The scarcity of edentates in the Deseado beds is in striking contrast to their abundance in the Santa Cruz formation. Whereas in this latter horizon over half of the finds are edentates, in the Deseado only eight per cent. of the total collection belong to this group, and this is doubtless a larger proportion than these animals represented in the fauna; for the hundreds of small plates in a carapace, when scattered greatly, increase the chance that some part of an individual will be found, and most of the eight per cent. of finds are single plates. Most of the plates found represent armadilloes, our collection containing but one plate of a glyptodont, and no gravigrades. Ameghino’s collections present about the same relations, but in the repeated trips he found a few more traces of glyptodons and a very few gravigrades.
This scarcity of edentates can not be taken to mean that they were not developed, for they are a peculiarly South American group, and as they were developing somewhere into their great complexity, I take it to mean that the climatic conditions were unfavorable in this particular section.
As noted above, all previous finds have been isolated plates. We were fortunate enough to find one specimen consisting of a carapace with ten rows of movable plates in place, and parts of four rows of the pelvic buckler together with over fifty isolated plates. A second specimen had some fifty associated plates which were mostly from the pelvic buckler.
Dasypoda
The representatives of this group are so poorly known in the Deseado beds that Ameghino has, in general, used the generic names of the Santa Cruz for their description, and, so far as known, they are little differentiated from those genera. There is as yet no material which shows the association of skeletal parts with the carapaces. Therefore, in this paper, comparisons are made wholly on the carapace, with the expectation that the skeleton, when found, will correspond.
The Deseado species are but little less specialized than the Santa Cruz, the carapace consisting of movable overlapping bands of plates both in the anterior and body portions, while over the pelvic region the plates are fixed, do not overlap, and form a pelvic buckler.
Ameghino has described a considerable number of genera based on isolated plates, to which I refer later. The chief genera which occur in these beds are also found in the Santa Cruz, and the distinguishing features are as follows:
| Cephalic Shield | Movable Plates | Pelvic Buckler | Ornamentation | |
|---|---|---|---|---|
| Proeutatus | Plates thin, | Plates thick, | 8 + probably | “Flask” figure |
| coarsely pitted | ⅓ overlapped | 10 rows | ||
| Prozaedius | Plates thin, | 4 bands, thin | 8 rows | 3 long ridges, |
| finely pitted | ¼ overlapped | median ridge | ||
| narrow | ||||
| Stenotatus | Plates thick, | Plates thick, | 11 rows | 3 long ridges, |
| coarsely pitted | and wide | all subequal | ||
| Proeuphractus | ¼ overlapped | No buckler | ||
| Peltephilus | 19 or 21 Plates | Wide and thin | Buckler | Large shallow |
| 2 or 4horns | 2-4 wide | pits | ||
This is the most frequently occurring genus in the Deseado, but is as yet represented only by isolated plates. The genus is distinguished by thick, relatively long and narrow, movable plates, each overlapped by about a third of its length. The plates of the pelvic buckler are shorter and thicker, the exposed surface of each being ornamented by a figure compared by Ameghino to a flask (see fig. 131), which figure is more distinct on the rear, fading away toward the front. On the plates of the pelvic buckler this figure is more accentuated, and from it, on either side, radiate two furrows dividing the surface into several (4 to 5) areas. The entire surface of each plate is irregularly punctate.
Fig. 131. A, movable plate;
B and
C, plates from
pelvic buckler—
natural size.
On the Chico del Chubut River, west of Puerto Visser, we found nine specimens of this species, all fragmentary, though one consists of over fifty more or less broken plates, mostly from the pelvic buckler. This is the only species of the genus from the Deseado, and corresponds to the description above. A movable plate generally measures about 28 mm. long by 10 mm. wide, and has four large piliferous pits on the posterior margin. A plate of the pelvic buckler varies greatly in size, but is always thick and has two to eight piliferous holes on the posterior margin. A typical plate measures 20 mm. long by 10 mm. wide.
Of this little genus, which is so strikingly like the living Zaedius, we found a carapace with ten rows of movable plates in place, parts of four rows of fixed plates from the pelvic buckler, and some caudal vertebrae. The genus is distinguished by its thin plates, there being fourteen bands of movable plates, and eight rows in the pelvic buckler. The movable plates are narrow, each overlapped about a fourth of its length, and have a faint ornamentation, with no piliferous pits except on the posterior margin. The fixed plates are similar, except that they are shorter, and have the ornamentation more accentuated, with radial grooves. Ameghino has described three species as follows:
In my specimen, the two anterior rows of movable plates lack the marginal piliferous pits, on the next two rows they are rudimentary (which is also true of the lateral plates even further back), while on the bulk of the movable plates and on those of the pelvic buckler there are two, three or four good-sized piliferous pits on the rear. I can therefore recognize but two species, P. impressus and P. tenuissimus.
Our specimen was found on the Chico del Chubut River, west of Puerto Visser, and preserves over two hundred plates, and eight caudal vertebrae. The anterior rows of plates of the carapace consist of thin plates overlapping about a fourth their length. Just behind the overlap, there is, on each, a group of small punctations, and the exposed part of the surface is divided by two shallow furrows, making three more or less equal ridges which die out toward the rear, leaving the posterior part of the plate plain. These most anterior plates are bent to one side and have no piliferous pits on the rear margin. The plates of the third and fourth rows are not bent, and have the sculpture more distinct, the extreme lateral plates having no piliferous pits, the median lateral plates with rudimentary piliferous pits, and the dorsal ones with well marked posterior pits. In each succeeding row toward the rear, the plates are more distinctly ornamented and have larger posterior marginal pits. I have no marginal plates.
Fig. 132. Portion of carapace—natural size;
unshaded plates are from cast; a and
b plates from pelvic buckler.
The plates of the pelvic buckler do not overlap, are shorter, have a very distinct figure, and, in addition to the longitudinal furrows, have a couple of radial furrows on either side, which divide the plate into four or five areas (see fig. 132 a and b).
The caudal vertebrae are short and thick, indicating a short tail. I found no plates which would indicate a caudal shield, which coincides with the experience among the Santa Cruz specimens. The figures are to scale and give most of the measurements.
There are ten rows of movable plates, probably two to three rows lacking.
There are twenty + plates to a row.
A typical movable plate measures 17 mm. long by 6 mm. wide.
There were at least four rows in the pelvic buckler, probably eight as in the Santa Cruz.
A typical fixed plate measures 10 mm. long by 5 mm. wide.
P. tenuissimus Amegh., 1902, Bol. Acad. Nac. Cienc. Cordoba, t. 17, p. 66.
This species is characterized by Ameghino on account of its small size. The movable plates have two furrows which converge toward the front, and between which is a median crest. In the furrows are two rows of perforations. A movable plate measures 9 mm. long by 4 mm. wide.
The genus is very like Prozaedius but differs in having thicker and wider movable plates, in having more rows of plates in the pelvic buckler (11), and in details throughout the skeleton. We found no representatives of the genus, but Ameghino has described a species (no figure), S. (Prodasypus) ornatus[22] based on isolated plates. A movable plate measures 18 mm. long by 6-7 mm. wide, while a fixed plate measures 9 mm. long, by 6-7 mm. wide.
Proeuphractus Amegh., 1886, Bol. Acad. Nac. Cienc. Cordoba, t. 9, p. 208.
This genus is seldom found, but is distinguished by Ameghino by the absence of a pelvic buckler, all the plates of the carapace being movable. From the Deseado beds, Ameghino describes two species, P. setiger and P. laevis, both based on isolated plates; the former distinguished by having no piliferous perforation in the furrows surrounding the central figure, and with well-developed pits on the posterior margin; while the latter has small piliferous perforations in the furrows and only rudimentary ones on the posterior margin. These features do not seem to me to distinguish species.
In addition to the foregoing, Ameghino has made a series of genera and species,[23] Archaeutatus, Amblytatus, Isutaetus, Sadypus, Hemiutaetus, Anutaetus, all based on isolated plates, and distinguished by variations in the central figure and the piliferous pits. I am unable to find a satisfactory basis for distinguishing the genera or species, and feel that, until more complete material is known, it is impossible to say which are valid genera or species.
While rare, this genus is well known from the Santa Cruz, and is characterized by the curious development of the head shield, which consists of nineteen or twenty-one definitely arranged head plates, the anterior ones being developed into horn-like projections. The plates of the carapace are wide, thin, and unique in each having two to four wide shallow pits on the exposed surface. We found the genus rare, only two isolated plates turning up. From the Deseado material Ameghino has made three species: P. protervus, of very large size; P. undulatus, of moderate size, with the median figure accentuated and ending in two pits and with piliferous depressions on the margin; and P. depressus, of the same size as the foregoing, with a faint central figure, often four pits on the exposed surface and no piliferous pits on the margin. We found but one species, one plate of which combines characters of both the last two as described, so that I feel that there should be but two species, P. protervus and P. undulatus.
Fig. 133. Two movable
plates—natural size.
One of the plates we found has the rough surface, obscure figure, two pits on the median part of the surface, and marginal piliferous pits, of which the first two features are characters of P. undulatus, the last is the feature of P. depressus, so I have combined the two species. A second plate does not have the marginal pits but is otherwise the same. I expect considerable variation in the pattern on plates from different regions of the carapace.
P. protervus, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 509.
This species, of which we found no representative, is very large. The plates of the type have two pits on the anterior part of the exposed surface and none on the margin. A movable plate measures 41 mm. long by 22 mm. wide. One of the horn-like plates from the cephalic shield is 35 mm. long, by 30 mm. wide, and has a height of 44 mm.
GLYPTODONTIA
This suborder is most sparingly represented, apparently on account of unfavorable habitat. Ameghino has described a few fragments of the carapaces of these forms, making the genera, Palaeopeltis, and Glyptatelus, both pre-Santa Cruz genera.
Palaeopeltis Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 659.
The basis of this genus is a few plates of a glyptodon-like animal of considerable size, but the plates are without ornamentation. This form Ameghino considers intermediate between glyptodonts and armadilloes. I feel that there is too little of the skeleton known to justify this conclusion, especially as glyptodonts of a considerably higher grade of specialization are contemporaries of this form.
Fig. 134. P. inornatus: a single
plate—natural size.
The species is founded on four plates which are without ornamentation, and externally smooth except for numerous vascular perforations. They are of considerable size and entirely characteristic. The one such plate which we found is shown in fig. 134.
Glyptatelus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 507.
The plates of the carapace are similar to those of Palaeohoplophorus, the O-figure being, however, nearer the rear of each plate, and the number of radial furrows being smaller, usually six. We found no specimens of this interesting form. Ameghino has made two species, G. tatusinus and G. malaspinensis.
G. tatusinus, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 507.
I reproduce Ameghino’s figure of this species which shows all that is known of the form.
Fig. 135. Four plates—natural size,
after Ameghino.
G. malaspinensis Amegh., 1902, Bol. Acad. Nac. Cienc., Cordoba, t. 17, p. 50.
This species is described (no figure) as about the same size as the preceding, but with subordinate figures in the central O-figure, and also outside of it. A dorsal plate measures 26 mm. long by 20 mm. wide.
GRAVIGRADA
Remains of this suborder are almost as rare as those of the glyptodonts, and apparently for the same reason, unfavorable habitat. We found no remains of this group, but Ameghino has described a skull and some teeth as belonging to this group; so, in order to present a complete view of the Deseado fauna, I give a digest of his descriptions.
H. antistis Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 505.
The species is based on a skull, not figured, of which Ameghino says: the size is small, the molars are compressed from front to back, and gives the following measurements:
| Length of cranium from front of max. to occ. condyles | 140 mm. |
| Length of four post, molars | 27 mm. |
| Distance from front of max. to back of last molar | 48 mm. |
Octodontotherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 656.
The genus is based on isolated teeth, each a mass of dentine surrounded by a thin layer of cement. The anterior tooth of the upper jaw is caniniform, the first molar ovoid in section, the last molar is bilobed, corresponding to Pseudolestodon. The first tooth of the lower jaw is also caniniform, but is two-faced as a result of wear. The intermediate upper and lower molars are rectangular prisms resembling those of Chlamdotherium.
In addition to the above, Ameghino simply gives the following measurements:
Fig. 136. A, lower molar, side view—natural size;
B, lower molar, cross section—natural size;
C, upper molar, cross section—natural size,
after Ameghino.
O. crassidens Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 505.
This second species is based on isolated teeth of larger size than the preceding, with measurements as follows:
The teeth of this type are a mass of dentine, each surrounded by a thin layer of cement, and each tooth subcylindrical in section, with the crown worn to two apposed oblique planes. The genus resembles Ortotherium.
Fig. 137. Type—natural size,
after Ameghino.
In addition to the above, Ameghino gives a figure, here reproduced, and the following measurements: Tooth, greatest diam. 12 mm., lesser diam., 10 mm.