Smallest organisms

Bee hummingbird (Mellisuga helenae) male, the smallest bird and smallest known dinosaur

Batodonoides vanhouteni, an extinct shrew-like mammal, thought to be the smallest mammal that ever lived

The smallest organisms found on Earth can be determined according to various aspects of organism size, including volume, mass, height, length, or genome size.

Given the incomplete nature of scientific knowledge, it is possible that the smallest organism is undiscovered. Furthermore, there is some debate over the definition of life, and what entities qualify as organisms; consequently the smallest known organism (microorganism) is debatable.