Paedophryne amauensis (Frog): Discovered in Papua New Guinea, this frog measures only about 7.7 millimeters (0.3 inches) in length, making it the smallest known vertebrate.
Etruscan Shrew (Suncus etruscus): The smallest mammal by mass, this tiny shrew weighs about 1.8 grams (0.063 ounces) and measures about 4 centimeters (1.6 inches) in length.
Bee Hummingbird (Mellisuga helenae): Found in Cuba, this is the smallest bird, measuring about 5.5 centimeters (2.2 inches) in length and weighing around 1.8 grams (0.063 ounces).
Kitti's Hog-Nosed Bat (Craseonycteris thonglongyai): Also known as the bumblebee bat, this is the smallest bat and mammal by skull size, with a wingspan of about 13 centimeters (5.1 inches) and a weight of 2 grams (0.071 ounces).
Pygmy Marmoset (Cebuella pygmaea): The smallest monkey, native to the rainforests of South America, measures about 12-15 centimeters (4.7-5.9 inches) long, excluding the tail, and weighs around 100-140 grams (3.5-4.9 ounces).
Speckled Padloper Tortoise (Homopus signatus): The smallest tortoise, found in South Africa, measures about 6-8 centimeters (2.4-3.1 inches) in length and weighs around 95-165 grams (3.4-5.8 ounces).
Philodina roseola (Rotifer): This microscopic, wheel-bearing animal measures only about 0.1-0.5 millimeters (0.0039-0.0197 inches) in length and is found in freshwater environments around the world.