Mammal. The giraffe is the tallest mammal, reaching as high as 5.5 meters (18 feet). Although their necks are much longer, giraffes have only seven vertebrae, the same number as most mammals. The giraffe's heart has to produce double the blood pressure of most large mammals in order to pump blood all the way up to the animal's brain. In the wild, giraffes almost never lie down because of vulnerability to predators. They usually sleep standing, sometimes sitting, and they give birth standing up. When giraffes sleep, they curl their necks and sleep for about five minutes at a time, sleeping no more than 30 minutes a day.