Anatomy

B. Pygmaeus is a dwarf sloth species which is closely related to the brown throated three-toed sloth(Bradypus Variegatus), and are similar in appearance with only minor differences. B. Pygmaeus is smaller, and approximately 40% lighter in body mass, and 15% shorter in body length. On average these sloths weigh 5.5-7.7 lbs and are 19-21 inches in length. The skull is 12-16% smaller than B. Variegatus. Cranial characteristics that identify B. Pygmaeus include absence of an external carotid foramen, large external auditory meatus, smaller stylomastid foramen, more thin and curved coronoid processes on mandible, and a smoother more concave ventral edge on the stylohyoid.

In initial species description, many characterize B. Pygmaeus as having a “hood” of hair, which projects over the brow, comparable to the hood of a monk. Despite numerous research no one has encountered this Pygmy sloth with hair folding over its forehead. These Pygmy sloths have long neck hair, beginning at the ventral part of the skull and hanging off the neck. Similar to other sloths, B. Pygmaeus hosts algae inside its fur, causing the hairs to be thick and spongy, and have traverse cracks that will increase with age. This algae is most visible on the top of head and neck, portions of the forelimbs, and upper backside.

Pygmy sloths do not have deciduous teeth, but instead have a single set of high-crowned, open-rooted teeth. These teeth grow continuously throughout life. Incisors are absent, and it’s not possible to distinguish between premolars and molars. The teeth of B. Pygmaeus lack enamel, but instead contain two different kinds of denting plus an outer layer of cementum. B. Pygmaeus has 18 teeth- 10 on the upper jaw, and 8 on the lower jaw. The upper anterior chisel-shaped teeth are tiny or absent, and the lower ones compressed anteroposteriorly.

The forelimbs of Pygmy sloths are just about equal in length to the hindlimbs. These long limbs are very strong in bone strength and muscles. The wide straight and relatively flat claws of this species resemble many mammals that dig. Pygmy sloths exhibit fusion of various manual phalanges including in the thumb, and the two phalanges at the base of the third digit, as well as the fusion of metacarpals to carpals.

The pelvis is massive and broad and unusual in that the ischia are connected to the vertebral column.

Keywords: deciduous teeth, carpals, pelvis, vertebral column, anteroposterior, carotid foramen, auditory meatus, stylomastid foramen, stylohyoid, pterygoid.