 7 mm., width 3½ mm.

Upper molar 1, length 7 mm., width 3½ mm.

=Prosotherium= Ameghino

Prosotherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 426.

In founding this genus, Ameghino says that lower pm. 1 is lacking, but

our specimens show it present as a vestige, and also show no trace of

lower inc. 3 against which Ameghino puts a question mark, making the

formula

1 0 4 3

-------

2 0 4 3

as given above. The upper molars are similar to those of _Pachyrukhos_

except that they have an inner fold which has been lost in

_Pachyrukhos_. The premolars are unlike the molars. Lower molar 3

is three-lobed. The description of the skeleton is given under the

specific description of _P. garzoni_, and this shows a remarkable

resemblance to the skeleton of _Pachyrukhos_, throughout, so that I

have no doubt but that _Prosotherium_ is the ancestor of _Pachyrukhos_,

the changes in the teeth proceeding in the line of simplification which

seems to be general in this order, and is in general characteristic of

forms in which the teeth become rootless.

Ameghino described four species, _P. garzoni_, _P. triangulidens_, _P.

robustum_, and _P. quartum_, the last two of which differ so little

from _P. triangulidens_, that I can not consider them as independent

species.

=Prosotherium garzoni= Ameghino

P. garzoni, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 426.

This, the most abundant species of typotheres, occurs in our

collection from the Chico del Chubut, west of Puerto Visser, fifteen

times; and in one case the major part of a skeleton was found,

consisting of the skull and jaws, vertebrae of each type, ribs, most of

the fore limb, the pelvis and a hind limb.

The animal as a whole is smaller than _P. triangulidens_ by about

12%, and is of lighter build. 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. In _P. triangulidens_, the duct is inside the

orbit. The heavy maxilla makes a strong process for the zygomatic arch,

extending fully half way back along this arch. The short, but fairly

stout jugale has but a short contact with the maxilla.

[Illustration: Fig. 30. Left upper dentition; left lower

dentition—natural size.]

[Illustration: Fig. 31. Left upper dentition No. 3083, showing

deciduous premolars.]

In the dentition, the premolar and molar teeth are covered with a thin

film of cement, which is thicker on the outside of the upper teeth and

on the inner side of the lower teeth. On the opposite sides of these

teeth this film is so thin that it is often in part worn off.

Specimen 3083 preserves three of the deciduous premolars. Pm. 2 is

simple and could readily be taken for the corresponding permanent

premolar, except that it is, as are all the deciduous premolars,

rooted. Deciduous premolars 3 and 4, on the other hand, have a marked

inflexion on the inner side, giving them the appearance of permanent

molars. The series measures 31 mm. of which the deciduous premolars

occupy just half.

The mandible is deep, especially the posterior portion; has a very

slender coronoid process; and a slightly rounded articular condyle,

which is a little longer than wide, so that it would seem to allow a

forward and backward motion of the lower jaw.

[Illustration: Fig. 32. Left mandible—natural size.]

The vertebrae are considerably crushed, but have in each case the

characteristics of the corresponding vertebra of _Pachyrukhos_.

Of the humerus, the head and distal ends are preserved, indicating a

rather long and slender bone, very like that of _Pachyrukhos_. About

three-fourths of the ulna is present, and it is also long and slender,

with a wide articular facet for the radius, which is entirely separate

from that for the humerus. Two metacarpals show the same elongation of

the limb, and the two phalanges preserved indicate a small front foot.

[Illustration: Fig. 33. Left side of pelvis—natural size.]

[Illustration: Fig. 34. Left femur—natural size.]

[Illustration: Fig. 35. Patella—natural size.]

[Illustration: Fig. 36. Tibia and fibula—natural size.]

The pelvis is elongated, slender and lightly built, indicating the same

characteristics in the whole hind limb. The femur has a small rounded

head on a well marked neck. It is excessively long, longer than that

of _Pachyrukhos_, and also straighter. It is further distinguished by

the third trochanter being swung onto the back side of the bone. The

tibia and fibula are separate throughout their entire length, in which

this genus is in strong contrast to _Pachyrukhos_, where these two

bones are fused, both distally and proximally.

[Illustration: Fig. 37. Calcaneum, astragulus and cuboid, from upper

side—natural size.]

[Illustration: Fig. 38. Astragulus from below—natural size.]

The astragulus is also quite characteristic, the trochlear surface

being entirely on the dorsal surface, and the condylar ridges being

relatively low and flat. This trochlear surface is far from being

symmetrical, the inner ridge being much flatter and lower than the

outer. The head of the astragulus is rounded, on a long neck, and

directed obliquely inward. The fibular facet for the fibula is

crescent-shaped and vertical except that the small proximal end of the

crescent flares out. The outline of the sustentacular facet is that of

an acute ovoid, and is situated mostly on the neck of this bone. The

ectal facet is roughly rectangular in outline, strongly concave, and is

separated from the sustentacular facet by a deep groove.

The calcaneum is of moderate size, has a narrow fibular facet, a broad

ectal facet, and a moderately large sustentacular one. The facet for

the cuboid is slightly concave, and occupies the whole of the distal

end of the calcaneum.

[Illustration: Fig. 39. Right foot—natural size.]

The metatarsals are moderately long and rather heavy, not quite as

long and slender as those of _Pachyrukhos_. The phalanges are also

shorter and slightly heavier than those of _Pachyrukhos_. We found

four proximal and four of the second series, all associated, which

probably indicates the full number of the toes. The ungual phalanges

are proximally narrow and high, then expand toward the tip, developing

into marginal expansions. There is but a trace of a cleft in the end of

these ungual phalanges.

MEASUREMENTS

Skull, greatest length 99 mm.

Upper dentition, length inc. 1 to m. 3 55 mm.

Upper dentition, length pm. 1 to m. 3 31 mm.

Upper dentition, incisor 1, width 6½ mm.

Upper dentition, molar 1, length 6 mm.

Upper dentition, molar, width 4½ mm.

Mandible, greatest length 82 mm.

Lower dentition, length inc. 1 to m. 3 53 mm.

Lower dentition, length pm. 1 to m. 3 32 mm.

Lower dentition, molar 1, length 6½ mm.

Lower dentition, molar, width 3 mm.

Third metacarpus, greatest length 28 mm.

Pelvis, length front to back 83 mm.

Femur, greatest length (computed) 93 mm.

Femur, diameter of middle of shaft 9 mm.

Tibia, greatest length 90 mm.

Astragulus, length 14 mm.

Astragulus, width 11 mm.

Calcaneum, length 25½ mm.

Metatarsus III, length 32 mm.

First phalanx of digit III, length 12 mm.

Ungual phalanx of digit III, length 9 mm.

To make the similarity of Prosotherium with Pachyrukhos clearer, I

have restored Prosotherium, figure 40, from which it will be seen that

this genus is also a hopping form with a plantigrade hind foot and a

semidigitigrade front foot. In general it compares very closely with

Pachyrukhos, but the limbs are shorter and the grade of specialization

is not quite as high. It is, however, very evidently the ancestor of

Pachyrukhos.

[Illustration: Fig. 40. Restoration of Prosotherium garzoni—⅓ natural

size. (Half tone.)]

=Prosotherium triangulidens= Ameghino

P. triangulidens Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 427.

P. robustum, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 427.

P. quartum Amegh., 1901, Bol. Acad. Nac. Cienc. Cordoba, t. 16, p. 371.

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. The same is the case

with _P. quartum_, which Ameghino distinguishes as being about the size

of _P. robustum_, and having lower pm. 1 present. The latter character

we found also characteristic of _P. garzoni_, so only size remains and

I do not consider less than 10% enough by itself to make a species.

MEASUREMENTS

Skull, length 110 mm.

Upper dentition, length inc. 1 to m. 3 57 mm.

Upper dentition, length pm. 1 to m. 3 35 mm.

Upper dentition, incisor 1, width 8 mm.

Upper dentition, molar 1, width 4½ mm.

Six specimens from Chico del Chubut

=Propachyrucos= Ameghino

Propachyrucos Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 425.

The genus is based on lower jaws, in which the characters of the

premolars, the molars and the first two incisors, resemble those of

_Pachyrukhos_; but in this genus the third incisor, the canine, and

the first premolar are retained and but little reduced. Ameghino has

described two species, _P. smithwoodwardi_, and _P. aequilatus_.

[Illustration: Fig. 41. Top view of the skull, palatal view—natural

size.]

=Propachyrucos smithwoodwardi= Ameghino

P. smithwoodwardi, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 425.

We did not find this species, but I reproduce Ameghino’s figure of it,

natural size. The length of the dentition from inc. 1 to m. 3 is 41

mm., height of mandible under m. 1 is 12 mm.

[Illustration: Fig. 42. P. smithwoodwardi after Ameghino, right

mandible—natural size.]

=Propachyrucos aequilatus= Ameghino

P. aequilatus, Amegh., 1901, Bol. Acad. Nac. Cienc. Cordoba, t. 16, p.

371.

This species is based on the anterior lobe of each lower molar, being

longer than the posterior. In size, molars 1 to 3 measure 24 mm.[13]

[Footnote 13: P. crassus has been described, (loc. cit., p. 425,) based

on pm. 2 and 3, of larger size than either of the foregoing but I do

not think that the genus can be determined on so small a fragment.]

=Phanophilus= Ameghino

Phanophilus, Amegh., 1903, Anal. Soc. Cienc., Argen., t. 56, p. 202.

This genus is based on isolated upper molars, characterized as similar

to _Protypotherium_, but having a pronounced median vertical column,

instead of a groove on the external face of the upper molars, a

character unique among typotheres. The position of the genus with this

scant information is uncertain. One species is described, _P. dorsatus_.

=Phanophilus dorsatus= Ameghino

P. dorsatus, Amegh., loc. cit. p. 202.

In our collection, two isolated upper molars of this unusual form

occur, corresponding in size and pattern to the one described by

Ameghino. The external column, as seen by fig. 42, is narrow and high.

A single tooth measures 5½ mm. from front to back, and 3¾ mm. in width.

[Illustration: Fig. 43. External view of molar 1—natural size.]

[Illustration: Fig. 44. Milk dentition, genus and species?—natural

size.]

Specimen 3142 gen. and sp.?

This specimen is the mandible with the milk dentition. The molars

present suggest _Prosotherium triangulidens_, but inc. 3 and the canine

are present, and the first two incisors are not enlarged, so it would

seem to represent a genus which I have not been able to identify. Molar

1 is bilobed and similar to that of _Prosotherium_. The deciduous

premolars are all present, all rooted, and all remarkable for their

great antero-posterior elongation. Roots of the incisors and canine

are present, that of the canine being the largest, and those of the

incisors being about equal in size. This would suggest such a form as

_Protypotherium_, were this genus represented in the Deseado beds.

=Interatheriidae=

The family is characterized by the incisors not being enlarged, by

upper and lower premolars and molars being inflexed on both the inner

and out sides, and by the inflated mastoid bulla being filled with

cancellous tissue. The only genus referable to this family, from the

Deseado beds, is _Archaeophylus_.

=Archaeophylus= Ameghino

Archaeophylus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 423.

The genus is based on a skull which preserved most of the upper

dentition except the incisors, and which shows the characteristics of

the family in their inception.

=Archaeophylus patrius= Ameghino

[Illustration: Fig. 45. Archaeophylus patrius after Ameghino, right

upper dentition—natural size.]

A. patrius Amegh., loc. cit.

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.

Trachytherus Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 623.

Eutrachytherus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 429.

This genus was first called _Trachytherus_, and when this was found to

be preoccupied, changed to _Eutrachytherus_. Ameghino gives the dental

formula as

3 0 4 3

-------,

2 1 4 3

but in my specimen which is a comparatively young individual, I find a

small alveolus for the upper canine, which modifies the formula to

3 1 4 3

-------.

2 1 4 3

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. The nasals are lacking, but the bounding bones show them to

have been unusually broad and flat. The maxilla extends up to the

nasals, and bounds the lower border of the orbit, and projects backward

in a heavy overhanging zygomatic process. The lachrymal bone is large

externally, with a large but low lachrymal tubercle just below which

is found the lachrymal duct, opening just in front of the margin of

the orbit. The frontals are short and wide, extending outward over the

orbit in a strong postorbital process which bounds half of the rear of

the orbit. The parietals, meeting medianly, rise in a strong sagittal

crest. Unfortunately the back part of the cranium is lacking. From

another specimen, which contained the brain cast, it is clear that the

bulla was much inflated and hollow, and that there was an inflation in

the upper part of the squamosum, as in _Prosotherium_, etc.

[Illustration: Fig. 46. E. spegazzinianus—½ natural size.]

One specimen with the facial portion badly weathered, but retaining

enough to identify the species as _E. spegazzinianus_, preserved the

brain case, so that it could be prepared out.

The most striking feature of this brain is its relatively large

size, _E. spegazzinianus_ being an animal about the size of a sheep,

and the brain is as large as that of the sheep, which is in strong

contrast to what would be expected of an Oligocene form. Compared

with the herbivorous Oligocene oreodont, _Eucrotaphus_, an animal of

approximately the same size, this brain is half again as large in every

way. A second striking feature is the short compact character of the

brain, the forebrain extending only a short distance in front of the

exit of the optic nerves, and extending backward so as to cover most

all of the cerebellum. Thirdly, the cerebral surface is considerably

convoluted, comparable to the convolution of a pig’s brain. These

features would indicate a specialization of the nervous system,

approximating that of the skeleton, and would indicate that this group

had advanced in intelligence and activity beyond the grade of nervous

development which is apparent in the contemporaries of the _Typotheria_.

The relatively small olfactory lobes are entirely beneath the frontal

lobes and are seen only on the side view, but as there is a large

hippocampal lobe behind them, it would only seem proper to attribute

to these animals a well-developed sense of smell. The frontal lobes

are unexpectedly large, and are not clearly bounded off from the

parietal lobes. The occipital lobes are also well developed and make

a large portion of the backward extension of the cerebrum. The large

size of this area, together with the fact that the optic nerves are

large, indicates a good visual development. The temporal lobes are also

large and extend well down on either side. And, finally, below all the

others, come the swollen hippocampal lobes which complete this large

cerebrum.

The cerebellum is small having neither considerable width or height,

and being overlapped by the cerebrum. The optic nerves are represented

by large projections leaving the twixt-brain well forward under the

forebrain. The medulla is not clearly marked except to show that it,

too, was of fair size.

[Illustration: Fig. 47. Cast of the brain; _A_, from above; _B_, from

the side—natural size. _Cer_, cerebellum; _F_, frontal lobe; _H_,

hippocampal lobe; _Oct_, occipital lobe; _Op_, optic nerve; _T_,

temporal lobe; _x_, cast of cavity in squamosal bone; _Na_, case of

interior of nasal cavity.]

Just behind the hippocampal lobes, and connecting with the cerebellum

appear two striking projections. These represent the two large cavities

in the upper part of the squamosum which are so characteristic of

typotheres. The two large cavities clearly opened into the brain case

by a broad connection which is especially wide at the lower ends. I

find no traces of a connection with the bulla as described by Sinclair

for _Pachyrukhos_. Further down are two small knobs apparently also

representing cavities in the squamosum, and also connected with the

brain case. In considering the brain these should be overlooked; but

they doubtless represent some nervous function to which I have as yet

no clue.

Ameghino considered that _Eutrachytherus_ was the connecting link

between _Archaeohyrax_ and _Typotherium_. I feel that this genus is

too highly specialized to be a connecting form, though it doubtless

belongs to the series which ends in _Typotherium_; and such a form as

_Argyrohyrax_ is more likely to be the really ancestral form.

Two species are described, _E. spegazzinianus_, and _E. conturbatus_,

which is about 15% smaller. Our collection offers a third species, _E.

grandis_, which is nearly 50% larger than the first named species.

=Eutrachytherus spegazzinianus= Ameghino

Trachytherus spegazzinianus Amegh., 1889, Act. Acad. Nac. Cienc.

Cordoba, t. VI, p. 919.

Trachytherus spegazzinianus Lydekker, 1894, Anal. Mus. La Plata, pt. 3,

p. 2.

Trachytherus spegazzinianus Amegh., 1895, Bol. Inst. Geog. Argen., t.

15, p. 622.

Eutrachytherus spegazzinianus Amegh., 1897, Bol. Inst. Geog. Argen., t.

18, p. 428.

This species was founded on the anterior part of a skull with the full

upper dentition. My specimen differs from Ameghino’s in having a tiny

alveolus for the upper canine, the difference being due to my specimen

being younger.

The upper dentition is very characteristic. Incisor 1 is a powerful,

deep-set, curved gnawing tooth, with a heavy layer of enamel on the

anterior face, and none on the other sides; and is moderately beveled

in the rear as a result of wear. The second and third incisors are

much smaller, each having enamel on the outer face only, and with a

marked tendency to become vestigal. The suture of the premaxilla comes

to the base of inc. 3. There follows a short diastema, then a tiny

alveolus for the canine, closely followed by the first premolar which

is also small. The second premolar shows no inflexion. Beginning with

the third premolar there is a strong inner inflexion, which in the

fourth premolar and molars is bifurcated. The molars are considerably

larger than the premolars, the second being the largest of the series.

With each successive molar, the inflexion is wider, so that in m. 3 the

tooth is divided into three lobes of nearly equal size. All premolars

and molars are rootless, curved, and set so deep in the jaw that they

almost meet in the median line. A typical molar measures 50 mm. in

length, of which only 7-8 mm. project above the border of the jaw. All

the back teeth are covered with a thick coating of cement.

[Illustration: Fig. 48. E. spegazzinianus, right upper dentition—natural

size.]

The arrangement of the teeth of the lower jaw is shown in fig. 25 h.,

after Ameghino. The first and second incisors are greatly enlarged.

Incisor 3 is lacking, and the canine vestigal. Pm. 1 is small and

single-lobed, the succeeding premolars and molars being large and

divided into two lobes by a deep external, and a shallow internal

infolding.

MEASUREMENTS

Skull, width between the orbits 60 mm.

Skull, width across the postorbital processes 88 mm.

Skull, height from m. 2 to top of frontal 77 mm.

Skull, width of palate opposite inc. 2 42 mm.

Skull, width of palate opposite m. 2 62 mm.

Dentition, length inc. 1 to m. 3 140 mm.

Dentition, incisor 1 ant.-post. length 11 mm. width 16 mm.

Dentition, pm. 3 length 11 mm. width 13 mm.

Dentition, m. 2 length 22 mm. width 16 mm.

=Eutrachytherus conturbatus= Ameghino

Trachytherus conturbatus Amegh., 1895, Bol. Inst. Geog. Argen., t. 15,

p. 623.

Eutrachytherus conturbatus Amegh., 1897, Bol. Inst. Geog. Argen., t.

18, p. 429.

This species is founded on upper teeth, which are said to be relatively

smaller anteriorly, and actually smaller throughout, by about 15% than

are those of the preceding species. Molar 1 measures 17 mm. long by 9

mm. wide.

=Eutrachytherus grandis= sp. nov.

This species is based on upper molars 1 and 2 of the left side, from

the Deseado beds, of the Chico del Chubut, west of Puerto Visser.

The teeth are typically those of the genus and differ only from

other species in their large size, being some 50% larger than the

corresponding teeth of _E. spegazzinianus_. Each is covered with a

layer of fully half a millimeter of cement.

[Illustration: M¹ M²

Fig. 49. E. grandis, molars of the left side—natural size.]

MEASUREMENTS

Upper molar 1, length 29 mm., width 21 mm.

Upper molar 2, length 30½ mm., width 18 mm.

=Argyrohyrax= Ameghino

Argyrohyrax Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 435.

The genus is distinguished by the full dentition in closed series,

and by the upper molars having a deep internal inflexion which is

bifurcated, making the teeth at least incipiently three-lobed. Incisor

1 is relatively somewhat wider than in the preceding genus. It seems

to me that it is from such a genus that _Typotherium_ arose, by the

reduction of the lateral incisors, the canine, and the first two

premolars, and by the increase of the bifurcated internal fold. Three

species have been described, _A. proavus_, the type species, _A.

acuticostatus_, of a little smaller size, and _A. proavunculus_ of

still smaller size.

=Argyrohyrax proavus= Ameghino

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

This species occurs three times in the Amherst collection. The best

specimen has pm. 1, 3, 4, and m. 1 and 2 of the upper jaw. The species

is characterized by a narrow furrow near the anterior external margin

of the premolars and molars; and by pm. 3 and 4 and the molars having

a deep internal bifurcated inflexion, which tends to make these teeth

three-lobed.

[Illustration: Fig. 50. Right upper dentition, the outline teeth after

Ameghino—natural size.]

The genus is known only by the upper dentition, and while I did not

find any associated lower teeth, I believe that some one of the genera

known only by the lower dentition, like _Plagiarthrus_, is that lower

dentition.

MEASUREMENTS

Upper dentition, length inc. 1 to m. 3 (@ Ameghino) 71 mm.

premolar 1, length 7 mm., width 4 mm.

premolar 3, length 7 mm., width 6 mm.

premolar 4, length 8 mm., width 6 mm.

molar 1, length 8 mm., width 6½ mm.

=Argyrohyrax proavunculus= Ameghino

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

The species is simply said to be much smaller than the preceding,

which, by the measurements, would figure out about 27%. The

measurements given are pm. 1 to m. 3, 33 mm.

=Argyrohyrax acuticostatus= Ameghino

A. acuticostatus Amegh. 1901, Bol. Acad. Nac. Cienc. Cordoba, t. 16, p.

361.

This species is described as differing from _A. proavus_ in being

somewhat smaller, but I find it about the same size. The specific

character is in the teeth being more compressed, and in the anterior

vertical margin of the upper molars being developed in the form of a

very salient crest.

=Isoproedrium= Ameghino

Proedrium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 623.

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

Isoproedrium, Amegh., 1903, Anal. Soc. Cient. Argen., t. 56, p. 18.

This genus is based on a toothless mandibular symphysis of large size,

on which the second incisor is indicated as larger than the first. We

found one lower jaw, which, though imperfect, confirms the above as a

genus and adds the following for generic characters; premolars with

a shallow inflexion on the inner and outer sides, the molars with a

shallow inner, and a narrow deep outer inflexion, heavy layer of cement

on the premolars and molars, enamel reduced on the anterior internal,

and the posterior internal corners of at least the premolars.

=Isoproedrium solitarium= Ameghino

loc. cit. above.

[Illustration: M1 4 3 2 pm1 2 i1

Fig. 51. Right mandible, dotted line indicated alveolus—natural size.]

I have assigned the specimen shown in fig. 51 to this species. Alveoli

of the first and second incisors show inc. 2 considerably larger than

inc. 1. About the third incisor and the canine my specimen shows

nothing, being broken down in that region. Pm. 1 is represented by a

moderately large alveolus, 10 mm. long. Pm. 2 is 13 mm. long by 10

mm. wide, and slightly constricted medianly as far as the enamel is

concerned, the furrow in either side being filled with cement. Pm. 3

is 18 mm. long by 12 wide and similar. There is only an alveolus for

pm. 4, which is 23 mm. long. M. 1 is incomplete, but was about 23 mm.

long by 10½ mm. wide and is distinguished by the deep outer inflexion.

Each tooth present is covered with a heavy layer of enamel nearly a

millimeter thick; and each of the teeth is unique in that the enamel is

wanting on the anterior internal and the posterior internal corners of

the teeth.