According to the University of Washington, the green lizard has the smallest brain. Referred to as Anolis Carolinensis, green anole or Carolina anole, the species has been studied by the scientific community. More » Science Biology Zoology

Leaving aside invertebrates, which are often microscopic, the smallest land vertebrate is Paedophryne amauensis. This tiny frog was discovered in the jungles of New Guinea, and adults are only 0.27 inch long. More » Science Biology

The smallest animal on earth is the tardigrade. The tardigrade is also known as the moss piglet or water bear. More » Science Biology Zoology
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The largest animal is the blue whale, Balaenoptera musculus, which grows to a maximum of 110 feet long. The smallest animal is the crustacean Stygotantulus stocki, which grows to 94 micrometers, or less than 0.004 inches... More » Science Biology Zoology

The animal with the largest brain is the sperm whale. Its brain weighs approximately 17 pounds and can grow to be nearly 500 cubic inches. More » Science Biology Zoology

An earthworm's ventral nerve cord carries signals from the brain to the body and allows for the coordination of the ganglia in each segment past the fourth. Ganglia are clusters of nerve cells, and an earthworm's brain i... More » Science Biology Zoology

Using the Beagle as an example breed, the domestic dog has a brain with an average weight of 2.54 ounces, or 72 grams. Of course, this brain size differs by breed. Dogs usually have a brain-to-body mass ratio of 1:125. More » Science Biology Zoology