A history of land mammals in the western hemisphere

by William Berryman Scott

Suborder †GLYPTODONTIA. †Glyptodonts

IX. †Glyptodontidæ.

†Glyptodon, Plio. and Pleist., N. and S. A. †Dœdicurus, Pleist., S. A. †Panochthus, do. †Sclerocalyptus, Plio. and Pleist., S. A. †Glyptotherium, mid. Plio., N. A. †Propalæohoplophorus, Deseado and Santa Cruz. †Cochlops, Santa Cruz. †Eucinepeltus, do. †Asterostemma, do.

In the section Pilosa, which includes the sloths (Tardigrada), anteaters (Vermilingua) and the extinct †ground-sloths (†Gravigrada), the skin is thickly clothed with long hair, and in the Loricata, armadillos and †glyptodonts, the head, body, tail and legs are more or less completely encased in an armour of bony scutes covered with plates of horn, but with some hairs also.

The name Edentata (toothless) is not very happily chosen, for only the anteaters are quite toothless. Almost all the genera have no teeth in the front of the mouth and the teeth are nearly always alike, so that the distinction of regions among them is entirely a matter of position in the jaws. In the tree-sloths and many †ground-sloths the foremost tooth in each jaw is a more or less enlarged, canine-like tusk. The teeth are always rootless, growing from permanent pulps, and are without enamel, made up of dentine, which is sometimes homogeneous and sometimes in layers of different hardness, and with a covering of cement, usually thin and film-like. The number of teeth varies from 4/4 to 10/10 or more, and their form usually approximates a simple cylinder, worn off flat at the end, though the ends may be bevelled or grooved, differences which are in no way due to pattern but simply to the mode of wear. In the †glyptodonts the teeth were divided by deep vertical grooves into two or three pillars, connected by narrow necks. In most of the edentates there is no change of teeth, the milk-dentition having been completely suppressed, but in the 9-Banded Armadillo (Tatu) each of the permanent teeth is preceded by a two-rooted milk-tooth, and some other armadillos have milk-teeth.

The skull varies much in form and proportions, according to the character of the food and method of feeding. The tree-sloths and †ground-sloths have short, rounded heads; in the †glyptodonts, the skull was short and remarkably deep vertically; while the armadillos have long, shallow heads, with tapering muzzle, the length and slenderness of which differ in the various genera. In the anteaters the skull is extraordinarily elongate and slender. The sagittal crest is seldom present at all and never prominent. The zygomatic arch may be complete or interrupted; in the tree-sloths, †ground-sloths, †glyptodonts and some extinct armadillos, there is a descending, plate-like process given off beneath the eye.

The backbone displays some of the most remarkable peculiarities of the order. The neck in the tree-sloths has eight or nine vertebræ, the only instances known among mammals in which the normal number of seven is departed from. In the armadillos and †glyptodonts several of the neck-vertebræ are coössified into a single piece, but the atlas is always free, so as to permit the movements of the head. In the posterior part of the dorsal and in the lumbar region the articulations between the successive vertebræ are by far the most complex and intricate known among mammals; in the tree-sloths these have degenerated, though still plainly indicated. In the †glyptodonts, which were covered with a huge, tortoise-like carapace, mobility of the backbone was needless, and so all of the dorsal vertebræ were united into one long piece and the lumbars were coössified with one another and with the sacrum. The sacrum consists, throughout the order, of a very large number of vertebræ and is attached to the hip-bones at two different points, instead of only one, as in other mammals. The tail varies much in length and thickness; in the tree-sloths it is extremely short and in the anteaters very long and bushy, prehensile in the arboreal members of the group; in the †ground-sloths, especially the gigantic forms, it was of immense thickness; while in most of the †glyptodonts a varying number of the terminal vertebræ were fused together. The sternal ribs are better developed than in any other mammals, and in the anteaters and †ground-sloths they articulate with the breast-bone by regular synovial joints, and each rib has head and tubercle like a vertebral rib.

In the limbs and feet there is great variety, according to the manner of their employment. The shoulder-blade has a very long acromion and very large coracoid, which long remains separate from the scapula; collar-bones are very generally present, though often in much reduced condition. The hip-bones have in the tree-sloths, †ground-sloths and †glyptodonts a much expanded anterior element, which in the other groups is narrow. The humerus usually has very prominent deltoid and supinator ridges and epicondylar foramen; the fore-arm bones are always separate, and there is generally much freedom of rotation of the manus. In the wrist there is no distinct central and usually there are the ordinary eight separate bones. The tibia and fibula are frequently coössified. The tree-sloths, which lead most strictly arboreal lives and are almost helpless on the ground, are unique among mammals in that the body is habitually suspended from the limbs, not carried upon them; the feet are curved hooks, which fit over the tree-branches and support the weight without muscular exertion. The limb-bones are very long and slender, the claws long, curved and sharp, and the metapodials of each foot, two or three in number, are fused into a single mass. In the †ground-sloths there was much change in foot-structure during the course of their recorded development; they were usually five-toed and the feet were armed with one or more great claws; the later and larger representatives of the suborder walked upon the outer edge of the feet.

The armadillos, which are largely burrowers, have five-toed feet and long, heavy, pointed claws, but in some of them the pes has a varying number of flat, hoof-like nails. The immense †glyptodonts had very short, broad feet, shod with hoofs, which, in some of the genera, were longer and more claw-like in the manus.