No animal on Earth has four knees, only two. All animal skeletons consist of essentially the same bones and joints, just expressed in different shapes or forms.
All creatures that exist with four limbs, comprising the legs and arms, fall in the category of tetrapods. This word comes from Greece and means "four legs." The animals in this group all share the same basic skeletal structure, which consists of two arms, two legs, a torso and a head. Since all animals belong to this group, all animals have only two "real" legs and two "real" arms. So, although evolution may have shaped some species' arms into shapes that appear to be legs, they are still essentially arms.
Take a horse for instance. The two front legs are actually arms, just shaped that way over millions of years of evolutionary pressure. Because of this, there are no physiological knees within the front two legs of a horse. They are actually elbows that have been shaped to serve a similar purpose to the kneecap on the hind legs. In fact, horses have specialized their arm shape so drastically over the years that their hooves are actually nothing but their middle fingers.
It should be pointed out that not every tetrapod is equipped with four limbs in modern times. Whales have partially lost some of their limbs, with fragments still being visible in skeletons. Additionally, snakes have completely lost all four of theirs.Learn More
Several animals on the African savannah work together to ensure survival, including baboons with impalas, zebras with wildebeests, oxpeckers with large animals and cattle egrets with buffaloes. Hyenas work together to hunt in packs for the mutual survival of the group, and lionesses hunt in much the same manner as they attempt to bring down zebras, gazelles and wildebeest.Full Answer >
Nineteen of the 20 species of armadillo are native to Latin America, with the other species, the nine-banded armadillo, being native to the United States. Armadillos are considered a threatened species as of 2014.Full Answer >
There are two sets of muscles that help annelids move. One expands, and the other contracts the body. Annelids alternate the use of these muscles to achieve locomotion.Full Answer >
Primary consumers feed solely on plants.Their food consists of leaves, grasses, fungus, flowering shrubs and other hedging plants. In the food chain, plants are the producers that are fed on by herbivores. Examples of primary consumers are cows, goats, antelopes, rabbits, giraffes and zebra.Full Answer >