Scientists have conducted isotopic analysis and found that the old horse became smaller in warmer climates and have gained a larger size for a cold snap. The research, carried out by eight institutions under the supervision of the University of Florida (USA) and the University of Nebraska, published in the current issue of the publication Science.Gruppa scientists from the University of Nebraska-Lincoln in collaboration with scientists from the Natural History Museum, University of Florida has examined the fossils of ancient horses (kind Sifrhippus ), which existed during the period of time marked by significant fluctuations in climate. About 55 million years ago on Earth there was the Paleocene-Eocene thermal maximum - the rapid rise in temperature of 10-20 degrees. Due to these climatic changes the surface of the ocean was warmer than 5 degrees, and the atmosphere and the ocean has been allocated a huge amount of carbon dioxide (CO2). When the odd-toed ungulates form Sifrhippus, the most ancient of all known horses today, 50 million years ago began to dwell in the forests North America’s more, they were the size of a domestic dog - about 5.6 kg. Warming of the climate occurred over 130,000 years, contributed to the fact that animals have decreased to 3.8 kg, to the size of normal cats. But then for the next 45,000 years, weight was 6.8 kg horses, since the temperatures on Earth have become biologists snizhatsya.Takie results obtained by studying the teeth of horses of various ages. Measuring the size of the teeth allowed them to determine the size of the equine body, and isotope analysis (measurement of the ratio of different isotopes of oxygen contained in the enamel of the teeth) spoke about the temperature fluctuations in the size of the animals that period.Vzaimosvyaz with ambient temperatures well known to biologists as Bergmann’s rule ecogeographic in which said that the colder the climate, the greater the size of the animal. It occurred among a variety of mammals. However, scientists can not answer the question: what is the essence of it - in the laws of conservation of heat or in the feeding habits of animals? In the new study, information on changing the oxygen isotopes in the teeth closely the Changes in the size of horses. This greatly impressed the coincidence of scientists. Thus, they concluded that this temperature was the main factor increasing or reducing the size of animal.