There is something strange going on with the crocodile’s wrinkled head

Feathers, hair and scales often appear in specific patterns. The spatial distribution of these keratin structures is genetically determined in most animals and is already established in the embryonic stage. But the crocodile’s wrinkled head is different, write Swiss evolutionary biologists and bioinformaticians in Nature.

These head scales are formed by a purely mechanical process during growth, the researchers previously noted. Now they have also discovered the precise mechanism of wrinkling. During rapid growth, the skin folds inwards in some places, creating the edges of the scales.

Self-organization – in which structures arise from a chaotic system – occurs frequently in nature. Consider, for example, the growth of snowflakes or pattern formation in drying clay, but also the skin-covering structures in animals. In the latter case, self-organization is already largely fixed in the genes.

A purely mechanical process

But something strange is going on with crocodiles. Lead author Michel Milinkovitch demonstrated using 3D graphics back in 2012 in Science that the arrangement of body scales in crocodiles is genetically determined, but that of head scales is not. The knobby, irregular polyhedra that cover the crocodile’s head and jaws fit neatly together and do not overlap. The shape, size and distribution of those scales appear completely random, and Milinkovitch concluded at the time that they were created by a purely mechanical process.

He now describes exactly how that process works with colleagues Nature. The scientists first studied scale formation through experiments with the embryos of Nile crocodiles. Extra large scales were created by the injection of a special protein that stimulated the growth of the epidermis. Slowing down that growth actually resulted in smaller, flatter head scales: comparable to those of the caiman, the South American cousin of the crocodile. The biologists then analyzed the precise architecture of individual scales using, among other things, fluorescent microscopy and computer simulations.

They came to the conclusion that the difference in stiffness between the epidermis and the underlying dermis plays a crucial role in scale formation. The fact that the epidermis grows relatively quickly is also important: the excess skin is, as it were, compressed, folds inwards and this creates the edges of the scales. Such ‘compression folds’ are not unique to the crocodile head; For example, you also encounter them in the earth’s crust, when rocks are compressed as a result of plate tectonics.

To share





Email the editor