ASTRAPOTHERIA
This group is composed of large, long limbed creatures, with a
highly specialized dentition, in which the canines of the upper
jaw are developed into great curved tushes, resembling those of
_Pyrotherium_; while the canines of the lower jaw are compressed in the
antero-posterior diameter and protrude laterally, like those of pigs.
Upper premolars 1 and 2 are reduced or lacking, while pm. 3 and 4 are
also reduced, but usually retained. The upper molars are brachydont,
and have a crown very like that of the molars of homalodontotheres.
The lower incisors are small, proclivous, and set at intervals around
the broad semicircle of the front of the fused lower jaws. The lower
canines are permanently growing teeth, smaller than the upper canines,
project laterally, and have the tips recurved. Premolars 1 and 2 are
usually lacking, pm. 3 more or less reduced, and pm. 4 is a normal,
short, molariform grinder. The lower molars have the same basal pattern
as in _Toxodonta_, the crown carrying two crescents with a plump pillar
in the basin of the posterior crescent, the pillar, however, being
situated far forward near the anterior horn of the rear crescent.
Lydekker made an order _Astrapotheria_ including the _Astrapotheria_
and _Homalodontotheria_, but as the dentition of the two groups is so
different, because of the enormous enlargement of the frontal region,
and because of the reduction of the premolars, I am convinced that
these two groups represent totally divergent lines of development; and
I have therefore made each of the groups a separate suborder.
Ameghino has described several genera, which make a progressive series
and show a constantly progressive variation as far as they are known.
GENUS FORMATION FORMULA
Albertogaudryi Casamayor ? 1 ? 3 Post, inner and
------- post. isolated.
? 1 ? 3 median. cusps
isolated.
Astraponotus Astraponotus ? 1 2 3 Post. inner cusp,
------- united with wall
? 1 ? 3 making small
lobe.
Parastrapotherium Deseado and Colpodon ? 1 2 3 Post. lobe large,
------- also a strong
3 1 2 3 crista.
Astrapothericulus Astrapothericulus ? 1 2 3
-------
3 1 2 3
Astrapotherium Santa Cruz 3 1 2 3
-------
3 1 1 3
In the Deseado beds, beside _Parastropotherium_, Ameghino has described
_Liarthrus_, based on an upper second premolar and part of another
tooth, but I can see no structural variation from _Parastropotherium_
or indeed from _P. holmbergi_; so I consider this genus as a synonym.
As to the genus _Traspoatherium_, I can not see in it any reason for
making a genus separate from _Parastrapotherium_.
=Parastrapotherium= Ameghino
Parastrapotherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 636.
Parastrapotherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 449.
Liarthrus Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 641.
Liarthrus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 451.
Traspoatherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 641.
Traspoatherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 450.
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 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. The lower jaws are similar to those of _Astrapotherium_,
except that the rami are deeper. The front ends are fused and expanded
making the anterior much enlarged, and causing the incisors to stand at
intervals as in _Coryphodon_. The symphysis is massive and prolonged
backward nearly to premolar 3. The rami are plump and unusually thick.
[Illustration: Fig. 102. Upper dentition of Astrapothericulus
iheringi—½ natural size.]
Of the upper dentition, Ameghino figures only the first molar and
the canine. I have given Ameghino’s figure of the upper dentition of
_Astrapothericulus_, to indicate what this would be like, for the
variation is only slight. The canine is a great tush, not unlike the
incisor-tush of _Pyrotherium_, oval in cross section with the greater
diameter from front to back. The first and second premolars have
disappeared. Premolars 3 and 4 are greatly reduced. The molars are very
like those of _Asmodeus_, large brachydont grinders, composed of an
outer wall, and an anterior and posterior lobe. The external cingulum
is a trace only, and the internal cingulum is developed in varying
degrees. The basin is deep and subdivided by a crista which rises from
the external wall, and as the surface is worn off unites with the
anterior lobe, cutting off a small pit. Behind the posterior lobe is a
small basin, bounded in the rear by a second crista from the rear end
of the external wall, which, as the tooth is worn down, unites with the
posterior lobes, cutting off a small posterior pit, suggestive of that
of homalodontotheres.
The three lower incisors are expanded at their ends into thick
shovel-like crowns, each with a strong crescentic cingulum on the
posterior face, and with a shallow furrow on both the front and back
faces. Relatively the incisors are much larger and longer than in
_Astrapotherium_.
The lower canine is flattened on the upper face, so that its cross
section is close to semicircular making a typical permanently growing
rooting implement. This tooth is relatively shorter and smaller than in
_Astrapotherium_.
Premolars 1 and 2 are wanting, a long diastema occupying the interval
between the canine and pm. 3. Premolar 3 is greatly reduced in size,
and in my specimen has fallen out, being represented by a small
alveolus. I judge that in old individuals it falls out. The fourth
premolar and the molars are typically those of _Toxodontia_. The young
show two plump crescents, with a low plump pillar, situated near the
anterior horn of the posterior crescent, which pillar, as the tooth
wears, unites with the anterior horn.
The scapula is a remarkably heavy and elongated bone, greatly arched
where it lay over the ribs. The spine is high and heavy, with the upper
margin developed into a thick ridge like a banister rail, which is
prolonged in front to, or a little beyond, the level of the glenoid
fossa, this distal portion being expanded into a broad plate more
than half as wide as the widest portion of the blade of the scapula.
The glenoid fossa is relatively small, oval in outline, and with the
long axis parallel to the long axis of the body. The anterior margin
of the articular surface is reflexed, apparently to come in contact
with the base of the greater tuberosity of the humerus. This glenoid
cavity is only large enough to actually cover about half of the head
of the humerus, and fits so that, in a position of rest, the glenoid
covered the outer part of the humeral head, and only articulated on
the inner part of the humerus head when the limb was bent inward. The
blade of the scapula is narrow, with the proximal end prolonged and
ending in a thick rugose mass. The anterior and posterior margins are
rugose and thickened, the great thickness of the proximal end being
due to the convergence of these thickened margins and the heavy spine.
Lastly, this thick proximal end is peculiar in having on its posterior
side a large rugose cavity, which was apparently to receive muscular
attachments.
For such a heavy animal, the humerus is extraordinarily long and
slender. The sessile head is strongly compressed from side to side,
very convex, and much larger than the glenoid fossa, its articular
surface extending onto the base of the greater tuberosity. This
tuberosity is heavy and thick, but does not project above the head. The
powerful deltoid ridge extends from the tuberosity two-thirds of the
way down the shaft. The shaft is unusually slender. Distally it expands
laterally to make the two large epicondyles, of nearly equal size. The
trochlea is relatively narrow, the internal surface being the narrower,
and rising to a high margin; while the external portion is wider,
rounded, and has a low margin. The supratrochlear fossa is moderately
deep, the anconeal fossa somewhat deeper, but there is no connecting
foramen.
Gaudry[17] figures a radius and ulna, both relatively long bones,
and closely apposed; so that there was no possibility of a rotary
motion of the forearm. The proximal end of the radius is expanded, so
that its articular surface is in contact with the full width of the
humeral trochlea on the anterior side. Below, the bone contracts to
a moderately slender shaft, and then expands distally into a heavy
club-like distal end. The ulna has a short but heavy olecranon process,
with a prominent coronoid process. The sigmoid notch is shallow, but
the articular surface expands on both sides, so that it covers the full
width of the humeral trochlea on the posterior side. Distally the ulna
is not so heavy as the radius.
[Footnote 17: Anal. Palaeontologie, t. 1, p. 5, 1906.]
Under the name _Pyrotherium romeri_, Ameghino[18] figures a carpus and
metacarpus, which Tournier[19] however assigns to _Parastrapotherium_,
probably _P. herculeum_; and figures a carpus and metacarpus of the
same type, but smaller, which he attributes to _Parastrapotherium_.
I, however, can not see how such a small foot can belong to so large
an animal, and feel that, until evidence of direct association
is given, it is best not to consider these feet as belonging to
_Parastrapotherium_, but rather to _Pyrotherium_.
[Footnote 18: Bol. Inst. Geog. Argen., t. 18, p. 442, fig. 25, 1897.]
[Footnote 19: Bul. Soc. Geol. France, ser. 4, t. 5, p. 305, 1905.]
Of the femur I have only the distal end, which, however, corresponds
completely with the one figured by Gaudry. It is a long bone, slightly
shorter than the humerus, with a small head, set on a short and poorly
outlined neck. The greater trochanter is wide and rugose, rising
to about the same height as the head. The lesser trochanter is not
distinguishable. About the middle of the shaft there is a powerful
third trochanter, which continues as a narrow ridge upward to the
greater trochanter, and downward in a similar narrow ridge almost to
the outer condyle. At the proximal end the shaft is greatly flattened,
but in the central and lower parts becomes almost circular in section.
The two condyles are set wide apart, project considerably behind the
posterior face of the shaft, and are only slightly convex. The trochlea
is of moderate width, short, and shallow.
Gaudry outlines a short, heavy, rugose calcaneum which has but a short
tuber; a flat navicular; a small cuboid; and an astragulus with only a
slight convexity of the trochlea, and with the navicular facet directed
obliquely forward, making an angle of 127° with the plane of the
trochlea, which, as he says, would indicate a semidigitigrade position
of the pes.
The following species are distinguished by Ameghino as coming from
the Deseado beds: _P. holmbergi_, _P. troussarti_, _P. lemoinei_, _P.
ephebicum_, _P. martiale_, _P. superabile_, _P. insuperabile_. The
various species are known from the same parts in but a few cases. Their
relative sizes are indicated from the following compilation of the
measurements given by Ameghino:
======================================================================================
| UPPER | LOWER | LOWER | LOWER
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+------+
|pm. 4|m. 1 |m. 2 | m. 3 |pm. 4|m. 1 |m. 2 |m. 3 |inc. 1 |pm. 4
| | | | | | | | |-m. 3 |-m. 3
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
P. holmbergi | |56-56| | | | | | | |
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
P. troussarti | | | | |24- |40- |57- |60- | | 180
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
P. lemoinei | | |34-34| | | | | | |
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
P. ephebicum | | | | | |31-16|42-21| | |
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
P. martiale |30-42| |82-83| | | | | | 550 |
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
P. superabile |30-43| | | | | | | | |
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
P. insuperabile |37-48| | |100-80|34-23| | | | |
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
P. (Liarthrus) copei |29-46| | | | | | | | |
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
P. (Traspoatherium) |19-27| | | | | | | | |
convexidens | | | | | | | | | |
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
Amherst specimen | | | | |28-26|43-28|58-32|70-36| 455 | 200
---------------------+-----+-----+-----+------+-----+-----+-----+-----+-------+-------
_P. holmbergi_ is the type species, and of considerable size, and to it
I have assigned my material. In such a large animal, variations in size
are to be expected. _P. troussarti_, as described, is a tenth smaller
than _P. holmbergi_, the only structural character differentiating
it being the isolation of the pillar in the lower molars, which is
a character due to youth; so I have considered it a synonym of _P.
holmbergi_. _P. ephebicum_ is a much smaller and distinct species,
with which I should associate the single upper molar to which the
name _P. lemoinei_ has been given. _P. martiale_ is a large species,
distinguished by the strong development of the cingulum on the internal
side of the upper molars, and on the inner side of the lower molars;
and by lower premolar 3 being well developed with two roots. _P.
superabile_ is of the same size as the foregoing, but has the cingulum
on upper premolar 4 (the only tooth known) less developed. I should
therefore consider it a synonym of _P. martiale_. _P. insuperabile_ is
the largest species, and is distinguished by the excessive development
of the cingulum. _Liarthrus_ is founded on an upper pm. 4 with a part
of pm. 3, but, as far as I can see, does not differ in character or
size from _P. holmbergi_. _Traspoatherium_ is based on upper premolars
which are distinguished by the roots being fused from side to side. I
think it is an age character and for the present would consider it the
same as _P. holmbergi_, probably the tooth being pm. 3.
=Parastrapotherium holmbergi= Ameghino
P. holmbergi Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 636.
P. holmbergi Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 449.
P. troussarti Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 638.
P. troussarti Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 449.
Liarthrus copei Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 641.
Liarthrus copei Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 451.
Traspoatherium convexidens Amegh., 1895, Bol. Inst. Geog. Argen., t.
15, p. 641.
Traspoatherium convexidens Amegh., 1897, Bol. Inst. Geog. Argen., t.
18, p. 450.
Parastrapotherium holmbergi Tournier, 1905, Bul. Soc. Geol. France,
ser. 4, t. 5, p. 305.
Astrapotherium holmbergi Gaudry, 1906, Anal. Palaeontologie, t. 1, p. 5.
To this, the type species, I have assigned all the material we found
on the Chico del Chubut, west of Puerto Visser, as enumerated under
the generic description. The lower jaws belonged to an old individual.
The humerus and scapulae were found associated, the femur isolated.
Of the upper dentition, the only available measurements are those of
Ameghino for the first molar, and the canine.
Upper dentition, canine, length 256 mm.
Upper dentition, molar 1, length 57 mm., width 57 mm.
[Illustration: Fig. 103. Upper molar 1 of the left side—natural size,
after Ameghino.]
The measurements of the complete pair of lower jaws which we found are
Lower dentition, length from inc. 1 to m. 3 455 mm.
Lower dentition, incisor 2, length 22 mm., width 22 mm.
Lower dentition, canine, ant. post. diam.
at alveolus 52 mm.
Lower dentition, canine, trans. diam.
at alveolus 26 mm.
Lower dentition, diastema from c. to pm. 3 116 mm.
Lower dentition, premolar 4, length 28 mm., width 26 mm.
Lower dentition, molar 1, length 43 mm., width 28 mm.
Lower dentition, molar 2, length 58 mm., width 32 mm.
Lower dentition, molar 3, length 70 mm., width 36 mm.
Height of mandible under molar 3 83 mm.
The scapula is a very long heavy bone, with a narrow blade, and a high
spine which has its upper margin thickened so as to appear like a
banister rail. We found one complete scapula and a second incomplete
one associated with it, which corresponded in all ways to the first
one.
[Illustration: Fig. 104. Lower jaws—⅕ natural size.]
[Illustration: Fig. 105. Dorsal view of right scapula—⅕ natural size.]
[Illustration: Fig. 106. Right humerus, posterior aspect—⅕ natural
size.]
[Illustration: Fig. 107. Left femur, posterior side—⅕ natural size;
outline of upper portion after Gaudry from Astrapotherium magnum.]
The following measurements are taken from specimen No. 3328:
Scapula, greatest length 694 mm.
Scapula, greatest width 283 mm.
Scapula, glenoid fossa, ant.-post. diameter 130 mm.
Scapula, glenoid fossa, transverse diameter 90 mm.
Scapula, height of spine 120 mm.
Scapula, width of enlarged margin of spine at the lower end 170 mm.
Scapula, width of margin in middle 45 mm.
The humerus was associated with the two scapulae mentioned above, and
is complete. For such a large animal, its length is excessive, greater
than that of the species assigned by Gaudry to _P. herculeum_ which
species has a skull larger than that of _P. holmbergi_.
Humerus, greatest length 720 mm.
Humerus, greatest width across proximal end 248 mm.
Humerus, least diameter of shaft 78 mm.
Humerus, width across the epicondyles 220 mm.
Humerus, width of trochlea on distal end 125 mm.
The femur which Gaudry figures as belonging to _Astrapotherium magnum_
corresponds, as far as the distal end will admit comparison, with
the one which we found in the Deseado beds, so that in restoring the
outline of the missing parts, I have based it on this _A. magnum_.
Femur, length (estimated) 480 mm.
Femur, width of distal end 135 mm.
Femur, width of trochlea 57 mm.
=Parastrapotherium ephebicum= Ameghino
P. ephebicum Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 639.
P. ephebicum Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 449.
P. lemoinei Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 640.
P. lemoinei Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 450.
Astrapotherium ephebicum Gaudry, 1904, Mem. Soc. Geol. France, t. 12,
p. 15.
Ameghino based this species on a portion of the mandible of an old
individual with molars 1 and 2. Its chief distinction lies in its small
size as compared with _P. holmbergi_. Gaudry assigned to this species
some upper teeth. We found no specimens of this species. The following
are the measurements of the type according to Ameghino.
Lower dentition, molar 1, length 31 mm., width 16 mm.
Lower dentition, molar 2, length 42 mm., width 21 mm.
=Parastrapotherium martiale= Ameghino:
P. martiale Amegh., 1901, Bol. Acad. Nac. Cordoba, t. 16, p. 402.
P. superabile Amegh., 1901, Bol. Acad. Nac. Cordoba, t. 16, p. 402.
[Illustration: Fig. 108. Upper molar 1 of the left side—natural size,
after Ameghino.]
The species seems to have been founded on abundant material,
representing an animal of larger size than _P. holmbergi_, which is
distinguished by the greater width of the crowns of the incisors, by
straight canines diverging but little, by a strong cingulum on the
outer side of the lower molars and the inner side of the upper molars,
and by the narrow symphysis of the lower jaws. _P. superabile_ was
distinguished by a difference in the arrangement of the roots of upper
pm. 4, but as the pattern of the crown is the same, as is also the
size, I feel that this difference is simply an individual variation.
The following measurements are given by Ameghino:
Upper dentition, length from pm. 3 to m. 3 240 mm.
Upper dentition, premolar 4, length 30 mm.
Upper dentition, premolar 4, width 43 mm.
Upper dentition, molar 2, length 82 mm.
Upper dentition, molar 2, width 83 mm.
Lower dentition, length from inc. 1 to m. 3 550 mm.
=Parastrapotherium insuperabile= Ameghino
P. insuperabile Amegh., 1901, Bol. Acad. Nac. Cordoba, t. 16, p. 403.
This is the largest of all the species, and is distinguished by the
enormous development of the cingulum on the anterior, inner, and
posterior sides of the upper molars, the same being uninterrupted and
so elevated, that the internal crests seem to rise out of a basin. The
following measurements are taken from Ameghino:
Upper dentition, premolar 4, length 37 mm., width 48 mm.
Upper dentition, molar 3, length 100 mm., width 80 mm.
Lower dentition, premolar 4, length 43 mm., width 23 mm.