Defense and Attack Strategies and Mechanisms in Biology - Biomimetics: Biologically Inspired Technologies - page 344

to the dolphin's response with a hydrophone. The dolphin was quite amenable to this game and
cooperated well. But by mistake the experimenter sent the dolphin a rather loud signal to which
the dolphin obviously objected. The dolphin looked at the experimenter through the walls of the
aquarium, then went to the hydrophone and blasted into it before the experimenter could rip off his
earphones. The experimenter experienced much pain! The implication is that we could probably
learn about physiologically damaging noise from dolphins and other cetaceans that are also much
more experienced with the technique, having been using it for longer than we have.

13.3 ANTILETHAL DEVICES

13.3.1 Body Armor

Many animals have a hard outer covering that serves as armor, but there are many different ways in
which the function is realized. Whereas the armor developed for individuals or vehicles is based on
the inevitability of attack, and relies on resisting by strength, biological armor can come in many
guises. Obvious ones are armadillo and tortoise, although nobody seems to have made any
measurements of the protection that is given. The same is not true of ankylosaurs (Figure 13.1)
and their relatives, herbivorous dinosaurs that grew to 10 m long during the late Jurassic and
Cretaceous. They had centimeter-sized osteodermal plates that covered back, neck, head, and also
protected the eyes. In polarized light, sections of the plates show where collagen — a normal
precursor of bone and an essential component of skin — was incorporated. Comparing similar
dermal bones from stegosaurus and crocodile, the polocanthids had extra collagen fibres that may
have stabilized the edges of the bony plates. But in nodosaurids — which also had plates between 2
and 5 cm thick, the collagen fibres ran parallel and perpendicular to the surface, and then at 45 8 to
each of these axes, providing reinforcement in all directions. Ankylosaurids had thinner plates that
were 0.5 to 1.0 cm thick, convex shaped, which will have increased their stiffness in bending, and
with the collagen fibres randomly arranged.
The dinosaur structure seems to be repeated in the bone-free collagenous skin of the white
rhinoceros, which is three times thicker and contains a dense and highly ordered three-dimensional
array of relatively straight and highly crosslinked collagen fibres. The skin of the back and sides
of the animal is therefore relatively stiff (240 MPa) and strong (30 MPa), with high breaking
energy (3 MJ m 3 ) and work of fracture (78 kJ m 2 ). These properties fall between those of tendon
and skin as would be expected from a material with a large amount of collagen (Shadwick
et al., 1992).

Figure 13.1 An ankylosaur.