“Ai siue Ignavus” - Bradypus tridactylus
The title “Ai siue Ignavus” translates to “Ai, or Lazy”, which were the two common names for the Pale-throated sloth at the time. The Bradypus genus is the genus of three-toed sloths, which are the ones who are descended from a common ancestor of the giant ground sloths - two-toed sloths are actually not closely-related to either three-toed or giant sloths.
Even though they’re not closely-related, both sloth families share a unique trait: they don’t have seven cervical vertebrae, which is a trait of almost all mammals, including those with very short necks (such as whales) and very long necks (such as giraffes). The two-toed sloths have only six cervical vertebrae, and the three-toed sloths have nine cervical vertebrae. The extra vertebrae in the three-toed sloths are what allow them to have such flexibility in their neck, and how they can turn their head 180 degrees.
A Description of the Nature of Four-Footed Beasts. Joannes Jonstonus, 1678.