It is true that the oldest horse, Hyracotherium, was the size of a fox. And it's equally true that the closest relatives of horses, donkeys and zebras are the rhinoceros. And the world's records in horse sizes do vary from a fox to a rhinoceros.
The largest horses in the world belong to the English breed Shire. These horses are often taller than 1.8 m (6 ft) and reach a weight of one tone (almost as much as a rhino), while average horses have 0.3-0.4 tones.
Still, the current Guinness World Record is held by a Belgian draft horse called Radar. Radar is about 6ft 7½in (1.99 m) tall. A horse's height is measured along the front leg to the top of the shoulder.
The Belgian draft horses are generally meek and due to their enormous size, they have a huge power: they can drag up to 5 tones and in some areas, they are still traditionally used with all the modern mechanization.
Radar, 9 years old, weighs 2,700 lbs (1,215 kg), as much as an average black rhino. He lives in Mount Pleasant, Texas.
Still, a Tennessee Shire horse located on a farm 65 mi (104 km) northeast of Chattanooga could be the tallest horse in the world. At an official measuring yesterday, Jenson Diplomat Tina measured 2.02 m (6 ft 8.5 in), but she weighs just ...1600 pounds (720 kg).
The documentation of her height will be sent to Guinness, based in London.
"She is still a teenager in horse years. But she is beginning to put on muscle and weight on her back as she grows. She still has at least two years of growth," said owner Jim Williams.
The smallest horses in the world belong to the Argentinean breed Falabella, which never reach a height which over 70 cm. Most Fallabellas are stubborn, clever and often dog-like in loyalty, which makes them ideal pets.
Still, Thumbelina, a 6-years-old miniature sorrel brown mare is the world's 'Smallest Living Horse', having a height of 17.5 inch (43 cm) and a weight of 57lbs (25 kg). The cocker spaniel-sized mare lives in St Louis.
The amazing pair Radar-Thumbelina will enter the 2008 edition of the Guinness Book Of Records in America, which is out next month.
"Radar looked a bit confused when he first met Thumbelina." said an onlooker.