Ornithischian dinosaurs

All ornithischians are thought to have been herbivorous and, rather like modern-day mammals, they seem to be far more diverse, and numerous, than their potential predators.

Thyreophorans (Figure 28) are a major group of ornithischians that

Ornithischian

30. Triassic saurischian dinosaurs. The early theropod Coelophysis, and sauropodomorph Plateosaurus.

Brachiosaurus

Brachiosaurus

are characterized by bearing bony plates in their body wall, clubs or spikes adorning their tails, and for having an almost exclusively quadrupedal method of locomotion. These types of dinosaur include the stegosaurs, named after the iconic Stegosaurus (well known for its tiny head, the rows of large bony plates on its back, and its spiky tail (Figure 31)); and the heavily armoured ankylosaurs including such creatures as Euoplocephalus. The latter was a huge tank-like animal that was so heavily armour-plated that even its eyelids were reinforced by bony shutters and its tail was terminated in a huge, bony club that it presumably used to skittle potential predators.

Cerapodans (Figure 28) were very different to thyreophorans. These were typically lightly built, unarmoured bipeds, although a few did revert to quadrupedal methods of locomotion. Ornithopods were one major group of cerapodans. Many of these dinosaurs were M medium-sized (2-5 metres long) and quite abundant (probably | filling the ecological niches occupied by antelopes, deer, sheep, and £ goats today). These animals, such as Hypsilophodon, were balanced at the hip (just like theropods), had slender legs for fast running, grasping hands, and, most importantly, teeth, jaws, and cheeks adapted for a diet of plants. Throughout the reign of the dinosaurs, small to medium-sized ornithopods were quite abundant, but through the Mesozoic a significant number of larger types evolved; these are known as iguanodontians (because they include animals such as Iguanodon). Most important of all the iguanodontians were the extraordinarily numerous duck-billed, or hadrosaurian, dinosaurs of the Late Cretaceous of North America and Asia. Some (but not all) of these dinosaurs did indeed have rather duck-shaped snouts, and others had a wide range of quite extravagant, hollow-crested headgear (see Chapter 7); this headgear may well have been used for social signalling, and more particularly for making loud, honking sounds. Marginocephalians were the other major cerapodan group and appeared in Cretaceous times. These included the extraordinary pachycephalosaurs ('thick-headed dinosaurs'); they had bodies that were very similar in general appearance to the ornithopods, but their heads were very odd-looking. The majority had a high dome of bone on the top, which looked vaguely similar to the headgear of hadrosaurians, except for the fact that pachycephalosaur headgear was made of solid bone. It has been suggested that these creatures were the 'headbangers' of the Cretaceous world - perhaps using head clashing in similar fashion to that seen among some cloven-hooved animals today.

Finally, there were the ceratopians, a group of dinosaurs that included the fabled Protoceratops referred to in the Introduction, as well as the well-known Triceratops ('three-horned face'). All had a singular narrow beak at the tip of the jaws and tended to have a ruff-like collar of bone at the back edge of the skull. While some of these dinosaurs, particularly the early ones, maintained r a bipedal way of life, a considerable number grew greatly in |

body size, with an enlarged head, which was adorned with a J'

huge frill-like collar and large eyebrow and nose horns. Their e

great bulk and heavy head led them to adopt a four-footed £

stance, and their similarity to modern-day rhinoceros has °

y not gone unnoticed. Clearly, as this all too brief survey shows, f dinosaurs were many and varied, judging by the discoveries £

made over the past 200 years. But even though to date |

about 900 genera of dinosaurs are known, this is only a tiny s fraction of the dinosaurs that lived during the 160 million years of their reign during the Mesozoic Era. Many of these will, unfortunately, never be known: their fossils were never preserved. Others will be discovered by intrepid dinosaur hunters in years to come.

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