to the Anteaters of the New World are chiefly adaptive and have nothing to do with real affinity, being merely an expression of a similar mode of life, it is curious to note that here and there we do find certain resemblances which do not seem to be susceptible of the latter explanation. The jugal bone, absent in Manis, is small in Myrmecophaga; the clavicle is absent and again small or rudimentary in the Anteaters; it is large in other Edentates. The third trochanter is absent, as in Myrmecophaga (and the Sloths). There are many scales on the body; in Myrmecophaga there are traces of these structures on the tail, as also in Tamandua. In the features mentioned, the Myrmecophagidae differ from either or from both of the two other American families (i.e. Dasypodidae, Bradypodidae) and agree with Manis. The facts are not a little remarkable.
Fig. 109.—Manis. Manis gigantea. × 1⁄12.
Order III. GANODONTA.[[113]]
Allied to the Edentata, and apparently representing the ancestral forms from which they, at any rate the Xenarthra were derived, is the order of the Ganodonta. Of this order a number of genera are now known, which can be ranged in a series which more and more approaches the Edentata as we pass from the older to the newer forms. This interesting and transitional series will be made manifest by a description of the characters of the various genera taken in their proper
chronological order. The following genera are included by Wortman in his family Stylinodontidae.
The earliest type of the Ganodonta is the genus Hemiganus, with but one species, H. otariidens. This animal lived during the deposition of the lowest Eocene strata, the Puerco beds of North America. It was about as big as a fair-sized Dog, and had powerful jaws. There were at least two pairs of incisors in the upper jaw, together with powerful canines and the full premolar and molar formula. In the lower jaw the canines were also strong, but the incisors are not certainly known to be more than two pairs. The enamel upon the posterior surface of the canine is thin, and in the case of the incisors the enamel seems to be limited to the anterior face. The lower molars are quadritubercular. It is believed from the presence of a suture on the upper surface of the premaxillary that the snout of the creature was tubular. The cervical vertebrae, only known by their centra, are like those of the Armadillos (and for the matter of that of the Whales) in the great transverse as opposed to the antero-posterior diameter. The feet are especially compared with those of the Ground Sloths. The single ungual phalanx is marked by a large subungual process, which is pierced by a considerable foramen. The tibia again is to be compared with that of the Armadillos.
In the Upper Puerco (Torrejon) beds the remains of Psittacotherium are found. This genus, when first discovered, was referred to the Tillodontia by some and to the Ungulates, the latter being a refuge for indeterminate Eocene mammals, just as the "Multituberculata" is for similarly-placed Secondary mammals. It is now known to be clearly a member of the order Ganodonta. Wortman thinks that there is but one species, P. multifragum. It seems to have had a general aspect much like that of Hemiganus—that is judging from the skull—and was not very greatly different in size. The facial portion of the skull is short, and the zygoma is deep. The infra-orbital canal is double, a feature which crops up in the Sloth, and has been mentioned in the later form of Ground Sloth, Megalonyx (but it must be remembered that the same characteristic is not unknown in Rodents). The dentition is reduced as compared with that of Hemiganus, that is to say, as far as concerns the molars and the incisors. There is but a single pair of incisors in each jaw; the canines are strong; the premolar and molar series seem to have been complete in the lower jaw,
but reduced by one premolar at least in the upper jaw. It is very important to notice that the incisors have enamel only on their anterior faces, and that the same is the case with the canines, the slender layer present behind the tooth in Hemiganus having vanished in this later form. The tooth pattern of the molars is like that of Hemiganus. The fore-limb is decidedly Edentate-like; but it is the foot which presents the strongest likenesses to that order. "If an anatomist," remarks Dr. Wortman, "had no other part of the skeleton than that of the foot to guide his judgment, and he should fail to detect a most striking similarity between it and that of the Edentata, especially the Ground Sloths, he would not only lay himself open to the criticism of being lacking in the ordinary powers of observation and comparison, but would be suspected of placing the matter upon a basis other than that established by such a method." It is not certain how many toes upon the fore-limbs were possessed by Psittacotherium, but the close resemblance to Mylodon is indeed striking, the third digit being in both forms the most pronounced. Some vertebrae of this Ganodont have been discovered which do not show the complex articular arrangements of later American Edentates. The sacrum, on the other hand, is very like that of the Sloth, and there is a foreshadowing of the attachment of the ilia to the sacrum by co-ossification which is met with in later Edentates. A still later type is the genus Calamodon, which has been shown to occur in Europe as well as in America. C. simplex was a larger beast than either of the genera that have already been treated of, thus affording another example of the increase in size of later as compared with earlier members of the same group, so pronounced among the Ungulata. The lower jaw has the same massive structure that characterises that bone in Hemiganus and Psittacotherium. There is but one incisor, but the premolar and molar series are complete. The canine is Rodent-like in appearance, being imbedded throughout the greater part of the lower jaw; it evidently grew from a persistent pulp. It is enamelled upon the anterior face only. The premolar and molar teeth are in this genus commencing to lose their enamel, which is distributed in the form of vertical bands, leaving interspaces which are not covered by enamel. These teeth, moreover, are decidedly hypselodont, more decidedly so than in Psittacotherium; they are, when unworn, quadricuspidate, with accessory cusps; when more worn, the teeth
are double-ridged, and that transversely to the long axis of the jaw; finally, the much-worn teeth have flattish crowns more or less surrounded by a ring of enamel.