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 |
| ? 1 ? 3 | isolated. median. | ||
| cusps isolated. | |||
| Astraponotus | Astraponotus | ? 1 2 3 | Post. inner cusp, |
| ? 1 ? 3 | united with wall | ||
| making small lobe. | |||
| Parastrapotherium | Deseado and Colpodon | ? 1 2 3 | Post. lobe large, also |
| 3 1 2 3 | also a strong 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.
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.
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.
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.
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 -m. 3 |
pm. 4 -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) 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.
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. |
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.
Fig. 104. Lower jaws—
⅕ natural size.
Fig. 105. Dorsal view
of right scapula—
⅕ natural size.
Fig. 106. Right humerus,
posterior aspect—
⅕ natural size.
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. |
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. |
P. martiale Amegh., 1901, Bol. Acad. Nac. Cordoba, t. 16, p. 402.
P. superabile Amegh., 1901, Bol. Acad. Nac. Cordoba, t. 16, p. 402.
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. |
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. |