The Stegosaurian Dinosaurs

given by Dr Susannah C. R. Maidment (Senior Researcher, Natural History Museum, London)

Abstract:
Stegosaurs are a group of dinosaurs characterized by the possession of two rows of plates and spines that extend from the neck to the end of the tail. They are known from the Middle Jurassic to the Early Cretaceous and have been found on all continents except Australia and Antarctica. Stegosaurs are part of a larger group of armoured dinosaurs, which also includes the ankylosaurs. Stegosaurs were four-legged plant-eaters and body mass estimates indicate they weighed about the same as a rhino. They were probably slow-moving, and not capable of running. They had very small teeth and do not appear to have chewed, but despite this, their bite forces indicate they could have eaten tough vegetation and small twigs. Several hypotheses have been put forward about the function of the plates of stegosaurs, but these have proven difficult to test. Different species appear to have had differently shaped plates, suggesting a role in display, and perhaps to deter predators. Two stegosaurs are known from North America: the iconic Stegosaurus, which is known from numerous skeletons from Colorado, Utah and southern Wyoming, and the less well-known Hesperosaurus, represented by just a few specimens from northern Wyoming and Montana. Both are known from the Morrison Formation, a suite of rocks laid down by rivers and on flood plains about 150 million years ago, and the two genera appear to have lived at the same time. Over 120 years of sampling in the south of the Morrison basin has failed to find any specimens of Hesperosaurus there, perhaps suggesting the two genera were ecologically segregated. Although stegosaurs are one of the most iconic dinosaurs, much remains unknown about their palaeobiology due to their sparse fossil record.

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