Guinea pigs (or Cavies) are small species of Rodent family. (petsnext.com)
The earliest known squirrels date from the Eocene and are most closely related to the mountain beaver and to the dormouse among living rodent families. (eol.org)
It's such a tough life that — to conserve energy — this member of the rodent family gave up regulating its temperature, and they are able to thrive in a low - oxygen, high — carbon dioxide environment that would suffocate or be very painful to humans. (sciencemag.org)