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Amblypoda

Amblypoda is a taxonomic hypothesis uniting a group of extinct, herbivorous mammals. They were considered a suborder of the primitive ungulate mammals, and have since been shown to represent a polyphyletic group.

Characteristics

The Amblypoda take their name from their short and stumpy feet, which were furnished with five toes each, and supported massive pillar-like limbs. The brain-cavity was extremely small and insignificant in comparison to the bodily mass, which was equal to that of the largest rhinoceroses. These animals are, in fact, descendants of the small ancestral ungulates which retained all the primitive characteristics of the latter accompanied by a huge increase in body size.

The Amblypoda are confined to the Paleocene and Eocene periods, and occur in North America, Asia (Mongolia, especially) and Europe. The cheek teeth are short crowned (brachyodont), with the tubercles more-or-less completely fused into transverse ridges, or cross-crests (lophodont type); and the total number of teeth is in one case the typical 44, but in another is less. The vertebra of the neck unite on nearly flat surfaces, the humerus has lost the foramen, or perforation, at the lower end, and the third trochanter to the femur may also be wanting. In the fore-limb the upper and lower series of carpal (finger) bones scarcely alternate, but in the hind-foot the astragalus overlaps the cuboid, while the fibula, which is quite distinct from the tibia (as is the radius from the ulna in the fore-limb), articulates with both astragalus and calcaneum.

Types of amblypods

The most generalized type is Coryphodon, representing the family Coryphodontidae, from the lower Eocene of Europe and North America, in which there were 44 teeth, and no horn-like excrescences on the long skull, while the femur had a third trochanter. The canines are somewhat elongated, and were followed by a short gap in each jaw, and the cheek-teeth were adapted for succulent food. The length of the body reached about six feet in some cases.

In the middle Eocene formations of North America occurs the more specialized Uintatherium (or Dinoceras), typifying the family Uintatheriidae. Uintatheres were huge creatures with long narrow skulls, of which the elongated facial portion carried three pairs of bony horn-cores, probably covered with short horns in life, the hind-pair being much the largest. The dental formula is i. 0/3, c. 1/1, p. 3/3·4, m. 3/3; the upper canines being long sabre-like weapons, protected by a descending flange on each side of the lower front jaw.

In the basal Eocene of North America, the Amblypoda were represented by extremely primitive, five-toed, small ungulates such as Periptychus and Pantolambda, each of these typifying a family. The full typical series of 44 teeth was developed in each, but whereas in the Periptychidae the upper molars were bunodont and tritubercular, in the Pantolambdidae they have assumed a selenodont structure. Creodont characters are displayed in the skeleton.