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Article. Images & Videos. Related. Encyclopædia Britannica, Inc. All vertebrates (animals with backbones) have a skull, which is the skeletal framework of the head. The skull is composed of bones and cartilage that work together to surround and protect the brain and some sense organs. The upper jaw, but not the lower, is part of the skull.
The brain is enclosed within a skull, forming the head. Vertebrates are also characterized by an internal skeleton that supports the body.
Horses belong to the family Equidae, along with zebras and asses. This family is in turn part of the order of one- and three-toed hoofed mammals, Perissodactyla, which also includes rhinoceroses and tapirs. The relationship of the horse to humans has been unique. The horse can be a partner and friend.
- Overview
- The first finds
Dinosaurs are a diverse group of reptiles that were the dominant terrestrial life form on Earth during the Mesozoic Era, about 245 million years ago. Dinosaurs went into decline near the end of the Cretaceous Period, about 66 million years ago.
How did most dinosaurs go extinct?
The decline of dinosaurs was most likely caused by many different factors. A popular theory is that an asteroid crashed into the Yucatán Peninsula 66 million years ago, causing enough terrestrial and asteroid material to be ejected into the atmosphere that sunlight was possibly blocked for several years. This would have severely impacted plant life and subsequently brought about the end of most dinosaurs.
Did dinosaurs have feathers?
Some species of dinosaurs, such as the dromaeosaur, have fossil records of their feathers. Early feathers were not evolved for flight; instead, scientists speculate that dinosaurs evolved feathers for other reasons, such as temperature regulation, camouflage, and balancing while running. While most species are often depicted as featherless, some researchers believe that feathers were commonplace on dinosaurs. Learn more.
Do dinosaurs exist today?
Before Richard Owen introduced the term Dinosauria in 1842, there was no concept of anything even like a dinosaur. Large fossilized bones quite probably had been observed long before that time, but there is little record—and no existing specimens—of such findings much before 1818. In any case, people could not have been expected to understand what dinosaurs were even if they found their remains. For example, some classical scholars now conclude that the Greco-Roman legends of griffins from the 7th century bce were inspired by discoveries of protoceratopsian dinosaurs in the Altai region of Mongolia. In 1676 Robert Plot of the University of Oxford included, in a work of natural history, a drawing of what was apparently the knee-end of the thighbone of a dinosaur, which he thought might have come from an elephant taken to Britain in Roman times. Fossil bones of what were undoubtedly dinosaurs were discovered in New Jersey in the late 1700s and were probably discussed at the meetings of the American Philosophical Society in Philadelphia. Soon thereafter, Lewis and Clark’s expedition encountered dinosaur fossils in the western United States.
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The earliest verifiable published record of dinosaur remains that still exists is a note in the 1820 American Journal of Science and Arts by Nathan Smith. The bones described had been found in 1818 by Solomon Ellsworth, Jr., while he was digging a well at his homestead in Windsor, Connecticut. At the time, the bones were thought to be human, but much later they were identified as Anchisaurus. Even earlier (1800), large birdlike footprints had been noticed on sandstone slabs in Massachusetts. Pliny Moody, who discovered these tracks, attributed them to “Noah’s raven,” and Edward Hitchcock of Amherst College, who began collecting them in 1835, considered them to be those of some giant extinct bird. The tracks are now recognized as having been made by several different kinds of dinosaurs, and such tracks are still commonplace in the Connecticut River valley today.
Better known are the finds in southern England during the early 1820s by William Buckland (a clergyman) and Gideon Mantell (a physician), who described Megalosaurus and Iguanodon, respectively. In 1824 Buckland published a description of Megalosaurus, fossils of which consisted mainly of a lower jawbone with a few teeth. The following year Mantell published his “Notice on the Iguanodon, a Newly Discovered Fossil Reptile, from the Sandstone of Tilgate Forest, in Sussex,” on the basis of several teeth and some leg bones. Both men collected fossils as an avocation and are credited with the earliest published announcements in England of what later would be recognized as dinosaurs. In both cases their finds were too fragmentary to permit a clear image of either animal. In 1834 a partial skeleton was found near Brighton that corresponded with Mantell’s fragments from Tilgate Forest. It became known as the Maidstone Iguanodon, after the village where it was discovered. The Maidstone skeleton provided the first glimpse of what these creatures might have looked like.
Two years before the Maidstone Iguanodon came to light, a different kind of skeleton was found in the Weald of southern England. It was described and named Hylaeosaurus by Mantell in 1832 and later proved to be one of the armoured dinosaurs. Other fossil bones began turning up in Europe: fragments described and named as Thecodontosaurus and Palaeosaurus by two English students, Henry Riley and Samuel Stutchbury, and the first of many skeletons named Plateosaurus by the naturalist Hermann von Meyer in 1837. Richard Owen identified two additional dinosaurs, albeit from fragmentary evidence: Cladeiodon, which was based on a single large tooth, and Cetiosaurus, which he named from an incomplete skeleton composed of very large bones. Having carefully studied most of these fossil specimens, Owen recognized that all of these bones represented a group of large reptiles that were unlike any living varieties. In a report to the British Association for the Advancement of Science in 1841, he described these animals, and the word Dinosauria was first published in the association’s proceedings in 1842.
3 days ago · horse, ( Equus caballus ), a hoofed herbivorous mammal of the family Equidae. It comprises a single species, Equus caballus, whose numerous varieties are called breeds. Before the advent of mechanized vehicles, the horse was widely used as a draft animal, and riding on horseback was one of the chief means of transportation.
Photos and Videos. See All Videos, Images and Interactives →. Topics. childhood disease and disorder: Musculoskeletal disorders. prenatal development: Skeletal system. human aging: Skeletal system. Human skeleton, the internal skeleton that serves as a framework for the body. This framework consists of many individual bones and cartilages.
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The Human Skeleton. from Bones. 750L - 890L. You have fewer bones in your body now than you did when you were born. Everybody starts life with more than 300 bones. By age 20, we have only about 206 bones.
