GENERAL INFORMATION (121)

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What Are Dinosaurs

Dinosaurs were a group of reptiles that lived during the Mesozoic Age (231-65 Ma) . They were all land animals, although they had close relatives both in the water and in the air above. They were characterized by skulls with two extra openings behind the eye holes, legs carried much more under their bodies than the usual reptilian 'straddling' posture, and foot bones resembling those of a bird. Most had tough reptilian skin but many were more active than any reptiles today.

Some were monstrous, some no bigger than a chicken. Some walked on all fours, some on 2 legs. Some were fierce carnivores , some docile herbivores . In fact there was probably a dinosaur for every sort of mammal of today except maybe those that burrow, climb, fly or live in water. They dominated life on earth for 140 million years - longer than any other group of vertebrates . By 1998 almost 400 genera have been well described, with new discoveries almost monthly. With recent finds from Antarctica, they have been unearthed on every continent.

How Do We Learn About Dinosaurs?

Because there are no dinosaurs alive today, our knowledge of them comes exclusively from their remains. The most common such remains are fossilized bones. From these bones we can deduce much about their size, shape and posture. For instance, small, fast dinosaurs tended to have hollow, lightweight bones, while those the size of elephants needed thick walled bones to support their enormous weight. Yet even many of these huge creatures had hollows in spinal bones and holes in the side of their skull to reduce weight.

Hip, thigh and ankle bones tell much about dinosaurs. Straight thigh bones with a sharply inturned top that slotted into a hole between the hip bones suggests that dinosaurs walked erect like horses and did not sprawl. High ankles and long foot bones prove that they walked on their toes. Long, thin shin bones imply speed. Stiff ankle joints suggest that they were at home on level ground - probably none climbed trees. Evidence from fossilized footprint tracks support these ideas (narrow tracks=erect posture, long strides=speed).

Bumps, grooves and scars on bones show muscle attachment and let us make educated guesses about body shape. The form of jaws and teeth indicate their food; the sizes and positions of holes in the skull reveal the size of their brain, ears, eyes and nostrils. Some had more brain than living reptiles, many had keen sight, hearing or sense of smell. The old idea of dinosaurs as merely ponderous, pea-brained giant reptiles is no longer sustainable. Many could breathe while eating due to the presence of a secondary palate , a very non-reptilian feature, and some may have had a long pre-hensile tongue.

Other fossilized remains also provide information. Footprints tell us how heavy the animals were, what their stride length (and thus their speed ) was, and how the legs were arranged relative to the body. In some cases they also provide clues to herding behaviour and in isolated instances show predator attacks. Coprolites provide some information about food, and a few instances of mummified or fossilized skin impressions confirm the existence of a scaly skin (and feathers and fur in early birds and pterosaurs respectively). Remains of eggs and nests provide important information on dinosaur reproduction.

Finally, the area where the fossils are found can not only enable us to date the remains, but also indicate the type of terrain and climate.

Some Dinosaur History

Fossilized remains have been known for hundreds of years since the first mosasaur jaw was found at Maastricht in Belgium in 1770. Many other fossils of marine reptiles and pterosaurs were subsequently found all over Europe, but it was not until the1820's and 1830's that the first dinosaur remains (teeth) were found in English gravel quarries. The strangeness of these were immediately recognized and it soon became clear that these new type of fossils showed characteristics of lizards, birds, mammals and crocodiles. In the early 1840's Sir Richard Owen coined the term dinosaur ('terrible lizard') for these strange creatures, and the first mounted skeleton (an Iguanodon) went on display at the Crystal Palace exhibition in London in 1854. This was displayed as basically just a very large lizard in keeping with the ideas of the time, and the characteristic thumb spike was initially positioned as a nose horn!

Even at this early stage, several investigators, among them Thomas Huxley, realized that these new animals strongly resembled birds in many important aspects, and went so far as to suggest that birds might be descended from dinosaurs. For reasons not always obvious, many of these early observations seemed to be forgotten or ignored in the early 1900's, and had to be 're-discovered', often in the face of considerable conservative opposition, in more recent times. Having been classified as reptiles because of the shape of the original teeth, they then became firmly identified with the characteristics of reptiles - they must have been cold-blooded, sluggish and slow because that is what reptiles are. This view persisted even in the face of obvious contradictions from the fossil evidence that showed a much greater similarity to birds than to any reptiles.

Prof. Leidy in New Jersey discovered a large collection of complete hadrosaur skeletons on which he spent most of his life's work. He noted the difference in size of the front and back legs, and in 1868 mounted the first ever bipedal dinosaur skeleton. This led to a re-evaluation of the Iguanodon remains and they too soon became bipedal . Interestingly, they are now portrayed as mostly quadruped once again, following observations that the tail was quite rigid and would have made an erect bipedal stance difficult.

Early American Discoveries

In 1877 the hub of dinosaur discovery moved from Europe to North America following the first complete skeleton discoveries at Como Bluff in Wyoming. These finds were dug for 15 years, and 2 of the best known names in dinosaur paleontology , Othniel Marsh and Edward Cope competed so vigorously over the finds that this era became known as the 'Bone Wars'. Marsh shipped 30 train cars of bones out, and both men became famous for their finds (Cope named 56 species, Marsh 80). No North American find has ever rivalled the Como Bluff location.

Dinosaurs Stand Up

At this stage the prevailing view was still that dinosaurs were big lizards. In 1909 Earl Douglas found sauropod bones in Utah that were to change that view. The rock in which they were embedded was extremely hard, and many bones had to be dynamited out of the rock. After 15 years work Douglas accumulated 350 tons of samples. When he mounted the specimens with an erect quadruped stance, with the legs near vertical and the feet beneath the body, he started 30 years of debate as to whether he was correct or whether a more characteristic splayed reptile stance should have been used. The argument continued until Roland Bird found 300m (1000 ft) of fossil dinosaur trackway in the bed of a Texas river. These were undoubtedly sauropod tracks and showed clearly that for both front and back legs the prints of opposite feet were consistent only with the fully erect construction of Douglas.

The Rest of the World Joins In

Dinosaur exploration moved further afield when Andrews and Osborn organized a series of 5 trips to the Gobi desert in Mongolia in the 1920's, and hit the jackpot almost immediately with some of the richest locations ever found (at Flaming Cliffs). On their second trip in 1923 they found the fossilized eggs of Protoceratops (now known in fact to belong to oviraptorosaurids ).

Dinosaurs Today

Throughout the first half of the twentieth century many discoveries were made, but generally interpreted in a conservative "dinosaurs are reptiles" manner. It was not until the 1960's and since that some of the most exciting ideas about dinosaurs have been debated and continue to be the source of considerable controversy in many circles. The questions of whether dinosaurs were really warm-blooded, how they came to be extinct, and behavioural questions about mating, caring for their young and migration are discussed in separate topics.

Although dinosaurs vanished 65 million years ago, they are still alive and well in the minds of people of all ages. As research continues and new finds are made there can only be one certainty - many more surprises are in store.

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