Final answer:
The biggest animal ever existed is measured by its size, particularly its length. Examples include the colossal squid, which can measure up to 14 feet, and the blue whale, which can reach up to 110 feet in length.
Step-by-step explanation:
The biggest animal that ever existed is measured based on its size, specifically its length. For example, the colossal squid is one of the largest invertebrates and can measure up to 14 feet in length. Some squids can even grow to almost 50 feet long. Another example is the blue whale, which is the largest living vertebrate and can reach up to 110 feet in length.