9. Skeletal Structure Evolution
Having developed particular adaptations for their particular way of life, sloth skeletal systems deviate greatly from normal mammalian bone form. With specific internal features that maximise strength while minimising weight, their bones have evolved to be denser yet lighter than those of other animals. Particularly in their limbs, the joint arrangements have changed to give stability in hanging poses precedence over walking abilities. Their pelvis has evolved to support their internal organs during inverted situations; their ribcage has developed unusual flexibility that lets them breathe comfortably in several positions. The mineral composition and bone density have changed to give maximal structural support with lowest metabolic maintenance needs. This amazing skeletal adaptation shows how well evolution may change fundamental body plans to produce extremely specialised structures.