Pyrotheriidae Ameghino
All the forms assigned to this family are supposed to be closely related to Pyrotherium and to have much the same structure. Ameghino has proposed the following genera, Pyrotherium, Parapyrotherium, Richardowenia, Archaeolophus, Propyrotherium.
Parapyrotherium is based on a small molar and a tush which Ameghino first described as Pyrotherium planum, later elevating the species to a genus, designated as Parapyrotherium, differentiated by the transverse crests being low and the valley at either end being blocked by an intertubercular ridge. Gaudry considered that this genus represented either the milk teeth of P. romeri, or a variation of that species. I can not see the basis of a new genus in the material.
The genus Richardoweni is based on half of a molar, which has the transverse crest interrupted in the middle. Too little is known of this form to base a valid genus or even to associate it with Pyrotherium.
Archaeolophus is founded on a small tush and part of an upper molar, also inadequate material for a genus. It is probably Pyrotherium.
Propyrotherium is a smaller form from the Astraponotus beds, apparently a good genus; the type species being P. saxeum, of considerable smaller size than any of the Deseado species. The distinctive features of the genus can not be given until more material is known.
Carlozitteli is based on a small form from the Casamayor with narrow molars. An incisiform tush is associated with the molar, which, if correctly associated, would indicate a wide deviation from Pyrotherium, and would probably be an ancestral form. A second species is reported from the lower Deseado beds, but I am a little skeptical as to the horizon.
Pyrotherium Ameghino
- Pyrotherium Amegh., 1889, Actas Acad. Nac. Cienc. Cordoba, t. VI, p. 617.
- Pyrotherium Lydekker, 1894, Anal. Mus. La Plata, Palaeontologia Argentina pt. 3, p. 4.
- Pyrotherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 609.
- Pyrotherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 441.
- Pyrotherium Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p. 19-43.
- Pyrotherium Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p. 223-4.
- Pyrotherium Gaudry, 1909, Anal. Palaeontologie, t. 4, p. 1-28.
- Parapyrotherium Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p. 29.
The type species of the genus is P. romeri, which is however a rare species, most of the material and the best known belonging to P. sorondoi. The Amherst Collection contains a skull, complete except that the top of the brain case is crushed in and the parietals lost; a second skull with the full upper dentition but lacking the cranium; four lower jaws; two isolated tushes; the atlas, axis, and cervicals 3 and 4; the humerus; the proximal end of the femur; and part of the front foot; all from the Chico del Chubut west of Puerto Visser. Gaudry had upper and lower dentition and the fore and hind limbs except the feet. Ameghino described the upper and lower dentitions and a fore foot, so that with our material we now have a basis for a fairly complete discussion, the vertebral column being the major part which is still lacking.
The first striking feature is the dental formula. As formerly given, it is inaccurate, there being two great tushes on either side of the upper jaw, instead of one, as described. At first sight, I thought it might be a meristic variation, but both of my skulls show the same arrangement on both sides, and these are the first two skulls which have been found complete to the front end, and neither is by any means a young individual. The dental formula would then read
- 2 0 3 3
- ———.
- 1 0 2 3
Upper incisor 1 is a rootless, permanently growing tush about a fourth smaller than inc. 2, but of the same character, being oval in cross section and having enamel on the front face only. These first incisors are directed downward, so that their ends stand between and very slightly in front of the second incisors. The end of each is worn bluntly round in contrast to the beveled end of inc. 2. The second incisor is larger, rootless, and permanently growing, with a hollow base, enamel on the front face only, and oval in cross section. Both these teeth have a layer of cement on them, extending some distance beyond the alveolus. The tips are worn in a long bevel on the posterior side, very much as is the case on the incisors of rodents.
The third upper incisor, the canine, and premolar 1 are lacking, a long diastema occupying their place, out of which they have been crowded by the development of the enormous root of inc. 2, which extends 150 mm. and more back into the jaw. P. romeri is distinguished from the others by pm. 1 being present.
The teeth of the upper premolar-molar series have their crowns expanded, and the two series of either side have moved toward each other; until in front they are in contact while in the rear they are only 50 mm. apart, narrowing the palate in a unique manner, and giving the impression that the palate is mostly a grinding surface. The premolars are completely molariform and the whole series is at an advanced stage of specialization.
Premolar 2 is three-rooted, with a triangular crown on which are three mamma-like tubercles, the larger one in front, and two behind. As the crown is worn, these unite into a flat, grinding surface, surrounding a central pit which opens behind. Premolars 3 and 4 and all the molars are large, four-rooted, quadrilateral teeth, each with two transverse crests running clear across the crown, and with a small cingulum across the anterior margin. Before they are worn, the top of each crest is tuberculated, and the cingulum is crenulated. In wearing, the anterior face of each crest is ground down; so that instead of the crown wearing to a level surface, it retains throughout life two oblique grinding surfaces.
The lower dentition is more reduced than the upper. When in position, the tips of the two lower tushes diverge, so as to come in contact with the tips of the second upper tushes, from which I conclude that the lower tush is the second, rather than the first incisor, the latter having been lost when the second became enlarged as was the case in elephants. This lower tush has the same oval cross section, enamel on the front face only, and beveled tip as the corresponding upper incisor; but, in the same individual, is somewhat longer and slenderer. When isolated, however, it is difficult to tell whether one is handling a small upper tush or a larger lower one.
The remaining incisors, the canine, the first and the second premolars are wanting, and their place is taken by a small diastema. The lower premolars and the molars are similar to those of the upper jaw, except the cingulum is on the posterior margin, and the wear is on the posterior face of each transverse crest.
The skull is very long and narrow, with wide and deep zygomatic arches. The nasal opening is moved back from the front of the snout to just opposite the orbit, leaving a long, narrow, but heavy snout, made up mostly of the premaxillae, on the anterior end of which is an oval boss, which must have served as an attachment for muscles. With the tushes developed so as to bite against each other, as in a gnawing animal, I can not see any possibility for the development of a pendant proboscis, but think that the snout must have been developed more like that of a pig, but probably to a greater degree. The premaxillae are long and heavy, and prolonged backward to contain the roots of the great tushes; but these bones are not developed on the palatal side of the snout at all. The maxillae are also massive, carrying the premolars and molars, and extending forward to the bases of the tushes. They have developed downward so as to carry the plane of the palate far below the plane of the basicranium, and causing the upward bend in the basicranial axis, which is so characteristic of elephants. This bend leaves the occipital condyles a full foot above the plane of the teeth. The maxilla extends upward so as to bound the major part of anterior margin of the nasal opening, and of the orbit, which latter opening is small and directed forward. The zygomatic process is large and makes a considerable portion of the arch. The jugal is a broad flat bone making up most of the zygomatic arch and extending back so as to take a small part in making the glenoid fossa, as in elephants.
The top of the brain case was crushed in before the burial of the animal, the anterior part being present, and about 40 mm. below its normal position, but the parietal region having been loose, exposed the brain cavity, the ear chamber and some of the cellular vacuities. The nasal bones are long and light in build, and are pushed back so that they lie between the postorbital processes of the frontals. The frontals were united medianly, and prolonged on either side of the nasals to make the postorbital processes. The back margin of the frontals is broken away. The parietals are lost, but it is apparent that there was a short sagittal crest. From the middle, high lambdoidal crests extend to either side, and become continuous with the upper margins of the zygomatic arches. The posterior face of the skull slopes back from the lambdoidal crests for a considerable distance, down to the moderate sized foramen magnum.
The squamosum is a large bone, with the lambdoidal crest and the extension of the zygomatic arch on its upper surface. It carries the major part of the glenoid fossa. Behind the auditory meatus is a large post-tympanic portion which extends down and unites with the pre-tympanic portion, completely inclosing the opening of the ear and crowding the tympanic from being exposed on the side of the skull. There is a very short paroccipital process, and this posterior portion of the squamosum is the part which resembles that of elephants, hyracoids and, to some extent, Toxodontia. There is, however, no cavity in the squamosum as in toxodonts generally. The tympanic bulla is small, but little swollen, and hollow. It is quite exactly like that of probocideans. The basioccipital is fused to the exoccipitals. The occipital condyles are very high above the plane of the teeth, are set wide apart, and are cylindrical bosses which would not allow a free movement of the head laterally, but only in the up and down direction. This last is again a feature of the elephants. The pterygoid bone is greatly enlarged to compensate for the bend in the basicranial axis, and the pterygoids, together with the alisphenoids, make broad plates bounding either side of the posterior nasal chamber, exactly as in Palaeomastodon. The palatal bones are slender in front, and broaden toward the rear, again, as in elephants.
On the interior of the brain case is the cavity for the brain which indicates that this organ was of diminutive size, measuring about 150 mm. in length by 50 mm. in width at the widest part. It indicates a brain with very small cerebral hemispheres, which, however, had a swollen posterior margin, a larger cerebellum, and a wide medulla oblongata. The impression which I obtained of this brain is strikingly like that given for Palaeomastodon. On either side of the brain cavity are a couple of vacuities, apparently for lightening the weight of the skull. At the inner end of the auditory meatus is a large ear chamber, divided into a smaller anterior or cochlear portion, and into a larger posterior ear chamber proper.
Fig. 109. Palatal views of the basicranial region of A. Pyrotherium, and B. Palaeomastodon, for comparisons; alc., alisphenoidal canal; als., alisphenoid bone; Bsp., basisphenoid bone; eu., Eustachian canal; f.l.m., foramen lacerum medium; f.l.p., foramen lacerum posterior; f.o., foramen ovale; i.c.c., foramen for the internal common carotid; mx., maxilla; oc.f., occipital foramen; pal., palatine bone; p.p.f., post-palatal foramen; pt., pterygoid bone; pt.s., and p.ty.sq., post-tympanic process of squamosum; sq., squamosum; st.m.f., stylomastoid foramen.
In [figure 109], I have placed a diagram of the base of the skull of Pyrotherium, along beside that of Palaeomastodon, for comparison of the basicranial foramena. The skull of Palaeomastodon is somewhat more elongated, especially in the posterior part. In both, there are two antorbital foramena; the post-palatal foramena of Pyrotherium are a trifle further back, but this palatal region in both is of the same type which is peculiar to elephants and Pyrotherium. In Pyrotherium the condylar foramen is separate, while in elephants it is fused in with the foramen lacerum posterior. This latter foramen in both cases is situated just back of the tympanic, and in Pyrotherium is of considerably larger size than in Palaeomastodon. The foramen lacerum medium is in front of the tympanic and in Pyrotherium appears considerably larger, mostly because it is under the margin of the tympanic in Palaeomastodon. The foramen for the internal common carotid in Palaeomastodon pierces the tympanic bone just to the inside of the middle line, while in Pyrotherium it is on the outer margin of the tympanic. The Eustachian canal is on the external border of the tympanic in both cases, but in Pyrotherium it is further back. The foramen ovale of Palaeomastodon is in the posterior part of the alisphenoid bone, but with the shorter alisphenoid of Pyrotherium, this foramen is pushed back to the posterior margin of the bone. In both cases, the alisphenoidal canal starts under the base of the fused alisphenoid and pterygoid, and opens into the orbit. The stylomastoid foramen of Pyrotherium is situated further out than in the case of Palaeomastodon. The fusion of the post-tympanic portion of the squamosum is, in Palaeomastodon, much further advanced than in Pyrotherium, so that the passage to the ear is not apparent in the basal view of the former, but makes a considerable notch on the under side of the skull of Pyrotherium.
The mandibles are excessively thick and heavy, being united at the symphysis, which extends back to the front of the second molar. The ascending rami are prolonged backward, but do not rise above the level of the articulation.
The atlas is a massive vertebra with the anterior cotyles deeply excavated, especially on the upper side, so that, as Gaudry suggested, the head must have been carried low. The flat posterior cotyles face obliquely downward. The neural arch is light and without a spine or an opening for the vertebral artery. The basal portion of the bone, however, is excessively heavy and thick; the socket for the odontoid process not reaching to the middle of the basal bar. The neural canal is oval in section, being a good deal wider than high, and of small size. The transverse processes are short, heavy projections, adapted to receive heavy muscles. On the ventral surface there projects from the posterior margin a strong hypophysis, which, as Gaudry has pointed out, is unusual, but which is a character of the atlas of the Palaeomastodon.
The axis is a short, heavy bone, with the anterior cotyles facing obliquely upward, a small neural arch, no spine, and with a thick odontoid process, which has the form of a quarter of a hemisphere set onto the front of the centrum.
Cervicals 3 and 4 are very short vertebrae with light neural arches and no spines. The neural canal is fully three times as high as wide. Thus it is entirely evident that the neck of Pyrotherium was extremely short, as is the case with elephants, which alone would not be significant, but coincides with many other elephant features. Gaudry described a lumbar vertebra which is also a short, heavy bone. Otherwise the vertebral column of Pyrotherium is unknown.
The distal end of the scapula is described by Gaudry as indicating a short, heavy bone, with the glenoid cavity compressed so as to be about twice as long as it is wide. The coracoid is a short, blunt process. The spine was broken off, but enough remained to indicate a moderately high spine, prolonged toward the humerus, and bent somewhat forward.
The humerus is a very characteristic bone, short and stout, but greatly flattened from front to back. It has a large sessile head, which is strongly convex, and projects internally over the margin of the shaft. The external tuberosity is large and rugose but does not project above the level of the head. The deltoid ridge is shifted to the external side of the bone, and makes a long, muscular ridge, while on the opposite external margin is a second ridge, and between the first and second ridges a long furrow or trough is inclosed. These terminate just below the middle of the bone in roughened bosses, which all but meet. The epicondyles are large and give the excessive width to the bone. The external condyle is prolonged upward and ends in a spur. The trochlea is of moderate width and gently undulated. The supratrochlear fossa is only slightly depressed, and the anconeal fossa is likewise shallow. The bone has no exact counterpart, but is similar to that of Moeritherium and Palaeomastodon, but in each case is more flattened and has the external ridges more developed.
Gaudry describes the radius and ulna. They are ridiculously short, and very massive. The ulna is stout with a massive olecranon which is directed well toward the rear. The sigmoid notch is shallow, the coronoid process short, and the articular area expanded so that the ulna covers the whole of the posterior of the trochlea of the humerus. The upper end of the radius is compressed antero-posteriorly, but distally it expands into a heavy bone. Its upper articulation is expanded, so that it comes in contact with the full width of the anterior portion of the trochlea of the humerus.
Fig. 110. Left carpus and
metacarpus, outlines
after Tournouer—
⅕ natural size.
The carpus and front foot are of questionable association. Ameghino described a front foot as P. romeri, and later Tournouer assigned this foot to Astrapotherium. However, I have seen no reason to think it belongs to Astrapotherium, being far too small, and so would for the present consider it as belonging to Pyrotherium. We found a couple of metapodials evidently belonging to the foot as described. This carpus is of the primitive type, the scaphoid and luna being large and receiving the radius; while the pyramidal is smaller, low and broad and received the ulna. The trapezium is larger than usual, being elongated and standing out from the trapezoid, and supporting a reduced first metacarpus. The trapezoid is also large and almost square in outline. The magnum is smaller and considerably flattened. The unciform is very large. These last three mentioned carpals carry the three medium metacarpals which are quite normal and seem to have carried most of the weight of the animal. Metacarpus V articulates on the outer side of the unciform. It is a massive nodular bone with but a tiny articulation for the phalanx, which seems on this toe to have been reduced. Metacarpals IV, III, and II are short, stout bones, flattened from front to back, and enlarged at either end. On each, the trochlea extends well onto both the dorsal and palmar surfaces, thus giving the toes a considerable range of movement, and indicating at least a semidigitigrade mode of walking.
Of the pelvis, the ilium is known as a broad, heavy bone with the acetabulum facing down. The hind limb is considerably longer than the front, and approximately pillar-like. The femur, as compared with the humerus, is quite a little longer, though, as femora go, it is not a long bone. The rounded sessile head stands high above the blunt, thick greater trochanter; the digital fossa is barely indicated; the rotular trochlea is short; the two condyles are subequal in size and set close together. The patella is short and nodular. The tibia is short and very heavy. The fibula is free its entire length and is a rather heavy bone. The astragulus is a lens-like bone with the trochlea but slightly convex, and the navicular facet directly below it, indicating a rectigrade foot.
Ameghino established the following species, P. romeri, P. sorondoi, P. giganteum, P. crassidens, P. trilophodon, P. pluteum. This is a very considerable number of species of such a large type to occupy a limited region. Gaudry has lumped them all under species P. romeri. This, I think, is too drastic and I would find at least two species. It is true that there is great individual variation in such large animals, due to age, food supplies and individual vicissitudes; but where there is a difference of dental formula or a structural divergence I should consider these as specific in character.
The type species is P. romeri (later spelled romeroi) which was based on a first and second upper premolar and an upper tush, all of smaller size than P. sorondoi and differing from all the others described in having pm. 1 present. Gaudry suggests that this may be the milk dentition but there is no evidence as yet to settle this, so I have left this species standing. Most of the material found by Ameghino, by Gaudry and by our party belongs to the type described as P. sorondoi, which is somewhat larger than P. romeri, and lacks pm. 1 in the upper jaw. This then is the usual species and to it belongs most of what is known. It varies some in size but the characters are very uniform. P. giganteum is based on the root of a large tush, 90 by 70 mm. in cross section, which Lydekker associated with P. romeri, and which Ameghino later took as the type of a new species. I can see in this only a large individual of P. sorondoi. P. crassidens is based on a last lower molar 90 by 80 mm. in diameter. It seems to me to be an upper molar and no larger than m. 2 in either of my skulls. P. trilophodon is based on a lower pm. 3, which, in every way, resembles the corresponding tooth in lower jaw of P. sorondoi. P. pluteum is based on three lower teeth of smaller size than the typical P. sorondoi, but the difference is small and there are no structural features accompanying it; so I consider it simply a smaller individual of P. sorondoi. In the generic discussion, Parapyrotherium planum was also assigned to P. sorondoi.
Pyrotherium romeri Ameghino
- P. romeri Amegh., 1889, Act. Acad. Nac. Cienc. Cordoba, t. VI, p. 618.
- P. romeri Lydekker, in part, 1894, Anal. Mus. La Plata,
- Palaeontologia Argen., t. III, supplement, p. 4.
- P. romeroi Amegh., 1894, Bol. Inst. Geog. Argen., t. 15, p. 612.
- P. romeroi Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 442.
- P. romeroi Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p. 32.
- P. romeri Gaudry, in part, 1909, Anal. Paleontologie, t. 4, p. 21.
This species is characterized by the presence of pm. 1 which is absent in other species. The tooth is of fair size, two-rooted, narrow in front and has a narrow rim of enamel around it; and measures 22 mm. long by 14 mm. wide. The second premolar is 30 mm. long by 33 mm. wide. A lower tush is also associated with these two teeth and is of smaller size than in the following species, being at the alveolus border 40 mm. by 29 mm. in cross section.
Pyrotherium sorondoi Ameghino
- P. sorondoi Amegh., 1894, Bol. Inst. Geog. Argen., t. 15, p. 613.
- P. sorondoi Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 443.
- P. sorondoi Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p. 30.
- P. sorondoi Amegh., 1906, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 8, p. 331.
- P. romeri Lydekker, in part, 1894, Anal. Mus. La Plata, Paleontologia
- Argentina, t. III, supplement, p. 4.
- P. romeri Gaudry, in part, 1909, Anal. Paleontologie, t. 4, p. 21.
- P. giganteum Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 447.
- P. crassidens Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p. 34.
- P. planum Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 446.
- Parapyrotherium planum Amegh., 1902, Anal. Mus. Nac. B. A., ser. 3, t. 1, p. 29.
- P. trilophodon Amegh., 1902, Anal. Mus. Nac. B. A., ser. 3, t. 1, p. 33.
- P. pluteum Amegh., 1901, Bol. Acad. Nac. Cienc. Cordoba, t. 16, p. 386.
- P. pluteum Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p. 29.
Fig. 111. Top of the skull—⅕ natural size; Mate to in 1 on
the left side is represented by an alveolus but the tooth had
fallen out before the death of the animal; a.c., ear chamber;
B, brain case; V, vacuities in the bone.
Fig. 112. Side view of the skull—⅕ natural size,
i.1, incisor 1 in outline restored from the right side;
i.2, incisor 2; J., jugale; M.1, first molar;
Mx., maxilla; pm.2, second premolar;
pmx., premaxilla; Pt., pterygoid; the dotted line
indicates position of nasal and frontal which are crushed
down in specimen.
The species varies in size and in the proportionate development of the tushes as would be expected in a large and slow-growing animal. Most all of the material found by any of the collectors falls clearly into this species. Our specimens all came from the Chico del Chubut, west of Puerto Visser, which point is about 250 miles north of the locality where Gaudry’s material was found.
The general features of the skull have been given under the generic description. The difference between this and the preceding species lies in the absence of pm. 1, and the somewhat larger size. Both of our major specimens are mutilated in places; and as the better skull was found with only the zygomatic arch exposed, we conclude that the parts missing were lost before burial. On the lower jaw the edges of some of the teeth were cracked off, and both the ascending rami are lacking, both things having happened before burial, this specimen being found well in the bank and never exposed to weathering. It appears as if the carcasses of the animals lay some time before being buried by the sediments. The scattered condition of all the finds indicates the same thing. The head of our femur is still marked by the teeth which cleaned the meat from the bone. The frequency of isolated tushes indicates that many jaws originally containing them have been either chewed to pieces or weathered away before burial. I do not think all the tushes found originally belonged to the lower jaw (Gaudry reports 18 tushes, all lower); for the upper and lower tushes when isolated are so much alike that it is difficult to distinguish them.
The size of the skull is indicated by the following measurements:
| Specimen No. 3207 | |
|---|---|
| Length from inc. 1 to occipital condyles | 720 mm. |
| Length from front of premax. to nasal opening | 225 mm. |
| Length of boss on premaxilla | 77 mm. |
| Length of nasal opening at top | 80 mm. |
| Width of nasal opening at top | 88 mm. |
| Length from premax. to lambdoidal crest | 540 mm. |
| Width across zygomatic arches | 350 mm. |
| Width across frontal bones | 90 mm. |
| Transverse diameter of the snout | 115 mm. |
Fig. 113. Base of the skull—⅕ natural size; i.1,
incisor the right side grown over toward
the center as its mate is wanting;
i.2, incisor 2; Pal., palatinum;
Pt., pterygoid.
The lower jaws were associated with the above skull, and are complete to behind the third molars on both sides. They are very short and heavy, especially in the anterior portion, the symphysis extending back to opposite the middle of the second molar. The height under molar 3 is 150 mm. See frontispiece.
From the upper dentition, I give the measurements of my two chief specimens, together with those given by Ameghino for his type of P. sorondoi, and the figures given by Gaudry; from which may be seen the amount of variation which individuals may show.
| Upper Dentition | Specimen No. 3207 | Specimen No. 3250 | Ameghino’s Type | Gaudry’s Specimen |
|---|---|---|---|---|
| Total length, inc. 1 to m. 3 | 530 mm. | |||
| Inc. 1, length above alveolus | 133 mm. | |||
| Inc. 1, antero-posterior diam. | 49 mm. | |||
| Inc. 1, transverse diam. | 37 mm. | 42 mm. | ||
| Inc. 2, length above alveolus | 174 mm. | |||
| Inc. 2, antero-posterior diam. | 59 mm. | 77 mm. | 65 mm. | |
| Inc. 2, transverse diam. | 40 mm. | 52 mm. | 41 mm. | |
| Premolar 2, length | 45 mm. | 52 mm. | 48 mm. | 40 mm. |
| Premolar 2, width | 36 mm. | 40 mm. | 30 mm. | 29 mm. |
| Premolar 3, length | 46 mm. | 49 mm. | 48 mm. | 40 mm. |
| Premolar 3, width | 57 mm. | 57 mm. | 46 mm. | 48 mm. |
| Premolar 4, length | 47 mm. | 51 mm. | 46 mm. | 43 mm. |
| Premolar 4, width | 63 mm. | 64 mm. | 58 mm. | 57 mm. |
| Molar 1, length | 55 mm. | 55 mm. | 57 mm. | 55 mm. |
| Molar 1, width | 68 mm. | 69 mm. | 61 mm. | 61 mm. |
| Molar 2, length | 68 mm. | 77 mm. | 70 mm. | 57 mm. |
| Molar 2, width | 85 mm. | 93 mm. | 75 mm. | 68 mm. |
| Molar 3, length | 75 mm. | 68 mm. | 83 mm. | 64 mm. |
| Molar 3, width | 86 mm. | 87 mm. | 82 mm. | 88 mm. |
For the lower dentition, I give the figures which Ameghino records for his P. sorondoi, those given by Gaudry for his P. romeri, and the measurements of specimen No. 3207. The tushes in the lower jaw I would designate as incisors 2; because when the jaws are closed these diverge and their tips bite against the tips of the upper incisors 2. The first incisor seems to have been gradually lost and no space left for it in the front of the mandible, just as it was reduced and lost in the development from Moeritherium to Polymastodon or equivalent types.
Fig. 114. Lower dentition—⅕ natural size; edges of teeth
broken off in my specimen are indicated in outline.
| Lower Dentition | Specimen No. 3207 | Ameghino’s Type | Gaudry’s Specimen |
|---|---|---|---|
| Incisor 2 to molar 3, length | 510 mm. | 540 mm.‡ | 415 mm.‡ |
| Premolar 2 to molar 3, length | 325 mm. | 280 mm. | 272 mm. |
| Inc. 2, length above alveolus | 133 mm. | 188 mm.‡ | 168 mm.‡ |
| Inc. 2, antero-posterior diam. | 55 mm. | 60 mm. | 66 mm. |
| Inc. 2, transverse diam. | 40 mm. | 36 mm. | 44 mm. |
| Premolar 3, length | 46 mm. | 50 mm. | 54 mm. |
| Premolar 3, width | 36 mm. | 31 mm. | 35 mm. |
| Premolar 4, length | 55 mm. | 45 mm. | 50 mm. |
| Premolar 4, width | 46 mm. | 45 mm. | 47 mm. |
| Molar 1, length | 65 mm. | 50 mm. | 51 mm. |
| Molar 1, width | 59 mm. | 52 mm. | 54 mm. |
| Molar 2, length | 73 mm. | 56 mm. | 66 mm. |
| Molar 2, width | 73 mm. | 63 mm. | 66 mm. |
| Molar 3, length | 69 mm. | 67 mm. | 71 mm. |
| Molar 3, width | 74 mm. | 66 mm. | 69 mm. |
| ‡ Figures taken from illustrations. | |||
Four cervical vertebrae were preserved with the skull number 3207, of which only about a third of the atlas is represented, but fortunately we found a complete atlas isolated and of the same size. The measurements for the atlas are taken from this separate specimen. While my skull, especially the teeth, seems to have been larger than the skull Gaudry described, the cervicals are a little smaller. I give the measurements of the cervicals which we found, comparing them with the figures given by Gaudry.
| Specimen 3344 | Gaudry’s Specimen | |
|---|---|---|
| Atlas, antero-posterior length (without hypophysis) | 120 mm. | 140 mm. |
| Atlas, greatest width | 304 mm. | 365 mm. |
| Atlas, height | 129 mm. | 140 mm. |
| Specimen 3207 | ||
| Axis, antero-posterior length | 116 mm. | 124 mm. |
| Axis, greatest width | 223 mm. | 248 mm. |
| Axis, width of odontoid process | 96 mm. | 88 mm. |
| Axis, length of odontoid process | 48 mm. | 44 mm. |
| Cervical 3, length of centrum antero-posterior | 47 mm. | 45 mm. |
| Cervical 3, width of centrum | 125 mm. | 145 mm. |
| ervical 3, height of centrum | 105 mm. | 100 mm. |
| Cervical 3, width of neural canal | 75 mm. | |
| Cervical 3, height of neural canal | 22 mm. | |
| Cervical 4, length of centrum antero-posterior | 45 mm. | |
| Cervical 4, width of centrum | 132 mm. | |
| Cervical 4, height of centrum | 105 mm. | |
The humerus is flattened from front to back in a striking manner, so that, seen from the side, it looks most slender; while in reality it is a very broad bone, nearly straight, and with marked rugosities for the attachment of the muscles. We found but one specimen of the humerus, an isolated bone a little smaller than that described by Gaudry.
| Specimen 3218 | Gaudry’s Specimen | |
|---|---|---|
| Humerus, total length | 470 mm. | 500 mm. |
| Humerus, width at proximal end | 232 mm. | 232 mm. |
| Humerus, width at middle of shaft | 165 mm. | 170 mm. |
| Humerus, antero-posterior diam. of shaft | 61 mm. | |
| Humerus, width across epicondyles | 230 mm. | 240 mm. |
We found neither the radius nor the ulna, but Gaudry figures both, giving the following measurements.
| Radius, length | 245 mm. |
| Radius, proximal diam. | 127 mm. |
| Ulna, length (calculated) | 280 mm. |
| Ulna, width of olecranon | 140 mm. |
Fig. 115. At., atlas; Ax., axis;
C.3, third cervical;
C.4, fourth cervical—
⅕ natural size; apophysis of atlas
is restored after Gaudry and the
neural arch of cervical 4 is
restored from the opposite side.
Fig. 116. Axis—⅕ natural size,
front view.
Fig. 117. Anterior face of the humerus—
⅕ natural size.
For the hind limb I give some of the figures which Gaudry gives accompanying his illustrations of the hind limb.
| Femur, length | 630 mm. |
| Femur, greatest proximal diameter | 240 mm. |
| Femur, distal diameter | 170 mm. |
| Tibia, length | 370 mm. |
| Tibia, greatest proximal diameter | 164 mm. |
| Tibia, greatest distal diameter | 114 mm. |
| Astragulus, antero-posterior diam. | 123 mm. |
| Astragulus, transverse diam. | 114 mm. |
| Astragulus, height | 65 mm. |
CHAPTER XIII
Rodentia
While all of small size, numerically the rodents make about a third of our collection, the number of genera and species being, however, relatively small. All are hystricomorphs with the pattern on the crowns of the teeth relatively simple. While the incisors are typically rodent-like, permanently growing teeth, the molars are all rooted, some being entirely brachydont, others beginning to show hypsodont features.
So far as yet known, the rodents make their first appearance in South America, in this Deseado formation. Were they, as Ameghino thought, developed there from such a form as Propolymastodon or Promysops of the Casamayor formation? Or did they migrate into Patagonia from some other section? For the former proposition to be convincing to me, it would require more complete material of the forms suggested than now exists.[20] Other groups of hystricomorphs occur in the Theridomyidae of the European Oligocene, and from the Oligocene of the Fayum.[21] Either the old world forms are descended from the South American forms, or vice-versa. The two African lower jaws are very much like those of Cephalomys, and my feeling is that the Patagonian forms are derived from some immigrant reaching that section before Deseado times.
The Deseado genera are not widely different from each other, but it is evident that they are the representatives of at least two families, and my expectation is that other families will be found eventually to be already represented.
Our material does not permit the discussion of the skeleton or even of the skull as a whole, for the specimens occur only as isolated jaws, palates, or even as isolated teeth. In a few cases, the upper and lower dentitions are associated, but in no case was skeleton material clearly associated with the teeth. The remains look very much like such as are often found today in the western United States under a hawk’s nest or below the roosting place of owls. I think most of our specimens passed, before burial, through the stomach of birds or carnivores.
Ameghino puts most of the forms in the family Cephalomidae, which he considers ancestral to Hystricomorpha in general. I feel, however, that it is better to assign the Deseado genera to the families which have persisted until recent times, as Scott and Ameghino, in another place, have done. There are six living families, four of which Scott found already represented in the Santa Cruz. Two of these clearly may be continued back into the Deseado, the Erethizontidae, and the Chinchillidae, nothing as yet having been found to represent the Santa Cruz families Cavidae and Octodontidae.