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.
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.
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. |
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. |
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.
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. |
CHAPTER XII
Proboscidea
Suborder Pyrotheria
This suborder was established by Ameghino to receive the peculiar genus Pyrotherium and related forms. These animals are of large size, massive build, with narrow elongated skulls, in which the nasal opening is situated far back, as in animals with a proboscis; with a tiny brain case surrounded by cellular spaces; with the maxillae, palatines, pterygoids and alisphenoids developed downward, so that the palatal plane makes a strong angle with the basicranial plane; and with the occipital condyles high up on the back of the skull. Then the first and second upper incisors and the second lower incisors are developed into enormous tushes with enamel on the anterior sides only. The remaining incisors, the canines, upper premolar 1, and lower premolars 1 and 2 are wanting; the remaining premolars and the molars being developed into great quadrilateral grinders, each with two transverse crests. The neck is short, the limbs massive and short, especially the lower members of each limb, and the feet were probably five-toed.
The relationship of these forms has been the subject of extended discussion: Ameghino seeing in this genus the ancestors of the Proboscidea, and comparing them with Palaeomastodon, Dinotherium and Barytherium, even finding resemblances to Diprotodon; Gaudry concludes that they are not proboscidians; and others have suggested that they were specialized toxodonts. I have prepared the following table of comparisons with Palaeomastodon, a toxodont, and Diprotodon.
Still other forms like Amblypoda and Arsinotherium have been suggested as having characters in common with Pyrotherium, and it is clear that, with such a variety of forms, some of the characters must be parallelisms due to a common adaptation, and only one of these varied groups can be the one to which Pyrotherium is related. For myself, I have made comparisons with the Amblypoda and Arsinotherium, and feel that such features as the massive limbs, shape of individual bones, etc., are due simply to the fact that all these are massive animals. In the case of Arsinotherium, there are some characters which are also common to hyracoids and elephants, like the position of various basicranial foramena, the prolongation backward of the jugal and the shape of the palatines. My conclusion is that Pyrotherium is related to the proboscideans, and came from the same stock which gave rise to hyracoids, elephants and Arsinotherium. I think further that Pyrotherium belongs definitely to the proboscidean line.
Referring back to the foregoing table. The development of tushes may be an adaptive character; but in the elephants it is inc. 2 of the upper and inc. 2 of the lower jaw which are so developed. In Pyrotherium, in the upper dentition, it is also inc. 2 which makes the tush, and inc. 1 is enlarged as in Moeritherium, and, so far as we know, has not been reduced in later forms as it was in the elephant line. In the lower jaw we have no final evidence which will show whether it is inc. 1 or inc. 2 which makes the tush; but the lower tush bites against upper inc. 2 and I have considered it to be incisor 2.
The loss of the teeth behind the tushes is a character to be expected in the development of tushes and gives no data. The bilophodont character of the back teeth has occurred many times in the animal kingdom and while it may be the inheritance of the early elephants it can not be used as an argument.
The position of the nasal opening looks very much like that of elephants, but again is coincident with the development of a proboscis. However, this has not occurred a great number of times in the animal kingdom, and where it has, it takes a variety of forms of modification. In Pyrotherium, the modification is of the type in elephants, and elephants only.
A very striking feature is the development of the dental region downward so that the basicranial axis is bent upward, making an angle of about 140 degrees. There are other cases of the bending of the basicranial axis; but in the other ungulates it is a bend downward, the reverse of what we find here and in elephants. To adjust the posterior part of the nasal chamber to this, the pterygoids and the alisphenoids are developed into great wing-like plates on either side. I find this modification of the basicranial axis and of the palatal, pterygoid and alisphenoid bones in no other group but the elephants. In Palaeomastodon it has been developed to a degree so that the angle is about 155 degrees.
The back of the palatine bones is also characteristic, for these begin as narrow pointed bones and behind the last molar expand into wide plates, just as in Palaeomastodon (and in no other groups), having the postpalatine foramen opposite or behind the last molar.
The post-tympanic region of the squamosum is modified so that this process unites with the anterior squamosal region to crowd out more or less completely the tympanic bone where it should surround the auditory meatus. This feature is common to the elephants, the hyracoids, and the toxodonts, so that I consider it a primitive feature indicative of the ultimate common ancestry of these groups. The tympanic bulla can be compared with that of elephants closely, and has much in common with that of toxodonts, but in this last group the tympanic is much more highly developed.
The premaxilla bone in Pyrotherium is crowded out, so that it makes no part of the palate, which is a character of elephants, and in contrast to toxodonts or other groups which have been mentioned. There are two antorbital openings as in elephants, and a feature not common, though not unknown. On either side of the brain case are cellular spaces with intercellular lamellae, which are so characteristic of elephants; a confirmatory feature, though in itself not conclusive.
The foramena on the base of the cranium are similar to those on the base of the cranium of elephants, though there are some variations, as for instance, the exoccipital foramen, is isolated in Pyrotherium, but fused with the posterior lacerum foramen in elephants, and other slight variations in position; but, on the whole, the foramena of Pyrotherium are much closer to those of elephants than of any other group. There is also much in common with toxodonts and with hyracoids, as would be expected if they have a common ancestry. There is no suggestion of a marsupial arrangement as would be necessary if related to Diprotodon.
The atlas of Pyrotherium is peculiar in having a marked hypophysis which is unusual, but is a feature of the atlas of Palaeomastodon and Moeritherium. The axis is peculiar in that the odontoid is flattened on the upper side and very short and wide. In this the form is unique. The continuation of the articular surface on the lower side of the odontoid with the articular surfaces of the ant. cotyles is a feature also of elephants. The remaining cervicals are greatly shortened almost to plates, which is elephantine again, though this short neck is approximated by Diprotodon, some Amblypods and Arsinotherium, so that it must be in general looked upon as an adaptive feature, though in its detail it shows again an elephant character.
The upper members of the limbs are longer than the lower, which is common to many massive animals. The humerus is tremendously flattened from front to back, even more so than in any of the animals used for comparison, though flattening is a feature of them and of the elephants the most so. With the flattening, the deltoid ridge is prolonged enormously making a crest along the outer side of the bone, which at the lower end rises in a prominent process, as in elephants (also in Diprotodon but in this case the rest of the bone is very different). In addition to this, the supinator ridge is prolonged upward until it almost meets the deltoid, ending in a sharp spur at the top. This spur is more marked in Pyrotherium than in elephants, although they show the same development of the supinator ridge.
The femur has the head much higher than the greater trochanter, which is a feature common to elephants, Diprotodon, Arsinotherium, etc., so that it must be looked upon as an adaptation. The third trochanter has disappeared, and in elephants, it is lost in the advanced forms, remaining however as a trace in Palaeomastodon.
The tibia is very short and massive and hardly gives any suggestions of relationship, except that it is not fused with the fibula at the upper end, in which it is in strong contrast to the toxodonts.
While in the [table of comparisons] numbers 1, 2, 3, 4, 8, 9, 10, 14, 17, 19, 20, and 21 may be, in part, or wholly, interpreted as adaptations, and alone would not be at all conclusive of relationship to elephants, numbers 1, 5, 6, 7, 8, 11, 12, 13, 15, 18, and 21 point toward the elephants as the close relatives of the Pyrotheria. In the first series of points there are none which mitigate against associating these two groups, while if the attempt is made to associate Pyrotherium with any group other than Proboscidea there are strong points, and a number of them, which would prevent this association. As a result of the foregoing, together with a feeling which continued handling of the specimens has given me, I can come to no other conclusion than that the Pyrotheria should be placed under Proboscidea.
In his Linea Filogenetica de los Proboscideos, Ameghino assigns to this suborder, or at least puts into the phylogenetic tree, a considerable number of forms from the Casamayor beds, all of them genera with bunodont molars, usually known by but one or two teeth, such as Asmithwoodwardi, Nephracodus, Cephanodus, Paulogervaisia, and the better known genera, Carloameghinia, and Didolodus, all of which he makes ancestral to Pyrotherium. So far as known, however, these forms show none of the peculiarities of the Pyrotherium skull or dentition, so that it is difficult for me to see any reason for including them even in the suborder. The genus Carlozittelia, from the upper Casamayor, is in a different position, having an enlarged upper incisor (found isolated) and molars of the bilophodont type. I should include this in the family Pyrotheridae and none of the others.