Soft tissues

Soft tissues of fossil creatures are preserved only rarely, and under exceptional preservational conditions, so palaeontologists have | developed techniques to decipher clues concerning this type of ; biology of dinosaurs both directly and indirectly. o n

Louis Dollo reported small patches of skin impression on parts § of the skeletons of Iguanodon. A number of the skeletons from § Bernissart are shown in a classic 'death pose' with the powerful neck muscles contracted, during rigor mortis, pulling the neck into a sharp curve and turning the head upward and backward. That this pose has been maintained during the time between death and eventual burial implies that the carcass of the animal had stiffened and dried out. Under such conditions, its tough, parchment-like skin would have formed a rigid surface against which the finegrained muds would have moulded themselves during burial. Provided that the entombing sediment compacted sufficiently to retain their shape, prior to the inevitable rotting and disappearance of the dinosaur's organic tissues, then (as with simple clay moulds) an impression of the texture of the skin surface would have been preserved in the sediment.

In the case of Iguanodon the texture of the skin impression that was

23. Iguanodon skin impression

preserved confirmed expectations: it shows a finely scaled, flexible covering, very similar in appearance to that seen on the skin of modern lizards (Figure 23). Clearly, the disappearance of the original tissue means that any traces of skin pigments have long vanished.

In addition to the detailed work that has to be done simply to describe the bones of the dinosaur's skeleton, it is also possible to focus on certain parts of the body, notably the hips, shoulders, and head, for clues concerning the arrangement of its muscles. The reason for this is that at the places where muscles and tendons attach to the surface of bones, tell-tale surface markings such as elevated ridges of bone or distinctively pitted muscle scars often form. Skeletal bone is a surprisingly plastic material. Bones must change shape as the body grows, or if it has to repair itself following trauma such as a fracture. What | may be less obvious is that even when the body is full grown, its ; bones continue to be remodelled in response to ever-changing o patterns of stress and strain. For example, an individual taking §

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