The Barbados threadsnake comes in as the smallest with adults being 4 inches long. Green anacondas are slightly shorter than the longest snakes (reticulated pythons), but still average around 15 feet long and are much heavier averaging 125 pounds.
The pygmy marmoset is the smallest monkey averaging 6 inches long and a quarter pound. Mandrills are the largest with males averaging around 80 pounds, but they can be up to 120 pounds.
Falabella horses are the smallest breed weighing as little as 40 pounds. Shires are generally the biggest breed at an average of up to 2400 pounds.
The dwarf sperm whale is the smallest whale at about 9 feet long and 550 pounds. The blue whale is not only the largest whale, but also the largest animal at about 100 feet long and close to 400,000 pounds!
The bee hummingbird is the smallest bird weighing around 2 grams (0.004 pounds). Ostriches are the largest birds averaging around 250 pounds. No wonder they can’t fly.
Fish (not including sharks)
Paedocypris progenetica is the tiniest little fish at about 1 cm long. The ocean sunfish (or mola mola) averages 2200 pounds, but can get to over 5000 pounds and 14 feet across the fins.
The dwarf lanternshark is the smallest shark coming in at about 7 inches long. The largest are whale sharks with an average length of 32 feet and weight of 20,000 pounds (great whites are about 15 feet long and 2000 pounds).
The smallest wild cat is the rusty-spotted cat weighing only around 2.5 pounds and 25 inches long. Tigers are the largest weighing about 850 pounds and 11 feet long.
Western pygmy blues have a wingspan of about half an inch and Queen Alexandra's birdwings come in with a wingspan of almost 10 inches.
Pea crabs get their name because they are about the size of a pea and are parasites that you may find inside an oyster. With a span of 12 feet between the claws and weighing over 40 pounds, the Japanese spider crab is the largest out there.
Pygmy rabbits come in as the smallest averaging about 1 pound. Continental giants are generally 15 to 20 pounds, but the biggest one ever was just under 50 pounds and over 4 feet long.
Patu marplesi is the tiniest little spider that is almost impossible to see at about half a millimeter long. The giant huntsman spider is something I never hope to see because it’s leg span is 12 inches.
The star sucker pygmy octopus is about a half an inch across and weighs 1 gram. The giant pacific octopus is upwards of 120 pounds and 20 feet across, but the largest ever was 300 pounds and 30 feet across.
Kitti's hog-nosed bats are the smallest bats and possibly the smallest mammals. They have a wingspan of about 5 inches and weigh around 2 grams. Large flying foxes are the biggest bat and they may only weigh around 2.5 pounds, but have wingspans of nearly 5 feet.
The 5 species of clam in the genus Waldo are probably the smallest clam at less than 5 mm long. The name Waldo was picked because they are so hard to find. Giant clams are the biggest with some about 4 feet long and 450 pounds.
Maui's dolphins are the smallest measuring around 5.5 feet long and just over 100 pounds. Orcas are actually the largest dolphin (despite being known as killer whales) with average lengths of 25 feet and weighing in around 13,000 pounds.
Speckled tortoises are the smallest at around 3.5 inches long and a quarter pound. Leatherback sea turtles are the biggest averaging 7 feet long and 1000 pounds, but the largest found was over 7 feet long and 2000 pounds.
Fennec foxes are the smallest weighing around 2.5 pounds and 8 inches tall. Red foxes are the largest weighing up to 30 pounds and 20 inches tall.
At 0.3 inches long, Paedophryne amauensis is the smallest frog and also the smallest known vertebrate. The goliath frog is the biggest and grows to just over a foot long and 7 pounds.