Sloths are obviously aliens.
Aliens, yes, and aliens of the time-traveling sort; their time-suits allow them to explore three parallel universes and yet retain a singular consciousness (there are no surprises when a sloth bumps into itself in the future).
As the sloth probes the vastness of the universe, a supercomputer in its suit triangulates its location across the time-space continuum and projects the output onto a planet as a physical manifestation of the sloth. This projection preserves a link to linear time – preventing disaster should all three universes simultaneously unravel.
The sloths we know are but anchors in the sea of time. How poetic.
Such mathematical calculations are almost impossibly astronomical, however, and the effect is similar to playing a fancy new game on an old computer: severe lag and total lameness. That is why sloths on earth are so slow – why they are able to lounge about in utter and singular defiance of "survival of the fittest."
Pretty clever for looking so stupid.
(click the image to see it larger)