Their armour was perfect; even their eyelids consisted of plates of bone. What are known as ankylosauruses are among the best armoured animals known to us. These herbivores were up to ten metres long, with a tail ending in a huge bony club – 'probably used as a weapon', says Torsten Scheyer, 'even though they definitely could not simply swing it back and forth; the whole construction was simply too stiff for that.'
Torsten Scheyer has examined the dinosaurs' armour as part of his diploma thesis. The results are astonishing: 'The armour plating is not nearly as similar to those of the crocodile as was previously assumed,' he adds. 'Their microstructure is substantially more complex, at least in some types of ankylosaurus.'
A complete set of dinosaur chain mail was composed of hundreds of thousands of bony armour plates known as osteoderms. Most of these were smaller than a European one-cent coin, but some also had a diameter of several dozen centimetres and ended in long points. 'Unlike tortoise shells, the individual plates lay next to each other. They were not fused together,' the PhD student Torsten Scheyer explains. This kind of armour was flexible and could thus not break so easily under pressure. Although modern crocodiles have a similar kind of armour, the individual plates have a much simpler structure.
By using a polarisation microscope Torsten Scheyer discovered that collagen fibres were interwoven in the bone calcium of the dinosaur's armour plating, forming mats which were interspersed with each other three-dimensionally. Within each mat the fibres were aligned parallel to one another, with the fibres at right angles to the layer above and below them. 'The armour was thereby endowed with great strength in all directions,' Torsten Scheyer stresses. Today's composite materials are based on the same principle, which are used to make the rotor blades for wind farms or bullet-proof vests – except that in these cases the collagen mats are replaced by glass or carbon fibres.
Collagen is a protein found in connective tissue, sinews or cartilage. The ankylosauruses' armour plating was formed in the layer of connective tissue, thereby surrounding the existing collagen network. In the process of fossilisation this network decays, being replaced by minerals. 'In the fossils the pattern of the fibres can often still be traced, even after hundreds of millions of years,' Torsten Scheyer adds.
Some armour plating is even more stable
Palaeontologists divide the ankylosaurus into three subdivisions. The bullet-proof vest structure can only be proved in one of these; a second type has a relatively simple kind of armour plating. In the third group the armour paradoxically consists of what is known as haversian bone, a form which was first described in human beings in the 17th century by the British anatomist Dr. Clopton Havers. In the course of people's lives their bones are restructured. The trabeculae in the inside of the bones dissolve and are replaced by numerous small tubes of bone known as osteons. This reduces the stability of the bones and is one cause of the well-known phenomenon of brittle bones among the elderly. Torsten Scheyer explains, 'Ankylosauruses have these osteons, too, but in contrast to humans these are also strengthened with fibres.'
Possibly these collagen fibres are the reason why this third type of armour plating is even more stable than the 'normal' ankylosaurus armour. 'In this third group the plates of bone are far thinner than in all the other ankylosauruses – this cuts down weight and nutrients.' He adds, however, that despite this the armour was probably difficult to crack, not only because of their reinforcement with fibres: 'These thin plates of bone were shaped in such a sophisticated way that they could cope with pressure much better and did not break so easily.'
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