About Dinosaurs


'Dinosaur' is the common name given to any of certain extinct reptiles, often very large, that thrived worldwide for some 150 million years and that died out at the end of the Mesozoic Era, about 66.4 million years ago. The popular name comes from the Greek words deinos (³terrible²) and sauros (³lizard²).

The English anatomist Richard Owen proposed the formal term Dinosauria to designate certain giant extinct animals represented by large fossil bones that had been unearthed at several locations in southern England during the early part of the 19th century. Originally applied to just a handful of incomplete specimens, the category Dinosauria now encompasses more than 550 generic names and at least 1,000 species. Not all of these are valid taxa, however, because of either inadequate specimens, duplication of names, or misidentification of findings as dinosaurian. Nevertheless, certain characteristics of the dinosaurs, such as diversity, longevity, and ubiquitous distribution, are well documented by abundant fossil remains recovered from every continent on Earth.

The extensive list of genera and species is testimony of the many different kinds of animals, with widely divergent lifestyles and adaptations, that are known as dinosaurs. Their remains are found in sedimentary rock strata laid down over a period ranging from roughly 230 to 66.4 million years ago (from the Middle Triassic Epoch to the end of the Cretaceous). The abundance of their fossil bones is substantive proof that dinosaurs were the dominant form of terrestrial animal life during the Mesozoic Era. It is likely that the known remains represent a very small fraction, probably less than 0.0001 percent, of all the dinosaurs that once lived. New kinds are added to the roster every year through scientific explorations around the world.

Before Richard Owen introduced the word in 1841, there was no concept of anything like a dinosaur. Quite probably, large fossil bones had been observed long before that time, but there is little record, and no existing specimens, of such findings before 1818. Dragons of Asian and Western legends would seem to have been generated by very early fossil discoveries (which later might have proved to be dinosaur remains), but there is no historical evidence to that effect.

Early 19th-century discoveries

The earliest published record of fossil remains that still exist for verification as dinosaurian was a note in the 1820 American Journal of Science and Arts by Nathan Smith. The bones had been found in 1818 by Solomon Ellsworth, Jr., while he was digging a well at his homestead just east of the Connecticut River in Windsor, Conn., U.S. 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 farther north, in Massachusetts. Pliny Moody, who discovered these tracks, attributed them to ³Noah's raven,² 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, discoverers respectively of Megalosaurus and Iguanodon . In 1824 Buckland published a description of the original specimen of Megalosaurus, which consisted of a lower jawbone with a few teeth. The following year Mantell published his ³Notice on the Iguanodon, a Newly Discovered Fossil Reptile, from the Sandstone of Tilgate Forest, in Sussex,² based on several teeth and some leg bones. Both men collected fossils as an avocation and are credited with the earliest published announcements of what later would be recognized as dinosaurs. In both cases, their finds were too fragmentary to permit a clear image of either original animal. In 1834 a partial skeleton was found near Brighton, Eng., which corresponded with Mantell's fragments from Tilgate Forest. It became known as the Maidstone Iguanodon, named 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 continental 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 named two other fragmentary specimens: a single large tooth that he called Cladeiodon and an incomplete skeleton composed of very large bones that he named Cetiosaurus . 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 termed these animals Dinosauria, and the word was first published in the association's Proceedings in 1842.

Reconstruction and classification During the decades that followed Owen's announcement, many other kinds of dinosaurs were discovered and named in England and Europe: Massospondylus in 1854, Scelidosaurus in 1859, Bothriospondylus in 1875, and Omosaurus in 1877. Popular fascination with the giant reptiles grew, reaching a peak in the 1850s with the first attempts to reconstruct two of them, Iguanodon and Hylaeosaurus, for the first world exposition, the Great Exhibition of 1851 in London's Crystal Palace. The sculptor Waterhouse Hawkins, under Owen's direction, created life-size models of these two genera, and in 1854 they were displayed together with models of other extinct and living reptiles, such as plesiosaurs, ichthyosaurs, and crocodiles.

Initially the category Dinosauria was adequate to include all of the large nonaquatic reptiles then known from Mesozoic strata of Europe. But by the 1880s it became evident that the Mesozoic fauna was more diverse and complex than had been realized. The first important attempt to establish a more instructive classification of the dinosaurs was made by the English biologist T.H. Huxley as early as 1868. Because he observed that these animals had a number of birdlike features, including their legs, he established a new order called Ornithoscelida. He divided the order into two suborders: first, the Dinosauria, including the iguanodonts, the large carnivores, or megalosaurids, and the armoured forms including Scelidosaurus; and second, the Compsognatha, for the very small, birdlike carnivorous form Compsognathus.

Huxley's classification was replaced by a radically new scheme proposed by his fellow Englishman H.G. Seeley in 1887. Seeley noticed that all dinosaurs possessed one of two distinctive pelvic designs, one like that of birds and the other like that of reptiles. Accordingly, he divided the dinosaurs into two orders, the Ornithischia (with a birdlike pelvis) and the Saurischia (with a reptilian pelvis). The Ornithischia included four suborders: Ornithopoda (Iguanodon and similar herbivores), Stegosauria (plated forms), Ankylosauria (Hylaeosaurus and other armoured forms), and Ceratopsia (horned dinosaurs, just then being discovered in North America). Seeley's second order, the Saurischia, included all the carnivorous dinosaurs, such as Megalosaurus and Compsognathus , as well as the giant herbivorous sauropods, including Cetiosaurus and several immense ³brontosaur² types that were turning up in North America.

In 1878 a spectacular discovery was made in the town of Bernissart, Belg., when several dozen complete, articulated skeletons of Iguanodon were accidentally uncovered in a coal mine during the course of mining operations. Under the direction of the Royal Institute of Natural Science of Belgium, in Brussels, thousands of bones were retrieved and carefully restored over a period of many years. The first skeleton was placed on exhibit in 1883, and today the public can view an impressive herd of Iguanodon. The discovery of these multiple remains gave the first hint that at least some dinosaurs may have traveled in groups. The supervisor of this extraordinary project was Louis Dollo, a zoologist who was to spend most of his life studying Iguanodon, working out its structure, and speculating on its living habits.

American hunting expeditions

England and Europe produced most of the early discoveries and students of dinosaurs, but North America soon began to contribute a large share of both. One leading student of fossils was Joseph Leidy of the Academy of Natural Sciences in Philadelphia, who named some of the earliest dinosaurs found in America, among them Palaeoscincus, Trachodon, Troodon, and Deinodon. Leidy is perhaps best known for his study and description of the first dinosaur skeleton to be recognized in North America, that of the duckbill found at Haddonfield, N.J., U.S., in 1858. He named the specimen Hadrosaurus foulkii. Leidy's theory that this animal probably was amphibious influenced views of dinosaur life for the next century.

Two Americans whose work in the second half of the 19th century had worldwide impact on the science of paleontology in general, and the growing knowledge of dinosaurs in particular, were O.C. Marsh of Yale College and E.D. Cope of the University of Pennsylvania and the Academy of Natural Sciences in Philadelphia. All previous dinosaur remains had been discovered by accident in well-populated regions with temperate, moist climates, but Cope and Marsh astutely focused their attention on the arid North American West, which had wide expanses of bare, exposed rock. In their intense quest to find and name new dinosaurs, these scientific pioneers became fierce and unfriendly rivals.

Marsh's field parties explored widely, exploiting dozens of now famous areas, among them Yale's sites at Morrison and Canon City in Colorado and, most important, Como Bluff in southeastern Wyoming. The discovery of Como Bluff in 1877 was a momentous event in the history of paleontology, generating a burst of exploration and study and a widespread public enthusiasm for dinosaurs. Como Bluff brought to light one of the greatest assemblages of dinosaurs, both small and gigantic, ever found. For decades the site went on producing the first known specimens of renowned dinosaurs like Stegosaurus, Camptosaurus, Camarasaurus, Laosaurus, Coelurus, and others. From the Morrison site came the original specimens of Allosaurus, Diplodocus, Atlantosaurus, and Apatosaurus (sometimes called Brontosaurus). Canon City provided bones of a host of dinosaurs, including Stegosaurus, Brachiosaurus, Allosaurus, and Camptosaurus.

Another major historic site was the Lance Creek area of northeastern Wyoming. There J.B. Hatcher discovered and collected dozens of horned dinosaur remains for Marsh and Yale College, among them the first specimens of Triceratops and Torosaurus. Marsh was aided in his work at these and other localities by the skills and efforts of many other collaborators like Hatcher‹William Reed, Benjamin Mudge, Arthur Lakes, William Phelps, and Samuel Wendell Williston, to name a few. Marsh's specimens now form the core of the Mesozoic collections at the National Museum of Natural History of the Smithsonian Institution and the Peabody Museum of Natural History at Yale University.

Cope's dinosaur explorations ranged as far as, or farther than, Marsh's, and his interests encompassed a wider variety of fossils. Due to a number of circumstances, however, Cope's dinosaur discoveries were fewer and his collections far less complete than those of Marsh. Perhaps his most notable achievement was finding and proposing the names for Coelophysis and Monoclonius . Cope's dinosaur explorations began in the eastern badlands of Montana, where he discovered Monoclonius in the Judith River Formation of the Cretaceous period. Accompanying him there was a talented young assistant, Charles H. Sternberg. Later Sternberg, with his three sons, went on to recover countless dinosaur skeletons from the Late Cretaceous Oldman and Edmonton formations along the Red Deer River of Alberta, Canada.

Dinosaur ancestors During the early decades of dinosaur discoveries, little thought was given to their evolutionary ancestry. Not only were few specimens known, and those specimens so unlike any living animal, but the concept of evolution itself was still a radical idea. With the growing acceptance of Charles Darwin's theory on the mutability of species during the last half of the 19th century, the question of dinosaurian origins acquired respectability and serious thought.

Early on, it was recognized that, as a group, dinosaurs appear to be most closely allied with crocodilians. Two anatomic features‹socketed teeth and a doubly fenestrated (diapsid) skull‹are present in both. The earliest crocodilians occurred nearly simultaneously with the first known dinosaurs, so neither could have given rise to the other. The most likely ancestry of dinosaurs lies within a poorly understood group of Triassic reptiles termed pseudosuchian ("false crocodile") thecodonts ("socket-toothed reptiles").

An early candidate for ancestor of the dinosaur was an advanced thecodont of South Africa, Euparkeria , of the Early Triassic epoch. Euparkeria was a diapsid with socketed teeth, a preorbital fenestra (opening), and semierect hind limbs‹conditions all equivalent to, or approaching, those of dinosaurs. New discoveries suggest an even more dinosaur-like creature in the Middle Triassic small South American form Lagosuchus.

The earliest appearance of "true dinosaurs" is almost impossible to pinpoint. First, it can never be known with certainty that the very first (or last) specimen of any kind of organism has been found. The stratigraphic succession is discontinuous and contains many gaps in the geologic record. Similarly, the fossil record of dinosaurs and other creatures contained in the rock strata is far from complete.

Second, evolution from ancestral to descendant form is usually a gradational process; consequently, in the transformation from a theoretical thecodont ancestor to a recognizable dinosaur, it is extremely difficult to determine at exactly what point every diagnostic feature of the dinosaurian condition first appeared. A true dinosaur possessed all of the following anatomic features: a diapsid skull, a preorbital fenestra, a mandibular fossa, a perforated hip socket, an offset femoral head, a fourth trochanter of the femur, a mesotarsal ankle joint, digitigrade feet, and at least four sacral vertebrae. The first such animal is still being sought.

Pre-Triassic and Early Triassic reptiles that had acquired some of these features, the archosaurians ("ruling lizards"), diversified along a variety of evolutionary pathways. Only a few, however‹possibly one‹passed on to the dinosaurs an improved stance and posture with a resulting improved gait, increased efficiency of food gathering and processing, apparently higher metabolic rates and cardiovascular nourishment, and, for most, an overall increase in size. All these trends, individually or in concert, probably contributed to the collective success of dinosaurs, which resulted in their dominance among the terrestrial animals of the Mesozoic.

Modern studies During the first century or more of dinosaur awareness, workers in the field more or less concentrated on the search for new specimens and new kinds of animals. Their discoveries then required detailed description and analysis followed by comparisons with other known kinds in order to classify the new finds and develop theories about dinosaur evolutionary relationships. All these pursuits continue, but newer methods of exploration and analysis have been adopted. Emphasis has shifted from purely descriptive procedures to quantitative analytical and multivariate statistical analysis and the application of such analysis to functional anatomic systems.

Functional anatomic studies make extensive use of living analogues that, together with both mechanical and theoretical models, make it possible to visualize certain aspects of the once living animal. For example, reconstruction of the limb musculature, combined with examination of the biomechanics of the leg and joint skeletomuscular system and analysis of trackways, can provide information about an animal's locomotion‹walking and running‹and estimates of normal walking and maximum running speeds. The same method has been applied to jaw mechanisms and tooth wear patterns for a better understanding of feeding habits and capabilities.

Original colours and patterns cannot be known, but it is possible to speculate on them with an understanding of the ecological functions of pattern and colour in modern analogues. Are large animals mostly brightly coloured or drab? How important is colour vision, and what kinds of organisms see colours? Dinosaur skin texture has rarely been preserved, but there are a few examples. Most show a knobby or pebbly surface and not a scaly texture such as might be expected in reptiles. What might that indicate about dinosaur environments or about dinosaur relatives? In short, modern inquiry focuses more on the biology of dinosaurs and their various modes of life than on their immense size and strange design.