Many domesticated breeds of anima have been selected for extreme traits such as large size. By selective breeding some true giants have be produced!
Some animals are small and cute, and others are enormous... and cute. Here are a few examples of animals that grew to impressive sizes compared to what is normal for their species. Some are from breeds that have been selected for large size, others have just lived longer than is normal or have a congenital condition that caused more growth.
Dolly the Mastiff
This dog became a minor internet celebrity after his (or her?) pictures started to circulate, some accompanied by a story about how the dog needed a new home because his owner could not afford to feed him! The dog is sometimes referred to as Dolly. Even online rumor hounds Snopes were not able to track down the real name and real story behind this picture of an enormous mastiff.
Other pictures of giant mastiff include this one with a couple and horse. This mastiff is aptly called Hercules and weighs in at over 280 pounds.
Which goes to show that this is a breed given to pretty impressive stature. All dogs descend from common wolf ancestors but have been selected for extreme differences in many qualities including size and weight.
Another mastiff called Hercules is reputed to weigh in at 282 pounds (128 kilograms).
Herman the Hare
German hares tend to be pretty large, but Hans Wagner's bunny Herman is bigger than most. He weighs in at 17 pounds (7.7 kilograms). Herman rose to fame after being featured in a 2006 New York Post article.
The authenticity of these and similar photos of giant rabbits has been confirmed by Hoax Slayer.
However, if reports are correct another German hare called Darius is a lot bigger than Herman at 49 pounds (22 kilograms).
Some animals that are hybrids of two different species grow larger than either parent type due to growth limiting factors being disabled.
One exampling being the Liger (lion x tiger). One well-known specimen going, once again, by the name of Hercules. Ligers have weighed in at up to 900 pounds (408 kilograms).
Chilli the Bull
At 6'6" at the shoulders Chilli the Freisan is pretty impressive. He lives on an animal sanctuary in the United Kingdom. Another Friesan bull called Trigger is just behind at 6'5". However, they both need to gain a few more inches to overtake the official world tallest cow, and Italian ox called Fiorino who measures in at 6'8".
Many species of freshwater fish will continue to grow as they age and can reach amazing sizes. However the largest known fish is a marine species called the whale shark which grows over 12 meters in length.
Some animals continue to grow so long as they remain alive. thus examples that live longer than usual can reach amazingly large body sizes.
Alligators are one example of this phenomenon and can grown to enormous sizes, such as this 'gater photographed in Georgia in 2004 carrying a full grown deer in its jaws.
Gucci the Bull Terrier
And then there is your garden-variety animals who get fat through too much food and not enough exercise. Like Gucci the dog who was actually seized by the authorities and slimmed down for the sake of her health. The authorities have intervened on behalf of a number of extremely over-weight dogs, essentially treating their care as a case of abuse due to the negative impact on their health and well-being.
It might seem odd to talk about the biggest example of a really small thing, but did you know that some bacteria are visible to the naked eye? Thiomargarita namibiensis, bacteria that lives in the soil, is a single cells life form that can grow up to 0.03mm long--about the size of a period printed in a standard font.